Capacitation
Encyclopedia
Capacitation is the penultimate step in the maturation of mammal
ian 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
.
By secreting sterol binding albumin, lipoproteins, proteolytic and glycosidasic enzymes such as heparin, the uterus
aids in the steps of capacitation.
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
.
) 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
is also part 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.
and Colin Russell Austin.
Historically, the term "capacitation" has evolved in meaning and this should be taken into account when consulting sources.
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian spermatozoa
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...
and is required to render them competent to fertilize an oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...
.
This step is a biochemical event; the sperm move normally and look mature prior to capacitation.
In vivo this step typically occurs after ejaculation
Ejaculation
Ejaculation is the ejecting of semen from the male reproductory tract, and is usually accompanied by orgasm. It is usually the final stage and natural objective of male sexual stimulation, and an essential component of natural conception. In rare cases ejaculation occurs because of prostatic disease...
, in the female reproductive tract
Sex organ
A sex organ, or primary sexual characteristic, as narrowly defined, is any of the anatomical parts of the body which are involved in sexual reproduction and constitute the reproductive system in a complex organism; flowers are the reproductive organs of flowering plants, cones are the reproductive...
.
In vitro, capacitation can occur in sperm that have either undergone ejaculation or have been extracted from the epididymis
Epididymis
The epididymis is part of the male reproductive system and is present in all male amniotes. It is a narrow, tightly-coiled tube connecting the efferent ducts from the rear of each testicle to its vas deferens. A similar, but probably non-homologous, structure is found in cartilaginous...
.
By secreting sterol binding albumin, lipoproteins, proteolytic and glycosidasic enzymes such as heparin, the uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
aids in the steps of capacitation.
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
Acrosome reaction
During fertilization, a sperm must first fuse with the plasma membrane and then penetrate the female egg in order to fertilize it. Fusing to the egg usually causes little problem, whereas penetrating through the egg's hard shell can present more of a problem to the sperm...
.
Result of capacitation
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. cholesterolCholesterol
Cholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...
) 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
Cyclic adenosine monophosphate
Cyclic adenosine monophosphate is a second messenger important in many biological processes...
levels and thus, an increase in motility. Hyperactivation
Hyperactivation
Hyperactivation is a type of sperm motility. Hyperactivated sperm motility is characterised by a high amplitude, asymmetrical beating pattern of the sperm tail...
is also part 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
The discovery of this process was independently reported in 1951 by both Min Chueh ChangMin Chueh Chang
Dr. Min Chueh Chang , often credited as M.C. Chang, was a Chinese American reproductive biologist. His specific area of study was the fertilisation process in mammalian reproduction...
and Colin Russell Austin.
Historically, the term "capacitation" has evolved in meaning and this should be taken into account when consulting sources.