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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.
Fertilisation or fertilization, also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Processes such as insemination or pollination which happen before the fusion of gametes are also sometimes informally called fertilisation. 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.
Inositol trisphosphate or inositol 1,4,5-trisphosphate abbreviated InsP3 or Ins3P or IP3 is an inositol phosphate signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the plasma membrane, by phospholipase C (PLC). Together with diacylglycerol (DAG), IP3 is a second messenger molecule used in signal transduction in biological cells. While DAG stays inside the membrane, IP3 is soluble and diffuses through the cell, where it binds to its receptor, which is a calcium channel located in the endoplasmic reticulum. When IP3 binds its receptor, calcium is released into the cytosol, thereby activating various calcium regulated intracellular signals.
During fertilization, a sperm must first fuse with the plasma membrane and then penetrate the female egg cell to fertilize it. Fusing to the egg cell usually causes little problem, whereas penetrating through the egg's hard shell or extracellular matrix can be more difficult. Therefore, sperm cells go through a process known as the acrosome reaction, which is the reaction that occurs in the acrosome of the sperm as it approaches the egg. The acrosome is a cap-like structure over the anterior half of the sperm's head.
Oogenesis, ovogenesis, or oögenesis is the differentiation of the ovum into a cell competent to further develop when fertilized. It is developed from the primary oocyte by maturation. Oogenesis is initiated in the embryonic stage.
The zona pellucida is a glycoprotein layer surrounding the plasma membrane of mammalian oocytes. It is a vital constitutive part of the oocyte. The zona pellucida first appears in unilaminar primary oocytes. It is secreted by both the oocyte and the ovarian follicles. The zona pellucida is surrounded by the corona radiata. The corona is composed of cells that care for the egg when it is emitted from the ovary.
Calcium signaling is the use of calcium ions (Ca2+) to communicate and drive intracellular processes often as a step in signal transduction. Ca2+ is important for cellular signalling, for once it enters the cytosol of the cytoplasm it exerts allosteric regulatory effects on many enzymes and proteins. Ca2+ can act in signal transduction resulting from activation of ion channels or as a second messenger caused by indirect signal transduction pathways such as G protein-coupled receptors.
Human fertilization is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union, leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. Scientists discovered the dynamics of human fertilization in the nineteenth century.
In biology, polyspermy describes an egg that has been fertilized by more than one sperm. Diploid organisms normally contain two copies of each chromosome, one from each parent. The cell resulting from polyspermy, on the other hand, contains three or more copies of each chromosome—one from the egg and one each from multiple sperm. Usually, the result is an unviable zygote. This may occur because sperm are too efficient at reaching and fertilizing eggs due to the selective pressures of sperm competition. Such a situation is often deleterious to the female: in other words, the male-male competition among sperm spills over to create sexual conflict.
Phosphoinositide phospholipase C (PLC) is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. These enzymes belong to a larger superfamily of Phospholipase C. Other families of phospholipase C enzymes have been identified in bacteria and trypanosomes. Phospholipases C are phosphodiesterases.
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.
A polar body is a small haploid cell that is formed at the same time as an egg cell during oogenesis, but generally does not have the ability to be fertilized.
Hyalin is a protein released from the cortical granules of a fertilized animal egg. The released hyalin modifies the extracellular matrix of the fertilized egg to block other sperm from binding to the egg, and is known as the slow-block to polyspermy. All animals have this slow-block mechanism.
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.
The cation channels of sperm also known as Catsper channels or CatSper, are ion channels that are related to the two-pore channels and distantly related to TRP channels. The four members of this family form voltage-gated Ca2+ channels that seem to be specific to sperm. As sperm encounter the more alkaline environment of the female reproductive tract, CatSper channels become activated by the altered ion concentration. These channels are required for proper fertilization. The study of these channels has been slow because they do not traffic to the cell membrane in many heterologous systems.
Sperm motility describes the ability of sperm to move properly through the female reproductive tract or through water to reach the egg. Sperm motility can also be thought of as the quality, which is a factor in successful conception; sperm that do not "swim" properly will not reach the egg in order to fertilize it. Sperm motility in mammals also facilitates the passage of the sperm through the cumulus oophorus and the zona pellucida, which surround the mammalian oocyte.
Zona pellucida sperm-binding protein 2 is a protein that in humans is encoded by the ZP2 gene.
The insect vitelline envelope is the outer proteinaceous layer outside the oocyte and egg. The vitelline envelope, not being a cellular structure, is commonly referred to as a membrane. However, this is a technical misnomer as the structure is composed of protein and is not a cellular component. It varies in thickness between different insects and even varies at different parts of the egg. It lies inside the outer shell of the egg, which is commonly referred to as the chorion.
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.
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.
References
- ↑ Saleh A, Kashir J, Thanassoulas A, Safieh-Garabedian B, Lai FA, Nomikos M (2020). "Essential Role of Sperm-Specific PLC-Zeta in Egg Activation and Male Factor Infertility: An Update". Front. Cell Dev. Biol. 8 (28). doi: 10.3389/fcell.2020.00028 . PMC 7000359 .
- ↑ Bianchi E, Doe B, Goulding D, Wright GJ (2014). "Juno is the egg Izumo receptor and is essential for mammalian fertilization". Nature. 508 (7497): 483–7. Bibcode:2014Natur.508..483B. doi:10.1038/nature13203. PMC 3998876 . PMID 24739963.
- ↑ Saunders C, Larman M, Parrington J, Cox L, Royse J, Blayney L, Swann K, Lai F (2002). "PLC zeta: a sperm-specific trigger of Ca(2+) oscillations in eggs and embryo development". Development. 129 (15): 3533–44. PMID 12117804.
- ↑ Yu, Yuansong; Nomikos, Michail; Theodoridou, Maria; Nounesis, George; Lai, F. Anthony; Swann, Karl (2012-01-15). "PLCζ causes Ca2+ oscillations in mouse eggs by targeting intracellular and not plasma membrane PI(4,5)P2". Molecular Biology of the Cell. 23 (2): 371–380. doi:10.1091/mbc.E11-08-0687. ISSN 1059-1524. PMC 3258180 . PMID 22114355.
- 1 2 3 4 5 6 Johnson, M. (2007). Essential Reproduction (6th ed.). Oxford: Blackwell. ISBN 9781405118668.
- ↑ Kashir, J.; Heindryckx, B.; Jones, C.; De Sutter, P.; Parrington, J.; Coward, K. (2010). "Oocyte activation, phospholipase C zeta and human infertility". Human Reproduction Update. 16 (6): 690–703. doi: 10.1093/humupd/dmq018 . PMID 20573804.
- ↑ Iba, T; Yano, Y; Umeno, M; Hinokio, K; Kuwahara, A; Irahara, M; Yamano, S; Yasui, T (2011). "Roscovitine in combination with calcium ionophore induces oocyte activation through reduction of M-phase promoting factor activity in mice". Zygote. 20 (4): 321–325. doi:10.1017/S0967199411000591. PMID 22008472.