Phosphorylation of histone H3S10 in animal chromosomes: is there a uniform pattern?

X Chromosome Inactivation during Grasshopper Spermatogenesis

Regulation of transcriptional activity during meiosis depends on the interrelated processes of recombination and synapsis. In eutherian mammal spermatocytes, transcription levels change during prophase-I, being low at the onset of meiosis but highly increased from pachytene up to the end of diplotene. However, X and Y chromosomes, which usually present unsynapsed regions throughout prophase-I in male meiosis, undergo a specific pattern of transcriptional inactivation. The interdependence of synapsis and transcription has mainly been studied in mammals, basically in mouse, but our knowledge in other unrelated phylogenetically species is more limited. To gain new insights on this issue, here we analyzed the relationship between synapsis and transcription in spermatocytes of the grasshopper Eyprepocnemis plorans. Autosomal chromosomes of this species achieve complete synapsis; however, the single X sex chromosome remains always unsynapsed and behaves as a univalent. We studied transcription in meiosis by immunolabeling with RNA polymerase II phosphorylated at serine 2 and found that whereas autosomes are active from leptotene up to diakinesis, the X chromosome is inactive throughout meiosis. This inactivation is accompanied by the accumulation of, at least, two repressive epigenetic modifications: H3 methylated at lysine 9 and H2AX phosphorylated at serine 139. Furthermore, we identified that X chromosome inactivation occurs in premeiotic spermatogonia. Overall, our results indicate: (i) transcription regulation in E. plorans spermatogenesis differs from the canonical pattern found in mammals and (ii) X chromosome inactivation is likely preceded by a process of heterochromatinization before the initiation of meiosis.

RepSox effectively promotes the induced differentiation of sheep fibroblasts into adipocytes via the inhibition of the TGF‑β1/Smad pathway

Previous reports have demonstrated that RepSox can function as a replacement for cMyc and Sox2 in the reprogramming of cells into induced pluripotent stem cells (iPSCs), as well as increasing the levels of bone morphogenetic protein (BMP)-3 and inducing the phosphorylation of Smad1 in mouse embryonic stem cells. In the present study, it was demonstrated that RepSox caused the visible morphological transformation of sheep fibroblasts; however, no significant alterations in cell proliferation, apoptosis or chromosome aberrations were observed. Moreover, RepSox increased the plasticity of long-term cryopreserved sheep fibroblasts, and further promoted differentiation into adipocytes. RepSox treatment led to a notable decrease in the expression of components of the transforming growth factor (TGF)-β signaling pathway, particularly Smad2/3 phosphorylation. RepSox also activated the BMP pathway, promoted the reprogramming of cells from fibroblasts into adipocytes and induced mesenchymal-epithelial transition. It is worth noting that RepSox notably increased the expression of octamer-binding transcription factor 4 and L-Myc, whereas Sox2 and Nanog expression were not detected. The results of high-throughput RNA sequencing revealed that the levels of differentially expressed genes (DEGs) involved in various metabolic processes were markedly upregulated in the RepSox-treated fibroblasts, while the DEGs in the majority of signaling pathways were markedly downregulated. On the whole, the present study demonstrates that RepSox can promote the plasticity of sheep fibroblasts and facilitates the differentiation of adipocytes via increasing BMP expression and inhibiting the activation of the TGF-β signaling pathway.

Male meiosis in Crustacea: synapsis, recombination, epigenetics and fertility in Daphnia magna

We present the first detailed cytological study of male meiosis in Daphnia (Crustacea: Branchiopoda: Cladocera)—an aquatic microcrustacean with a cyclical parthenogenetic life cycle. Using immunostaining of the testes in Daphnia magna for baseline knowledge, we characterized the different stages of meiotic division and spermiogenesis in relation to the distribution of proteins involved in synapsis, early recombination events and sister chromatid cohesion. We also studied post-translational histone modifications in male spermatocytes, in relation to the dynamic chromatin progression of meiosis. Finally, we applied a DNA fragmentation test to measure sperm quality of D. magna, with respect to levels of inbreeding. As a proxy for fertility, this technique may be used to assess the reproductive health of a sentinel species of aquatic ecosystems. Daphnia proves to be a model species for comparative studies of meiosis that is poised to improve our understanding of the cytological basis of sexual and asexual reproduction.

Histone modifications related to chromosome silencing and elimination during male meiosis in Bengalese finch

We report here that a germline-restricted chromosome (GRC) is regularly present in males and females of the Bengalese finch (Lonchura domestica). While the GRC is euchromatic in oocytes, in spermatocytes this chromosome is cytologically seen as entirely heterochromatic and presumably inactive. The GRC is observed in the cytoplasm of secondary spermatocytes, indicating that its elimination from the nucleus occurs during the first meiotic division. By immunofluorescence on microspreads, we investigated the presence of histone H3 modifications throughout male meiosis, as well as in postmeiotic stages. We found that the GRC is highly enriched in di- and trimethylated histone H3 at lysine 9 during prophase I, in agreement with the presumed inactive state of this chromosome. At metaphase I, dimethylated histone H3 is no longer detectable on the GRC and its chromatin is more faintly stained with DAPI. The condensed GRC is underphosphorylated at serine 10 compared to the regular chromosomes during metaphase I, being phosphorylated later at this site after the first meiotic division. From these results, we proposed that trimethylation of histone H3 at lysine 9 on the GRC chromatin increases during metaphase I. This hypermethylated state at lysine 9 may preclude the phosphorylation of the adjacent serine 10 residue, providing an example of cross-talk of histone H3 modifications as described in experimental systems. The differential underphosphorylation of the GRC chromatin before elimination is interpreted as a cytologically detectable byproduct of deficient activity of Aurora B kinase, which is responsible for the phosphorylation of H3 at serine 10 during mitosis and meiosis.