Characteristics Of Spermatozoa And Its Arrival To The Egg

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DISCUSSION
Spermatozoa and its Arrival to the Egg
Before embarking in the complexity of CatSper channels, the particular characteristics of sperm and its movement towards the egg in female that allows for fertilization should be addressed. Spermatozoa are differentiated motile cells that have two main structures: the head, which houses packed DNA, and the flagellum, the motility portion that transports the sperm genetic information to the egg (1). Within the spermatozoa head both a vesicle which covers the head, known as the acrosome, and the nucleus reside; whereas the flagellum (tail) is divided by the principal and end piece (4). It is in this principal flagellum piece that we can localize the CatSper channels (2,4,5). Moreover, between
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Capacitation reflects sperm’s new ability to fertilize the egg after exposure of the female tract environment(1). Capacitation occurs when the sperm is exposed to the alkaline environment of the female reproductive tract (1) and as a consequence leads to bounded glycoproteins, plasma proteins and membrane-bounded cholesterols to be detached (7). An important connection between the behavior of CatSper channels and the ability of sperm to become capacitated has been identified (4). Potentiation of the sperm in the female reproductive tract after a rise in intracellular sperm pH during capacitation suggests that this process activates CatSper channels to induce an increased sperm intracellular Ca2+ concentration (4,5). To the purposes of CatSper channels, capacitation results in elevated intracellular Ca2+ (4,5). Moreover, capacitation leads to hypermotility which refers to the increase of the angles in the flagellum which results in a faster motility force (8). Thus, capacitation, CatSper channels, and hypermotility all appear to be linked. Sperm exposure to the alkaline female environment results in capacitation and hypermotility which along with CatSper channels allow for the entry of Ca2+ into the cell which in turn continues to potentiate motility forces of the sperm and increase the chances for fertilization. The close relationship between CatSper ion channels …show more content…
As previously mentioned, CatSper channels are activated by Ca2+ concentrations; thus, it is crucial to understand the structure in which this ion makes its way to the sperm cytoplasm. The CatSper channel is composed of a transmembrane protein that contains 4 non-identical alpha (α) subunits and thus form a heterotetrameric Ca2+ channel and its pore (4). The first discovered subunit was termed the CatSper1 channel which was found exclusively in sperm cells and thus linked its function to sperm’ unique purpose: fertilization (2). Later on, CatSper 2-4 and their "helper" subunits known as CatSper β (beta), CatSper γ (gamma), and CatSper δ (delta), all known as auxiliary channels, have been identified (1, 3, 4, 9, 10). Within each CatSper channel (1 through 4), there are six transmembrane sections divided into a sensory domain and a pore-creator domain (4). It is also important to identify the structure of the auxiliary channels. The CatSper β channel was first discovered by databases and reverse transcriptase methods (4). The CatSper β channel has two transmembrane sections along with a cytoplasmic small domain and a extracellular large domain (9). On the other hand, both the CatSper γ channel(10) and the CatSper δ channel(3) are composed of one transmembrane section each that

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