Constitutive nuclear lamina-genome interactions are highly conserved and associated with A/T-rich sequence

In metazoans, the nuclear lamina is thought to play an important role in the spatial organization of interphase chromosomes, by providing anchoring sites for large genomic segments named lamina-associated domains (LADs). Some of these LADs are cell-type specific, while many others appear constitutively associated with the lamina. Constitutive LADs (cLADs) may contribute to a basal chromosome architecture. By comparison of mouse and human lamina interaction maps, we find that the sizes and genomic positions of cLADs are strongly conserved. Moreover, cLADs are depleted of synteny breakpoints, pointing to evolutionary selective pressure to keep cLADs intact. Paradoxically, the overall sequence conservation is low for cLADs. Instead, cLADs are universally characterized by long stretches of DNA of high A/T content. Cell-type specific LADs also tend to adhere to this “A/T rule” in embryonic stem cells, but not in differentiated cells. This suggests that the A/T rule represents a default positioning mechanism that is locally overruled during lineage commitment. Analysis of paralogs suggests that during evolution changes in A/T content have driven the relocation of genes to and from the nuclear lamina, in tight association with changes in expression level. Taken together, these results reveal that the spatial organization of mammalian genomes is highly conserved and tightly linked to local nucleotide composition

MarvelD3 couples tight junctions to the MEKK1-JNK pathway to regulate cell behavior and survival

MarvelD3 is a transmembrane component of tight junctions, but there is little evidence for a direct involvement in the junctional permeability barrier. Tight junctions also regulate signaling mechanisms that guide cell proliferation; however, the transmembrane components that link the junction to such signaling pathways are not well understood. In this paper, we show that MarvelD3 is a dynamic junctional regulator of the MEKK1-c-Jun NH2-terminal kinase (JNK) pathway. Loss of MarvelD3 expression in differentiating Caco-2 cells resulted in increased cell migration and proliferation, whereas reexpression in a metastatic tumor cell line inhibited migration, proliferation, and in vivo tumor formation. Expression levels of MarvelD3 inversely correlated with JNK activity, as MarvelD3 recruited MEKK1 to junctions, leading to down-regulation of JNK phosphorylation and inhibition of JNK-regulated transcriptional mechanisms. Interplay between MarvelD3 internalization and JNK activation tuned activation of MEKK1 during osmotic stress, leading to junction dissociation and cell death in MarvelD3-depleted cells. MarvelD3 thus couples tight junctions to the MEKK1-JNK pathway to regulate cell behavior and survival

Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.

BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362

HNF-6 contrôle la maturation et la prolifération des hépatocytes au cours du développement embryonnaire

