Lasp anchors the Drosophila male stem cell niche and mediates spermatid individualization

Lasp family proteins contain an amino-terminal LIM domain, two actin-binding nebulin repeats and a carboxyl-terminal SH3 domain. Vertebrate Lasp-1 localizes to focal adhesions and the leading edge of migrating cells, and is required for cell migration. To assess the in vivo function of Lasp, we generated a null mutant in Drosophila Lasp. Lasp1 is homozygous viable, but male sterile. In Lasp mutants the stem cell niche is no longer anchored to the apical tip of the testis, and actin cone migration is perturbed resulting in improper spermatid individualization. Hub cell mislocalization can by phenocopied by expressing Lasp or βPS integrin RNAi transgenes in somatic cells, and Lasp genetically interacts with βPS integrin, demonstrating that Lasp functions together with integrins in hub cells to anchor the stem cell niche. Finally, we show that the stem cell niche is maintained even if it is not properly localized.