INSERTIONAL MUTATION OF THE DROSOPHILA NUCLEAR LAMIN DM(0) GENE RESULTS IN DEFECTIVE NUCLEAR ENVELOPES, CLUSTERING OF NUCLEAR-PORE COMPLEXES, AND ACCUMULATION OF ANNULATE LAMELLAE

Nuclear lamins are thought to play an important role in disassembly an d reassembly of the nucleus during mitosis. Here, we describe a Drosop hila lamin Dm(0) mutant resulting from a P element insertion into the first intron of the Dm(0) gene. Homozygous mutant animals showed a sev ere phenotype including retardation in development, reduced viability, sterility, and impaired locomotion. Immunocytochemical and ultrastruc tural analysis revealed that reduced lamin Dm(0) expression caused an enrichment of nuclear pore complexes in cytoplasmic annulate lamellae and in nuclear envelope clusters. In several cells, particularly the d ensely packed somata of the central nervous system, defective nuclear envelopes were observed in addition. All aspects of the mutant phenoty pe were rescued upon P element-mediated germline transformation with a lamin Dm(0) transgene. These data constitute the first genetic proof that lamins are essential for the structural organization of the cell nucleus.