Embryonic liver development is controlled at the transcriptional level by a network of liver-enriched transcription factors (LETFs), which regulate their mutual expression as well as that of common target genes. An important factor in this network is HNF-6. Whereas the interactions and roles of LETFs are well defined in the adult and the early embryonic liver, much less is known about their mode of action at late stages of development. The goal of the present thesis is to elucidate the role of HNF-6 in the maturation and proliferation of hepatocytes during development, and to provide a better insight into the position of HNF-6 within the LETF network. Here we show that HNF-6 plays an important and time-specific role in late embryonic liver development. On the one hand, it controls the acquisition of mature hepatocyte functions, on the other hand, it regulates epithelial and non-epithelial cell proliferation. In both cases, HNF-6 modulates the expression of genes involved in the processes. HNF-6 regulates the time-specific expression of glucose-6-phosphatase (g6pc) gene, a marker of hepatocyte maturation, via synergistic and interdependent interactions with HNF-4 and coactivator PGC-1alpha. Our study of those interactions allow us to propose a new mechanism whereby temporal specificity of gene expression requires threshold concentrations of transcription factors and their coactivators during liver development. In addition, HNF-6 controls proliferation in the liver, again in a time-specific manner, by regulating the expression of several cell cycle genes. This indirect mechanism is likely to involve HNF-6-mediated modulation of a mitogenic signal, the nature of which remains to be determined. In conclusion, our work defines a central role for HNF-6 in the hepatic network of transcription factors. Through its interactions with other factors, HNF-6 controls the timing of cell maturation and proliferation in the embryonic liverLe développement embryonnaire du foie est contrôlé au niveau transcriptionnel par un réseau de facteurs de transcription hépatiques (LETFs), qui régulent mutuellement leur expression et contrôlent l'expression de gènes cibles communs. Un facteur important de ce réseau est HNF-6. Si les interactions et les rôles des LETFs sont bien décrits chez l'adulte et dans le foie embryonnaire précoce, en revanche on connaît peu de choses sur leur action dans le foie à des stades tardifs du développement. L'objectif de cette thèse est d'élucider le rôle de HNF-6 dans la maturation et la prolifération des hépatocytes à ces stades, et de mieux définir la place de HNF-6 au sein du réseau des LETFs dans ces processus. Nous montrons ici que HNF-6 joue un rôle central et temporellement spécifique dans le développement tardif du foie. Il contrôle d'une part l'acquisition de fonctions matures de l'hépatocyte, d'autre part la prolifération de manière globale dans le foie en fin de gestation. Dans les deux cas, HNF-6 intervient en contrôlant l'expression de gènes impliqués. HNF-6 régule la spécificité temporelle de l'expression de la glucose-6-phosphatase (g6pc), un marqueur hépatocytaire, via une relation synergique et interdépendante avec le facteur HNF-4 et le coactivateur PGC-1alpha. Notre étude de ces relations nous a permis de décrire un mécanisme nouveau selon lequel la spécificité temporelle de l'expression génique nécessite des concentrations seuils de facteurs de transcription et de leurs coactivateurs au cours du développement hépatique. En outre, HNF-6 contrôle la prolifération dans le foie, également de manière temporellement spécifique, en régulant l'expression de plusieurs gènes impliqués dans le cycle cellulaire. Ce mécanisme indirect implique probablement la modulation par HNF-6 d'un signal mitogène dont la nature reste à déterminer. Nos travaux assignent ainsi à HNF-6 un rôle central dans le réseau des facteurs de transcription hépatiques. Par ses interactions avec d'autres facteurs, HNF-6 contrôle la spécificité temporelle de la maturation et de la prolifération des cellules dans le foie embryonnaireThèse de doctorat en sciences biomédicales (SBIM 3) -- UCL, 200

Proliferation-Independent Initiation of Biliary Cysts in Polycystic Liver Diseases

Biliary cysts in adult patients affected by polycystic liver disease are lined by cholangiocytes that proliferate, suggesting that initiation of cyst formation depends on proliferation. Here, we challenge this view by analyzing cyst-lining cell proliferation and differentiation in Cpk mouse embryos and in livers from human fetuses affected by Autosomal Recessive Polycystic Kidney Disease (ARPKD), at early stages of cyst formation. Proliferation of fetal cholangiocyte precursors, measured by immunostaining in human and mouse livers, was low and did not differ between normal and ARPKD or Cpk livers, excluding excessive proliferation as an initiating cause of liver cysts. Instead, our analyses provide evidence that the polycystic livers exhibit increased and accelerated differentiation of hepatoblasts into cholangiocyte precursors, eventually coalescing into large biliary cysts. Lineage tracing experiments, performed in mouse embryos, indicated that the cholangiocyte precursors in Cpk mice generate cholangiocytes and periportal hepatocytes, like in wild-type animals. Therefore, contrary to current belief, cyst formation in polycystic liver disease does not necessarily depend on overproliferation. Combining our prenatal data with available data from adult livers, we propose that polycystic liver can be initiated by proliferation-independent mechanisms at a fetal stage, followed by postnatal proliferation-dependent cyst expansion

The Onecut transcription factors HNF-6/OC-1 and OC-2 regulate early liver expansion by controlling hepatoblast migration

Liver development in mammals is initiated by the formation of a hepatic bud from the ventral foregut endoderm. The hepatic cells then proliferate and invade the septum transversum mesenchyme, and further differentiate to give rise to hepatocytes and biliary cells. By analyzing mice that are knockout for the transcription factors Hepatocyte Nuclear Factor-6 (HNF-6)/Onecut-1 (OC-1) and OC-2, we show here that these factors redundantly stimulate the degradation of the basal lamina surrounding the liver bud and promote hepatoblast migration in the septum transversum. Gene expression analysis indicates that HNF-6 and OC-2 belong to a gene network comprising E-cadherin, thrombospondin-4 and osteopontin, which regulates liver bud expansion by controlling hepatoblast migration and adhesion. This network operating at the onset of liver development contains candidate genes for investigation of liver carcinogenesis

