D quadrant specification in the leech Helobdella: actomyosin contractility controls the unequal cleavage of the CD blastomere.

ABSTRACT: The unequal division of the CD blastomere at second cleavage is critical in establishing the second embryonic axis in the leech Helobdella, as in other unequally cleaving spiralians. When CD divides, the larger D and smaller C blastomeres arise invariantly on the left and right sides of the embryo, respectively. Here we show that stereotyped cellular dynamics, including the formation of an intercellular blastocoel, culminate in a morphological left-right asymmetry in the 2-cell embryo, which precedes cytokinesis and predicts the chirality of the second cleavage. In contrast to the unequal first cleavage, the unequal second cleavage does not result from down-regulation of one centrosome, nor from an asymmetry within the spindle itself. Instead, the unequal cleavage of the CD cell entails a

SUBMITTER: Lyons DC 

PROVIDER: S-EPMC3077801 | biostudies-literature | 2009 Oct

REPOSITORIES: biostudies-literature