Structural organization and biological roles of the nuclear lamina

The nuclear lamina is a protein meshwork that lies on the nucleoplasmic side of the nuclear envelope and is associated with the peripheral chromatin. It is involved in several biological activities including: the mitotic disassembly and reassembly of the nuclear envelope, determination of the size and shape of the nucleus, higher order chromatin organization, cell differentiation, and apoptosis. Lamins are the major proteins of the nuclear lamina. They are type V intermediate filaments and, like all intermediate filaments, they form filamentous structures. Lamins can interact in vitro with specific DNA sequences, with chromosomal proteins and with several proteins of the inner nuclear membrane, including otefin, LBR, LAP1 and LAP2. In this paper we show that Drosophila lamin Dm0 and otefin proteins are required for the assembly of the Drosophila nuclear envelope. We also demonstrate that the lack of lamin Dm0 activity causes the dissociation of peripheral chromatin from the nuclear envelope, accumulation of annulate lamellae and lethality. In addition, we show that the carboxy (tail) domain of lamin Dm0 can interact in vitro with chromosomes and the central (rod) domain of lamin Dm0 is essential and sufficient for the in vitro assembly of lamin Dm0 into filamentous structures. These results are discussed in relationship to the biological roles of the nuclear lamina.