Cyclin D and cdk4 Are Required for Normal Development beyond the Blastula Stage in Sea Urchin Embryos

Abstract

cdk4 mRNA and protein are constitutively expressed in sea urchin eggs and throughout embryonic development. In contrast, cyclin D mRNA is barely detectable in eggs and early embryos, when the cell cycles consist of alternating S and M phases. Cyclin D mRNA increases dramatically in embryos at the early blastula stage and remains at a constant level throughout embryogenesis. An increase in cdk4 kinase activity occurs concomitantly with the increase in cyclin D mRNA. Ectopic expression of cyclin D mRNA in eggs arrests development before the 16-cell stage and causes eventual embryonic death, suggesting that activation of cyclin D/cdk4 in cleavage cell cycles is lethal to the embryo. In contrast, blocking cyclin D or cdk4 expression with morpholino antisense oligonucleotides results in normal development of early gastrula-stage embryos but abnormal, asymmetric larvae. These results suggest that in sea urchins, cyclin D and cdk4 are required for normal development and perhaps the patterning of the developing embryo, but may not be directly involved in regulating entry into the cell cycle.

This work was supported by NIH grants GM 58921 (W.F.M.) and HD28152 and HD01170 (G.M.W.) and a grant from the NSF (IBN-9816683) to G.M.W. B.J.S. was supported by National Cancer Institute Training Grant T32CA09156 and postdoctoral fellowship F32GM20151.

We thank Bob and Lynne Angerer for advice on microinjection of the antisense oligonucleotides, Randy Thresher and Lilly Reed for assistance with microinjection and photography, and Bob Duronio, Yue Xiong, and Dave McClay for many helpful discussions.