D blastomere (S)
D founder cell (S)

Embryonic founder cell. Gives rise to 20 somatic muscle cells and no other cell types.

Class D motor neurons are a subset of the ventral cord motor neurons which drive the bodywall muscles. They are postulated to serve as cross-inhibitors, causing muscle relaxation of bodywall muscles on the opposite side from the muscles undergoing strong contraction during the propagation of a sinusoidal body wave. This class includes VD and DD neurons.

See DD neurons
See VD neurons

Ventral cord "dorsal A" motor neurons, innervate dorsal muscles, and are cholinergic. Function in backward locomotion. Receive input from the driver interneuron AVA, modulator interneuron AVD and AVE. Send output to inhibitory VD neurons.

See Locomotion circuit

DAuer Formation abnormal mutant

See Dauer
See Dauer constitutive
See Dauer defective

An alternative larval stage which C. elegans enters in preference to becoming an L2 larva when placed under conditions of environmental stress, low food supply, or crowding (Cassada and Russell, 1975; Riddle, 1978). This stage has a longer, thinner body shape than the L2 larva, is less active, and able to cross physical barriers (by ignoring aversive stimuli) to escape its current conditions. The dauer larva has a closed mouth and does not feed. Its intestinal cells are filled with electron dense storage granules. Upon reaching more favorable conditions the dauer molts directly into the L3 stage and resumes normal development. A dauer larva can remain in this stage for four to eight times the normal 3-week life span of nondauer animals. It is covered cuticle, and most tissues may be reduced in volume.

Mutants are available which increase (DAuer Formation constitutive; daf-c) or decrease (DAuer Formation defective; daf-d) entry to the dauer state, and some of these genes may be involved in producing longer lifespan.

Alternatively, the “dauer larva” can also refer to an obligate L3 stage (in some species, an L2 stage) in many parasitic nematode species, which stall their development until they locate the necessary host to support final stages of differentiation (Bird and Bird, 1991). Many of these dauers are known to adopt characteristic coiled postures, as well as ceasing to feed.

See Hu, 2007 in WormBook for more detail.

See Diapause
See Lethargus

Animals that have entered into the dauer state show several general changes in overt behavior. They stop their pharyngeal pumping, there is a modest decline in their rate of body motion, however, they exhibit a complex dispersal behavior. The dispersal behavior motivates the animal to move away from its present surroundings, ignoring aversive stimuli such as osmotic barriers, and to find a more attractive environment in which to resume normal growth. Dauers can often lie motionless and very straight, as if lacking normal muscle tone. However, they remain responsive to touch or chemical stimuli and can then move quickly.

See Dispersal

A mutant phenotype in which animals will spontaneously enter the dauer state even under favorable conditions for normal growth and development (Riddle et al., 1981; Riddle and MacMorris, 1981).

See Dauer defective

The progression of developmental changes through which a larval animal becomes a dauer larva.

See Dauer formation

The resumption of normal development and behavior that occurs after a dauer larval molts into an L3 stage larva.

See Dauer recovery

A process through which a dauer larva reverts to normal developmental programs (Cassada and Russell, 1975). This process can be stimulated by the animal finding a suitable environment (a fresh food supply, for instance) or can sometimes occur spontaneously. A series of steps occurs, including the resumption of pharyngeal pumping, an increase in body motions, a swelling of the body volume to about the diameter of a normal juvenile L2, the shedding of the dauer cuticle, and after the cuticle is shed, a rapid resumption of longitudinal growth.

See Dauer arrest

Dauer larva are much more successful in living at extreme conditions, such as high or low temperatures (outside the normal range of 15-25^o C), the presence of dilute acids, detergents, anesthetics, or even fixatives. This resistance is due in part to their thickened cuticle, but also to their greatly reduced pharyngeal pumping, both of which combine to deny access of toxic agents to the internal tissues (Cassada and Russell, 1975).

See Cryptobiosis
See Diapause

DB1
DB2
DB3
DB4
DB5
DB6
DB7

DB motor neurons (S)

Ventral cord "dorsal B" motor neurons, innervate dorsal muscles and are cholinergic. Function in forward locomotion. Receive input from the driver interneuron PVC and modulator interneuron AVB. Send output to inhibitory VD neurons.

