The MS lineage of C. elegans produces three distinct muscle types. During embryonic development the MS lineage gives rise to both body-wall and pharyngeal muscle and also to the M mesoblast. The 2 sex myoblasts divide and form the 8 uterine and 8 vulval muscles. Using polarized light microscopy it was determined that the Egl phenotype is a result of the absence of the sex muscles. One of the newly identified alleles results in an Egl phenotype similar to the original sem-2 allele.
Mutant embryos fail to elongate their heads resulting in a bloated head appearance.
It appears as though all hypodermal and muscle cells are present but are possibly defective in their migrations or positioning. Work is currently underway to narrow the rescuing region to a single gene.