PART/CELL NAME |
ABBREVIATION
SYNONYMS (S)
ANTONYMS (A) |
LINEAGE |
DESCRIPTION |
M cell |
Sex myoblast (S) |
|
A postembryonic mesoblast that lies in the posterior body region and gives rise
to sexually dimorphic muscles in males and hermaphrodites. A
descendant of MS.ap, M is born in an anterior position on the left
side of the embryo and then migrates to the posterior and right side.
In the hermaphrodite, the M lineage gives rise to six cell types: body wall muscles, nonmuscle
coelomocytes and four classes of sex muscles including those of the
uterus and vulva. In males, M descendants give rise to cells in the tail including some bodywall muscles and to sex muscles of the tail (Herman, 2006).
See Sex myoblast
|
M line |
|
|
A planar structure within the muscle sarcomere which lies midway
within the thick filament (A) band, attaching to the plasma membrane at its base and
running up towards the inward surface of the myofilament lattice.
The plane of the M line runs parallel to the axis of the A band,
slightly off axis from the longitudinal body axis. It may organize
the orientation of the myosin lattice and perhaps the stagger
between adjacent sarcomeres (Waterston et al., 1986). |
"m" neuron |
FLPL
FLPR
|
ABplapaaapad
ABprapaaapad |
Sensory head neurons with ciliated endings, but
not part of a sensillum and are not open to the outside. Functions
with 2 other classes of mechanosensory neurons to mediate nose touch
avoidance and initiate backwards movement. |
M phase |
Mitotic phase (S) |
|
A stage in the cell cycle during which mitosis occurs. It is recognized best by light
microscopy rather than by TEM methods. (For overview of cell
division in C. elegans see Oegma and Hyman, 2006). |
M1, M2, M3, M4, M5 |
|
|
These are the names of individual pharyngeal motor neurons (Albertson and Thomson, 1976). |
m1-m8
(pm1-pm8) |
|
|
Pharyngeal muscle cells, which make 8 consecutive
rings of radial musculature encircling the pharyngeal lumen. Most are
arranged in a three-fold symmetrical manner. All except pm6-8 are
syncytial; pm1 has 6 nuclei while each pm2-5 cell has 2 nuclei, as a
result of cell fusions (Albertson and Thomson, 1976; Avery and Thomas, 1997). |
m8 muscle cell (pm8) |
|
|
A single muscle cell lying at the posterior
end of the pharynx which completely encircles the pharyngeal lumen.
m8 may act as a sphincter to control the lumenal opening, or possibly
the pharyngeal-intestinal valve just behind it, to restrict
regurgitation from the intestine (Albertson and Thomson, 1976). |
Main body syncytium |
|
|
Refers to the hyp7 syncytium, the largest component of the hypodermis. This tissue eventually contains 110
nuclei and encloses the major portion of the animal’s body
length in a circumferential toroid that includes the ventral and
dorsal hypodermal ridges, as well as most of the lateral hypodermal
cords over that region. |
Major
sperm protein |
MSP |
|
The dynamic polymerization of MSP drives C.
elegans sperm motility via "treadmilling"(Smith, 2006). |
Male |
|
|
A rare (1/2000) sexual form in normal Caenorhabditis elegans whose body undergoes a dramatic
sexual transformation during development, especially of the tail, in order to breed sexually with the
hermaphrodite (Emmons, 2005). Unlike the hermaphrodite, the male’s reproductive tract forms only
Tetraploid adults can generate two classes of hermaphroditic
progeny: “high frequency male producers” which yield much
higher fractions of male progeny, and “low frequency
producers” which yield relatively few males (Nigon, 1949; 1951).
See Hermaphrodite
See High incidence of males
See Intersex
See Spontaneous male
|
Male mating behavior |
|
|
Males go through specific behaviors to initiate
and undergo mating with hermaphrodites (see mating movie). These behaviors include:
responding to contact, turning, vulval location, spicule insertion
and sperm transfer (Barr and Garcia, 2006). |
Male specific |
|
|
Cells, tissues, or functions that are found
only in the male animal but not in the hermaphrodite.
|
Male stock |
|
|
A culture of C. elegans in which male
animals are produced at relatively high frequency by repeated
backcrossing of males into a relatively small number of
hermaphrodites. Since hermaphrodites can self-propogate and produce
virtually all hermaphrodite progeny when not mated, it is difficult
to maintain a culture with a high proportion of male progeny except
by this backcrossing method, or by choosing a him mutant
strain to increase the rate of male production.
