JAK/STAT signalling in Drosophila controls cell motility during germ cell migration

The gonad is formed from two populations of cells originating at different locations: the primordial germ cells (PGCs), giving rise to either sperm or oocytes, and the somatic gonadal mesoderm precursors (SGPs), which support development of the gametes. Following the PGCs' migration during gastrulation, these two populations meet, forming the immature gonad. We present evidence that during embryonic development, the PGCs require the canonical JAK/STAT signalling cascade to migrate efficiently towards the SGPs. Loss of function for any element of the JAK/STAT pathway causes frequent germ cell mislocalisation. We have found that wild-type germ cells produce filopodia while they migrate through the mesoderm towards the gonad. Our observations suggest that PGCs use filopodia to migrate and to keep contact with each other. Interestingly, activation of the JAK/STAT pathway is required for these filopodia to form, and ectopic JAK/STAT activation enhances their formation.