TorsinA controls TAN line assembly and the retrograde flow of dorsal perinuclear actin cables during rearward nuclear movement

Abstract

In fibroblasts and myoblasts polarizing for migration, retrograde actin flow moves the nucleus rearward, orienting the centrosome toward the leading edge. The nucleus engages moving dorsal actin cables through linear arrays of nesprin-2G and SUN2 called TAN lines. In this study, Saunders et al. report that the nuclear envelope–localized AAA+ ATPase torsinA and its activator, LAP1, are required for TAN line assembly and retrograde dorsal actin cable flow.

Abstract

The nucleus is positioned toward the rear of most migratory cells. In fibroblasts and myoblasts polarizing for migration, retrograde actin flow moves the nucleus rearward, resulting in the orientation of the centrosome in the direction of migration. In this study, we report that the nuclear envelope–localized AAA+ (ATPase associated with various cellular activities) torsinA (TA) and its activator, the inner nuclear membrane protein lamina-associated polypeptide 1 (LAP1), are required for rearward nuclear movement during centrosome orientation in migrating fibroblasts. Both TA and LAP1 contributed to the assembly of transmembrane actin-associated nuclear (TAN) lines, which couple the nucleus to dorsal perinuclear actin cables undergoing retrograde flow. In addition, TA localized to TAN lines and was necessary for the proper mobility of EGFP-mini–nesprin-2G, a functional TAN line reporter construct, within the nuclear envelope. Furthermore, TA and LAP1 were indispensable for the retrograde flow of dorsal perinuclear actin cables, supporting the recently proposed function for the nucleus in spatially organizing actin flow and cytoplasmic polarity. Collectively, these results identify TA as a key regulator of actin-dependent rearward nuclear movement during centrosome orientation.