See Spontaneous male
|
Male tail |
|
|
The male tail contains both male-specific and
sexually dimorphic structures that allow the male to initiate mating
with the hermaphrodite and to transfer sperm into her vulva. |
Mantle |
|
|
A specialized extracellular matrix
surrounding the touch receptor neurons. Its production appears to
require the touch cell processes to be in close apposition of to the
hypodermis (Driscoll and Kaplan, 1997). |
Marginal cell |
Marginal fiber (archaic) |
|
Transitional
epithelial cells of the pharynx that separate each of the three
syncytial pharyngeal muscle cells from each other. There are a total
of 7 cells: 3 mc1, 3 mc2 and a syncytial mc3 cell with 3 nuclei.
These cells are probably non-contractile, but are filled with
radially oriented intermediate filament bundles. They lie in rows at
the corners of the lumen and supply reinforcing strength to the
organ. |
Masculinization |
|
|
Transformation of cell fates to produce male
cell fates in place of female cell fates. A masculinizing mutation
may transform the ratio of germ cell fates to produce more sperm and
fewer oocytes. Transformation of somatic cell fates may
produce body parts in a genetic hermaphrodite to form a male tail,
cloaca or vas deferens.
See Feminization
|
Mate-finding |
Mate searching (S) |
|
Behaviors that cause sexually adult animals to
be attracted and to approach members of the opposite sex. In C.
elegans, such behaviors include the “leaving
behavior” in males, in which they depart from a food source to
find a suitable hermaphrodite (Simon and Sternberg, 2002; Lipton and Emmons, 2003; Lipton et al, 2004). There is apparently no
detectable preference among fertile hermaphrodites to aggregate in
the presence of adult males (Simon and Sternberg, 2002).
See Leaving behavior
See Pheromone
|
Maternal effect |
Maternal expression (S) |
|
Expression of maternal effect genes is required
in the mother for normal development of her offspring.
See mes
|
Maternal effect lethal |
Mel (S)
|
|
A special class of sterilizing mutations that
prevent the development of the progeny of hermaphrodites homozygous
for the mutation. In contrast to the zygotic lethals, which prevent
the development of the individuals homozygous for the mutation, the
gene product from maternal effect lethals is required in the mother
for the successful completion of the development of her offspring (Kemphues, 2005). After mating with a wild type
male, progeny are generally viable (rescued) and develop normally
as heterozygotes. |
Mating behavior |
|
|
To attract males for mating, hermaphrodites
provide chemosensory and mechanosensory cues (Barr and Garcia, 2006). Males respond to these
cues and undergo a complex behavior pattern to successfully copulate
with the hermaphrodite (see mating movie). This behavior includes: response, turning,
vulva location, spicule insertion, ejaculation and plugging (Barr and Garcia, 2006). Hermaphrodites also
exhibit behaviors that resist his efforts at effective mating (Emmons, 2005).
See Male mating behavior
See Mating resistance
|
Mating efficiency |
|
|
A measurement of the mating ability of a male
adult, in particular the animal’s fertility as opposed to its
mating behavior per se (Hodgkin, 1983; Hodgkin et al., 1988). Assays for
male mating efficiency are used to determine the ability of mutant
males to be used in genetic crosses (Emmons, 2005). |
Mating plug |
|
|
See Copulatory
plug |
Mating resistance |
|
|
Hermaphrodites have been shown to exhibit two
behaviors associated that reduce the likelihood of effective mating
with a male: sprinting (hermaphrodites move forward quickly away from
a male after being touched by him) and sperm expulsion (after male
ejaculation, contractions of the hermaphrodites uterus may expel the
seminal fluid through the vulva) (Emmons, 2005).
See Sperm expulsion
See Sprinting
|
Matrix |
Ground
substance (S) |
|
Flocculent or lacey dense substance which
fills vesicles or regions of space inside the animal; may be
intracellular or extracellular.
Also refers to the large internal space of the mitochondrion which contains a mixture of hundreds of enzymes that catalyze the
oxidation of pyruvate and other small organic molecules, copies of
the mitochondrial DNA genome, special mitochondrial ribosomes and
tRNAs (Alberts et al., 2002).
See Extracellular matrix
|
Matrix layer |
Intermediate layer (S) |
|
A portion of the medial layer of the cuticle.
See Basal layer
See Cortical layer
|
Matricide |
|
|
The killing of an adult mother by her progeny.
This is a common endpoint in cases of internal hatching in C.
elegans, either due to poor success at egg-laying (since
progeny are produced internally by self-fertilization), or due to
mutations that block normal development of the vulval opening (egl
phenotype). Theoretically, there may also be cases in which
the progeny produce a toxic agent that proves fatal to the mother
(Mylonakis et al., 2002).
