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Ultrastructural studies of centipede and other myriapod ovaries reveal direct soma-germline contact across the basement membrane, a structure typically regarded as a cellular barrier.

These findings, in the journal Biology Letters, suggest a previously unrecognized form of interaction between somatic and germ cells in animals, challenging established views in zoology and cell biology.

Animal organs are enclosed by a specialized epithelial layer. Epithelial cells typically exhibit apicobasal polarity: their apical surfaces contact other cells or the environment, whereas their basal surfaces are separated from neighboring cells by a wall-like structure, the basement membrane. For example, follicle cells, i.e., somatic cells surrounding oocytes, interact directly with female germ cells on their apical side and contribute to egg production.

However, on the basal side, the basement membrane blocks their contact with other cells.

Contrary to this general understanding, this study revealed that, unlike in other animals, the ovarian follicle cells in two myriapod species, Thereuonema tuberculata and Hanseniella caldaria, face oocytes on their basal side and extend cytoplasmic processes through the basement membrane to establish oocyte contact.

These observations also suggest that this follicle cell-oocyte interaction is initiated before the basement membrane forms during oogenesis.

These findings demonstrate that the basement membrane does not always act as a barrier between somatic and germ cells and reveal a novel mode of cell-cell interaction: epithelium cells can completely penetrate the basement membrane to make direct contact with other cells.