A spermatozoon is a motile sperm cell produced by male animals relying on internal fertilization. A spermatozoon is a moving form of the haploid cell that is the male gamete that joins with an ovum to form a zygote.
Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a zygote and initiate its development into a new individual organism or offspring. While processes such as insemination or pollination, which happen before the fusion of gametes, are also sometimes informally referred to as fertilisation, these are technically separate processes. The cycle of fertilisation and development of new individuals is called sexual reproduction. During double fertilisation in angiosperms, the haploid male gamete combines with two haploid polar nuclei to form a triploid primary endosperm nucleus by the process of vegetative fertilisation.
The acrosome is an organelle that develops over the anterior (front) half of the head in the spermatozoa of humans and many other animals. It is a cap-like structure derived from the Golgi apparatus. In placental mammals, the acrosome contains degradative enzymes. These enzymes break down the outer membrane of the ovum, called the zona pellucida, allowing the haploid nucleus in the sperm cell to join with the haploid nucleus in the ovum. This shedding of the acrosome, known as the acrosome reaction, can be stimulated in vitro by substances that a sperm cell may encounter naturally, such as progesterone or follicular fluid, as well as the more commonly used calcium ionophore A23187. This can be done to serve as a positive control when assessing the acrosome reaction of a sperm sample by flow cytometry or fluorescence microscopy. This is usually done after staining with a fluoresceinated lectin such as FITC-PNA, FITC-PSA, FITC-ConA, or fluoresceinated antibody such as FITC-CD46.
The zona pellucida is the specialized area surrounding mammalian oocytes (eggs). It is also known as an egg coat. The zona pellucida is essential for oocyte growth and fertilization.
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, capacitation occurs after ejaculation, when the spermatozoa leave the vagina and enter the upper female reproductive tract. The uterus aids in the steps of capacitation by secreting sterol-binding albumin, lipoproteins, and proteolytic and glycosidasic enzymes such as heparin.
Acrosin is a digestive enzyme that acts as a protease. In humans, acrosin is encoded by the ACR gene. Acrosin is released from the acrosome of spermatozoa as a consequence of the acrosome reaction. It aids in the penetration of the Zona Pellucida.
Human fertilization is the union of an egg and sperm, occurring primarily in the ampulla of the fallopian tube. The result of this union leads to the production of a fertilized egg called a zygote, initiating embryonic development. Scientists discovered the dynamics of human fertilization in the 19th century.
The cortical reaction is a process initiated during fertilization that prevents polyspermy, the fusion of multiple sperm with one egg. In contrast to the fast block of polyspermy which immediately but temporarily blocks additional sperm from fertilizing the egg, the cortical reaction gradually establishes a permanent barrier to sperm entry and functions as the main part of the slow block of polyspermy in many animals.
The corona radiata is the innermost layer of the cells of the cumulus oophorus and is directly adjacent to the zona pellucida, the inner protective glycoprotein layer of the ovum. Cumulus oophorus are the cells surrounding corona radiata, and are the cells between corona radiata and follicular antrum. Its main purpose in many animals is to supply vital proteins to the cell. It is formed by follicle cells adhering to the oocyte before it leaves the ovarian follicle, and originates from the squamous granulosa cells present at the primordial stage of follicular development. The corona radiata is formed when the granulosa cells enlarge and become cuboidal, which occurs during the transition from the primordial to primary stage. These cuboidal granulosa cells, also known as the granulosa radiata, form more layers throughout the maturation process, and remain attached to the zona pellucida after the ovulation of the Graafian follicle. For fertilization to occur, sperm cells rely on hyaluronidase to disperse the corona radiata from the zona pellucida of the secondary (ovulated) oocyte, thus permitting entry into the perivitelline space and allowing contact between the sperm cell and the nucleus of the oocyte.