See Bag of worms
See Egl
|
MCM |
Male Cell of Mystery MCML
MCMR
|
ABplpaapapap
ABprpaapapap |
Male-specific interneuron born in L4 stage, daughter of the AMso cell, undergoes transdifferentiation from a glial to neuron fate. Its cell body lies among the glial cell bodies in the male head, and has synaptic connections in the adult male nerve ring; required for a form of associative sexual conditioning in the adult male |
Mechanoreceptor neurons |
MRNs |
|
These neurons generate electrical signals in
response to mechanical stimuli and transmit those signals to other
neurons. One group, the touch receptor neurons (ALML/R, PLML/R, AVM, and PVM), are nonciliated,
while the ciliated MRNs include ASH, CEP, ADE and PDE, as well as 42
male-specific sensory neurons that innervate the male tail (Goodman, 2006).
|
Mechanosensation |
|
|
Detection of mechanical stimuli to the body. C. elegans sense a variety of mechanical stimuli including:
gentle touch, harsh touch, nose touch and texture (Chalfie, 2006).
See Nose touch
|
Mechanosensory ending |
Mechanocilium (S)
Mechanoreceptor (S) |
|
A rather wide variety of neuronal
specializations have been ascribed a sensory role which is imputed
to be mechanosensory, but rather few have proven physiological
responses. Most of these endings involve morphological
specializations embedded in or immediately under the cuticle,
sometimes showing physical attachment via hemidesmosomes or adherens
junctions. Several involve endings embedded in the hypodermis of a
sensillum. Many neurons project long morphologically unspecialized
processes in longitudinal nerves which are suspected to allow for
stretch sensation (see proprioception), but where no obvious physical
attachments are noted even by electron microscopy. The dendrites of
the touch neurons, which transduce light touch, are not really
“endings” in the conventional sense as their major
processes extend longitudinally for many microns, glued to the
cuticle and hypodermis via an external mantle.
See Nose touch
|
Mechanosensory nerve |
|
|
Cephalic nerve cord + labial nerve, which
travel as a bundle from the lip to nerve ring cell bodies. |
Mechanotransduction |
|
|
The biophysical process by which a
mechanosensory ending converts a mechanical stimulus into a neuronal
signal. Most of the proteins thought to form the transduction
channels in ciliated MRNs are members of the transient receptor
potential (TRP) channel superfamily. Members of the DEG/ENaC
superfamily have been found to compose channels that operate in
nonciliated MRNs (Goodman, 2006; Driscoll and Kaplan, 1997). |
Median zone |
Medial layer (S)
Mesocuticle (S) |
|
An internal compartment of the cuticle that may show substantial variations
between developmental stages, or between species. This layer may be
entirely missing in larval cuticles, but is very prominent in adults. It may include several distinct layers, including the fibril
layer, the matrix layer and a thin boundary zone, which separates it
from the underlying basal zone of the cuticle. This region can
display struts, globular bodies and fluid-filled spaces.
See Basal layer
See Boundary zone
See Cortical layer
See Fibril layer
See Matrix layer
See Strut
|
Meiofauna |
|
|
The collection of animals that are too small to
be easily seen by eye (those larger species comprise the
“macrofauna”), but are larger than the species that can
only be observed with a microscope (the “microfauna”).
They can pass through a .5 mm sieve, but are retained on a .045 mm
sieve. C. elegans, with an adult body length of one micron,
is just barely visible to the eye, and belongs among the
meiofauna. Nematodes generally are thought to comprise 70-100%
of the meiofauna biomass in most habitats, and their total
metabolism may equal 15% of that of the macrofauna (Nicholas, 1975). |
Meiosis |
M phase (S) |
|
A
characteristic series of steps (constituent parts of meiosis)
through which dividing germ cell nuclei mature into
fertilization-competent haploid oocytes or sperm; these include
meiosis prophase I (which itself includes 5 steps),
completion of meiotic division I (meiotic metaphase I and anaphase I), and meiotic division II (meiotic metaphase II and
anaphase II), and telophase (Alberts et al., 2002). In C. elegans the
processes of meiotic maturation, ovulation and fertilization are all
temporally coupled (Greenstein, 2005). The meiotic divisions of C. elegans spermatogenesis are coordinated with the
morphogenesis of fibrous body-membranous organelles which segregate
into spermatids (L'Hernault, 2006). |
Membrane |
|
|
An enclosing or separating tissue, usually a
lipid bilayer that acts as a boundary.
See Basal lamina
See Basement membrane
See Nuclear envelope
See Plasma membrane
See Stacked membrane
|
Membranous organelle |
MO
Special membrane structure (S) |
|
A very distinctive organelle found in the
periphery of the cytoplasm of the maturing spermatid and
spermatozoan. They contain very electron dense stacked membrane
structures that can eventually fuse with the plasma membrane of the
sperm, perhaps leading to formation of the pseudopod. The membranous
organelle (MO) has also been called the “special membrane
structure” by Wolf et al. (1978) and may be formed from
pre-existing “special vesicles” and fibrous bodies, which
disappear as the MO’s develop. The organelle consists of two
lobes separated by an electron dense collar; the larger lobe is
sometimes called the “body lobe”, while the smaller lobe
is the “head lobe” (Nelson and Ward, 1980; Achanzar and Ward, 1997). The MO develops in close association with the fibrous
body (FB), which is composed of the major sperm protein
filaments, and surrounds it, separated by a collar region (L'Hernault, 2006). The membranous organelle
eventually fuses with the plasma membrane and contributes to the
creation of the motile pseudopod of the activated spermatozoon,
providing both membrane and glycoproteins (Roberts et al., 1986). Fibrous material
originating within the MO passes through the fusion pore and
provides components to the outside surface of the sperm’s
plasma membr
ane (Achanzar and Ward, 1997).
