Soma-germ contact across the basement membrane in the ovary.

Epithelial cells interact with other cells and environments at their apical side, while the basement membrane typically impedes such interaction at the basal surface. One notable instance is communication between soma and germ cells within the ovary across numerous bilaterian taxa. This contact underlies proper oogenesis and subsequent embryogenesis. Throughout the history of morphology and cell biology, there has been an emphasis on this heterocellular interaction primarily occurring at the apical side of epithelial cells. Contrary to this long-standing understanding, we uncover that ovarian follicle cells in two myriapod species belonging to phylogenetically basal myriapod clades extend their cytoplasmic processes, penetrating the basement membrane to establish direct contact with oocytes. These discoveries demonstrate that the ovarian soma-germ interaction transverses the basement membrane, suggesting that the basal matrix is not always a physical barrier to soma-germ communication. Furthermore, we find that the ovarian somatic cells in a myriapod directly connect with the oogonia or young oocyte before forming their basement membrane. These results encourage reconsidering the conventional view of soma-germ interaction and suggest an overlooked construction manner of heterocellular communication in epithelial cells.