See Locomotion circuit

Dorsal cord

See Dorsal cord

DD1
DD2
DD3
DD4
DD5
DD6

DD motor neurons (S)

Ventral cord "dorsal D" motor neurons, function as reciprocal inhibitors during sinusoidal movement of the animal. Receive input from VA, VB and VC class motor neurons. Contain GABA as neurotransmitter. Change their pattern of motor synapses during postembryonic development from ventral to dorsal.

See VD cells
See Locomotion circuit

DE1
Z1.papaaa
Z4.apaaaa
DE2
Z1.papaap
Z4.apaaap
DE3
Z1.papapa
Z4.apaapa
DE4
Z1.papapp
Z4.apaapp
DE5
Z1.pappaa
Z4.apapaa
DE6
Z1.pappap
Z4.apapap
DE7
Z1.papppa
Z4.apappa
DE8
Z1.papppp
Z4.apappp

A characteristic body posture often adopted by the animal at the onset of a reversal. This motion is very similar to an omega turn, except that the latter always includes direct contact of the head and body during the turn (Miller et al., 2005). The animal simultaneously contracts all ventral bodywall muscles along the midbody to perform this bend, bringing the head to a position almost in reverse to its previous direction of motion. 
A similar sharp bending of the posterior ventral body muscles often occurs in the male while searching for the vulva of the hermaphrodite; he performs this bend when reversing direction while traveling in close contact with the hermaphrodite’s body.

See Omega turn
See Reversal

DMP

Defecation cycle (S)

In C. elegans, defecation occurs approximately every 45 seconds and through a stereotyped sequence of muscle contractions. This sequence of events includes posterior body contraction (pBoc), relaxation, anterior body contraction (aBoc), expulsion of gut contents by enteric muscle contraction (Emc) and opening of anus (Exp), and intercycle period. In the male, the control of anal seal differs dramatically from the hermaphrodite, otherwise DMP is similar to that of hermaphrodite's (Avery and Thomas 1997). Bodywall muscles, intestinal muscles, the anal depressor muscle, the anal sphincter muscle and the AVL and DVB neurons all work together to carry out defecation.

An axenic medium in which all components can be separately listed and identified; many axenic media have included additives such as “liver extract” that are sufficient to grow nematodes for many generations, but where the exact chemical nature of some additive(s) is uncertain. If a defined medium consists entirely of well-defined chemicals, it is termed a holidic medium; if it includes one tissue extract, it is termed a meridic medium. Defined media for raising nematodes were reviewed in detail by Nicholas (1975).

See Axenic medium
See Holidic medium
See Meridic medium
See Xenic medium

Two pairs of specialized sensory papillae one of which lies along the left and right side of the head, at the back of the pharynx, at the same level as the excretory pore (anterior deirid) and the other lies along the posterior half of the body (posterior deirid).

Z disc (S)
Z body (S)

This is a specialized form of hemi-adherens junction found in nematode muscles that acts as the attachment plaque for thin filaments onto the cell membrane. It forms the basis for organizing the bodywall muscles into obliquely striated muscles. The dense body in bodywall muscles is especially large, indenting far into the cytoplasm to border each sarcomere, thus providing a long row of coherent attachment sites at regular intervals. Other muscle types in C. elegans have smaller dense bodies or only dense plaques that usually fail to extend away from the cell membrane, but consist of very thick hemi-adherens junctions. The dense body is also connected across the cell membrane to the underlying basal lamina and to the hypodermis and cuticle, acting as a site of anchorage for muscle to the bodywall and exoskeleton of the animal. This intercellular attachment may represent a category of “focal adhesion”.

See Dense plaque
See Focal adhesion
See Hemi-adherens junction
See Z disc

DCV

Dark-cored vesicles (S)

A class of membrane-bound vesicles found inside neurons, gland cells, and some epithelial cells in which the central core appears darkly stained when viewed in thin section by electron microscopy. Vesicle populations can differ widely in diameter and in contents, according to their functions, and perhaps subject to changes in fixation and staining protocols.

