Assembly of Drosophila lamin Dm(0) and C mutant proteins studied with the baculovirus system

Despite extensive knowledge of the in vitro polymerization properties of nu clear lamins, it is still not well understood how the nuclear lamina assemb les in vivo. To learn more about the relationship between in vitro and in v ivo polymerization of nuclear lamins, we expressed Drosophila lamin Dm(0) m utant proteins, having well defined alterations of their in vitro polymeriz ation properties, in Sf9 cells using the baculovirus system. All lamin Dm(0 ) mutants assembled into fibrillar aggregates indistinguishable in morpholo gy from those assembled by the wildtype protein. However, in contrast to wi ld-type lamin Dm(0), mutant proteins were extracted with buffers of physiol ogical ionic strength and pH containing Triton X-100. These results indicat e that various types of lamin diner-dimer interactions can be disrupted wit hout affecting the morphology of the lamin Dm(0) polymer. However, all type s of dimer-dimer interactions tested appear to be important for full polyme r stability. In addition, we analyzed the polymer formation of two Drosophi la lamin C mutants and found that a segment in the carboxy-terminal tail do main is required for assembly of lamin C paracrystals at the nuclear lamina .