Sex-specific chromatin remodelling safeguards transcription in germ cells.

Stability of the epigenetic landscape underpins maintenance of the cell-type-specific transcriptional profile. As one of the main repressive epigenetic systems, DNA methylation has been shown to be important for long-term gene silencing; its loss leads to ectopic and aberrant transcription in differentiated cells and cancer1. The developing mouse germ line endures global changes in DNA methylation in the absence of widespread transcriptional activation. Here, using an ultra-low-input native chromatin immunoprecipitation approach, we show that following DNA demethylation the gonadal primordial germ cells undergo remodelling of repressive histone modifications, resulting in a sex-specific signature in mice. We further demonstrate that Polycomb has a central role in transcriptional control in the newly hypomethylated germline genome as the genetic loss of Ezh2 leads to aberrant transcriptional activation, retrotransposon derepression and dramatic loss of developing female germ cells. This sex-specific effect of Ezh2 deletion is explained by the distinct landscape of repressive modifications observed in male and female germ cells. Overall, our study provides insight into the dynamic interplay between repressive chromatin modifications in the context of a developmental reprogramming system.

Variants in Maternal Effect Genes and Relaxed Imprinting Control in a Special Placental Mesenchymal Dysplasia Case with Mild Trophoblast Hyperplasia.

Placental mesenchymal dysplasia (PMD) and partial hydatidiform mole (PHM) placentas share similar characteristics, such as placental overgrowth and grape-like placental tissues. Distinguishing PMD from PHM is critical because the former can result in normal birth, while the latter diagnosis will lead to artificial abortion. Aneuploidy and altered dosage of imprinted gene expression are implicated in the pathogenesis of PHM and also some of the PMD cases. Diandric triploidy is the main cause of PHM, whereas mosaic diploid androgenetic cells in the placental tissue have been associated with the formation of PMD. Here, we report a very special PMD case also presenting with trophoblast hyperplasia phenotype, which is a hallmark of PHM. This PMD placenta has a normal biparental diploid karyotype and is functionally sufficient to support normal fetal growth. We took advantage of this unique case to further dissected the potential common etiology between these two diseases. We show that the differentially methylated region (DMR) at NESP55, a secondary DMR residing in the GNAS locus, is significantly hypermethylated in the PMD placenta. Furthermore, we found heterozygous mutations in NLRP2 and homozygous variants in NLRP7 in the mother's genome. NLRP2 and NLRP7 are known maternal effect genes, and their mutation in pregnant females affects fetal development. The variants/mutations in both genes have been associated with imprinting defects in mole formation and potentially contributed to the mild abnormal imprinting observed in this case. Finally, we identified heterozygous mutations in the X-linked ATRX gene, a known maternal-zygotic imprinting regulator in the patient. Overall, our study demonstrates that PMD and PHM may share overlapping etiologies with the defective/relaxed dosage control of imprinted genes, representing two extreme ends of a spectrum.

Daxx interacts with and modulates the activity of CREB.

The phosphorylation of cAMP response element-binding protein (CREB) induced by the cAMP-dependent protein kinase A (PKA) elicits the recruitment of CREB-binding protein (CBP) for activating cAMP responsive gene expression. Several reports indicate that proteins binding to CREB and/or CBP play important roles in modulating the CREB-dependent transactivation. Here, we show that Daxx interacts with CREB and modulates CREB-mediated transcription. Daxx was identified as a CREB-interacting protein by a yeast two-hybrid screen. Depletion of endogenous Daxx by specific shRNA or overexpression of Daxx resulted in decreased or increased levels of the cAMP/PKA-induced reporter activity and target gene expression, respectively. In vitro and in vivo binding studies revealed that Daxx C-terminal domain binds to CREB basic leucine zipper domain. The binding of Daxx to CREB correlates with its repressive effect on a CRE-mediated reporter activity induced by forskolin or PKA. Furthermore, the results of electrophoresis mobility shift assays and chromatin immunoprecipitation experiments showed that Daxx attenuated the DNA binding potential of the CREB. Our study provides a previously undescribed role of Daxx in repressing cAMP-responsive gene expression and also a mechanism underlying the repressive effect of Daxx on CREB transcriptional potential.