Role of the Transcriptional Corepressor Bcor in Embryonic Stem Cell Differentiation and Early Embryonic Development

Bcor (BCL6 corepressor) is a widely expressed gene that is mutated in patients with X-linked Oculofaciocardiodental (OFCD) syndrome. BCOR regulates gene expression in association with a complex of proteins capable of epigenetic modification of chromatin. These include Polycomb group (PcG) proteins, Skp-Cullin-F-box (SCF) ubiquitin ligase components and a Jumonji C (Jmjc) domain containing histone demethylase. To model OFCD in mice and dissect the role of Bcor in development we have characterized two loss of function Bcor alleles. We find that Bcor loss of function results in a strong parent-of-origin effect, most likely indicating a requirement for Bcor in extraembryonic development. Using Bcor loss of function embryonic stem (ES) cells and in vitro differentiation assays, we demonstrate that Bcor plays a role in the regulation of gene expression very early in the differentiation of ES cells into ectoderm, mesoderm and downstream hematopoietic lineages. Normal expression of affected genes (Oct3/4, Nanog, Fgf5, Bmp4, Brachyury and Flk1) is restored upon re-expression of Bcor. Consistent with these ES cell results, chimeric animals generated with the same loss of function Bcor alleles show a low contribution to B and T cells and erythrocytes and have kinked and shortened tails, consistent with reduced Brachyury expression. Together these results suggest that Bcor plays a role in differentiation of multiple tissue lineages during early embryonic development

Intrinsic programs regulating dendrites and synapses in the upper layer neurons of the cortex

Dendrites and spines are key regulators of neuronal function often affected in cognitive disorders. Neuronal subclasses are characterized by a wide range of dendritic morphologies that aid their specific functions. However, how subclass-specific dendritic trees arise during vertebrate development remains largely unknown. We have recently reported that the restricted expression of Cux1 and Cux2 genes in the upper layers of the cerebral cortex determines the specific morphology of dendrites and spines and the function of these neurons. Since Cux genes are the vertebrate homologs of Drosophila Cut, which specifies the dendritic morphologies of certain sensory neuron populations, our findings suggest that mechanisms of dendrite differentiation are conserved between Drosophila and mammals, which had yet to be demonstrated. Importantly, we found that Cux genes not only modulate dendritic branching, but also dendritic spine morphogenesis, the functional synapse and cognition. Dendritic spine stabilization was partly mediated by direct repression of genes of the Xlr family, previously implicated in cognitive defects in a model of Turner syndrome. Hence, our work indicates that neuronal subclass specific determinants may intrinsically affect synaptic activity beyond expected. The functions of Cux1 and Cux2 were additive and complement each other to establish the final pattern of the dendritic tree and the number and strength of the synapses. This work unravels novel mechanisms of dendritogenesis and synaptogenesis and illustrates how regulating dendritic structures contributes to the specialization of upper layer neurons. It will be interesting to dissect how these mechanisms regulate cortical activity, area specialization and cognitive functions

Targeting G-quadruplex DNA as cognitive function therapy for ATR-X syndrome

難治性疾患「ATR-X症候群」の治療に新たな光 --重度知的障がいに対する新しい治療薬候補の発見--. 京都大学プレスリリース. 2018-05-22.Alpha-thalassemia X-linked intellectual disability (ATR-X) syndrome is caused by mutations in ATRX, which encodes a chromatin-remodeling protein. Genome-wide analyses in mouse and human cells indicate that ATRX tends to bind to G-rich sequences with a high potential to form G-quadruplexes. Here, we report that Atrx mutation induces aberrant upregulation of Xlr3b expression in the mouse brain, an outcome associated with neuronal pathogenesis displayed by ATR-X model mice. We show that ATRX normally binds to G-quadruplexes in CpG islands of the imprinted Xlr3b gene, regulating its expression by recruiting DNA methyltransferases. Xlr3b binds to dendritic mRNAs, and its overexpression inhibits dendritic transport of the mRNA encoding CaMKII-α, promoting synaptic dysfunction. Notably, treatment with 5-ALA, which is converted into G-quadruplex-binding metabolites, reduces RNA polymerase II recruitment and represses Xlr3b transcription in ATR-X model mice. 5-ALA treatment also rescues decreased synaptic plasticity and cognitive deficits seen in ATR-X model mice. Our findings suggest a potential therapeutic strategy to target G-quadruplexes and decrease cognitive impairment associated with ATR-X syndrome

Triangulating the sexually dimorphic brain through high-resolution neuroimaging of murine sex chromosome aneuploidies

Murine sex chromosome aneuploidies (SCAs) provide powerful models for charting sex chromosome influences on mammalian brain development. Here, building on prior work in X-monosomic (XO) mice, we use spatially non-biased high-resolution imaging to compare and contrast neuroanatomical alterations in XXY and XO mice relative to their wild-type XX and XY littermates. First, we show that carriage of a supernumerary X chromosome in XXY males (1) does not prevent normative volumetric masculinization of the bed nucleus of the stria terminalis (BNST) and medial amygdala, but (2) causes distributed anatomical alterations relative to XY males, which show a statistically unexpected tendency to be colocalized with and reciprocal to XO-XX differences in anatomy. These overlaps identify the lateral septum, BNST, ventral group thalamic nuclei and periaqueductal gray matter as regions with replicable sensitivity to X chromosome dose across two SCAs. We then harness anatomical variation across all four karyotype groups in our study—XO, XX, XY and XXY—to create an agnostic data-driven segmentation of the mouse brain into five distributed clusters which (1) recover fundamental properties of brain organization with high spatial precision, (2) define two previously uncharacterized systems of relative volume excess in females vs. males (“forebrain cholinergic” and “cerebelo-pontine-thalamo-cortical”), and (3) adopt stereotyped spatial motifs which delineate ordered gradients of sex chromosome and gonadal influences on volumetric brain development. Taken together, these data provide a new framework for the study of sexually dimorphic influences on brain development in health and disrupted brain development in SCA