MICROINJECTION OF SUC1 TRANSCRIPTS DELAYS THE CELL-CYCLE CLOCK IN PATELLA-VULGATA EMBRYOS

The suc1 protein is a cell cycle regulator whose precise function rema ins to be elucidated. The suc1 cDNA of the mollusk Patella vulgata was cloned and sequenced. It encodes a 9 kD protein showing a strong simi larity with its human counterparts and to a lesser extend with its yea st counterparts. The expression of suc1 in maturing oocytes was shown to be tightly cell cycle-regulated. The abundance of the suc1 transcri pts is high in prophase- and metaphase-arrested oocytes but drops dram atically upon exit from M-phase, after fertilization. The microinjecti on of suc1 synthetic messengers into embryonic blastomeres delayed the cell cycle clock, thus disrupting the perfect cell cycle synchrony ex hibited by the blastomeres of early Patella embryos. Interestingly, th is suc1 delaying effect was significantly reversed when cyclin B messe ngers were co-injected with suc1 messengers. These results show that P atella embryos offer a quite valuable model to study cell cycle regula tion. Moreover, they support the existence of a negative control exert ed by suc1 on the cell cycle traverse in a higher eukaryote.