Imprinted inactivation of the paternal X chromosome in marsupials is the primordial mechanism of dosage compensation for X-linked genes between females and males in Therians. In Eutherian mammals, X chromosome inactivation (XCI) evolved into a random process in cells from the embryo proper, where either the maternal or paternal X can be inactivated. However, species like mouse and bovine maintained imprinted XCI exclusively in extraembryonic tissues. The existence of imprinted XCI in humans remains controversial, with studies based on the analyses of only one or two X-linked genes in different extraembryonic tissues. Here we readdress this issue in human term placenta by performing a robust analysis of allele-specific expression of 22 X-linked genes, including XIST, using 27 SNPs in transcribed regions. We show that XCI is random in human placenta, and that this organ is arranged in relatively large patches of cells with either maternal or paternal inactive X. In addition, this analysis indicated heterogeneous maintenance of gene silencing along the inactive X, which combined with the extensive mosaicism found in placenta, can explain the lack of agreement among previous studies. Our results illustrate the differences of XCI mechanism between humans and mice, and highlight the importance of addressing the issue of imprinted XCI in other species in order to understand the evolution of dosage compensation in placental mammals.

An emerging body of evidence points to impairments in neuroplasticity, cell resilience, and neuronal survival as major pathophysiological mechanisms in bipolar disorder. Neuronal survival is influenced by several factors including an orchestrated action of neurotransmitters, hormones, and neurotrophins. Patients with bipolar disorder exhibit increased peripheral level of inflammatory mediators such as cytokines, mainly during acute mood episodes. These mediators interact in several pathways involved in regulation of mood and energy including hypothalamic-pituitary-adrenal axis and monoamine metabolism. Importantly, inflammatory cytokines have a potential role in controlling neuronal and glial cell loss that occurs during mood episodes, especially during mania, as they are the most powerful extracellular stimuli to apoptosis. Bipolar patients have been reported to show imbalanced peripheral production of cytokines both at the mRNA and protein levels, associated signal transduction machinery, as well as to have specific functional polymorphisms in the genes that encode these cytokines. Interestingly, lithium, valproate, and several antidepressants have demonstrated to have immunomodulatory properties. Growing evidence supports the involvement of inflammatory mechanisms in bipolar disorder, opening new paths of investigation using immunomodulatory medications. These findings can offer not only an opportunity of treating mood symptoms but also understanding and reverting neurobiological changes associated with the disorder.

Since the derivation of the first human embryonic stem cell (hESC) lines by Thomson and coworkers in 1998, more than 1,200 different hESC lines have been established worldwide. Nevertheless, there is still a recognized interest in the establishment of new lines of hESC, particularly from HLA types and ethnic groups currently underrepresented among the available lines. The methodology of hESC derivation has evolved significantly since 1998, when human LIF (hLIF) was used for maintenance of pluripotency. However, there are a number of different strategies for the several steps involved in establishing a new line of hESC. Here we make a survey of the most relevant parameters used between 1998 and 2010 for the derivation of the 375 hESC lines deposited in two international stem cell registries, and able to form teratomas in immunocompromised mice. Although we identify some trends in the methodology for establishing hESC lines, our data reveal a much greater heterogeneity of strategies than what is used for derivation of murine ESC lines, indicating that optimum conditions have not been consolidated yet, and thus, hESC establishment is still an evolving field of research.

X chromosome inactivation (XCI) is a comprehensively studied phenomenon that helped to highlight the heritable nature of epigenetic modifications. Although it consists of the transcriptional inactivation of a whole X chromosome in females, some genes escape this process and present bi-allelic expression. Using human fibroblasts with skewed inactivation, we determined allele-specific expression of two X-linked genes previously described to escape XCI in rodent/human somatic cell hybrids, MAOA and GYG2, and the pattern of DNA methylation of their 5' end. Results from these complementary methodologies let us to conclude that both genes are subjected to X inactivation in normal human fibroblasts, indicating that hybrid cells are not an adequate system for studying epigenotypes. We emphasize the need of an analysis of XCI in normal human cell lines, helping us to determine more precisely which X-linked genes contribute to differences among genders and to the phenotypes associated with sex chromosomes aneuploidies.

X chromosome inactivation (XCI) in human and mice involves XIST/Xist gene expression from the inactive X (Xi) and repression from the active X (Xa). Repression of the XIST/Xist gene on the Xa has been associated with methylation of its 5' region. In mice, Dnmt1 has been shown to be involved in the methylation and transcriptional repression of Xist on Xa. We examined maintenance of XIST gene repression on Xa in HCT116 cell lines knockout for either DNMT1 or DNMT3B and for DNMT1 and DNMT3B simultaneously. Methylation of the XIST promoter and XIST transcriptional repression is sustained in DNMT1-, DNMT3B- and DNMT1/DNMT3B knockout cells. Despite global DNA demethylation, the double knockout cells present only partial demethylation of the XIST promoter, which is not sufficient for gene reactivation. In contrast, global DNA demethylation with 5-aza-2'-deoxycytidine leads to XIST expression. Therefore, in these human cells maintenance of XIST methylation is controlled differently than global genomic methylation and in the absence of both DNMT1 and DNMT3B.