Capacitation mammalian sperm

The mechanism by which albumin (in many cases bovine serum albumin BSA) promotes capacitation in mammalian sperm is intriguing as it is believed to function during capacitation in vitro as a sink for the removal of cholesterol from the sperm plasma membrane (Go and Wolf, 1985 Langlais and Roberts, 1998 Cross, 1998). The association between cholesterol removal from the sperm plasma membrane, albumin, and capacitation was first proposed by Davis and colleagues (1980). Removal of this sterol likely accounts for the membrane fluidity changes observed during capacitation (Wolf et al., 1986). The consequence of the removal of this sterol is that the cholesterol to phospholipid ratio in the membrane decreases, and such changes in... 

The extracellular Ca and HCO," requirement for both protein tyrosine phosphorylation and capacitation represents a novel regulatory mechanism of cellular signaling since these ions have been shown to be activators of the mammalian sperm adenylyl cyclase (Hyne and Garbers, 1979 Okamura et al., 1985 Garty and Salomon,1987 Visconti et al., 1995b). Since there appears to be a relationship between Ca, HC03 , and increased adenylyl cyclase activity, experiments were designed to determine whether the action of these ions on protein tyrosine phosphorylation and capacitation involved a cAMP-mediated pathway. As previously stated, protein tyrosine phosphorylation does not occur when sperm are incu-... 

Mammalian sperm contain tyrosine kinase activities (Berruti and Martegani, 1989). In addition, the tyrosine phosphorylation of a limited array of sperm proteins is increased during capacitation (Leyton and Saling, 1989 Duncan and Fraser, 1993 Visconti et al., 1995a,b Morte et al., 1998). In general, the relevant kinase and phosphatase enzymes have not yet been identified (Morte et al., 1998). 

In Chapter 3, Kopf and coauthors summarize recent studies on capacitation of mammalian sperm. The chapter examines the role of media constituents, membrane events, and transmembrane and intracellular signaling during sperm capacitation. The authors provide detailed information about the biochemical and molecular events that form the basis of this critical event in mammalian fertilization. 

Langlais, J. and Roberts, K.D. (1985). A molecular membrane model of sperm capacitation and the acrosome reaction of mammalian spermatozoa. Gamete Res. 72 183-224. 

Mammalian fertilization is the result of a precisely regulated series of cellular interactions. This process can be divided into a number of component stages, including the following (i) the early events that precede egg fusion, consisting of the preliminary event of sperm capacitation, sperm penetration of the cumulus oophorus, zona pellucida adhesion, initiation and completion of acrosome reactions, penetration of the zona pellucida, egg plasma membrane contact and fusion and (ii) the late events that occur within the egg that consist of sperm nuclear decondensation followed by pronuclear consolidation and syngamy. 

The early stages of fertilization begin prior to gamete contact with the process of sperm capacitation. Sperm that are released from mammalian caudae epididymides are able to carry out only a restricted set of physiological processes and are unable to fertilize eggs. Capacitation describes the time-dependent development of fertility. This process was first identified during in-vivo experiments as a temporal delay in fertilization when animals were mated after the time of ovulation (Austin, 1951, 1952 Chang, 1951). 

Florman, H.M. and Babcock, D.F. (1990). Progress towards a molecular mechanism of sperm capacitation. In Elements of Mammalian Fertilization. Basic Concepts. (Wassarman, Ed.), pp. 105-132. CRC Press. Boca Raton, FL. 

Once the spermatozoa enter the oviductal isthmus, things become more complicated. The mammalian oviductal isthmus was convincingly demonstrated to serve as a sperm reservoir or storage site after ejaculation (Figure 4) [11, 67, 71, 117, 159, 160]. (Defective, nonmotile spermatozoa and cells vwth disrupted membranes are apparently not stored they appear to be passively and rapidly transported away towards the peritoneal cavity—see [116] for a review.) Spermatozoa that are not yet capacitated, that is, immature spermatozoa that have not yet acquired fertilizing potential [80, 186], attach to the oviductal epithelium and are released only when they become capacitated, i.e., only when they acquire a state of readiness to fertilize the egg. 

Rgure 5. The steps for which mammalian spermatozoa must be capacitated and hyperactivated. The simplified scheme shows the events that affect, and the processes in the female genital tract that are regulated by, sperm capacitatlon. Bold colored arrows represent sequence of events. Thin black arrows represent modulation of processes. (Taken with permission from Jaiswal and Eisenbach [80].)... 

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