Fig. 4. Optimized in vitro conditions partially rescue the cytokinesis defect of cyk-3 embryos. (a) In EGM, wild-type blastomeres can divide normally. Cells of the P-lineage divide in a linear cleavage pattern (white arrow); cells of the AB lineage divide in a spiral cleavage pattern (white arrowhead). (b) cyk-3 mutant embryos under the same conditions frequently show cleavage furrows (black arrowhead), indicating that cytokinesis is not a primary defect.