A-type and B-type lamins initiate layer assembly at distinct areas of the nuclear envelope in living cells

Abstract

To investigate nuclear lamina re-assembly in vivo, Drosophila A-type and B-type lamins were artificially expressed in Drosophila lamin Dm 0 null mutant brain cells. Both exogenous lamin C (A-type) and Dm 0 (B-type) formed sub-layers at the nuclear periphery, and efficiently reverted the abnormal clustering of the NPC. Lamin C initially appeared where NPCs were clustered, and subsequently extended along the nuclear periphery accompanied by the recovery of the regular distribution of NPCs. In contrast, lamin Dm 0 did not show association with the clustered NPCs during lamina formation and NPC spacing recovered only after completion of a closed lamin Dm 0 layer. Further, when lamin Dm 0 and C were both expressed, they did not co-polymerize, initiating layer formation in separate regions. Thus, A and B-type lamins reveal differing properties during lamina assembly, with A-type having the primary role in organizing NPC distribution. This previously unknown complexity in the assembly of the nuclear lamina could be the basis for intricate nuclear envelope functions.