Cell migration through epithelial tissues occurs during development, infection, inflammation, wound healing and cancer metastasis. But how do cells overcome the impermeable junctions between epithelial cells? Leukocytes move out of blood vessels by loosening endothelial cell-cell junctions but do all cells actively remodel tissue barriers during migration? According to Jessica Seifert and Ruth Lehmann, who are studying Drosophila primordial germ cell (PGC) migration through the endodermal epithelium to the gonadal mesoderm, the answer to this question is no (see ). Although PGC migration requires activation of the G protein-coupled receptor Trapped in endoderm 1 (Tre1) within PGCs, the timing of PGC migration is dictated by the developmental stage of the endoderm. Now, using live imaging and genetic manipulation, the researchers show that PGCs take advantage of developmentally regulated epithelial remodelling, which causes discontinuities in the endoderm, to gain access to the gonadal mesoderm. Thus, Seifert and Lehmann conclude that, rather than actively remodelling tissue barriers, some migrating cells exploit existing tissue permeability.
