B-24 PROTEIN STORED IN LAMPBRUSH SPHERES IS INVOLVED IN EARLY CLEAVAGE IN URODELE AMPHIBIANS

A cDNA encoding a protein (B-24) belonging to the Mcm/P1 family ts as isolated from the newt Triturus carnifex In eukaryotes, the members of the Mcm/P1 family are essential factors in the DNA replication proces s. B-24 protein (TcMcm3) is present in salamandrid ovarian oocytes and early embryos; its role was tested by injecting specific anti-B-24 mo noclonal antibodies into the cytoplasm of one blastomere of two-cell s tage embryos. The injected blastomere encountered cleavage arrest eith er soon after the injection or following one or two divisions; later, it degenerated. Instead, the uninjected blastomere went on developing and organizing a hemi-embryo, which does not grow beyond the tailbud s tage. These results are consistent with the hypothesis that the B-24 p rotein is involved in DNA replication at cleavage. The B-24 protein st udied here appears to play a specific role in early development; other variants of the Mcm3 group seem to be employed by different adult tis sues. (C) 1998 Wiley-Liss, Inc.