Lamin-A/C/LAP2α/BAF1 protein complex regulates the mitotic spindle assembly and positioning

Abstract

Some nuclear proteins crucial in interphase relocate to other places during the G2-M phase transition to take their mitotic functions. However, how they perform these functions and the underlying mechanisms remain largely unknown. Here we report that a fraction of the nuclear periphery proteins lamin-A/C, LAP2α and BAF1 relocate to the spindle and the cell cortex in mitosis. RNAi knockdown of these proteins induces short and fluffy spindle formation and disconnection of the spindle with the cell cortex. Disrupting the microtubule assembly leads to accumulation of these proteins in the cell cortex, whereas depolymerizing the actin microfilaments results in the short spindle formation. We further demonstrate that these proteins are part of a stable complex that links the mitotic spindle to the cell cortex and the spindle matrix by binding with the spindle-associated dynein and the actin filaments in the cell cortex and the spindle matrix. Together, our findings unveil a unique mechanism that the nuclear periphery proteins lamin-A/C, LAP2α and BAF1 are assembled into a protein complex in mitosis to regulate the mitotic spindle assembly and positioning.