The Drosophila KASH domain proteins Msp-300 and Klarsicht and the SUN domain protein klaroid have no essential function during oogenesis

Proteins harboring a C-terminal KASH (Klarsicht/Anc-1/Syne Homology) domain, which attaches to the nucleus, have been identified in many different organisms. Two KASH proteins are known from Drosophila, Msp-300 and Klarsicht, the latter of which plays a role in nuclear migration during eye development. Here, we show that a complete deletion of Msp-300 leads to larval lethality. This lethality appears to be due to Msp-300 isoforms containing the N-terminal actin binding, but not the C-terminal KASH domain. Msp-300 and Klar are expressed during oogenesis and localize to the nuclear envelope of the germ line nuclei. However, neither Msp-300 single mutants nor Msp-300; klar double mutants cause defects in nuclear migration or anchoring during oogenesis. Germ line nuclear envelope localization of both KASH domain proteins depends on klaroid, the only Drosophila SUN domain homolog expressed in females. Like Msp-300 and klar, klaroid is also dispensable for normal ovarian development.