PSEUDOCLEAVAGE IS DISPENSABLE FOR POLARITY AND DEVELOPMENT IN C-ELEGANS EMBRYOS

The first cleavage of the Caenorhabditis elegans embryo is asymmetrica l, producing daughters with different cell fates. During the first cel l cycle, P granules, cytoplasmic components that are segregated to the germ-line, are localized to the posterior of the embryo. It has been hypothesized that the asymmetrical behavior of the daughters of the fi rst division results from a similar localization of developmental dete rminants. A process called pseudocleavage also occurs during the first cell cycle: Anterior cortical contractions culminate in a single part ial constriction of the embryo called the pseudocleavage furrow. Coinc ident with pseudocleavage, there is an anteriorly directed flow of cor tical cytoplasm and a posteriorly directed flow of internal cytoplasm. Foci of filamentous cortical actin become asymmetrically distributed into an anterior cap. Roles for these various first cell cycle events in cytoplasmic localization and development have been suggested but re main unclear. We have isolated a maternal effect mutation, nop-1(it142 ), which abolishes the anterior cortical contractions and the pseudocl eavage furrow. In addition, cortical actin foci remain uniformly distr ibuted in most embryos. Despite these defects, cytoplasmic and cortica l streaming is present and P granules are localized to the posterior o f early embryos. In most embryos from mutant mothers, development proc eeds normally and the embryos hatch and grow into fertile adults. We c onclude that the pseudocleavage contractions and furrow are dispensabl e for the development of C. elegans. (C) 1995 Academic Press, Inc.