Worm Breeder's Gazette 14(5): 53 (February 1, 1997)
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.
Johns Hopkins University, Department of Biology
him hermaphrodites produce a high incidence of male progeny due to X chromosome loss during meiosis. Among these genes, him-4 is unique since mutant animals also exhibit pleiotropic defects in cell adhesion. For example, uterine attachment to the body wall occurs when a uterine cell (utse) induces seam cells to flatten and assemble intermediate filaments and hemidesmosomes that hold the uterus inside the body cavity. In him-4 mutants these anchorages fail and the uterus everts through the vulva when egg-laying begins. In addition, mechanosensory neurons that are normally attached to the cuticle via intermediate filaments and hemidesmosomes in the hypodermis are unattached in him-4 mutants. him-4 males are sterile because linker cell migration is defective, probably as a result of reduced adhesion of the male gonad to the body wall. Of the 15 him-4 alleles that we have isolated, 14 exhibit both meiotic and cell adhesion phenotypes. rh306 has defects in uterine attachment and linker cell migration, but not the meiotic or mechanosensory neuron defects. To determine the molecular defects that could account for these diverse phenotypes, we have initiated a molecular analysis of the him-4 locus. him-4 was located on LGX between RFLPs on cosmids K04F12 and F58E9. Microinjection of cosmid pools in this interval resulted in rescue when cosmids F15G9 and W07D2 were co-injected, but not when either cosmid was injected alone. For this reason we believe that the most likely candidate for the him-4 gene is F15G9.4, a large (40 kb) putative gene, predicted to span the overlap region of these two cosmids. The predicted gene product is a 5239 amino acid secreted protein. At the amino terminus is a signal sequence followed by 2 copies of a unique repeat. The most prominent feature of the predicted product is an uninterrupted stretch of 48 immunoglobulin C2 repeats similar to those found in N-CAM. At the C terminus are two calcium binding EGF repeats surrounded by two stretches of unique sequence containing 6 orphan cysteines. The protein could form a 200 nm rod with specialized adaptors at either end that might span the basement membrane between hemidesmosome inducing cell (e.g. utse) and responding epithelial cell. Several of the Ig repeats contain RGD sequences in conserved locations that make them candidates for integrin recognition. A GFP reporter construct containing 3.5kb of the upstream untranslated sequence is expressed most prominently in body wall muscle and also in the hermaphrodite distal tip cell. It is not obvious what role this putative cell adhesion molecule has in meiosis. Continuing molecular analysis and protein localization studies are being conducted to determine how this molecule can account for the diverse activities of him-4. Schematic diagram of predicted gene F15G9.4 product