The JIL-1 kinase interacts with lamin Dm₀ and regulates nuclear lamina morphology of Drosophila nurse cells

We have used a yeast two-hybrid screen to identify lamin Dm₀ as an interaction partner for the nuclear JIL-1 kinase. This molecular interaction was confirmed by GST-fusion protein pull-down assays and by co-immunoprecipitation experiments. Using deletion construct analysis we show that a predicted globular domain of the basic region of the COOH-terminal domain of JIL-1 was sufficient for mediating the molecular interactions with lamin Dm₀. A reciprocal analysis with truncated lamin Dm₀ constructs showed that the interaction with JIL-1 required sequences in the tail domain of lamin Dm₀ that include the Ig-like fold. Further support for a molecular interaction between JIL-1 and lamin Dm₀ in vivo was provided by genetic interaction assays. We show that nuclear positioning and lamina morphology were abnormal in JIL-1 mutant egg chambers. The most common phenotypes observed were abnormal nurse cell nuclear lamina protrusions through the ring canals near the oocyte, as well as dispersed and mislocalized lamin throughout the egg chamber. These phenotypes were completely rescued by a full-length JIL-1 transgenic construct. Thus, our results suggest that the JIL-1 kinase is required to maintain nuclear morphology and integrity of nurse cells during oogenesis and that this function may be linked to molecular interactions with lamin Dm₀.