Worm Breeder's Gazette 10(1): 111
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.
The EMS-induced mutation pal-2(e2260), isolated in a screen for abnormal male mutations, causes the production of ectopic Posterior Alae in the tail region of mutant males, where normally no alae are present. Unlike other mutations which cause a similar Pal phenotype, such as mutations in mab-3 or mab-5, 60) males possess the full complement of rays. These rays, however, are somewhat abnormal in appearance, implying a morphogenetic defect; pal- 2(e2260) males mate poorly. Otherwise, pal-2 males appear completely wild-type, as do pal-2 hermaphrodites. pal-2 maps very close to fem-3 on linkage group IV, and is covered by eDf18 and eDf19. For both deficiencies, deficiency heterozygote males appear identical in terminal phenotype to e2260 homozygotes, showing that e2260 is a reduction- or loss-of-function allele. Towards the end of the L4 stage in wild-type males, 'tail seam' activity, which does not lead to alae formation, is produced by the ray precursor posterior daughters R1.p through R5.p. Lineage analysis of pal-2(e2260) males indicates that the ray precursor cell divisions, as well as nuclear positions, are essentially wild-type (5 sides examined). However, R1-5.p have characteristics of the alae-producing body seam, allowing alae formation to extend ventro-posteriorly to the fan, around ray 1, with alae-like dots then continuing dorso-posteriorly up the fan. R1.p and R2.p clearly participate in alae formation, being located in the body seam band, while R3.p, R4.p, and R5.p, which still seem to be part of a tail-seam-like bag, appear to be responsible for the alae-like dots. The anterior movement of the R1-5.p nuclei during L4 lethargus occurs normally. Thus, it appears that pal-2(e2260) males may retain partial tail seam function. This interpretation is consistent with the staining pattern observed with a monoclonal antibody, NE2/1B4-14, isolated in an unrelated study (H. Schnabel, J. Priess, S. Green, and T. Lowe, personal communication), which appears to recognize a cuticular product of seam cells that do not form adult alae. This antibody stains in a thin fibrous band laterally along the body of late embryos and wild-type larvae of both sexes (many larvae do not stain, indicating a correlation with seam activity), but not adult hermaphrodites. Wild-type adult males stain in a band approximately where the tail seam is located in the L4 stage, starting laterally slightly anterior to the tail, and continuing posteriorly where the fan attaches to the body. pal-2(e2260) adult males display greatly reduced staining, with the anterior part of the lateral band eliminated. Two explanations could account for the phenotype of e2260 males. It might be that incorrect tail morphogenesis causes the Rn.p cells to join the body seam inadvertently, or it might be that the Rn. p cells are transformed in cell fate, with a secondary effect on ray morphogenesis. The study of double mutants supports the latter possibility. The mutation lin-22(n372) causes V1-V4 to be transformed into a V5-like lineage, thus resulting in the production of ectopic ray precursor cells in mutant males (Fixsen and Horvitz, WBG 7 #2: 40). Consequently, lin-22 males produce only 10% of wild-type alae on average, as measured in relative fraction of body-length. The double mutant lin-22 owever, produce 56% of wild- type alae in body-length (more than 30 animals of each genotype examined). Many of these animals can be seen to have ectopic ray papillae in the midst of stretches of wild-type alae; occasionally, round knobs of sclerotic material are also present, possibly resulting from cuticular confusion. A similar suppression effect can be observed in double mutants with lin-32(e1926) males (Kenyon and Hedgecock, WBG 8 #2: 19), which frequently possess a gap in their alae around the postdeirid region (17/41 sides examined); the lineage basis for this phenotype is not known. In pal-2(e2260); 926) males this alae defect is completely suppressed (32/32 sides). It therefore appears that pal-2 is a gene involved in the specification of a differentiated cell fate. Like other genes involved in generating sexual dimorphism in the male lateral hypodermis (see WBG 9 #3: 96), a mutation in pal-2 causes a transformation towards the formation of body seam. Finally, the phenotype of pal-2(e2260) is additional evidence that the tail seam plays a relatively minor role in male tail morphogenesis, consistent with the laser ablation experiments of Sulston et al. (Dev. Biol. 78: 542 (1981)).