See Collar
See Fibrous body
|
Memory |
|
|
C. elegans has demonstrated the
ability to learn from mechanosensory, chemosensory and thermosensory
input. They exhibit habituation as well as associative forms of
learning and show both short-term and long-term memory. Additionally
the appear to be able to integrate and remember experiences across
different sensory modalities (See review by Rankin, 2004).
See Adaptation
See Habituation
See Learning and Memory
See Imprinting |
Meridic medium |
|
|
An axenic medium containing one component that
is not well-characterized, such as a tissue extract.
See Holidic medium |
Meromyarian |
|
|
A condition in which a nematode muscle quadrant
contains relatively few cells (ranging from 2-5 cells across, as in C. elegans); as opposed to “polymyarian” muscles
(in some very large species such as Ascaris) where there
are many cells side by side within a quadrant (Schneider, 1866; Chitwood and Chitwood, 1950). In
“holomyarian” muscles, there are never more than 2 cells
across within each quadrant.
See Holomyarian
|
Mes |
Maternal effect sterile |
|
Mutations in these genes causes a sterile
effect due to loss of mature germ cells implying that the mes genes
are essential for germline proliferation and/or maturation (Capowski et al., 1991; Paulsen et al., 1995). Some mes mutants
appear to contain necrotic germ cells (Garvin et al., 1998). |
Mesenteron |
Intestine
(archaic) |
|
See Intestine |
Mesoblast |
M
Blast cells (S) |
|
Precursor, or stem cell, of the muscle cells
and coelomocytes. In C. elegans, non gonadal mesoderm
arises from a single postembryonic mesoblast cell (M). M is born on the left, next to the pharynx.
It migrates posteriorly, remains on the midline for
some time, but then shifts to the right-hand side of the intestine
(Sulston et al., 1983).
See M cell
|
Mesocuticle |
Medial layer (S) |
|
See Median zone |
Mesoderm |
|
|
In higher animals, this term refers to the
cell layer from which the musculature develops. In C.
elegans, this tissue consists principally of the daughters of
just two cells in the early embryo, the MS (primary mesoderm) and D (secondary mesoderm) blast cells. The term is
used to collectively refer to both these blast cells and to all
developed musculature in a given animal of any age.
See M cell |
Mesorhabdion |
|
|
Specialized zone of cuticle lining the
mesostom or buccal regions, secreted by the pharyngeal
epithelium.
|
Mesostom |
|
|
A portion of the buccal cavity underlain by
the buccal epithelial cells. |
Metacorpus |
Median bulb (S)
First bulb (S)
|
|
The anterior bulb of the pharynx. |
Metaneme |
|
|
A type of stretch receptor, known for some
nematode species, but not C. elegans (Lorenzen, 1994). |
Metarhabdion |
Glottoid apparatus (S) |
|
Specialized zone of cuticle lining the metastom, a portion of the buccal passage formed
by the pm1 muscles. In particular, this cuticle includes the
flaps that may govern flow in/out of the pharynx proper. |
Metastom |
Glottis
(S) |
|
Archaic term referring to that portion of the
pharynx formed by the pharyngeal muscles pm1. |
Micro-adherens junctions |
|
|
Extremely small transient
junctions that have been proposed to occur between hypodermal
filapodia in advance of dorsal/ventral cell fusions in the embryo
(Podbilewicz, 2000). |
Microfilament |
|
|
An extremely thin elongated cytoplasmic
filament, composed of actin protein, which can assemble into any of
several distinct forms, including a gel-like meshwork (g-actin), a
tight bundle of parallel fibers (larger bundles are often called
stress fibers, smaller bundles are often called f-actin), or can be
interspersed with other filamentous proteins (e.g. myosin) to form a myofilament lattice, as in muscle cells. These are each important “cytoskeletal proteins” which physically hold
the cell’s organelles to one another internally, and which
connect via plasma membrane attachments (intercellular junctions) to
hold cells together into a coherent tissue. The actomyosin
(actin + myosin) lattice is especially important in establishing
asymmetric distribution of proteins in one-cell stage embryos (Gonczy and Rose, 2005) and in the force
generation in all muscles.
When cytoskeletal proteins are compared in
cross section, microfilaments < intermediate filaments
< thick filaments < microtubules.
