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Capacitation is the penultimate step in the maturation of mammalian spermatozoa and is required to render them competent to fertilize an oocyte. This step is a biochemical event; the sperm move normally and look mature prior to capacitation. In vivo this step typically occurs after ejaculation, in the female reproductive tract. In vitro, capacitation can occur in sperm that have either undergone ejaculation or have been extracted from the epididymis.
Non-mammalian spermatozoa do not require this capacitation step and are ready to fertilize an oocyte immediately after release from the male. After this capacitation the sperm must undergo activation involving the acrosome reaction.
Result of capacitation
Capacitation involves the destabilisation of the sperm head membrane rendering it more fusigenic. This change is facilitated by the removal of sterols (e.g. cholesterol) and non-covalently bound epididymal/seminal glycoproteins. The result is a more fluid membrane with an increased permiability to Ca2+.
An influx of Ca2+ produces increased intracellular cAMP levels and thus, an increase in motility. Hyperactivation is also part of capacitation and is the result of the increased Ca2+ levels. The tripeptide FPP (fertilization promoting factor) produced by the male is essential for capacitation. It has a synergistic stimulatory effect with adenosine that increases adenyl cyclase activity in the sperm. FPP is found in the seminal fluid, and comes into contact with the spermatozoa upon ejaculation.
Historically, the term "capacitation" has evolved in meaning and this should be taken into account when consulting sources.
- Essential Reproduction, Johnson, 6th edition, Blackwell Publishing
- Chang, M. C. (1951) “Fertilizing capacity of spermatozoa deposited into the fallopian tubes,” Nature, vol. 168, pages 697-698.
- Austin, C. R. (1951) “Observations of the penetration of sperm into the mammalian egg,” Australian Journal of Scientific Research, Series B, vol. 4, pages 581-596.
- Austin, Colin Russell: obituary: “Colin Austin,” Australian Academy of Science Newsletter, No. 60, page 11 (August-November 2004). Available on-line at: http://www.science.org.au/newsletters/aas60.pdf .
- Beaudin, Stacey; Kipta, Donna; and Orr, Annamarie. (October 9, 1996). Current research into sperm capacitation: An Essay on Visconti, et al. Development 121: 1129-1150 (1995). Verified availability 2005-04-06.
- Visconti, Pablo E.; Bailey, Janice L.; Moore, Grace D.; Pan, Dieyun; Olds-Clarke, Patricia; and Kopf, Gregory S. (1995). Capacitation of mouse spermatozoa: I. Correlation between the capacitation state and protein tyrosine phosphorylation. Development 121, 1129-1137. PMID 7743926. full article text available on-line
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