Fusion of plasma membranes between Chlamydomonas reinhardtii gametes has been studied by freeze-fracture electron microscopy of unfixed cells. The putative site of cell fusion developes during gametic differentiation and is recognized in thin sections of unmated gametes as a plaque of dense material subjacent to a sector of the anterior plasma membrane (Goodenough, U.W., and R.L. Weiss. 1975.J. Cell Biol. 67:623-637). The overlying membrane proves to be readily recognized in replicas of unmated gametes as a circular region roughly 500 nm in diameter which is relatively free of "regular" plasma membrane particles on both the P and E fracture faces. The morphology of this region is different for mating-type plus (mt+) and mt- gametes: the few particles present in the center of the mt+ region are distributed asymmetrically and restricted to the P face, while the few particles present in the center of the mt- region are distributed symmetrically in the E face. Each gamete type can be activated for cell fusion by presenting to it isolated flagella of opposite mt. The activated mt+ gamete generates large expanses of particle-cleared membrane as it forms a long fertilization tubule from the mating structure region. In the activated mt- gamete, the E face of the mating structure region is transformed into a central dome of densely clustered particles surrounded by a particle-cleared zone. When mt+ and mt- gametes are mixed together, flagellar agglutination triggeeeds to fuse with an activated mt- region. The fusion lip is seen to develop within the particle-dense central dome. We conclude that these mt- particles play an active role in membrane fusion.
Article| January 01 1977
Membrane differentiations at sites specialized for cell fusion.
D A Goodenough,
R L Weiss
D A Goodenough
U W Goodenough
Online ISSN: 1540-8140
Print ISSN: 0021-9525
J Cell Biol (1977) 72 (1): 144–160.
R L Weiss, D A Goodenough, U W Goodenough; Membrane differentiations at sites specialized for cell fusion.. J Cell Biol 1 January 1977; 72 (1): 144–160. doi: https://doi.org/10.1083/jcb.72.1.144
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