Characterization of the role of the Aurora B kinase in quiescent lymphocytes

The role of the Aurora B kinase in mediating cellular functions outside mitosis was investigated. A SILAC-based approach was used to show that Aurora B interacts with proteins implicated in gene regulation and chromatin organization in G1 activated B cells. Among these interactors, I identified the PRC1 component Ring1B as a new partner of Aurora B. Both proteins are bound to the promoters of highly expressed genes in resting B and T lymphocytes. Quiescent resting B cells require the maintenance of a transcriptional programme that keeps the cells viable and ready to proliferate upon encounter with a specific antigen. Aurora B and Ring1B physically co-occupy the same promoters in resting B cells but, upon activation, Aurora B is replaced by MSK1 on its target genes, whereas Ring1B binding is preserved. Analysis of the active promoters in resting B cells shows that other PRC1 components, such as Cbx7 and Bmi1, and the histone deubiquitinase USP16, together with Aurora B and Ring1B, bind almost exclusively to the regulatory elements of active promoters and are not found at repressed genes. Binding of PRC2 components and deposition of the H3K27me3 and H2Aubq marks are largely confined to silent genes. By employing conditional knockout mouse models, I showed that removal of either Aurora B or Ring1B results in a global reduction in the binding of unphosphorylated and serine 5-phosphorylated RNA Polymerase II to active promoters. This phenomenon is also accompanied by a reduction in the production of transcripts from Aurora B and Ring1B target genes and reduced cell viability. Aurora B is also required to maintain high levels of phosphorylated H3S28 and low levels of the repressive H2Aubq mark at active promoters. These results identify a new role for both Aurora B and Ring1B in the regulation of active transcription in quiescent lymphocytes

Mutations in thyroid hormone receptor α1 cause premature neurogenesis and progenitor cell depletion in human cortical development.

Mutations in the thyroid hormone receptor α 1 gene (THRA) have recently been identified as a cause of intellectual deficit in humans. Patients present with structural abnormalities including microencephaly, reduced cerebellar volume and decreased axonal density. Here, we show that directed differentiation of THRA mutant patient-derived induced pluripotent stem cells to forebrain neural progenitors is markedly reduced, but mutant progenitor cells can generate deep and upper cortical layer neurons and form functional neuronal networks. Quantitative lineage tracing shows that THRA mutation-containing progenitor cells exit the cell cycle prematurely, resulting in reduced clonal output. Using a micropatterned chip assay, we find that spatial self-organization of mutation-containing progenitor cells in vitro is impaired, consistent with down-regulated expression of cell-cell adhesion genes. These results reveal that thyroid hormone receptor α1 is required for normal neural progenitor cell proliferation in human cerebral cortical development. They also exemplify quantitative approaches for studying neurodevelopmental disorders using patient-derived cells in vitro.NIHR Cambridge Biomedical Centr

Cortisol in hair: do habitat fragmentation and competition with golden jackal (Canis aureus) measurably affect the long-term physiological response in European wildcat (Felis silvestris)?

Measurements of cortisol levels in hair are a non-invasive method to study potential chronic stress that may affect carnivores’ welfare. Using hair from 15 frozen and 18 taxidermied road-kill individuals, we aimed to provide information on the long-term physiological response of European wildcats (Felis silvestris silvestris) to habitat fragmentation and potential interspecific competition with golden jackals and red foxes. Our findings revealed that wildcats seemed to be unaffected by habitat fragmentation, suggesting that the facultative specialist behaviour of the species may lead to better toleration of human-altered environments. Red fox presence did not affect cortisol levels. However, significantly higher cortisol levels were measured in hairs of wildcats exposed to golden jackals, suggesting that the potential competition between the two species may lead to an increase in allostatic load in wildcats

A H3K9/S10 methyl-phospho switch modulates Polycomb and Pol II binding at repressed genes during differentiation

Methylated histone H3K9 and H3K27 are canonical epigenetic silencing modifications in metazoan organisms, but the relationship between the two modifications has not been well characterised. We show that H3K9me3 coexists with H3K27me3 in pluripotent and differentiated cells. However, we find that the functioning of H3K9me3 is altered by H3S10 phosphorylation in differentiated postmitotic osteoblasts and in cycling B cells. Deposition of H3K9me3/S10ph at silent genes is partially mediated by the mitogen and stress activated kinases (MSK1/2) and the Aurora B kinase. Acquisition of H3K9me3/S10ph during differentiation correlates with loss of paused S5 phosphorylated RNA polymerase II, which is present on Polycomb-regulated genes in ES cells. Reduction of the levels of H3K9me3/S10ph by kinase inhibition results in increased binding of RNAPIIS5ph and of the H3K27 methyltransferase Ezh1 at silent promoters. Our results provide evidence of a novel developmentally regulated methyl-phospho switch that modulates Polycomb regulation in differentiated cells and stabilises repressed states