See Actin |
Microscopy |
|
|
Due to its transparency and easy of manipulation, C. elegans is an ideal organism for microscopic observaton of both live and fixed animals or tissues.
See Confocal microscopy
See DIC microscopy
See Electron microscopy
See Four dimensional microscopy
See Multiphoton fluorescence microscopy |
Microtubule |
|
|
A robust macromolecular array which forms long
extended cytoskeletal elements with a hollow core. The tubule is made
principally of tubulin protein, which forms parallel strings of
“protofilaments” along the sides of the tubule.
Individual species of tubulin proteins generally form homomeric
macromolecular arrays such that each tubule consists of an odd number
of protofilaments. In C. elegans, 11, 13, or 15 protofilament microtubules are most common. Microtubules can rapidly
change in length, except when stabilized by capping proteins, and
can assemble into arrays with one another to form microtubule
bundles (as inside the nerve axon) or flexible asters (as in the mitotic spindle). Microtubule-based motors
(such as kinesins and dyneins) can slide microtubules past one
another to generate considerable forces in moving o
rganelles within the cell cytoplasm, or can move cargoes within the
When cytoskeletal
proteins are compared in cross section, thin filaments < intermediate filaments < thick filaments < microtubules.
See Tubulin |
Microtubule ring |
|
|
See Ciliary necklace |
Microvillus/ Microvilli/ Microvillar
|
|
|
Open tubular extension at the
apical surface of some epithelial cells.
1) Found in intestinal cells and some neighboring cells in
the alimentary system. Dense collections of microvilli are bounded
basally by a terminal web and together constitute a “brush
border”.
2) Similar microvilli have been seen in the immature
spermatheca prior to adulthood (Southgate and White, unpublished
data).
3) Some researchers consider the finger-like extensions of the AFD dendrite to be comparable to microvilli (Ashton and Schad, 1996).
See Brush border
See Finger-like projections |
Midbody |
Central body (S)
Midsection (S) |
|
The body region which is behind the head and neck but
in front of the tail, where the tissues are comprised of the
bodywall, intestine and gonad tissues.
|
Midintestine |
|
|
The middle region of the intestine, lying between the anterior and
posterior regions. It consists of a rather simple tubular epithelium
that becomes pushed to the dorsal side of the pseudocoelomic cavity
by the vulva. |
Midline |
|
|
The midline defines a plane running along the
dorsal/ventral axis, separating the left and right halves of the
body. Most features in the bodywall are symmetric across the
midline, except for the major nerve cords. Most internal organs in
the adult are not symmetric across the axis. The ventral midline is
an important landmark in axon guidance; e.g. “midline
crossing” or decussation.
See Ventral midline |
Midline crossing |
|
|
See Decussation |
Migration |
Longitudinal aspect (S)
|
|
This term has been used in many different
contexts to describe directed movements of individual cells or
groups of cells within the body relative to neighboring cells within
a tissue. It also refers to movements of cell parts (process
extension, growth cone motions), organelle movements (such as
nuclei, centrosomes, etc) and relative movements of molecular
assemblies within a cell.
The term could also be used to describe directed motions of
whole animals or even populations of animals with respect to an
environmental signal. |
Mitochondrion/ Mitochondria |
|
|
Intracellular organelle that completes the metabolism of sugars and produces ATP providing the energy required for much of the cell's processes. Each mitochondrion is bounded by two specialized membranes (an outer and inner membrane) which create two separte compartments - the internal matrix and intermembrane space. They are found in large numbers in tissues that have a high energy requirement such as muscle and sperm cells. |
Mixed modality |
Polymodal (S) |
|
Neurons having more than one principle
function within the wiring. For instance, several cells serve both a
sensory and a motor function and are termed sensorimotor cells. Many
more cells may serve as both sensory cells and as interneurons, or as
motor cells and as interneurons, but are less easily categorized
since the “interneuron” status is less easily
defined.
The same term may also refer to neurons which transduce
several different categories of sensation, such as olfaction and
osmosensation or chemosensation, or chemosensation and
mechanosensation. |
Molt |
Moult (S)
Molting (S)
Ecdysis (S) |
|
The end of each larval stage in C. elegans is marked
with a molt where new, stage-specific cuticle is synthesized and the
old one is shed (Cassada and Russell, 1975). Molting is almost
simultaneous for the cuticular covering of all hypodermal tissues and
those of the external openings. The buccal cavity, rectal cuticle and the coats of the excretory duct and sensilla are all replaced at
each molt along with the outer cuticle of the bodywall. Before the
molt, the animal enters a brief lethargus stage. Molting is
1) Apolysis: The separation of old cuticle from the hypodermis
2) Synthesis: the formation of new cuticle arising from the hypodermis, and
3) Ecdysis: t he shedding of the old cuticle
Cuticle protein synthesis has been found to be high during
molting and is very much reduced during intermolt periods.
