Membrane fusion during spermiogenesis in Ascaris.
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abstract
Membrane fusion events occurring during experimentally induced spermiogenesis in Ascaris were examined using freeze-fracture electron microscopy. In addition to redistribution of cellular organelles during spermiogenesis, certain cytoplasmic elements termed membranous organelles become positioned in the posterior sperm cytoplasm and subsequently develop continuities with the plasma membrane via pores. As a result of this membrane fusion, the electron-dense contents of the organelle are secreted and the limiting membrane of the organelle becomes a stable, uniformly distributed specialization of the plasma membrane. Distinct particle arrays characterize the plasma membrane at presumptive fusion sites. Intramembranous events of the fusion process include the development of a circular, necklace-like array of particles on the P face of the plasma membrane followed by the development of a rosette of five to seven particles internal to the necklace-like array but which remain on the E face of the membrane. Completion of fusion is recognized by the loss of rosette particles and the disaggregation of particles comprising the necklace-like array at the neck of the pore. At this point, freeze-etching reveals the presence of an aqueous channel to the interior of the organelle. 1978 Academic Press, Inc.
