Intercellular junctions between the follicle cells and oocytes of Xenopus laevis.

During development, the oocytes of Xenopus laevis establish junctional contact with the follicle cells enveloping them. These junctions have alternatively been described as desmosomes and as gap junctions. In this paper the morphology of these junctions has been examined in gonadotropin-stimulated and unstimulated animals at all stages of development. Contact between the oocyte and follicle cell plasma membranes is visible in stage I oocytes as thickenings in the membranes, separated by intercellular spaces of 20nm or greater. By stage III in unstimulated oocytes and stage II in gonadotropin-stimulated oocytes, intermembrane spaces at these junctional contacts are often reduced to 2 to 7 nm in width. These narrow intermembrane spaces persist through early stage IV, with greater frequency of occurrence in oocytes taken from hormonally stimulated animals. The closeness of these junctional contacts, and the permeability of the junctional spaces to intercellular tracer substances, supports the evidence that these are gap junctions.