Furthermore, the cuticle ultrastructure and protein composition
differ at each molt (White, 1988).
The timing of the four molts is not regulated by any
external signal in C. elegans, unlike in many parasitic
species, though molting out of the dauer stage is highly sensitive to
external conditions. Little is known how the molt cycle is driven
internally as C. elegans lacks ecdysone and its receptor.
Presumably, another sterol hormone functions in role (Antebi, 2006).
See Apolysis
See Ecdysis
See Exsheathment
See Lethargus |
Molting fluid |
|
|
A secretion from internal stores that may
supply enzymes required for molting, thought to aid in the digestion
of the old exoskeleton. This fluid may come from the excretory glands (Davey, 1971; Rogers and Head, 1978) and/or
pharyngeal glands (Hall and Hedgecock, 1991; Adams et al., 1996).
Release of the molting fluid has been postulated to follow reception
of an external signal (at least in parasitic nematodes) and release
of a hormonal intermediate from neurosecretory neurons.
See Exsheathment
See Molt
|
Monadic synapse |
|
|
A synapse having only one postsynaptic process.
See Dyadic
synapse
See Triadic synapse
|
Monocentric chromosomes |
|
|
The placement of the microtubules occurs at one
specific region (the centromere) and chromosomes move toward the
poles during anaphase with the centromere leading.
This is in
contrast to holocentric chromosomes where microtubules bind to the
chromosomes along their entire length. While C. elegans chromosomes have a holokinetic organization, they do share many
features and behaviors with monocentric chromosomes (Albertson et al., 1997).
See Holocentric chromosomes
|
Monodelphic |
|
|
Possessing a one-armed gonad. Males always have
monodelphic gonads, but females/hermaphrodites vary across species
whether or not they are monodelphic or didelphic (two-armed) as is
the case for C. elegans hermaphrodites (Sommer, 2005).
See Amphidelphic
See Didelphic
|
Monopolar |
|
|
A neuron with a single process extending from
the soma. |
Monoxenic medium |
|
|
A simple growth medium for raising nematodes,
containing a single well-characterized species (monoculture) of
bacteria. A growth culture containing two mixed species would be
termed a “dixenic” medium.
See Axenic medium |
Monster |
|
|
An embryo or young animal which has undergone
extremely abnormal development due to mutation or physical
disruption is often called a (developmental)
“monster”. Such terminal phenotypes (arrest stages)
are generally lethal and rarely result in fertile adults (Denich et al., 1984; Schierenberg and Junkersdorf, 1992; Schlicht and Schierenberg, 1991).
See Arrest stage
See Embryonic arrest
See Terminal phenotype |
Morphogenesis |
|
|
The development of the shape of tissues, organs
and organisms. Morphogenesis of the C. elegans embryo occurs
during the last half of embryogenesis, a five hour period which
follows the “proliferation phase”. Most cells exit the
cell cycle and begin to differentiate in order to produce the
detailed features of each tissue prior to hatching. This stage is
mostly controlled by the development of the epidermis (Chisholm and Hardin, 2005). |
Morula stage |
|
|
An early stage of embryonic development in which
the embryo consists of compact ball of 12-32 cells. The cells begin
to differentiate and then once a fluid filled space forms, called the
blastocystic cavity, the morula becomes a blastocyst. |
Mosaic development |
|
|
A general means of tissue development (found
prominently in nematodes, including C. elegans) in which
individual cell lineages tend to operate independently of their
neighbors, such that intercellular regulatory mechanisms are
diminished or absent. The whole embryo becomes a patchwork or
“mosaic” structure of cell groups that are operating in
isolation from most outside influences. If certain stem cells are
lost or damaged, no other cells can be upregulated to provide more
cells or any regenerative capacity in replacement of the lost tissue.
While mosaic development is very prominent in C. elegans embryos, significant examples of regulation have been experimentally
determined (Sulston and White, 1980).
See Regulation / Regulative potential
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Mother centriole |
Parent centriole (S) |
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In a metaphase or anaphase spindle body, the
“mother centriole” lies closest to most microtubule
minus ends, and to the centrosome, whereas the “daughter
centriole” lies off to the side (O’Toole et al., 2003). |
Motile/ Motility |
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The relative degree of spontaneous and
independent movement of an animal, a cell, an organelle, or cell
part (growth cone). Often
it refers to the movement of the gamete (sperm), but C.
elegans sperm move by a unique crawling mechanism.
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Motorneuron |
Motoneuron (S)
Motor neuron (S) |
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A neuron which forms synapses (neuromuscular
junctions) onto one or more muscle cells.
