MOESIN crosslinks actin and cell membrane in Drosophila oocytes and is required for OSKAR anchoring

In Drosophila, development of the embryonic germ cells depends on posterior transport and site-specific translation of oskar(osk) mRNA and on interdependent anchoring of the osk mRNA and protein within the posterior subcortical region of the oocyte [1-3]. Transport of the osk mRNA is mediated by microtubules, while anchoring of the osk gene products at the posterior pole of the oocyte is suggested to be microfilament dependent [4-7]. To date, only a single actin binding protein (Tropomyosinil) has been identified with a putative role in osk mRNA and protein anchoring [4]. This communication demonstrates that mutations in the Drosophila moesin (Dmoe) gene that encodes another actin binding protein result in delocalization of osk mRNA and protein from the posterior subcortical region and, as a consequence, in failure of embryonic germ cell development. In Dmoe mutant oocytes, the subcortical actin network is detached from the cell membrane, while the polarized microtubule cytoskeleton is unaffected. In line with the earlier observations [6, 8], colocalization of ectopic actin and OSK protein in Dmoe mutants suggests that the actin cytoskeleton anchors OSK protein to the subcortical cytoplasmic area of the Drosophila oocyte.