During the haploid phase of mammalian spermatogenesis, nucleosomal chromatin is ultimately repackaged by small, highly basic protamines to generate an extremely compact, toroidal chromatin architecture that is critical to normal spermatozoal function. In common with several species, however, the human spermatozoon retains a small proportion of its chromatin packaged in nucleosomes. As nucleosomal chromatin in spermatozoa is structurally more open than protamine-packaged chromatin, we considered it likely to be more accessible to exogenously applied endonucleases. Accordingly, we have used this premise to identify a population of endonuclease-sensitive DNA sequences in human and murine spermatozoa. Our results show unequivocally that, in contrast to the endonuclease-resistant sperm chromatin packaged by protamines, regions of increased endonuclease sensitivity are closely associated with gene regulatory regions, including many promoter sequences and sequences recognized by CCCTC-binding factor (CTCF). Similar differential packaging of promoters is observed in the spermatozoal chromatin of both mouse and man. These observations imply the existence of epigenetic marks that distinguish gene regulatory regions in male germ cells and prevent their repackaging by protamines during spermiogenesis. The ontology of genes under the control of endonuclease-sensitive regulatory regions implies a role for this phenomenon in subsequent embryonic development.

Sperm chromatin reveals two characteristic features in that protamines are the predominant nuclear proteins and remaining histones are highly acetylated. histone h4 acetylated at lysine 12 (h4K12ac) is localized in the post-acrosomal region, while protamine-1 is present within the whole nucleus. chromatin immunoprecipitation in combination with promoter array analysis allowed genome-wide identification of h4K12ac binding sites. previously, we reported enrichment of h4K12ac at cTcF binding sites and promoters of genes involved in developmental processes. here, we demonstrate that h4K12ac is enriched predominantly between ± 2 kb from the transcription start site. In addition, we identified developmentally relevant h4K12ac-associated promoters with high expression levels of their transcripts stored in mature sperm. The highest expressed mRNa codes for testis-specific phD finger protein-7 (phF7), suggesting an activating role of h4K12ac in the regulatory elements of this gene. h4K12ac-associated genes revealed a weak correlation with genes expressed at 4-cell stage human embryos, while 23 h4K12ac-associated genes were activated in 8-cell embryo and 39 in the blastocyst. Genes activated in 4-cell embryos are involved in gene expression, histone fold and DNadependent transcription, while genes expressed in the blastocyst were classified as involved in developmental processes. Immunofluorescence staining detected h4K12ac from the murine male pronucleus to early stages of embryogenesis. aberrant histone acetylation within developmentally important gene promoters in infertile men may reflect insufficient sperm chromatin compaction, which may result in inappropriate transfer of epigenetic information to the oocyte.

An understanding of the epigenetic mechanisms involved in sperm production and their impact on the differentiating embryo is essential if we are to optimize fertilization and assisted reproduction techniques in the future. Male germ cells are unique in terms of size, robustness, and chromatin structure, which is highly condensed owing to the replacement of most histones by protamines. Analysis of sperm epigenetics requires specific techniques that enable the isolation of high quality chromatin and associated nucleic acids. Histone modification, DNA methylation and noncoding RNAs have important, but so far underestimated, roles in the production of fertile sperm. Aberrations in these epigenetic processes have detrimental consequences for both early embryo development and assisted reproductive technology. Emerging computational techniques are likely to improve our understanding of chromatin dynamics in the future.

Interleukin (IL)-17 is a 30- to 35-kDa homodimeric polypeptide cytokine cloned in 1993 and originally named cytotoxic T lymphocyte-associated antigen-8 (CTLA-8). Sequencing the human genome resulted in the discovery of an additional five members of the IL-17 family that were consecutively named IL-17B to IL-17F. IL-17A is exclusively produced by a newly identified CD4+ T-helper subset that was recently named Th17. Differentiation of these cells from naive CD4+ T cells requires both TGF-beta and IL-6. IL-15 and, especially, IL-23 are required for these cells' survival and efficient IL-17 production. IL-17 binding to an IL-17 receptor expressed on epithelial, endothelial, and fibroblastic stromal cells triggers the activation of transcription factor NF-kappaB and mitogen-activated protein kinase (p-38), which in turn results in the secretion of IL-1, TNF-alpha, IL-6, IL-8, or prostaglandin E2. The IL-17 family plays a key role in the regulation of immune and inflammatory response, in the homeostasis of several tissues, and the progression of autoimmune diseases. In addition, IL-17 exerts synergistic effects with TNF-alpha and IL-1 in the induction of joint inflammation and cartilage and joint destruction. Given these properties, it is not surprising that in certain pathological conditions, for example rheumatoid arthritis, Th17 cells emerge as a new pathological cell type that, by IL-17 production and release, contributes to their pathogeneses.

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