Localization of Drosophila formin, Cappuccino, influences posterior oocyte organization

Cappuccino (Capu) and Spire build actin networks in numerous systems, including the mouse oocyte, melanocytes, and the Drosophila oocyte. As observed in mammalian systems, the localization of the Capu homologues (FMN1/2), influences the function of the actin network. Therefore, we established and interrogated the impact of altering Capu’s localization in the Drosophila oocyte to better understand its role and that of the actin mesh it builds. This mesh restricts bulk cytoplasmic flows, streaming, but otherwise remains undescribed functionally. Using a gene specific driver, capu-Gal4, to better study Capu transgenes, we found that fertility was markedly decreased when restricting Capu to membranes in the oocyte, although its canonical role in actin mesh assembly was apparently unaltered. Instead, we observed a defect in posterior anchoring of the mRNA oskar during mid-oogenesis. However, the defect did not fall into the traditional posterior group phenotype. The data suggest that Capu, independently of Spire, tethers the posterior determinants to the cortex but does not anchor them to each other, supporting that Capu localization influences the posterior oocyte organization.