Worm Breeder's Gazette 14(2): 60 (February 1, 1996)
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.
|1||Dept. of Genetics, Box 357360, University of Washington. Seattle, WA. 98195-7360|
|2||HHMI/Division of Biology, 156-29, Caltech. Pasadena, CA. 91125|
|3||IMBB/ Biology, Simon Fraser University. Burnaby, BC. V5A 1S6|
Mutations in egl-38 have been recovered in screens based on three different phenotypes: Egl, Mab, and Let. Trent et al. (1983) recovered n578, the first allele of egl-38. n578 hermaphrodites are strongly egg-laying defective, and were originally noted to be defective in vulva morphogenesis. In a screen for mutations that disrupt male tail development, we recovered sy294. sy294 hermaphrodites are Egl, males have severe tail deformities, and both males and hermaphrodites frequently die. sy294 was previously known as lin-50. Finally, in screens for unc-22-linked lethal mutations on LG IV, Denise Clark (1990) identified 24 mutations that were uncovered by mDf7, but complemented sDf2. We found that one of these mutations, s1775, fails to complement both n578 and sy294. We have been investigating the cellular basis for these mutant phenotypes. In addition to the vulval morphogenesis defect, there are other defects associated with the egg-laying system of egl-38(n578) animals. In N2 during the L3 lethargus, the anchor cell (AC) is nestled between the four great-granddaughters of P6.p that will later form the most dorsal toroidal cell of the vulva - vulF (White, 1988). In n578, the anchor cell is mis-positioned with respect to these cells - it is positioned more laterally and ventrally. In addition, we have observed defects in the ventral uterine uv1 cells. In N2, they each extend a process that contacts vulF. The uv1 nuclei remain in close proximity to the corresponding vulval nuclei during mid-L4 and are located in a distinct lateral position in mid to late L4 (Newman, White, and Sternberg, this WBG). In many n578 animals, the uv1 nuclei are not in their correct positions. We are presently performing lineage analysis to assess the exact fate of the uv1 cells. Development of a proper uterine-vulval connection involves interaction between the AC, vulF, uv1, and utse cells. A number of these components are altered in n578. Further analysis of egl-38 may help to elucidate the sequence of events involved in establishing this connection. In males, both n578 and sy294 confer a morphological defect to the tail. In sy294 males the lineages of the rectal epithelial cells F and U are disrupted. Specifically, the F and U cell progeny often divide prematurely. Although the lineage defect is variable, in some cases the U cell divides with the timing and axes of Y.p (Fig.1). This suggests that one function of egl-38 is to make U different from its posterior neighbor, Y, or possibly the daughter, Y.p. The B cell lineage is also disrupted in egl-38 mutants. Since F, U, and Y are required for the normal development of B (Chamberlin and Sternberg, 1993), we are investigating if egl-38 is required for B cell development, or if the defect results as a secondary effect of disruption of F and U fate. The lethality associated with egl-38 mutations generally correlates with heavy damage or "scarring" at the rectum. L1's die at hatching, often exploding at the rectum and immediately disintegrating. Older larvae die either prior to, or immediately following a molt. The male lineage results suggest that egl-38 is required for normal development of F and U, and we speculate that F and U play an important role in maintaining the integrity of the rectum. Thus, the lethality may result directly from misspecification of F and U. We have quantified the lethality associated with two alleles of egl-38 in Table 1. Since sy294/s1775 animals survive more frequently than sy294/Df, s1775 may not represent a null allele of egl-38. However, the arrest phenotype of eDf19/mDf7 animals is not qualitatively different from s1775/Df or s1775/s1775, suggesting that s1775 at least represents a strong reduction-of-function mutation. Deficiency mapping indicates that egl-38 is uncovered by both eDf19 and mDf7, but complemented by eDf18 and sDf2. Several combinations of multi-point mapping with different alleles position egl-38 to the right of elt-1 and egl-20, but to the left of daf-14 and unc-43. Testing cosmids in the corresponding region of the physical map, we have rescued egl-38, and we are working to molecularly identify the gene. Figure 1. Wild-type lineage of male U and Y cells (Sulston and Horvitz, 1977; Sulston et al. 1980), and U cell lineage from an egl-38(sy294) male. For this animal, the early portion of the egl-38(sy294) U lineage was inferred (dotted line), based on the U lineage directly observed in other egl-38 animals, and on the presence and position of cells. Although the presumptive U cell did not appear to divide during the late L1 stage, during the L2 stage the cell divided with the timing and axes of its posterior neighbor, Y.p. In addition, the ten progeny were morphologically similar to normal Y.p progeny. Table 1. The numbers indicate the percent of animals in each class for different egl-38 genotypes. All data represent zygotic egl-38 genotype, derived from heterozygous parents. Each genotype represents data for over 200 animals, except for sy294/mDf7 (over 100 animals). Although similar quantification has not been completed for n578, n578/Df animals are frequently viable indicating n578 retains more essential activity than sy294. We thank Takao Inoue, Gregg Jongeward, and Barbara Page for sharing genetic and transgenic strains, and data prior to publication. We also thank Alan Coulson and colleagues for cosmids. References Chamberlin, H.M. and P.W. Sternberg, 1993. Development, 118, 297-324. Clark, D.V., 1990. PhD thesis, Simon Fraser University, Burnaby BC, Canada. Sulston, J. E. and H. R. Horvitz, 1977. Dev. Biol. 56, 110-156. Sulston, J. E., D. G. Albertson, and J. N. Thomson, 1980. Dev. Biol. 78, 542-576. Trent, C., N. Tsung, and H.R. Horvitz, 1983. Genetics, 104, 297-324. White, J., 1988. In The Nematode Caenorhabditis elegans, Cold Spring Harbor Laboratory, 81-122.