NEURONAL SUPPORT CELLS OF THE MALE SENSILLA - HOOK
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1 Hook Composition and Structure
The sensory hook is a sclerotized cuticular structure, located immediately anterior of the cloaca and shaped like a shield (MaleHookFIG 1). The hook contains the processes of two sensory neurons, HOA and HOB, a sheath cell (HOsh), a socket cell (HOso) and 4 hypodermal cells (P10.papp, P11.ppaa, P11.ppap, P11.ppp and P12.pa/hyp12) (MaleHookFIG 2A-C; MaleHookTABLE 1). Hook cell bodies are located in the preanal ganglion (PAG).
MaleHookFIG 1: The male hook. A. Nomarski image of the adult male tail region with the cell bodies of the hook indicated, ventral view. Cell body positions are variable. B. SEM of male tail tip featuring the fan, spicules and hook, ventral view. (PCS) Post-cloacal sensilla.
MaleHookTABLE 1: Summary of hook cells.
HOA and HOB neurons share several features in common with RnA and RnB neurons of the rays: HOB has dilated cisternae in its cell body, expresses PKD-2 and LOV-1 (like RnB; MaleHookFIG 2D; Barr and Sternberg, 1999), has a distinct basal body and electron dense material in its tip; HOA (like RnA) has a striated rootlet (MaleHookTABLE 1; Sulston et al., 1980).
MaleHookFIG 2A: Illustration of the hook. Cross section of the hook with the locations of the neurons and support cells highlighted, longitudinal view. *PVX is not considered a hook neuron. (Adapted from Sulston et al., 1980.)
MaleHookFIG 2B&C: TEMs of the hook. B. TEM from hook region indicated in A, transverse view. (AJ) Adherens junction. (Image source: [MRC] 1310.) C. TEM from hook region indicated in A, transverse view. (Image source: [MRC] 1388.)
MaleHookFIG 2D: HOA and HOB neurons. TEM from hook region featuring hook cell bodies in preanal ganglion (PAG). (N) Nucleus; (Nl) nucleolus. (Image source: N2Y [MRC] L1027.)
2 Hook Neuron Connectivity
In male mating behavior, the hook acts partially redundantly with the post-cloacal sensilla (PCS) in location of the vulva and inducing spicule prodding behavior (Liu and Sternberg, 1995; Barr and Sternberg, 1999; Garcia et al, 2001). Consistent with this, PCS neurons are major targets of HOB (Sulston et al., 1980). Stimulation of spicule prodding however, is likely to be indirect as hook neurons do not innervate spicule protractor muscles. HOB and HOA are connected to each other along their lengths both by numerous gap junctions and a few chemical synapses.
3 Hook Development
Hook cells are derived from the 3 posterior ventral Pn.p cells P10.p-P12.p (MaleHookFIG 3). The strategy used to pattern these precursors and establish hook cell fates bears remarkable similarity to that used to pattern the hermaphrodite vulva, also Pn.p cell-derived (P3.p-P8.p cells; Hermaphrodite handbook - Egg-laying apparatus). Male P10.p and P11.p cells, along with P9.p, form a hook sensillum competence group (HCG) in which all cells have equal potential to generate hook cell lineages. This competence requires the activity of a Wnt pathway (with frizzled receptor LIN-17) and a Hox gene (MAB-5). Also as in the vulva, cell-cell signaling events establish differences among HCG cells so that each adopts a different fate: 1° , 2° or 3° (defined by the lineage pattern): P11.p adopts a 1° fate, P10.p 2° and P9.p 3° fate (fusion with hyp 7 or division followed by fusion of its daughters) (Sulston and White,1980). In contrast to vulval patterning however, Wnt, and not EGF signaling, establishes 1° fate among the HCG (Yu et al., 2009).
MaleHookFIG 3: Lineal origin of hook cells. Cells of the adult hook are colored. 1°, 2° and 3° are fates established by patterning of the hook sensillum competence group (HCG) P9.p-P11.p (Yu et al., 2009). (Adapted from Sulston et al., 1980.)
Barr, M.M. and Sternberg, P.W. 1999. A polycystic kidney-disease gene homologue required for male mating behaviour in C. elegans. Nature 401: 339-40. Abstract
Garcia, L.R., Mehta, P. and Sternberg, P.W. 2001. Regulation of distinct muscle behaviors controls the C. elegans male's copulatory spicules during mating. Cell 107: 777-788. Article
Liu, K.S. and Sternberg, P.W. 1995. Sensory regulation of male mating behavior in Caenorhabditis elegans. Neuron 14: 79-89. Article
Sulston, J.E. and White, J.G. 1980. Regulation and cell autonomy during postembryonic development of Caenorhabditis elegans. Dev. Biol. 78: 577-97. Abstract
Sulston, J.E., Albertson, D.G. and Thomson, J.N. 1980. The Caenorhabditis elegans male: Postembryonic development of nongonadal structures. Dev Biol. 78: 542-576. Article
Yu, H., Seah, A. Herman, M.A., Ferguson, E.L., Horvitz, H.R. and Sternberg, P.W. 2009. Wnt and EGF pathways act together to induce C. elegans male hook development. Dev. Biol. 327: 419-32. Article
This chapter should be cited as: Lints, R. and Hall, D.H. 2009. Male neuronal support cells, hook. In WormAtlas. doi:10.3908/wormatlas.2.12
Edited for the web by Laura A. Herndon. Last revision: July 19, 2013.