Worm Breeder's Gazette 11(3): 65
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Mutations in egl-5 result in a highly penetrant Egl phenotype as a consequence of improperly specified HSN identity (Trent et al. 1983, Desai et al. 1989). Blast cells in the tails of egl-5 males (and hermaphrodites) undergo abnormal lineages, underlying the egl-5 Mab ( Chisholm, WBG 10.2). egl-5 mutants are also insensitive to tail touch, coil when backing up, and are constipated. Touch: Most (over 95%) egl-5 mutants are tail Mec. About a quarter are also Tab, that is, completely insensitive to strong touch in the tail (some also show a variable response to strong touch). The latter phenotype is phenocopied by laser killing of the PVC tail interneurons (Chalfie et al. 1985) and is also seen in deg-1(u38) mutants, in which (amongst other things) the PVCs degenerate postembryonically ( Chalfie, WBG 10.3) in characteristic vacuoles. All 8 egl-5 alleles suppress PVC degenerations in doubles with u38; the frequency of vacuoles is reduced to 10-20% of that in u38 alone. n989 and e2399 are the strongest suppressors (10%); strangely, the amber allele n945 suppresses the most weakly (48%), and the non-Mec non-Mab non-Unc allele n1439 to a similar extent (42%). In conclusion, PVC identity seems partially changed in egl-5, and this may underlie the tail touch defects, although the n1439 phenotype implies that a PVC may not be susceptible to u38 yet still function. and Go: In egl-5 L1s the direction of coiling is biased ventrally ( about 5:1), but by L4 this bias has vanished. The early bias might suggest that the DD neurons are defective, since these are the only class innervating ventral muscles at this stage. To see if the Unc phenotype could be traced to specific wiring defects I reconstructed part of the posterior ventral cord and preanal ganglion from an adult n945 hermaphrodite (beautifully sectioned by Nichol Thomson). Analysis of the reconstruction is almost complete, and some defects predictable from the lineage have been seen: for instance, the DVB process is absent. Some of the PAG neurons appear normal (PVT, PVPs, DD6), but others are not (VA12, AS11, VD12, 13, DA8, 9) and some classes have not been identified, notably AVA and AVD. The abnormalities in connectivity cannot easily be interpreted as transformations of neuron class. In summary, no smoking gun has yet been found for the coiling phenotype. Defective expulsion: Adult egl-5 mutants are constipated as the result of a progressive defect in the expulsion motion (exp) of the defecation cycle. The defect is progressive, becoming stronger until about 2 days after the L4 moult (which is when I score it). In strong alleles only 1/4 to 1/8 cycles are exp+. The other cycles either completely lack exp(exp-) or have a partial exp movement (exp(W)) in which only the intestinal muscle contracts (normally both it and the anal depressor contract). The phenotype is strongest in n988 and weakest in n1439. The egl-5 Exp differs from that seen in the putative GABA metabolism mutants unc-25 and unc-47, in which both larvae and adults completely lack exps in 7/8 cycles (S. Mclntire, J. Thomas, p.c.); partial exps have also been seen in egl-2 (J. Thomas, p.c.). Some postembryonic neurons not produced in egl-5 may be involved in control of expulsion, but attempts to phenocopy the egl-5 Exp defect by killing the precursors to postembryonic neurons affected by egl-5 (P12, K and Y) were only partially successful, producing a weak Exp(W) and Exp- (most cycles were still exp+).Noted in passing: Two details of the male phenotype have been examined further. First, the male sex muscles were examined under polarized light. The muscles are very variable in disposition, often highly disorganized. At low frequency (highest, at 10%, in n945) an extra dorsal coelomocyte (dcc) has been seen. Extra dccs are seen in N2 at very low frequency ( approx. 1%). The extra dcc might arise from the rhs homolog of SM2L. pp, although no regulation is seen if SM2L.pp is killed in N2 (Sulston and White, 1980). Secondly, the abnormal gonads in egl-5 males have occasionally been seen to produce tissue with morphology (in Nomarski) similar to that of hermaphrodite uterus (cells with highly infolded membranes enclosing a central lumen). This is seen in 5-10% of males, and is extremely variable in size and placing. Like WT hermaphrodite uterus, the 'uterus-like' stuff stains strongly with peanut lectin, giving a distinctive crumpled-tube pattern (WT male gonads appear to stain only very weakly, and variably, in the vas). It may be that egl- 5 male gonads are being partially sexually transformed (a conceivable interpretation of the lineages), but perhaps this differentiation pathway is occasionally taken when the cells are confused.