Identification of new in vivo phosphosites on lamin Dm - the evidence of heterogeneity of phosphorylation sites in different Drosophila tissues.

Changes in the nuclear structure and function during the cell cycle are thought to be correlated with lamins phosphorylation. Here, we report the identification of new in vivo phosphorylation sites on Drosophila melanogater lamin Dm using immunoisolation and mass spectrometry with collision-induced peptide fragmentation (Electrospray-Linear Trap Quadrupole- Fourier Transform Ion Cyclotron Resonance MS/MS). We identified S19 and confirmed previously suggested S595 as phosphorylated amino acid residues on embryonic lamin Dm. We also found that T597 is phosphorylated in vivo in cultured Kc cells while S595 in embryos, which suggests that different neighboring phosphoacceptors may be modified within the same region. We demonstrate also that Drosophila melanogaster lamin Dm in very early (syncytial) embryos is almost completely dispersed through the entire embryo. Only fraction of lamin Dm is associated with nuclei and nuclear envelopes. In later stages, due to the synchronization of mitosis, lamin Dm may be both nuclear and cytoplasmic in the same embryo. Our results provide a new and essential data for better understanding of the lamin phosporylation in development and cell cycle regulation in Drosophila.