Dense core vesicles have sometimes been associated with neuropeptides in higher animals, but little is known about their contents in C. elegans. In C. elegans, only a few neurons have prominent dense core vesicles as their primary vesicle type (e.g. NSM, HSN). In most amphid neurons, they co-exist with the more ubiquitous, electron-lucent, 35 nm, synaptic-like vesicles. The sizes of DCV's in C. elegans vary from 37 nm (e.g. in ASE neuron) to 53 nm (e.g. in ASK neuron) (White et al., 1986). Excretory glands contain very large dense core vesicles, while some sheath cells and hypodermal cells sometimes have smaller dense core vesicles.

See Vesicle

A modified form of the dense body that forms where two adjoining bodywall muscle cells meet at their lateral membranes. At normal dense bodies within a single muscle, two myofilament lattices extend away in opposite directions within the cell, kept in alignment through the strong adherence to the dense body. At dense plaques, the two myofilament lattices within two adjoining bodywall muscles extend away from either side of the plaque, thus causing the sarcomeres of adjoining cells to be in rigid alignment.
Many other muscles cells in the nematode have dense plaques rather than dense bodies organizing their myofilament lattice, and only form one sarcomere per cell, rather than forming multiple sarcomeres in a striated pattern.
The dense plaque is also connected across the cell membrane to the underlying basal lamina and often to the hypodermis and cuticle, acting as a site of anchorage for muscle to the bodywall and exoskeleton of the animal.

See Dense body

Desmosomes are adhesive intercellular junctions that anchor the intermediate filament network to the plasma membrane. They function both as an adhesive complex and as a cell-surface attachment site for intermediate filaments, and hence integrate the intermediate filament cytoskeleton between cells and play an important role in maintaining tissue integrity.

Hemidesmosomes are similar in morphology to halves of desmosomes and function as an anchoring junction of the cell to a non-cellular substrate. In C. elegans, hemidesmosomes within hypodermis (also called fibrous organelles) function to anchor muscle sarcomere to exoskeleton (cuticle) and allow for transmission of muscle tension laterally to the cuticle (Hahn and Labouesse, 2001).

Unlike tight junctions (zona occludentes) where adjacent cell membranes appear to form a tight seal, in both desmosomes and hemidesmosomes, adjacent cell membranes are visibly separated and the gap is filled with dense fibrous material.

Note that in early C. elegans literature the term "desmosome" was used in reference to several forms of adherens or septate junctions, but is now considered an invalid term. “Belt desmosomes” referred to zonula adherens junctions that mark the lateral borders of many epithelial cells where they surround a lumen, as in the intestine.

See Adherens junction
See Fibrous organelle
See Hemidesmosomes
See Septate junction

An abnormal stoppage of normal tissue development due to adverse environmental factors (starvation, crowding, anoxia) or a genetic defect. Arrest often takes place at characteristic times in the cell cycle, or due to the lack of a key regulatory signal required to stimulate further morphogenetic steps. If arrest occurs during early or late embryogenesis, it is called an "embryonic arrest" and is lethal. Alternatively, postembryonic development (i.e. postembryonic cell division) can be arrested in the newly hatched L1 larva in the absence of food. Arrested L1 animals are viable for up to 6 days. When they are placed in the presence of food, postembryonic development resumes normally in these animals (Hong et al., 1998). Similarly, the dauer larva is a morphologically specialized and developmentally arrested third-stage larva that can survive four to eight times the 3-week life span of animals that have bypassed the dauer stage. The developmental choice to enter the dauer stage is temporally and environmentally controlled.

See Dauer

An early embryo in which the lipid layer (as well as the eggshell) has been physically dissected or otherwise removed from the specimen.

See Lipid layer

A chemical stain for nuclei which is commonly used in fixed specimens and produces a bright blue label. DAPI forms fluorescent complexes with natural double-stranded DNA, showing a fluorescence specificity for AT, AU and IC clusters.

