Cummins J M, Robson S K, Rouse G W
Department of Anatomy, University of Queensland, St. Lucia, Australia.
Gamete Res. 1988 Sep;21(1):11-22. doi: 10.1002/mrd.1120210103.
Acrosome reactions were induced in seminal spermatozoa of the megachiropteran Pteropus poliocephalus, the grey-headed flying fox, using the ionophore A23187 (10 microM in Tyrodes solution with 1% w/v BSA). Samples were taken at 0, 10, and 120 minutes and fixed for electron microscopy. Initial motility of approximately 70% decreased to approximately 10% over 2 hours. The first motile spermatozoa without acrosomal caps were seen after 6 minutes, and by 90 minutes approximately 60% of motile spermatozoa had completed the acrosome reaction. The first sign of the reaction (by TEM) appears to be swelling and cavitation of the acrosomal matrix within the apical and principal segments, followed or possibly accompanied by fusion and fenestration of the outer acrosomal and plasma membranes and dispersion of the matrix except from the equatorial segment. The end-product of the reaction thus conforms to that seen in other eutherian mammals. However, the reaction exposes a uniquely moulded organization of subacrosomal material ("pseudoperforatorium"), shaped like an anvil over the rostral rim of the flattened nucleus and encased by the remaining inner acrosomal membrane. This has two "lateral" spikes on each side that extend approximately to the same width as the head in the region of the equatorial segment. While these barbs could serve to stabilize or anchor the apical segment of the acrosome, their exposure following the acrosome reaction suggests some specific mechanical role in penetration of the zona pellucida or in protecting more caudal structures from abrasive damage.
