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.

How Does a Large Extracellular Matrix Protein Affect Meiosis?

Bruce Vogel, Ed Hedgecock

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
         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