Influence of the polyamine spermine on the organization of cortical filaments in isolated cortices of Xenopus laevis eggs.

Microinjection of spermine into Xenopus laevis eggs induces precocious furrowing, and together with known spermine-actin interactions, suggests that spermine may be affecting cortical microfilaments involved in cytokinesis. An electron microscopic study of injected eggs revealed that the ultrastructure of the induced furrows was similar to that of both artificially activated eggs and fertilized eggs. In isolated egg cortices, increasing spermine concentrations (1, 3 and 10 mM) resulted in marked changes in cortical microfilament organization. At low concentrations, spermine appeared to stabilize microfilaments and at higher concentrations induced lateral associations between filaments and formation of bundles. The actin nature of these cortical microfilaments was confirmed by immunocytochemistry. The electrophoretic profiles of proteins from control and spermine-treated isolated cortices were similar. Although the total protein content of isolates in 3 and 10 mM spermine was elevated, the relative actin content remained constant. The results are in agreement with previous in vitro studies of polyamine interactions with actin and support the hypothesis that a polyamine-actin interaction may be important in the regulation of cytokinesis.