Nuclei function as wedges to pry open spaces and promote collective, confined cell 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 spaces in artificial environments, but how nuclei affect collective cell migration into tissues in vivo is unknown. Here, we use the border cells in the fly ovary to study nuclear dynamics in collective, confined in vivo migration. We find that transient deformation and movement of the nucleus into the lead cell protrusion pries apart substrate cells to facilitate collective movement of cell clusters into spaces much smaller than even a single nucleus. Depletion of the Drosophila B-type lamin, Lam, compromises nuclear integrity, impedes border cell detachment, and hinders stabilization of a single lead protrusion. Together, these data indicate that cells can use nuclei as wedges to facilitate collective movement into confined space. Summary During confined, collective border cell migration, the lead cell nucleus functions as a wedge to pry apart substrate nurse cells. Although both A- and B-type lamins are expressed, the B-type is essential while the A-type is dispensable.