See Polymodal input
See Sensorimotor neuron
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Motor end plate |
Muscle plate (S) |
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Mouth |
Buccal opening (S) |
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An opening at the anterior end surrounded by
six symmetrical lips and sensilla. |
MS blastomere |
MS founder cell (S)
MSt blastomere (S) |
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An embryonic founder cell, born on the ventral side from EMS, whose daughter cells, E and MS, give rise to many cell types, most of which are
mesodermal, including somatic muscles, glands, coelomocytes, somatic
gonad precursors, as well as some neurons. |
MSM |
Medial submedial neuron |
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A distinct papillary organ, located slightly
posterior in the lips and containing the dendrite of the OLQ neuron. |
Multiphoton fluorescence microscopy |
MPFE |
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A type of microscopy that combines laser scanning microscopy with multiphoton fluorescence excitation to generate high resolution 3D images of fluorescent signals in live animals.
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Multivulva phenotype |
Muv |
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An aberrant condition in which an animal has
more than one vulva, or more likely, one functional vulva and one or
more extra “pseudovulvae” (see Sternberg, 2005). Many mutants are known
to lead to this condition by the generation of excess cells from the Pn.p lineages; these include lin-1, lin-3 and lin-7 (Horvitz and Sulston, 1980; Sulston and Horvitz, 1981).
See Pseudovulva
See Vulvaless phenotype
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Murder |
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A postulated mechanism for the initiation of
cell death, in which one cell dies as a result of an external signal
from another "killer cell", or dies due to phagocytosis by
a neighboring cell while still healthy (Sulston and White, 1980; White et al., 1991).
See Engulfment
See Killer cell
See Suicide
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Muscle |
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Somatic cell(s) whose principal function is to
provide contractile forces, either to modify body posture or to
control the position or motions of particular tissues or organs. In
the nematode, which lacks a skeleton, most muscles are anchored to
the cuticle. The body’s high turgor pressure provides rigidity
to the cuticle, which can then respond to muscle contractions to
modify the body shape.
Some muscle cells in C. elegans act alone, but the principal muscles of the bodywall and pharynx operate in groups, either in synchrony, in sequence, or in
opposition to provide coordinated, smoothly controlled motions.
Individual muscle cells are often small in size, spindle shaped, and
consist of single sarcomeres or obliquely striated sarcomeres (as in
bodywall muscle).
Several cell types have smooth muscle properties,
including the gonad sheath, the uterine muscles, and the anal
sphincter muscle. Some muscle types are sex-specific, including the vulval and uterine muscles of the hermaphrodite,
and the large variety of specialized muscles in the male tail.
See Bodywall muscle
See Diagonal muscle
See Dilator muscle
See Erector muscle
See Extensor muscle
See Myoepithelium
See Oblique muscle
See Pharyngeal muscle
See Retractor muscle
See Sphincter muscle
See Uterine muscle
See M line
See Z disc
See Actin
See Myosin
See Titin
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Muscle arm |
Innervation process (S)
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A process extension from the muscle belly by
which the muscle cells reach to the nerve cords to obtain
innervation. This extended muscle process is a common feature
of practically all somatic muscles, but is not found in the pharynx,
where neurons extend processes to the muscle cell directly. The
typical bodywall muscle has 3 to 5 muscle arms.
See Muscle belly
See Muscle plate
See Plexus
See Spur
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Muscle belly |
Sarcoplasm (S) |
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The cytoplasmic swelling surrounding the
muscle cell nucleus, which contains many mitochondria and ribosomes,
but excludes that portion of the cell devoted to the sarcomeres.
Muscle cells are mostly spindle-shaped, with sarcomeres extending to
the distal, thinner portions of the spindle, while the nucleus lies
within the fatter muscle belly.
See Muscle arm
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Muscle fiber |
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That portion of the muscle quadrant that
contains the myofilament lattice. This term is not often
used in nematode literature. It might refer to the myofilament
lattice within a since muscle cell, or to the collection of sarcomeres within a single muscle
cell.
See Sarcomere
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Muscle plate |
Motor end plate (S)
Plexus (S) |
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Specialized interdigitating ends of the muscle
arms form a localized plexus along certain portions of the
longitudinal nerve cords and nerve ring. This plexus, known as the
“muscle plate”, is the site of muscle innervation by the
motorneurons. This portion of each muscle arm tends to be
very thin and electron lucent, lacking any cytoplasmic organelles.
The chemical synapses formed by the motor axons are called
neuromuscular junctions (NMJs).
Some gap junctions (GJs) may also
occur here between nerve and muscle or between nearby muscle arms.
The most distinctive muscle plates form just underneath the nerve
ring (forming a complete cylinder), and opposite the principal motor
neuron axons of the ventral and dorsal nerve cords (as lengthwise
bands) (Ware et al., 1975).
