Worm Breeder's Gazette 12(4): 50 (October 1, 1992)

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.

The Pseudocleavage Furrow is Dispensable for Embryonic Development

Melissa Lamb, Lesilee Simpson Rose, Ken Kemphues

Section of Genetics and Development, 101 Biotechnology, Cornell University Ithaca, New York 14853

In early one-cell embryos, prior to pronuclear migration, a series of anterior cortical contractions resolve into a single incomplete medial furrow called a psuedocleavage furrow. The pseudocleavage furrow disappears as the female pronucleus migrates through it to join the male pronucleus in the posterior.

The role of the pseudocleavage is unclear, but because it occurs at a time when cytoplasmic rearrangements are taking place, and because mutations affecting cytoplasmic localization also lead to defects in pseudocleavage, we and others have wondered whether it plays an essential role in cytoplasmic localization.

In the course of a mutant hunt we discovered that one maternal effect lethal line produced embryos that failed to undergo a pseudocleavage. The absence of pseudocleavage, however, segregated independently of the maternal effect lethal phenotype. We have now isolated a stable viable line that produces embryos with no pseudocleavage and no other obvious defects. Although we have examined only a few very early embryos from this line by time-lapse video microscopy, we find that in these embryos both the pseudocleavage furrow and the anterior contractions preceding it are absent. To convince ourselves that embryos lacking pseudocleavage were viable, we followed three such embryos from early pronuclear stage to hatching.

We conclude, therefore, that the pseudocleavage furrow is dispensable.

We are now studying the other events of the first cell cycle (asymmetric microfilament distribution, cytoplasmic streaming and P granule localization) in embryos from this line to determine if any of them are also absent.

We will also study the genetic basis for the absence of pseudocleavage furrows in this strain.