No abstract

The signal transducer and activator of transcription-3 (Stat3) protein is activated by the interleukin 6 (IL-6) family of cytokines, epidermal growth factor, and leptin. A protein named PIAS3 (protein inhibitor of activated STAT) that binds to Stat3 was isolated and characterized. The association of PIAS3 with Stat3 in vivo was only observed in cells stimulated with ligands that cause the activation of Stat3. PIAS3 blocked the DNA-binding activity of Stat3 and inhibited Stat3-mediated gene activation. Although Stat1 is also phosphorylated in response to IL-6, PIAS3 did not interact with Stat1 or affect its DNA-binding or transcriptional activity. The results indicate that PIAS3 is a specific inhibitor of Stat3.

Holoprosencephaly (HPE) is a common developmental defect of the forebrain and frequently the midface in humans, with both genetic and environmental causes. HPE has a prevalence of 1:250 during embryogenesis and 1:16,000 newborn infants, and involves incomplete development and septation of midline structures in the central nervous system (CNS) with a broad spectrum of clinical severity. Alobar HPE, the most severe form which is usually incompatible with postnatal life, involves complete failure of division of the forebrain into right and left hemispheres and is characteristically associated with facial anomalies including cyclopia, a primitive nasal structure (proboscis) and/or midfacial clefting. At the mild end of the spectrum, findings may include microcephaly, mild hypotelorism, single maxillary central incisor and other defects (Fig. 1). This phenotypic variability also occurs between affected members of the same family. The molecular basis underlying HPE is not known, although teratogens, non-random chromosomal anomalies and familial forms with autosomal dominant and recessive inheritance have been described. HPE3 on chromosome 7q36 is one of at least four different loci implicated in HPE. Here, we report the identification of human Sonic Hedgehog (SHH) as HPE3-the first known gene to cause HPE. Analyzing 30 autosomal dominant HPE (ADHPE) families, we found five families that segregate different heterozygous SHH mutations. Two of these mutations predict premature termination of the SHH protein, whereas the others alter highly conserved residues in the vicinity of the alpha-helix-1 motif or signal cleavage site.

Wnt signalling, which is transduced through beta-catenin/TCF4, maintains the undifferentiated state of intestinal crypt progenitor cells. Mutational activation of the pathway initiates the adenomacarcinoma sequence. Whereas all other differentiated epithelial cells migrate from the crypt onto the villus, Paneth cells home towards the source of Wnt signals--that is, the crypt bottom. Here, we show that expression of a Paneth gene programme is critically dependent on TCF4 in embryonic intestine. Moreover, conditional deletion of the Wnt receptor Frizzled-5 abrogates expression of these genes in Paneth cells in the adult intestine. Conversely, adenomas in Apc-mutant mice and colorectal cancers in humans inappropriately express these Paneth-cell genes. These observations imply that Wnt signals in the crypt can separately drive a stem-cell/progenitor gene programme and a Paneth-cell maturation programme. In intestinal cancer, both gene programmes are activated simultaneously.

The HMG-box transcription factor Sox9 is expressed in the intestinal epithelium, specifically, in stem/progenitor cells and in Paneth cells. Sox9 expression requires an active β-catenin–Tcf complex, the transcriptional effector of the Wnt pathway. This pathway is critical for numerous aspects of the intestinal epithelium physiopathology, but processes that specify the cell response to such multipotential signals still remain to be identified. We inactivated the Sox9 gene in the intestinal epithelium to analyze its physiological function. Sox9 inactivation affected differentiation throughout the intestinal epithelium, with a disappearance of Paneth cells and a decrease of the goblet cell lineage. Additionally, the morphology of the colon epithelium was severely altered. We detected general hyperplasia and local crypt dysplasia in the intestine, and Wnt pathway target genes were up-regulated. These results highlight the central position of Sox9 as both a transcriptional target and a regulator of the Wnt pathway in the regulation of intestinal epithelium homeostasis.

T cell development and selection are coordinated in the thymus by a specialized niche of diverse stromal populations. Although much progress has been made over the years in identifying the functions of the different cell types of the thymic stromal compartment, there is no comprehensive characterization of their diversity and heterogeneity. Here we combined massively parallel single-cell RNA-sequencing, spatial mapping, chromatin profiling and gene targeting to characterize de novo the entire stromal compartment of the mouse thymus. We identified dozens of cell states, with thymic epithelial cells (TECs) showing the highest degree of heterogeneity. Our analysis highlights four major medullary TEC (mTEC I-IV) populations, with distinct molecular functions, epigenetic landscapes and lineage regulators. Specifically, mTEC IV constitutes a new and highly divergent TEC lineage with molecular characteristics of the gut chemosensory epithelial tuft cells. Mice deficient in Pou2f3, a master regulator of tuft cells, have complete and specific depletion of mTEC IV cells, which results in increased levels of thymus-resident type-2 innate lymphoid cells. Overall, our study provides a comprehensive characterization of the thymic stroma and identifies a new tuft-like TEC population, which is critical for shaping the immune niche in the thymus.

TCF and SOX proteins belong to the high mobility group box transcription factor family. Whereas TCFs, the transcriptional effectors of the Wnt pathway, have been widely implicated in the development, homeostasis and disease of the intestine epithelium, little is known about the function of the SOX proteins in this tissue. Here, we identified SOX9 in a SOX expression screening in the mouse fetal intestine. We report that the SOX9 protein is expressed in the intestinal epithelium in a pattern characteristic of Wnt targets. We provide in vitro and in vivo evidence that a bipartite β-catenin/TCF4 transcription factor, the effector of the Wnt signaling pathway, is required for SOX9 expression in epithelial cells. Finally, in colon epithelium-derived cells, SOX9 transcriptionally represses the CDX2 and MUC2 genes, normally expressed in the mature villus cells of the intestinal epithelium, and may therefore contribute to the Wnt-dependent maintenance of a progenitor cell phenotype.

Tuft cells represent a fourth type of intestinal secretory cell that constitutes the primary source of endogenous intestinal opioids and are the only epithelial cell that constitutively express cyclooxygenases.