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2 results

  • Chapter 5

  • R. John Aitken, University of Newcastle, New South Wales
  • Book:
    The Infertility Trap
    Published online:
    05 May 2022
    Print publication:
    05 May 2022, pp 180-202

  • Summary

    The miracle of conception – how we all got to be here Successful conception requires spermatozoa to exhibit a wide range of sophisticated behaviours and biochemical changes. They are capable of exhibiting rheotaxis, thermotaxis and chemotaxis on their voyage to the site of fertilization in the oviduct. Once these cells have successfully engaged the cervix and uterotubal junction they come to rest in the isthmic region of the Fallopian tubes, where they are thought to bind to the oviductal epithelium and enter a state of quiescence. They are ultimately awakened from this gentle slumber by a signal coincident with ovulation and break away from the isthmic epithelium in a frenzied state of hyperactivation. These hyperactivated cells then bring their receptors-for-the-egg to the cell surface and go in search of their prey, aided by signals given out by the egg bearing a come-hither message. At this point in development, it is a race to find the fittest spermatozoa capable of engaging in the myriad cellular interactions required to achieve fertilization. It is a race that only one cell can win out of the ~200 million that started the race. Each one of us is the result of an incredibly complex obstacle race where all of the other competitors died.

  • Stages leading to and following fusion of sperm and egg plasma membranes

  • Frank J. Longo, Susan Cook, David H. McCulloh, Pedro I. Ivonnet, Edward L. Chambers
  • Journal:
    Zygote / Volume 2 / Issue 4 / November 1994
    Published online by Cambridge University Press:
    26 September 2008, pp. 317-331

  • The site of gamete interaction of electrophysiologically recorded Lytechinus variegatus eggs, fixed with osmium tetroxide (O5O4) and/or glutaraldehyde (GTA) at varying intervals after the onset of the increase in membrane conductance induced by an attached sperm, has been examined by high-voltage and conventional transmission electron microscopy. Although GTA and a GTA-O5O4 mixture iduced different electrical responses, specimens prepared with the two fixatives were ultrastructurally similar. In specimens observed within 5 s of the change in conductance, the acrosomal process projected through the vitelline layer and abutted the egg plasma membrane. A conspicuous layer of bindin surrounded the acrosomal process and connected the sperm to the egg's vitelline layer. In a fortuitous specimen fixed within 4 s following the change in conductance, the area of contact between the gamete plasma membranes possessed a trilaminar structure that separated the egg's and sperm's cytoplasms. The morphology of this area of contact was consistent with previously proposed intermediates of membrane fusion. Five to six seconds after the change in conductance, the sperm was connected to the egg via a narrow cytoplasmic bridge that consisted of the former acrosomal process and a projection of the egg cortex. The region of the bridge midway between the fused gametes was encircled by dense material that marked the site of sperm-egg fusion. Gamete interactions in which the activation potential was recorded (unclamped egg) were comparable in time and ultrastructure to events taking place in voltage-clamped eggs except for one major difference. Intact cortical granules (one to three) were observed beneath the tip of the incorporating sperm in unclamped eggs fixed following the onset of the activation potential, whereas all cortical granules dehisced in clamped eggs.