Effect of Microtubular Poisons on Cleavage Furrow Formation and Induction of Furrow-like Dent in Amphibian Eggs.

The effects of the microtubular poisons colchicine, vinblastine and nocodazole, on cleavage furrow formation and induction of furrow-like dents in eggs of the newt, Cynops pyrrhogaster, were examined. Solutions of the poisons were injected beneath the cortex around the small initial furrow, or around the advancing tip of the furrow of eggs during the first cleavage. This resulted in prompt block of the progress of the furrow at the injection site, and subsequent total regression of the furrow or incomplete cleavage. The ability of the cortex of a cleavage-arrested blastomere to form a furrow-like dent was tested by inhibiting furrow formation of one blastomere of two-cell embryos by injection of the microtubular poisons, and then transplantation of the blastomere under the cortex of the animal half with furrow-inducing cytoplasm (FIC) taken from normally cleaving eggs. No dent was formed. Moreover, FIC from eggs treated with a poison had no ability to induce a dent on the surface of normally cleaving eggs. These results show that microtubule structures are directly involved in formation of a cleavage furrow.

ON PROPAGATION OF CORTICLA FACTOR AND CYTOPLASMIC FACTOR PARTICIPATING IN CLEAVAGE FURROW FORMATION OF THE NEWT'S EGG.

From Cynops pyrrhogaster eggs just after the start of the first cleavage, a fragment of cortical layer with a small entire cleavage furrow was cut out. In the fragment, the cortex had already acquired susceptibility to and the subcortical cytoplasm had already accquired inducibility for furrow formation. The fragment was transplanted to the animal hemisphere of uncleaved fertilized eggs or eggs immediately after the onset of the first cleavage, from which a portion of the host cortex was removed. Observation was made on division of the graft, and on propagation of the cortical susceptibility and the cytoplasmic inducibility of the graft onto the host egg. The transplant divided succesively on the host egg in many cases, but the furrow of the graft never advanced to the surface of the host egg. Neither the cortical factor nor the cytoplasmic factor was transmitted across the graft to the recipient egg.

INDUCTION OF A FURROW-LIKE DENT ON THE SURFACE OF THE NEWT EGG BEFORE THE ONSET OF CLEAVAGE.

Sawai (2) found in the amphibian egg that furrow-inducing cytoplasmic component (FIC) was localized along the cleavage furrow, which could induce a furrow on the polar surface of cleaving egg under which FIC was injected. But this procedure failed on the surface of uncleaved fertilized egg. In the present experiments, an attempt was made to induce a cleavage furrow on the surface of uncleaved egg of the newt, Cynops pyrrhogaster. A piece of the cortex was cut from the uncleaved egg, which was transplanted to the egg just before or just after the onset of the cleavage, using a fine glass needle. After the transplantation FIC was injected beneath the graft with a capillary. The graft reacted to FIC and a furrow-like dent was induced at the position. Besides, stiffness of the graft increased during the cleavage of the host egg. In contrast to the cortical grafting, a large amount of the cytoplasm excluding FIC was injected under the cortex of an uncleaved egg. After several minutes FIC was deposited at the site. A furrow-like dent was formed there in many cases.