Nuclear lamins promote protrusion dynamics and collective, confined migration in vivo

Cells migrate collectively through confined environments during development and cancer metastasis. The nucleus, a stiff organelle, impedes single cells from squeezing into narrow channels within artificial environments, but how nuclei affect collective cell migration into compact tissues in vivo is unknown. Here, we use border cells in the fly ovary to study nuclear dynamics in collective, confined in vivo migration. Border cells delaminate from the follicular epithelium and squeeze into tiny spaces between cells called nurse cells. The lead cell nucleus transiently deforms as it extends into the lead cell protrusion, which then widens. The nuclei of follower cells deform less. Depletion of the Drosophila B-type lamin, Lam, compromises nuclear integrity, hinders expansion of a leading protrusion, and impedes border cell movement. Cortical myosin II accumulates behind the nucleus and moves it into the protrusion in wildtype but not Lam-depleted cells. These data suggest that the nucleus stabilizes lead cell protrusions to help cells wedge open spaces between nurse cells. SummaryDuring Drosophila border cell migration, the B-type lamin Lam maintains nuclear envelope integrity, stabilizes the lead cell protrusion, and promotes cluster invasion between nurse cells. The nucleus may function as a wedge to prom collective, confined in vivo movement.