Spermatogenesis

Testis specific variants of H2A, H2B, and H3 have been identified in the rat and mouse (see for example. Refs. [112] and [113]). Two testis specific H2Bs have been 

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In mammals the histones are removed and replaced by transition basic proteins in mid-spermatids and then the transition basic proteins are replaced by protamines in late spermitids and sperm [119]. In mouse and rat sperm, histones removal is complete or nearly so [119,120], but in humans 15% of the DNA remains associated with histones [121]. In bovine sperm more than 99% of the histones are removed, but CENP-A is quantitatively retained [122]. This retained CENP-A could be part of an epigenetic mark that allows the positions of the centromeres to be retained in sperm and on the paternal chromosomes of the zygote. 

Recently, a human sperm H2B was identified that is part of protein complex that specifically binds the telomere DNA repeat [123]. This telomere-binding complex is extracted by conditions (a solution containing 0.5% Triton X-100 and 100 mM NaCl) that do not extract nucleosomal H2B, suggesting that this H2B is not extracted from a typical nucleosomal structure. The structure of this sperm H2B has not been determined. 

During the first few cell divisions of the sea urchin embryo the major histones incorporated into the chromatin are the cleavage stage or CS variants [124]. CS histones are stored in the egg and are translated from stored mRNAs [124-126]. CS H2A, CS H2B, and CS H3 have distinct sequences, while the sequence of the H4 

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In addition to their endocrine disrupting properties, it must be appreciated that many of the chemicals in question possess more general toxic properties, which may be potentiated by metabolism by the organism. Several PAHs, PCBs and PCDDs are carcinogenic, while certain phthalate esters can enhance the excretion of zinc, potentially leading to zinc deficiency. Zinc, an essential element, plays a vital role in spermatogenesis and mature T-cell production. Deficiency may result in abnormalities of the male reproductive system, depletion of spermatogenesis and suppression of the immune system. 

It is widely accepted that men with testicular cancer have a higher incidence of abnormalities associated with impaired spermatogenesis, both in the cancerous testis but also in the contralateral testis. Men diagnosed as having testicular cancer often have very poor semen quality, with sperm concentrations of less than 10 million/ml compared to healthy men with > 50 million/ml." It is thought that gonadal function is abnormal even before testicular cancer develops, ... 

GDNF Family - GDNF, NRTN, ARTN, and PSPN RET Alternative splicing results in three isoforms Required for enteric neuron development, kidney development, and spermatogenesis... 

M (reduced sperm count Sinha et al. 1995 changes in enzyme activity Technical indicating altered spermatogenesis)... 

In summary, although the available reproductive studies indicate endosulfan has no adverse effects on reproductive performance in animals, adverse effects on male reproductive organs have been seen in young rats and mice. The lack of effects seen in the studies that examined reproductive performance (specifically fertility rate) in treated males and females seems difficult to explain, given the finding of altered spermatogenesis in the more recent studies. 

Horiguchi, T., Kojima, M., and Kaya, M. et al. (2002). Tribntyltin and triphenyltin induce spermatogenesis in ovary of female abalone, Haliotis gigantea. Marine Environmental Research 54, 679-684. 

Reproductive values indicated no dominant lethal mutations during 35 days post-treatment (Table IV). The period examined corresponded to postmeiotic stages of spermatogenesis. The incidence of pregnancies at all mating trials in the treated groups remained lower than the control. 

In male rats 2,3,7,8-tetrachlorodibenzo-p-dioxin induced hyperplastic changes and sperm granulomas in the epididymis, but no apparent lethal mutations were noted during post-meiotic phases of spermatogenesis. 

Land PC, Owen EL, Linde HW. 1981. Morphologic changes in mouse spermatozoa after exposure to inhalation anesthetics during early spermatogenesis. Anesthesiology 54 53-56. 

ATANASSOVA N, MCKINNELL C, TURNER K J, WALKER M, FISHER J S, MORLEY M, MILLAR M R, GROOME N p, SHARPE R M (2000) Comparative effects of neonatal exposure of male rats to potent and weak (environmental) estrogens on spermatogenesis at puberty and the relationship to adult testis size and fertility evidence for stimulatory effects of low estrogen lew eh,. Endocrinology. 141 3898-907. 

Azoospermic Having no living spermatozoa in the semen, or failure of spermatogenesis. 

Zimmerman MA, Zimmerman S, Raj AY, Effects of cannabinoids on spermatogenesis in mice. In Nahas GG et al, eds. Marijuana and Medicine. Totowa, NJ Humana Press, 1999 347-358. 

Chapman, D. L., and Wolgemuth, D. J. (1993). Isolation of the murine cyclin B2cDNA and characterization of the lineage and temporal specifity of expression of the B1 and B2 cyclins during oogenesis, spermatogenesis, and early embryogenesis. Development 118 229-240. 

Goldberg, R. B., Geremia, R., and Bruce, W. R. (1977). Histone synthesis and replacement during spermatogenesis in the mouse. Differentiation 7 167-180. 

Winer, M. A., and Wolgemuth, D. J. (1993). Patterns of expression and potential functions of proto-oncogenes during mammalian spermatogenesis. In The Molecular Biology of the Male Reproductive System (De Kretser, D. M., ed.), pp. 143-179. Academic Press, San Diego. 

Wolfes, H., Kogawa, K., Millette, C. F., and Cooper, G. M. (1989). Specific expression of nuclear proto-oncogenes before entry into meiotic prophase of spermatogenesis. Science 245 740-743. 

Yoshinaga, K., Nishikawa, S., Ogawa, M., Hayashi, S.-I., Kunisada, T Fujimoto, T and Nishikawa, S-I. (1991). Role of c-kit in mouse spermatogenesis identification of spermatogonia as a specific site of c-kit expression and function. Development 113 689-699. 

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