The pathways leading from cell specification to the generation of organ, tissue and animal form are not well understood. In C. elegans, specification of epidermal cells is followed by the migration of these cells to seal the embryo (enclosure) and constriction of these cells to generate the vermiform morphology (elongation). In a previous screen for enclosure defective mutants, we identified a maternal effect temperature-sensitive allele,
jc1(WBPaper00023223). We determined that
jc1 is an allele of the C. elegans Pax/2/5/8 homologue
egl-38.
egl-38(
jc1) displays the
egl-38 Unc and Egl phenotypes, fails to complement
egl-38(
sy294) and is rescued by cosmids that include the entire
egl-38 locus and regulatory sequences.
egl-38::GFP reporters that include only
egl-38and the immediate surrounding sequences show expression in some embryonic epidermal cells and neuroblasts, suggesting that
egl-38 may be required in both cell types during enclosure. We analyzed a previously isolated, strong allele of
egl-38,
s1775 and found that introduction of a single
s1775 allele from males into wild-type hermaphrodites results in enclosure and elongation defects, indicating that
s1775 is a semi-dominant, zygotic allele. Furthermore, progeny of
jc1/Df animals have a fully penetrant embryonic lethal phenotype and display a higher percentage of enclosure phenotypes than
jc1/jc1 progeny or
s1775. These findings suggest that
jc1 and
s1775 are non-null alleles of
egl-38. To determine how
egl-38 regulates enclosure and elongation, we tested various cell junction and cell morphological markers in
egl-38(
jc1) animals and discovered that
egl-38 is required for the expression of some proteins involved in actomyosin contraction. One such protein is VAB-9, an adherens junction component and a putative tetra-span integral membrane protein. Surprisingly, we found that both
vab-9 and
egl-38 were required for the junctional localization of the myosin phosphatase MEL-11. Furthermore, mutations in
vab-9 suppress the semi-dominant enclosure and elongation phenotypes of
mel-11(
it26). In parallel with these experiments, we carried out a screen for suppressors of the
egl-38(
jc1)phenotype and identified three extragenic suppressor, one of which results in fully penetrant elongation defects in an otherwise wild-type background. This allele,
cv1, is incompletely semi-dominant;
cv1/+ larvae display some tail tip morphogenetic defects. We are currently cloning
cv1 and analyzing genetic doubles between
vab-9,
egl-38,
cv1 and previously identified mutants involved in actomyosin contraction during enclosure and elongation. These experiments will order
egl-38 and
vab-9 activity relative to genes involved in actomyosin contraction.