EFFECTS OF EXOGASTRULA-INDUCING PEPTIDES ON CELL-PROLIFERATION IN EMBRYOS OF THE SEA-URCHIN ANTHOCIDARIS-CRASSISPINA

The effects were examined of exogastrula-inducing peptides (EGIPs), fo und in embryos of the sea urchin Anthocidaris crassipina and known to be homologous to EGF, on cell proliferation in restricted areas of emb ryos at the early stages of development. Blastomeres of embryos were m echanically separated into macromeres and mesomeres at the 16-cell sta ge. Although the number of isolated blastomeres increased linearly in the culture system in vitro, EGIPs inhibited or retarded the division of macromeres during the period between 16 hr and 20hr after fertiliza tion, which corresponded to the times of gastrulation in normal embryo s, but they did not affect the division of mesomeres. These difference s in the proliferation of blastomeres were confirmed immunohistochemic ally with a BrdU-specific antibody on whole embryos. Furthermore, the distribution of the cytoskeleton in embryos during early development w as examined with a tubulin-specific antibody for microtubules and with NBD-phallacidin for microfilaments. We found local differences in the distribution of cytoskeletal elements of a normal embryo, as well as differences between normal and EGIPs-treated embryos. These results su ggest that EGIPs inhibit or retard the division of the progeny of macr omeres, namely, the blastomeres of the vegetal-plate area, via a distu rbance in the development of the cytoskeleton at the early gastrula st age, leading to exogastrulation.