Worm Breeder's Gazette 11(5): 70
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.
Basal laminae first appear at gastrulation, separating the tissue layers (endoderm, mesoderm, ectoderm) and regulating their morphogenesis. In particular, a delimiting basal lamina is a prerequisite for tissue polarization, i.e., conversion from mesenchyme to epithelium (1). Embryonic hypodermis, pharynx, and intestine polarize during gastrulation, but gonads polarize late in larval development. As a consequence, gonadal myoepithelia are large and accessible throughout their morphogenesis. Several known mutants are defective in epithelialization of male or female gonads (2). In epi-1(rh152), polarization is defective and most adults are sterile. The basal lamina surrounding the germ cells is weak and sometimes herniates, allowing germ cells to escape into the coelomic cavity. In a stronger allele, rh165, the basal lamina of the gonad is breached entirely and germ cells proliferate throughout the body cavity, typically in close apposition to other tissues. Interestingly, only a minority of germ cells enter meiosis. We have examined L4 larvae and adults from rh165 strains by electron microscopy. Although pharyngeal basal laminae appear relatively intact, other basal laminae are breached at numerous sites. The body cavity contains sheets of detached matrix arranged in large onion-like stacks or whorls. Whereas wildtype tissues are separated by apposed basal laminae, mutant tissues, e.g., hypodermis and intestine, often fuse together at places of direct cell contact. Without an intact hypodermal basal lamina, axon fascicles are frequently displaced into the body interior. Myofilaments, anchored at muscle-hypodermal appositions in wild type, assemble ectopically at muscle-intestinal appositions in these mutants. Because gonadogenesis is severely disturbed, rh165 homozygotes are sterile. It is unknown whether maternal expression of epi-1(+) is necessary for the formation of embryonic epithelia. epi-1 is very closely linked to mec-3 on LGIV. John Yochem and Iva Greenwald (Princeton University) have identified a laminin A chain gene approximately 200 kb rightward of mec-3 (3). Based on the cellular phenotype, and coincidence of genetic and physical map positions, we suspect epi-1 alleles may be mutations of this laminin A gene. Although specific functions of individual laminin chains are largely unknown, A chains are proposed to organize epithelial polarization (4).