See Anatomical methods
See Excitation-emission spectrum for DAPI

An obligate state of arrested development or quiescence, especially common among various parasitic nematode species. Animals may go into diapause at a particular season, or upon reaching a certain stage in development, after which they await a particular signal to exit and resume development (Bird and Bird, 1991). The exit signal may be a change in environment, the passage into an obligate host, etc. C. elegans enters diapause if it is starved at the time of hatching (Baugh and Sternberg, 2006; Fukuyama et al., 2006). In laboratory culture, starved plates typically accumulate animals in L1 diapause and in the dauer stage. This developmental arrest continues until the animals are fed again. Insulin signaling appears to regulate a stop in the cell cycle during diapause, as daf-2 mutants go into L1 diapause constitutively, even when fed (Baugh and Sternberg, 2006; Vowels and Thomas, 1992).

See Cryptobiosis
See Dauer

Differential interference contrast imaging. This type of micrscopy is used to visualize transparent structures in phase microscopy. This is achevied by visualizing in phase microscopy and taking advanatage of the different refractive indexes within the sample. As the samples do not need to be stained or fixed for visualization, DIC microscopy is particularly suited for time lapse observations of live cells and animals.

For methods see Shaham, 2006.

The small membrane saccules of the Golgi apparatus.

Having two a two-armed gonad as is the case for C. elegans hermaphrodites, but not males which are always monodelphic. Evolutionary diversification has resulted in female monodelphy as well (See Sommer, 2005).

See Amphidelphic
See Monodelphic

See 1,1-dioctadecyl-3,3,3,3-
tetramethylindocarbocyanin

A cytoplasmic feature noted in some neuron cell bodies which have been used to differentiate between two classes of sense cells in the lumbar ganglia of the male tail (Sulston et al., 1980). By comparison to more recent fixations, these cisternae appear to correspond to rough endoplasmic reticulum; thus the dilations appear to be swellings between leaflets of the RER.

See Cistern / Cisternae
See Rough endoplasmic reticulum

Dilator ani (S)
Anal dilator muscle (S)
Rectal muscle (S)
Anal sphincter (S)
Rectal sphincter muscle (S)

A vital, lipophilic fluorescent dye (observed through the rhodamine filter) that is used to stain certain sensory neurons with endings open to outside in C. elegans. These neurons are: ASK, ADL, ASI, AWB, ASH and ASJ in the head and PHA and PHB in the tail.

See Anatomical methods
See Dye filling defective

3,3'-dioctadecyl
oxacarbocyanine perchlorate

A vital, lipophilic fluorescent dye (observed through the orange/yellow- FITC filter) that is used to stain certain sensory neurons with endings open to outside in C. elegans. These neurons are: ASK, ADL, ASI, AWB, ASH and ASJ in the head and PHA and PHB in the tail.

See Anatomical methods
See Dye filling defective

A sexual reproduction method in which there are separate male and female individuals in the population that generate sperm and oocytes respectively. C. elegans, which has males and hermaphrodites, are considered a dioecious species.

See Amphimictic
See Andric index
See Automictic
See Gonochoristic
See Thelytoky

A rapid behavioral change in which an animal quickly recovers from a habituated state to a stimulus. This change can be caused by a brief train of electric shocks or another strong noxious stimulus (See Rankin’s description in Hart, 2006).

See Habituation
See Tap response

An elementary behavior in which animals tend to move apart from one another when faced with crowded or aversive conditions in the absence of food. This is the opposite from aggregation.

See Aggregation
See Nictation
See Social feeding

DTC

Gonadal leader (S)
Cap cell (S)

A somatic cell with several important functions within the gonad (ovary); it lies at the distal tip of the germline in the hermaphrodite. The cell performs a “leader function” as it guides and shapes the outgrowth of the mitotic germ cells by squeezing on the most distal germ cells while crawling along the bodywall to force the germline to extend into a long tubular shape. It also secretes the LAG-2 signal that influences nearby germ cells to remain in mitosis in the ovary.

This cell follows an alternate fate in the male gonad as the male DTCs do not migrate; this function is fulfilled by the male linker cell.