Decapacitation factor (DF) is composed of sperm surface-associated proteins which modulate the fertilizing ability of spermatozoa. Decapacitation is a reversible process that converts fertile, capacitated sperm to less-fertile uncapacitated sperm. This activity is achieved by interaction between cholesterol, phospholipids and fibronectin-like substances and delivered via small vesicles in seminal plasma. DF prevents onset of capacitation. Many DFs are released in secretions from the epididymis and accessory organs of the male reproductive system. However, some DFs have been identified that are located on the acrosome of sperm. Normally, capacitation is initiated through the loss of DF before the spermatozoa can perform the acrosomal reaction. Physiologically decapacitation will inhibit the acrosomal reaction as DFs reassociate onto the sperm surface. For example, one way this can be achieved is through spermatozoal membrane stabilization by maintaining physiological cholesterol/phospholipid ratio.
The vitelline membrane or vitelline envelope is a structure surrounding the outer surface of the plasma membrane of an ovum or, in some animals, the extracellular yolk and the oolemma. It is composed mostly of protein fibers, with protein receptors needed for sperm binding which, in turn, are bound to sperm plasma membrane receptors. The species-specificity between these receptors contributes to prevention of breeding between different species. It is called zona pellucida in mammals. Between the vitelline membrane and zona pellucida is a fluid-filled perivitelline space.
Zona pellucida sperm-binding protein 3, also known as zona pellucida glycoprotein 3 (Zp-3) or the sperm receptor, is a ZP module-containing protein that in humans is encoded by the ZP3 gene. ZP3 is the glycoprotein in the zona pellucida most important for inducting the acrosome reaction of sperm cells at the beginning of fertilization.
Glycodelin(GD) also known as human placental protein-14 (PP-14)progestogen-associated endometrial protein (PAEP) or pregnancy-associated endometrial alpha-2 globulin is a glycoprotein that inhibits cell immune function and plays an essential role in the pregnancy process. In humans is encoded by the PAEP gene.
Zona pellucida sperm-binding protein 2 is a protein that in humans is encoded by the ZP2 gene.
Zona pellucida sperm-binding protein 4, ZP-4 or avilesine, named after its discoverer Manuel Avilés Sánchez is a protein that in humans is encoded by the ZP4 gene.
Oocyteactivation is a series of processes that occur in the oocyte during fertilization.
Cortical granules are regulatory secretory organelles found within oocytes and are most associated with polyspermy prevention after the event of fertilization. Cortical granules are found among all mammals, many vertebrates, and some invertebrates. Within the oocyte, cortical granules are located along the cortex, the region furthest from the cell's center. Following fertilization, a signaling pathway induces the cortical granules to fuse with the oocyte's cell membrane and release their contents into the oocyte's extracellular matrix. This exocytosis of cortical granules is known as the cortical reaction. In mammals, the oocyte's extracellular matrix includes a surrounding layer of perivitelline space, zona pellucida, and finally cumulus cells. Experimental evidence has demonstrated that the released contents of the cortical granules modify the oocyte's extracellular matrix, particularly the zona pellucida. This alteration of the zona pellucida components is known as the zona reaction. The cortical reaction does not occur in all mammals, suggesting the likelihood of other functional purposes for cortical granules. In addition to modifying the oocyte's extracellular matrix and establishing a block to polyspermy, the exocytosis of cortical granules may also contribute towards protection and support of the developing embryo during preimplantation. Once the cortical granules complete their functions, the oocyte does not replenish them.
Izumo sperm-egg fusion protein 1 is encoded in humans by the IZUMO1 gene. In mammalian fertilisation, IZUMO1 binds to its egg receptor counterpart, Juno, to facilitate recognition and fusion of the gametes.
Globozoospermia is a rare and severe form of monomorphic teratozoospermia. This means that the spermatozoa show the same abnormality, and over 85% of spermatozoa in sperm have this abnormality. Globozoospermia is responsible for less than 0.1% of male infertility. It is characterised by round-headed spermatozoa without acrosomes, an abnormal nuclear membrane and midpiece defects. Affected males therefore suffer from either reduced fertility or infertility. Studies suggest that globozoospermia can be either total or partial, however it is unclear whether these two forms are variations on the same syndrome, or actually different syndromes.
Paul Michael Wassarman is an American biologist who has been Professor in the Dept. of Cell, Developmental, and Regenerative Biology at the Icahn School of Medicine at Mount Sinai since 1996. His laboratory identified and characterised proteins that make up the zona pellucida (ZP) of mammalian eggs and determined their role in fertilisation.