See Gap junction
See Neuromuscular
junction
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Muscle quadrant |
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Longitudinal bodywall muscles are grouped into
four groups known as the muscle quadrants. Each quadrant comprises a
double row of elongated muscle cells that lie very close together,
covered by a common basal lamina which separates them from
neighboring territories of hypodermis and nerves in the bodywall,
and from the pseudocoelomic fluid more centrally. |
Muscle stabilization |
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Structures and/or developmental events by which
the body muscles are anchored to the bodywall in order to provide
strong resistance to the forces of muscle contraction, so that
muscle contraction causes motion of the whole body rather than
damage to the sarcomere. |
Mutagenesis/ Mutagenized |
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A procedure used to increase the rate of
genetic mutations within a population of animals. In C.
elegans, common mutagenic agents include ethylmethane sulfonate
(EMS), X-rays, and transposon (Tc1) insertion.
Mutagenesis has been
used to create large libraries of nematodes harboring deletions in
their DNA. Screening these libraries has resulted in the isolation of
lines carrying deletions in specific genes. Deletion strains produced
by The C. elegans Knockout Consortium are
freely available to researchers upon request.
See EMS
See RNAi
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Mutualism |
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Describes a lifestyle in which two species
live together, to the benefit of both organisms. In many cases of
mutualism, the relationship is obligate, and neither species can
thrive apart from the other. If only one species derives obvious
benefits, it is generally considered commensalism. It has been
suggested that C. elegans may have a commensal relationship
with pillbugs in the wild, living under the shell of the pillbug and
perhaps consuming bacteria there (Baird et al., 1994).
See Commensal
See Free-living
See Parasite
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Myoblast |
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Stem cell that divides to produce muscle cells. |
Myoepithelial/ Myoepithelium |
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Describing any tissue that shares properties
of both muscle and of epithelial tissue. Some single sarcomere
muscles, such as pharyngeal muscle cells, have this character since
they secrete cuticle for the pharyngeal lumen, and cuticle secretion
is generally considered an epithelial function. Some smooth muscle
tissues, such as the somatic sheath of the gonad, also fit this
definition, as they completely enclose the germline cells. |
Myofilament |
Myofiber (S) Myofibril (S) |
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A generic name referring to both the thick and thin filaments (myosin and actin respectively). They make up the “myofilament lattice”, a well organized
network of parallel filaments that are intermingled to form the sarcomere in “obliquely striated” and
“single sarcomere” muscles, but can also lie in more d
ispersed, disorganized arrays within smooth muscles. |
Myofilament lattice |
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The organized set of overlapping thick and thin filaments (myosin and actin respectively) that together compose the
dominant feature of the muscle sarcomere, anchored on each end to the dense bodies, or Z bands. Each thick
filament is surrounded by
evenly spaced thin filaments, all lying in parallel; they are
believed to slide past one another during muscle contraction. Thin
filaments outnumber thick filaments by a ratio of 5:1 in mature
bodywall muscles.
Orderly development of the lattice can be
monitored under polarized light by light microscopy, or in thin
sections by electron microscopy, and is disrupted in many
mutants.
See Myofilament
See Obliquely striated
See Sarcomere
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Myogenesis |
Muscle development (S) |
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The set of developmental steps involved in
muscle differentiation and growth, including the gradual
construction of the early sarcomere, the mature sarcomere, and the
increase in sarcomere numbers per cell. |
Myogenic control of locomotion |
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A theory that the basic pattern of locomotion in nematodes is patterned by the direct interconnections between muscle cells (via muscle arm gap junctions) and not due to the pattern of synaptic inputs from motor neurons (Crofton, 1971).
See Neurocratic control of locomotion |
Myosin |
Thick filament (S) |
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Very large elongated macromolecular protein
that forms the major cytoskeletal element within muscle cells, the thick filament. Two isoforms of myosin heavy
chain, A and B, are localized to different regions of individual
thick filaments in bodywall muscle (Miller et al., 1983), binding to a paramyosin (Moerman and Fire, 1997) core protein to form a long straight
filament with myosin motors oriented in opposite directions at each
end of the thick filament. Each myosin heavy chain contains a motor
domain that translocates myosin relative to adjacent actin thin
filaments to provide the force of muscle contraction. |
Myosin rod |
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The central portion of the myosin heavy chain
molecule, a coiled-coil domain which is long and straight, with
a globular motor domain on one end and a non-helical tailpiece on
the other end (Epstein, 1990; Hoppe and Waterston, 2000). |
Myosin tailpiece |
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The non-helical portion of the myosin heavy
chain protein, which lies at the opposite end of the myosin rod from
the motor domain, and is thought to be involved in thick filament
assembly (Hoppe and Waterston, 2000). |
Myotactin |
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Membrane protein involved in the assembly and
positioning of muscle/hypodermal fibrous organelles (hemi-adherens
junctions) (Hresko et al., 1999).
See Fibrous
organelle
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