See Anchor cell
See Linker cell

Dorsal nerve cord

See Dorsal cord

A synaptic vesicle that has become linked to the active zone at the pre-synaptic membrane of a synapse. Once docked, the vesicle becomes “primed” for fusion to the membrane in order to release the vesicle contents into the extracellular cleft of a synapse.

The process through which a synaptic vesicle becomes ready for membrane fusion at an active zone of a synapse, presumably by attaching to some component of the presynaptic density or the presynaptic membrane.

See Richmond, 2005 for more detail.

The upper or back side of an animal.

An event occurring during embryogenesis, after gastrulation, in which the hypodermis stretches across the dorsal side of the embryo to fuse and fully enclose the embryo in a full tube of hypodermis.

See Chisholm and Hardin, 2005 for more detail.

This term can refer to either of two anatomical structures:

1) A longitudinal nerve tract that runs on the left side of the dorsal hypodermal ridge in C. elegans. Dorsal cord is made of processes of ventral cord motor neurons that send commissures to the dorsal side, as well as processes of certain head and tail neurons. Dorsal cord itself contains no associated cell bodies along its length.

2) Less frequently it refers to the dorsal hypodermal cord (i.e., dorsal hypodermal ridge).

See Dorsal hypodermal ridge
See Hypodermal ridge
See Nerve
See Ventral cord

The smallest of the four principal hypodermal ridges running along the length of the body from the nose to the tail. The dorsal ridge contains no nuclei but is syncytial with the larger lateral ridges.

See Dorsal cord
See Hypodermal ridge

DNC

Dorsal cord (S)

Any ray in the male tail that opens to the outside on the dorsal surface of the fan; the pattern of these opening is highly stereotyped, such that certain rays always open dorsally (rays 1, 5 and 7), others ventrally (rays 2, 4 and 8), and a few at the lateral margin of the fan (rays 2 and 9).

See Ray

Left and right sided longitudinal nerve tracts that run between the dorsal cord and the tracts formed by ALM/ALN neurons. It is formed by the processes of SIAD, SIBD, SMBD, SMDD and SDQ neurons.

See Cord

A bilateral pair of minor commissures in the tail between the dorsal cord and the lumbar ganglia. In the C. elegans hermaphrodite it carries the axons of DA8 (left side) and DA9 (right side), but may include more processes in the adult male.

See Commissure
See Lumbar commissure

DRG

Dorsorectal ganglion (S)
Dorsal-rectal ganglion (S)

The dorso-rectal ganglion lies above and behind the rectum in the tail, in close continuity with the anal hypodermal ridge. It contains 3 neuron cell bodies (DVA, DVB and DVC) that send their neuronal processes into the ventral nerve cord via dorso-rectal commissures that encircle the anus. The ganglion contains no local neuropil in the hermaphrodite. In the adult male tail, this ganglion gains additional neurons and some local neuropil.

See Dorso-rectal commissure

The mechanism by which an organism compensates for unequal numbers of X chromosomes between the sexes so that somatic cells of either sex express equal levels of X-linked gene products. There are diverse strategies employed by different species to achieve dosage compensation. In C. elegans, males have one X (XO) and females have two (XX). A protein complex binds both X chromosomes of hermaphrodites and reduces transcript level by half.

See Meyer, 2005 for more information.

See Sex determination

A behavioral state in which the nematode often stops, reverses or turns, and moves at low speed, tending to remain in the same general area on the culture plate (Cheung et al., 2005).

DX1/2
DX1/2
DX3/4
DX3/4

F.lvda
F.rvda
U.laa
U.raa

In many portions of the C. elegans nervous system, this is the most common form of synapse, with one presynaptic process contacting two other postsynaptic processes simultaneously at one place; A --> B+C. It is also the most common form of neuromuscular junction (NMJ).

See Monadic synapse
See Triadic synapse

A mutant phenotype in which vital dyes such as FITC, DIL and DIO fail to fill the sensory neurons that are open to outside and are normally stained by incubation of the animal in these dyes (Starich et al., 1995; Hedgecock et al., 1985).

A microtubule-based motor protein, which is generally specialized to carry cargoes towards the minus-end of the microtubule.

See Kinesin