Threshold Levels of Hepatocyte Nuclear Factor 6 (HNF-6) Acting in Synergy with HNF-4 and PGC-1α Are Required for Time-Specific Gene Expression during Liver Development

During liver development, hepatocytes undergo a maturation process that leads to the fully differentiated state. This relies at least in part on the coordinated action of liver-enriched transcription factors (LETFs), but little is known about the dynamics of this coordination. In this context we investigate here the role of the LETF hepatocyte nuclear factor 6 (HNF-6; also called Onecut-1) during hepatocyte differentiation. We show that HNF-6 knockout mouse fetuses have delayed expression of glucose-6-phosphatase (g6pc), which catalyzes the final step of gluconeogenesis and is a late marker of hepatocyte maturation. Using a combination of in vivo and in vitro gain- and loss-of-function approaches, we demonstrate that HNF-6 stimulates endogenous g6pc gene expression directly via a synergistic and interdependent action with HNF-4 and that it involves coordinate recruitment of the coactivator PGC-1α. The expression of HNF-6, HNF-4, and PGC-1α rises steadily during liver development and precedes that of g6pc. We provide evidence that threshold levels of HNF-6 are required to allow synergism between HNF-6, HNF-4, and PGC-1α to induce time-specific expression of g6pc. Our observations on the regulation of g6pc by HNF-6 provide a model whereby synergism, interdependency, and threshold concentrations of LETFs and coactivators determine time-specific expression of genes during liver development

Expression of genes in <i>Cpk</i> livers.

<p><b>(A)</b> Gene set enrichment analysis revealed enrichment of apical junction proteins. The gene set is shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0132295#pone.0132295.s003" target="_blank">S3 Table</a>. <b>(B)</b> Manual microdissection of WT and <i>Cpk</i> portal tracts at E17.5 on formalin-fixed, paraffin-embedded livers. Representative H&E staining of 2 individuals of each genotype are shown. The area of microdissected tissue is delineated by a dotted line. Bar, 400 μm. <b>(C-J)</b> qRT-PCR analysis in WT and <i>Cpk</i> portal tracts. Shown here are differentiation markers of <b>C:</b> cholangiocytes, <b>D:</b> hepatocytes and mesenchyme (<i>Sm22a</i>); markers of signaling activity of the <b>E:</b> Wnt/βCatenin, <b>F:</b> Notch, <b>G:</b> FGF and VEGF, <b>H:</b> YAP/Hippo pathways (n = 3 for WT, n = 5 for cpk). All gene expression data were normalized for the expression for the biliary marker Sox9. Student’s t-test was applied to determine significant difference (*, p<0.05).</p

Cysts form in <i>Cpk</i> embryos, without excessive proliferation and with normal differentiation of ductal plate cells into periportal hepatocytes.

<p><b>(A)</b> Time-course analysis of biliary cyst formation in <i>Cpk</i> mouse embryos. First signs of biliary cysts can be observed at E16.5; full-blown cysts are observed with 100% penetrance from E17.5. *, cysts, pv, portal vein; dp, ductal plate. Bars: 100 μm. <b>(B)</b> Scheme of the Sox9 lineage tracing experiment experiment. Pregnant mothers bearing <i>Sox9-CreER;Rosa</i>^<i>YFP</i><i>;Cpk</i>^<i>mut</i> embryos were injected at E14.5 with a single dose of tamoxifen, and newborn pups were collected at P1. <b>(C)</b> Sox9⁺ ductal plate cells can give rise to periportal hepatocytes in <i>Cpk</i> livers. Lineage tracing of <i>Sox9-CreER;Rosa</i>^<i>YFP</i><i>;Cpk</i>^<i>mut</i> ductal plate cells detected differentiation of periportal HNF4⁺/Sox9^-/YFP⁺ hepatocytes in <i>Cpk</i> mouse livers at P1. Bars: 100 μm.</p