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This article is about a biological process related to reproduction. For the conceptual approach to development, see Capacity building.

Capacitation is the penultimate^[1] 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 by incubating sperms that have either undergone ejaculation or have been extracted from the epididymis in a defined medium for several hours.

The uterus aids in the steps of capacitation by secreting sterol-binding albumin, lipoproteins, proteolytic and glycosidasic enzymes such as heparin.

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.

Capacitation[edit]

Capacitation involves the destabilisation of the acrosomal sperm head membrane allowing greater binding between sperm and oocyte. This change is facilitated by the removal of steroids (e.g. cholesterol) and non-covalently bound epididymal/seminal glycoproteins. The result is a more fluid membrane with an increased permeability to Ca²⁺.

An influx of Ca²⁺ produces increased intracellular cAMP levels and thus, an increase in motility. Hyperactivation coincides with the onset of capacitation and is the result of the increased Ca²⁺ levels. The tripeptide FPP (fertilization promoting peptide) produced by the male is essential for capacitation (high levels of FPP prevent capacitation, the proper concentration occurs after ejaculation in the female reproductive tract where the concentration drops after mixing with vaginal secretions and/or becomes less active due to the pH of the vagina). It has a synergistic stimulatory effect with adenosine that increases adenylyl cyclase activity in the sperm. FPP is found in the seminal fluid (FPP produced in prostate gland), and comes into contact with the spermatozoa upon ejaculation.

Discovery[edit]

The discovery of this process was independently reported in 1951 by both Min Chueh Chang^[2] and Colin Russell Austin.^[3]^[4]

Historically, the term "capacitation" has evolved in meaning and this should be taken into account when consulting sources.

Footnotes[edit]

^ 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 .

References[edit]

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

External links[edit]

Sperm Capacitation at the US National Library of Medicine Medical Subject Headings (MeSH)

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STUDY QUESTION: How does oxidative stress impact upon human sperm-egg interaction and in particular the formation of zona pellucida-receptor complexes on the sperm surface SUMMARY ANSWER: Oxidative stress during human sperm capacitation resulted in the chemical alkylation of the molecular chaperone
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日本産科婦人科學會雜誌 63(10), 1936-1955, 2011-10-01
… Since the discovery of these various phenomena that occur to sperm at the time of fertilization, and the realization that capacitation can be generated in vitro, research into IVF began and progressed on many species of mammals. … However, the substantial difference between humans and other mammals was the wide variation in the time required for capacitation among human individuals. …
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… Glycoproteins (GPs) are known to be involved in the phenomenon of sperm maturation and capacitation. …
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