Posterior localization of the Drosophila Gi alpha protein during early embryogenesis requires a subset of the posterior group genes.

Shortly after fertilization in Drosophila embryos, the G-protein alpha subunit, Gi alpha, undergoes a dramatic redistribution. Initially granules containing Gi alpha are present throughout the embryonic cortex but during nuclear cleavage they become concentrated at the posterior pole and are lost by the blastoderm stage. Mutations that eliminate anterior structures bicoid, swallow, and exuperantia did not prevent the posterior accumulation of Gi alpha. Likewise, embryos from mothers with dominant gain of function mutations in the Bicaudal D gene show normal polarization of Gi alpha granules. By contrast, a subset of mutations which eliminate posterior structures, cappuccino, spire, staufen, mago nashi, valois, and oskar, prevented the posterior accumulation of Gi alpha. It is important to note that mutations in posterior genes lower in the putative hierarchy vasa, tudor nanos, and pumilio did not affect Gi alpha redistribution. From these results we conclude that Gi alpha redistribution to the posterior pole depends on maternal factors involved in the localization of the posterior morphogen nanos.