Dynamics of histone H2A, H4 and HS1ph during spermatogenesis with a focus on chromatin condensation and maturity of spermatozoa.

Histones and histone phosphorylation play vital roles during animal spermatogenesis and spermatozoa maturation. The dynamic distribution of histones H2A and H4 and phosphorylated H2A and H4 at serine 1 (HS1ph) was explored in mammalian and Decapoda germ cells, with a special focus on the distribution of H2A, H4 and HS1ph between mouse condensed spermatozoa chromatin and crab non-condensed spermatozoa chromatin. The distribution of histone marks was also analysed in mature spermatozoa with different chromatin structures. Histone H2A and H4 marks were closely associated with the relatively loose chromatin structure in crab spermatozoa. The significant decrease in the HS1ph signal during spermatogenesis suggests that eliminating most of these epigenetic marks in the nucleusis closely associated with spermatozoa maturity.

Cloning and Functional Analysis of Histones H3 and H4 in Nuclear Shaping during Spermatogenesis of the Chinese Mitten Crab, Eriocheir sinensis.

During spermatogenesis in most animals, the basic proteins associated with DNA are continuously changing and somatic-typed histones are partly replaced by sperm-specific histones, which are then successively replaced by transition proteins and protamines. With the replacement of sperm nuclear basic proteins, nuclei progressively undergo chromatin condensation. The Chinese Mitten Crab (Eriocheir sinensis) is also known as the hairy crab or river crab (phylum Arthropoda, subphylum Crustacea, order Decapoda, and family Grapsidae). The spermatozoa of this species are aflagellate, and each has a spherical acrosome surrounded by a cup-shaped nucleus, peculiar to brachyurans. An interesting characteristic of the E. sinensis sperm nucleus is its lack of electron-dense chromatin. However, its formation is not clear. In this study, sequences encoding histones H3 and H4 were cloned by polymerase chain reaction amplification. Western blotting indicated that H3 and H4 existed in the sperm nuclei. Immunofluorescence and ultrastructural immunocytochemistry demonstrated that histones H3 and H4 were both present in the nuclei of spermatogonia, spermatocytes, spermatids and mature spermatozoa. The nuclear labeling density of histone H4 decreased in sperm nuclei, while histone H3 labeling was not changed significantly. Quantitative real-time PCR showed that the mRNA expression levels of histones H3 and H4 were higher at mitotic and meiotic stages than in later spermiogenesis. Our study demonstrates that the mature sperm nuclei of E. sinensis contain histones H3 and H4. This is the first report that the mature sperm nucleus of E. sinensis contains histones H3 and H4. This finding extends the study of sperm histones of E. sinensis and provides some basic data for exploring how decapod crustaceans form uncondensed sperm chromatin.

[Genes involved in spermatogenesis].

During mammalian spermatogenesis, primordial germ cells develop into spermatogonia, giving rise to spermatocytes that undergo two meiotic divisions to become round spermatids. These cells differentiate into spermatozoa during spermiogenesis. Spermatogenesis is a complex process of cell differentiation controlled by many factors, among which gene regulation in the spermatogenic cells plays a pivotal role. Genes important for male gametogenesis involved in highly con-served landmark events such as meiotic recombination, formation of the synaptonemal complex, sister chromatid cohesion, spermiogenesis during postmeiotic stages, and checkpoints and factors required for the meiotic cell cycle. Spermatogenesis is characterized by phase-specific expression of many genes exclusively expressed in the spermatogenic cells. With the development and application of technologies like gene cloning, gene expression and functional characterization, many spermatogenesis-related genes have been found in the past few years, and some of them have been proved to play an important role in spermatogenesis. Here, we review the advances in this field with an emphasis on spermatogenesis-associated genes such as cyclins, proto-oncogenes, azoospermia factor genes, cytoskeleton genes, heat shock genes, nucleoprotein transition genes, centrin genes and apoptosis genes.