Intake of phosphatase-active plasma membrane into the cytoplasm of oocytes from sexually immature hamsters.

When thiamine pyrophosphate is used as substrate, heavily stained complexly branching cytoplasmic structures are seen in developing oocytes of the hamster between 8 and 12 days after birth. This coincides with the onset of the dictyate stage of first meiotic prophase. The structures appear to arise from the oocyte plasma membrane in two ways: (1) by proliferation and infolding of the membrane, and (2) by membrane being pushed into the cytoplasm by invaginating follicle cell processes. This appears to be followed by proliferation of the invaginated plasma membrane within the oocyte cytoplasm. Incubations with ATP or beta-glycerophosphate, with and without the inhibitor L-p-bromotetramisole, indicate that the staining is not due to the action of either ATPase or alkaline phosphatases. The origin and possible developmental significance of the reactive structures are discussed.