Fig. 11. Cell polarization, cell proliferation, cell differentiation and migration defects in epi-1 mutants. (A) In this predicted epi-1 null mutant, epi-1(rh199), cell polarity is disrupted such that, in the muscles, additional dense bodies (arrows) form ectopically on the pseudocoelomic side of the cell, and sarcomeres (s') organize in an unusual position away from the epidermis. Normally positioned dense bodies (arrowheads) and sarcomeres (s) are observed on the epidermal (e) side of the muscle cells. Dense bodies are analogous to vertebrate Z-lines and function to maintain the alignment of the thin filaments. A displaced muscle cell distorts the shape of a nerve (n). (B) Strong epi-1 alleles cause sterility owing to failure of gonadogenesis during the third larval stage. The gonadal basement membrane is weakened or missing, and the gonadal sheath fails to enclose the germline, which permits germ cells to escape into the body cavity and to invade neighboring tissues. In this epi-1(rh165) mutant, germ cells (asterisks) have invaded the intestine (i). A basement membrane separates the intestine from the gonad arm below it, however no basement membrane separates the gonad (g) and the thin layer of epidermis (e) and here the tissues adhere to one another (arrows). (C) In epi-1 mutants, the development of the body wall muscles is compromised. In this epi-1(rh165) mutant, the muscle cells (m) of a quadrant show incomplete differentiation. The organization of the sarcomere is primitive, with poor segregation of thick and thin filaments and little evidence of dense bodies to anchor them. The entire muscle has failed to settle closely onto the bodywall and the intervening epidermis (e), normally a thin layer, is abnormally wide (double-headed arrows). (D) Axon migration and nerve positioning defects are often observed in epi-1 mutants. In this epi-1(rh191) mutant, the right bundle of the ventral cord (white arrow) is mispositioned to the dorsal side of the ventral epidermal ridge (e). At the normal position of the right bundle, four or five axons are seen (black arrow). In addition, two or three axons are mispositioned to the lateral side of the ridge (arrowheads). Interestingly, a basement membrane appears to be associated with each of these individual axons, a phenotype never observed in wild type. Scale bars: 5 µm in A; 10 µm in B; 2.5 µm in C; 1 µm in D.