Mammalian Spermatozoa

The occurrence of sperm chemotaxis in mammals was established in vitro only at the last decade. As a matter of fact, until then there had been resistance to the concept of mammalian sperm chemotaxis for two main reasons. First, in mammals in which fertilization is internal and very large numbers of spermatozoa are ejaculated directly into the female reproductive tract (4 0X10 in humans [185] 10 -10 in mammals in general [66]), chemotaxis was believed to be unnecessary because a sufficient number of spermatozoa would reach the egg coincidentally. Second, technical difficulties in studying mammalian sperm chemotaxis prevented the acquisition of conclusive evidence. The primary technical difficulty was a very low signal-to-noise ratio in the measurements, resulting from the fact that only a small fraction of the sperm 

---

Human sperm chromosomes retain a high fertilizing ability after a high dose of X-irradiation, although mammalian spermatozoa have little capacity to repair DNA damage induced by radiation (Kamiguchi et al. 1990). Radiation-induced death of lymphoid cells in rats is associated with damage to the cell itself but may also be due to secretions from irradiation-activated natural killer cells that induce pycnosis and interphase death in lymphoid cells (Eidus et al. 1990). 

Takano H, Yanagimachi R, Urch UA (1993) Evidence that acrosin activity is important for the development of fusibility of mammalian spermatozoa with the oolemma Inhibitor studies using the golden hamster. Zygote, 1 79. 

Selenium plays a special role in development and protection of spermatozoa (Chapter 15). Tire selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx Eq. 15-58, Table 15-4) has a high activity in the testis and in spermatids. However, in mature spermatozoa it forms an enzymatically inactive oxidatively crosslinked capsular material around the midpiece of the cell perhaps providing mechanical stability.268 A similar 34-kDa selenoprotein is present in sperm nuclei and may be essential for condensation of DNA.269 Sperm tails contain specialized cytoskele-tal proteins which form "outer dense fibers."270 In contrast to mammalian spermatozoa, nematode sperm move by ameboid motility that depends upon a specialized actin-like molecule.271 Sperm cells are unusually rich in polyamines, most of which are bound to RNA and DNA (Chapter 24). 

Fehr J, Meyer D, Widmayer P, Borth HC, Ackermann F, Wilhelm B, Gudermann T, Boekhoff I. Expression of the G-protein alpha-subunit gustducin in mammalian spermatozoa. J. Comp. Physiol. A Neuroethol. Sens Neural Behav. Physiol. 2007 193 21-34. 

Davis, B.K. (1978). Inhibition of fertilizing capacity in mammalian spermatozoa by natural and synthetic vesicles. In Symposium on the Pharmacological Effects of Lipids, Champaign, IL. (Kabara, J., Ed.), pp. 145-157. The American Oil Chemist s Society. 

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. 

Okamura, N., Tajima, Y., Soejima, A., Masuda, H., and Sugita, Y. (1985). Sodium bicarbonate in seminal plasma stimulates the motility of mammalian spermatozoa through the direct activation of adenylate cyclase. J. Biol. Chem. 260 9699-9705. 

Glassner, M., Jones, J., Kligman, I., Woolkalis, M.J., Gerton, G.L., and Kopf, G.S. (1991). Immunocytochemical and biochemical characterization of guanine nucleotide-binding regulatory proteins in mammalian spermatozoa. Dev. Biol. 748 438-450. 

Parkkila, S., Kaunisto, K., Kellokumpu, S., and Rajaniemi, H. (1991). A high activity carbonic anhydrase isoenzyme (CA II) is present in mammalian spermatozoa. Histochem. 95 477-482. 

Roldan, E.R.S. and Harrison, R.A.P, (1989). Polyphosphoinositide breakdown and subsequent exocytosis in the Ca Vionophore-induced acrosome reaction of mammalian spermatozoa. Biochem. J. 259 397-406. 

Yanagimachi, R. and Noda, Y.D. (1970). Physiological changes in the postnuclear cap region of mammalian spermatozoa A necessary preliminary in the membrane fusion between sperm and egg cells. J. Ultra. Res. 37 486-493. 

The rotation of spermatozoa around their long axis is not restricted to human spermatozoa the spermatozoa of all species appear to do so [75], In each species the spermatozoa rotate both clockwise and counterclockwise, but the proportion of the clockwise-rotating and counterclockwise-rotating populations varies between species. Interestingly, the majority of sea urchin and starfish spermatozoa rotate clockwise (viewed from the anterior end), and their flagella form right-handed waves. In contrast, the majority of mammalian spermatozoa rotate counterclockwise and their flagella form left-handed waves which, in the case of human and bull spermatozoa, look like a three-dimensional left-handed helicoid [75]. 

Perhaps the most striking changes in sperm motility occur as mammalian spermatozoa move through the female genital tract (Figure 4). In speeies... 

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].)... 

Ishijima, S. and Mohri, H. (1990). Renting patterns of mammalian spermatozoa, in Controls of Sperm MotUity Biological and Clinical Aspects (C. Gagnon, ed.), pp. 29-42. CRC Press, Boca Raton, FL. 

Farrington J, Jones ML, Tunwell R, Devader C, Katan M, Swann K 2002. Phospholipase C isoforms in mammalian spermatozoa potential components of the sperm factor that causes Ca2+ release in eggs. Reproduction 123(l) 31-39. 

The use of quantitative PCR (QPCR), based in the blockage of amplification caused by some DNA insults, is being assayed for a more precise identification of damage to nuclear (nDNA) and mitochondrial (mtDNA) mammalian spermatozoa genomes (Rennets and Aitken, 2005).This is particularly interesting in species whose genome is sequenced (such as zebra-fish and rainbow trout and sea bass, very soon), as results can be analysed on ships themselves. 

Nucleoproteins are difficult to extract from mammalian spermatozoa this is not surprising because the nucleus of mammalian spermatozoa is protected against mechanical damage by a special keratinous membrane. The nuclear protein, like keratin, is rich in sulfur, but it contains more arginine than regular keratin. Studies on disrupted bull sperm nuclei revealed that the arginine content of mammalian sperm is intermediate between that of protamine and that of histone. Whether protamines are in fact present in mammalian sperm is not known. Analysis of a protein hydrolysate obtained after extraction of bull sperm does, however, indicate that a basic protein, relatively rich in arginine, is present in mammalian sperm. 

It has been proved impossible to extract basic protein from mammalian spermatozoa by the usual methods. This has led to the sponge hypothesis advanced by Bril-Petersen and Westenbrink (1963), according to which the whole nucleus of the mammalian spermatozoon is regarded as a sponge consisting of a keratinoid network, held together by numerous disulfide bonds and associated with DNA to make the protein resistant against extraction or destruction. 

Bril-Petersen, E., Westenbrink, H. G. K. A structural basic protein as a counterpart of deoxyribonucleic acid in mammalian spermatozoa. Biochim. biophys. Acta (Amst.) 76, 152—154 (1963). 

Henricks, D. M., Mayer, D. T. Isolation and characterization of a basic keratin-like protein from mammalian spermatozoa. Exp. Cell Biol. 40, 402—412 (1965). 

Yoshioka, T., T. Suzuki and T. Uematsu. 1989. Biotransformation of N-substituted aromatic compounds in mammalian spermatozoa. Nonoxidative formation of N-hydroxy-N-arylacetamides from nitroso aromatic compounds. J. Biol. Chem. 264 12432-12438. 

---