Reorganization of the nuclear architecture in the Lamin B mutant lacking the CaaX box.

Lamins interact with the nuclear membrane and chromatin but the precise players and mechanisms of these interactions are unknown. Here, we tested whether the removal of the CaaX motif from Lamin B disrupts its attachment to the nuclear membrane and affects chromatin distribution. We used  homozygous mutants that lack the CaaX box. We found that the mutant Lamin B was not confined to the nuclear periphery but was distributed throughout the nuclear interior, colocalizing with chromosomes in salivary gland and proventriculus. The peripheral position of Lamin C, nuclear pore complex (NPC), heterochromatin protein 1a (HP1a), H3K9me2- and H3K27me3-associated chromatin remained intact. The fluorescence intensity of the DAPI-stained peripheral chromatin significantly decreased and that of the central chromatin significantly increased in the proventriculus nuclei of the mutantflies compared to wild-type. However, the mutation had little effect on chromatin radial distribution inside highly polytenized salivary gland nuclei.