ADAMS, N.L.*; FOLTZ, K.R.: UV radiation delays mitosis and dephosphorylation of cyclin dependant kinase 2 in sea urchin embryos

Ultraviolet radiation (UVR) causes dosage-dependent delays in cell division. Multiple molecular targets of UVR have been investigated in mammalian somatic cells, but they have not been identified conclusively in embryonic cells. Our main objective has been to identify molecular targets of UVR that lead to delays in division in echinoderm embryos by investigating signal transduction pathways that affect DNA synthesis and cell division. As a first step, we defined the UV-sensitive periods in eggs and embryos of the purple sea urchin, Strongylocentrotus purpuratus, using controlled UVR wavelengths and dosages. Using cleavage delay as an endpoint, UV-irradiation of sea urchin eggs and early embryos caused delays in division, with the most sensitive stage being between 30-45 minutes after fertilization, just after DNA synthesis. We investigated effects of UVR on DNA synthesis using incorporation of tritiated thymidine and found that UV-irradiation of eggs does not affect DNA synthesis directly. In addition, we used SDS PAGE with western blotting analysis to investigate whether UVR affects specific signaling pathways, such as activation of the mitosis promoting factor (MPF), cyclin B/cyclin-dependent kinase 2 (cdc2), which controls entry into mitosis and that is known to be operating in early embryos. UV-irradiation of eggs delayed dephosphorylation of cdc2 at tyrosine 15, which is necessary for activation of the MPF. These data indicate that UV-induced cleavage delays may be due in part to the delay in activation of MPF. [Funding was provided by an NIH NRSA postdoctoral fellowship to N. Adams and NSF grants to K. Foltz].