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The facultative heterochromatic X chromosome in leptotene spermatocytes of the grasshopper Eyprepocnemis plorans showed marked hypoacetylation for lysine 9 in the H3 histone (H3-K9) with no sign of histone H2AX phosphorylation. Since H3-K9 hypoacetylation precedes the meiotic appearance of phosphorylated H2AX (γ-H2AX), which marks the beginning of recombinational DNA double-strand breaks (DSBs), it seems that meiotic sex-chromosome inactivation (MSCI) in this grasshopper occurs prior to the beginning of recombination and hence synapsis (which in this species begins later than recombination). In addition, all constitutively heterochromatic chromosome regions harbouring a 180-bp tandem-repeat DNA and rDNA (B chromosomes and pericentromeric regions of A chromosomes) were H3-K9 hypoacetylated at early leptotene even though they will synapse at subsequent stages. This also suggests that meiotic silencing in this grasshopper might be independent of synapsis. The H3-K9 hypoacetylated state of facultative and constitutive heterochromatin persisted during subsequent meiotic stages and was even apparent in round spermatids. Finally, the fact that B chromosomes are differentially hypoacetylated in testis and embryo interphase cells suggests that they might be silenced early in development and remain this way for most (or all) life-cycle stages. Copyright © 2007 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

It is widely accepted that the H2AX histone in its phosphorylated form (γ-H2AX) is related to the repair of DNA double-strand breaks (DSBs). In several organisms, γ-H2AX presence has been demonstrated in meiotic processes such as recombination and sex chromosome inactivation during prophase I (from leptotene to pachytene). To test whether γ-H2AX is present beyond pachytene, we have analysed the complete sequence of changes in H2AX phosphorylation during meiosis in grasshopper, a model organism for meiotic studies at the cytological level. We show the presence of phosphorylated H2AX during most of meiosis, with the exception only of diplotene and the end of each meiotic division. During the first meiotic division, γ-H2AX is associated with i) recombination, as deduced from its presence in leptotene-zygotene over all chromosome length, ii) X chromosome inactivation, since at pachytene γ-H2AX is present in the X chromosome only, and iii) chromosome segregation, as deduced from γ-H2AX presence in centromere regions at first metaphase-anaphase. During second meiotic division, γ-H2AX was very abundant at most chromosome lengths from metaphase to telophase, suggesting its possible association with the maintenance of chromosome condensation and segregation. Copyright © 2007 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]