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Pure hair and nail ectodermal dysplasia (PHNED) is a congenital disorder characterized by reduced or absent hair and dystrophic nails. PHNED is caused by pathogenic variants in genes involved in hair and nail development, including HOXC13. Previously reported biallelic HOXC13 pathogenic variants led to PHNED by either disrupting protein expression through nonsense‐mediated decay or altering the DNA‐binding affinity of the homeobox domain of HOXC13. Here, we report a case of HOXC13‐related PHNED with a rare homozygous variant, c.931C>T, p.Arg311Trp. Similarly to previously reported missense variants, p.Arg311Trp resides in the homeobox domain of HOXC13 and was assumed to lead to the decreased transcriptional activity of target genes. However, in contrast with previously reported variants, in vitro overexpression assays revealed that the p.Arg311Trp variant decreases HOXC13 protein stability, which is corroborated by a series of in silico predictions. Computational models further suggest that p.Arg311Trp results in a structural rearrangement with loss of interhelical connection between Arg311 in α‐helix 3 and Glu276 in α‐helix 1. Altogether, our results suggest a novel molecular mechanism causative of PHNED, whereby biallelic pathogenic variants in HOXC13 may result in decreased protein stability and consequently decreased transcriptional activity of target genes essential for hair and nail development. [ABSTRACT FROM AUTHOR]

Liver sinusoidal endothelial cells (LSECs) are highly specialised endothelial cells that form the liver microvasculature. LSECs maintain liver homeostasis, scavenging bloodborne molecules, regulating immune response, and actively promoting hepatic stellate cell quiescence. These diverse functions are underpinned by a suite of unique phenotypical attributes distinct from other blood vessels. In recent years, studies have begun to reveal the specific contributions of LSECs to liver metabolic homeostasis and how LSEC dysfunction associates with disease aetiology. This has been particularly evident in the context of non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of metabolic syndrome, which is associated with the loss of key LSEC phenotypical characteristics and molecular identity. Comparative transcriptome studies of LSECs and other endothelial cells, together with rodent knockout models, have revealed that loss of LSEC identity through disruption of core transcription factor activity leads to impaired metabolic homeostasis and to hallmarks of liver disease. This review explores the current knowledge of LSEC transcription factors, covering their roles in LSEC development and maintenance of key phenotypic features, which, when disturbed, lead to loss of liver metabolic homeostasis and promote features of chronic liver diseases, such as non-alcoholic liver disease. [ABSTRACT FROM AUTHOR]

Liver kinase B1 (LKB1/STK11) is an important regulator of pancreatic β-cell identity and function. Elimination of Lkb1 from the β-cell results in improved glucose-stimulated insulin secretion and is accompanied by profound changes in gene expression, including the upregulation of several neuronal genes. The mechanisms through which LKB1 controls gene expression are, at present, poorly understood. Here, we explore the impact of β cell- selective deletion of Lkb1 on chromatin accessibility in mouse pancreatic islets. To characterize the role of LKB1 in the regulation of gene expression at the transcriptional level, we combine these data with a map of islet active transcription start sites and histone marks. We demonstrate that LKB1 elimination from β-cells results in widespread changes in chromatin accessibility, correlating with changes in transcript levels. Changes occurred in hundreds of promoter and enhancer regions, many of which were close to neuronal genes. We reveal that dysregulated enhancers are enriched in binding motifs for transcription factors important for β-cell identity, such as FOXA, MAFA or RFX6 and we identify microRNAs (miRNAs) that are regulated by LKB1 at the transcriptional level. Overall, our study provides important new insights into the epigenetic mechanisms by which LKB1 regulates β-cell identity and function.