In the absence of the induction, E develops like its sister, MS, producing pharyngeal tissue and body wall muscle. We have identified five alleles of a gene, mom-2, that appears to be required for induction of intestinal cells.
All alleles show a recessive, maternal-effect, embryonic lethal phenotype.
Lineage analysis shows that the two daughters of E, Ea and Ep, divide precociously and fail to gastrulate. To determine if mom-2 function is needed for rotation of the mitotic spindle in EMS, we observed the cleavage axis of EMS in a subset of the blastomere recombination experiments described above. In all cases, spindle rotation occured normally, indicating that mom-2 is not required in either P2 or EMS for this event. One candidate for a molecule that is differentially inherited by E and MS is the protein encoded by the pop-1 gene, which helps specify the fate of the MS blastomere.