Summary Dietary, microbial, and inflammatory factors modulate the gut-brain axis and influence physiological processes ranging from metabolism to cognition. The gut epithelium is a principle site for detecting such agents, but precisely how it communicates with neural elements is poorly understood. Serotonergic enterochromaffin (EC) cells are proposed to fulfill this role by acting as chemosensors, but understanding how these rare and unique cell types transduce chemosensory information to the nervous system has been hampered by their paucity and inaccessibility to single cell measurements. Here, we circumvent this limitation by exploiting cultured intestinal organoids together with single cell measurements to elucidate intrinsic biophysical, pharmacological, and genetic properties of EC cells. We show that EC cells express specific chemosensory receptors, are electrically excitable, and modulate serotoninsensitive primary afferent nerve fibers via synaptic connections, enabling them to detect and transduce environmental, metabolic, and homeostatic information from the gut directly to the nervous system.

A novel region referred to as the POU-domain is present in two tissue-specific transcription factors, Pit-1 and Oct-2, that activate expression of genes specifying pituitary and lymphocyte phenotypes. We report the identification of multiple new members of a large family of POU-domain genes expressed in adult brain, and document that all the known mammalian POU-domain genes, including Pit-1 and Oct-2, are expressed widely in the developing nervous system.

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Vertebrate members of the nuclear receptor NR5A subfamily, which includes steroidogenic factor 1 (SF-1) and liver receptor homolog 1 (LRH-1), regulate crucial aspects of development, endocrine homeostasis, and metabolism. Mouse LRH-1 is believed to be a ligand-independent transcription factor with a large and empty hydrophobic pocket. Here we present structural and biochemical data for three other NR5A members-mouse and human SF-1 and human LRH-1-which reveal that these receptors bind phosphatidyl inositol second messengers and that ligand binding is required for maximal activity. Evolutionary analysis of structure-function relationships across the SF-1/LRH-1 subfamily indicates that ligand binding is the ancestral state of NR5A receptors and was uniquely diminished or altered in the rodent LRH-1 lineage. We propose that phospholipids regulate gene expression by directly binding to NR5A nuclear receptors.

Development of the anterior pituitary gland involves proliferation and differentiation of ectodermal cells in Rathke's pouch to generate five distinct cell types that are defined by the trophic hormones they produce. A detailed ontogenetic analysis of specific gene expression has revealed novel aspects of organogenesis in this model system. The expression of transcripts encoding the alpha-subunit common to three pituitary glycoprotein hormones in the single layer of somatic ectoderm on embryonic day 11 established that primordial pituitary cell commitment occurs prior to formation of a definitive Rathke's pouch. Activation of Pit-1 gene expression occurs as an organ-specific event, with Pit-1 transcripts initially detected in anterior pituitary cells on embryonic day 15. Levels of Pit-1 protein closely parallel those of Pit-1 transcripts without a significant lag. Unexpectedly, Pit-1 transcripts remain highly expressed in all five cell types of the mature pituitary gland, but the Pit-1 protein is detected in only three cell types--lactotrophs, somatotrophs, and thyrotrophs and not in gonadotrophs or corticotrophs. The presence of Pit-1 protein in thyrotrophs suggests that combinatorial actions of specific activating and restricting factors act to confine prolactin and growth hormone gene expression to lactotrophs and somatotrophs, respectively. A linkage between the initial appearance of Pit-1 protein and the surprising coactivation of prolactin and growth hormone gene expression is consistent with the model that Pit-1 is responsible for the initial transcriptional activation of both genes. The estrogen receptor, which has been reported to be activated in a stereotypic fashion subsequent to the appearance of Pit-1, appears to be capable, in part, of mediating the progressive increase in prolactin gene expression characteristic of the mature lactotroph phenotype. This is a consequence of synergistic transcriptional effects with Pit-1, on the basis of binding of the estrogen receptor to a response element in the prolactin gene distal enhancer. These data imply that both transcriptional and post-transcriptional regulation of Pit-1 gene expression and combinatorial actions with other classes of transcription factors activated in distinct temporal patterns, are required for the mature physiological patterns of gene expression that define distinct cell types within the anterior pituitary gland.

Products of steroidogenic factor 1 (SF-1) and Wilms' tumor 1 (WT1) genes are essential for mammalian gonadogenesis prior to sexual differentiation. In males, SF-1 participates in sexual development by regulating expression of the polypeptide hormone Müllerian inhibiting substance (MIS). Here, we show that WT1 -KTS isoforms associate and synergize with SF-1 to promote MIS expression. In contrast, WT1 missense mutations, associated with male pseudohermaphroditism in Denys-Drash syndrome, fail to synergize with SF-1. Additionally, the X-linked, candidate dosage-sensitive sex-reversal gene, Dax-1, antagonizes synergy between SF-1 and WT1, most likely through a direct interaction with SF-1. We propose that WT1 and Dax-1 functionally oppose each other in testis development by modulating SF-1-mediated transactivation.

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Steroidogenic factor 1 (SF-1), an orphan nuclear receptor, regulates the enzymes that produce sex steroids, and disruption of the Ftz-F1 gene encoding SF-1 precludes adrenal and gonadal development. We now study the role of SF-1 at other levels of the hypothalamic/pituitary/gonadal axis. In Ftz-Fl-disrupted mice, immunohistochemical analyses with antibodies against pituitary trophic hormones showed a selective loss of gonadotrope-specific markers, supporting the role of SF-1 in gonadotrope function. In situ hybridization analyses confirmed these results; pituitaries from Ftz-Fl-disrupted mice lacked transcripts for three gonadotrope-specific markers (LH~, FSH~, and the receptor for gonadotropin-releasing hormone), whereas they exhibited decreased but detectable expression of the ~-subunit of glycoprotein hormones. SF-1 transcripts in the developing mouse pituitary, which first became detectable at embryonic day 13.5-14.5, preceded the appearance of FSH~ and LH~ transcripts. In adult rat pituitary cells, SF-1 transcripts colocalized with immunoreactivity for the gonadotrope-specific LH. Finally, SF-1 interacted with a previously defined promoter element in the glycoprotein hormone ~-subunit gene, providing a possible mechanism for the impaired gonadotropin expression in Ftz-Fl-disrupted mice. These studies establish novel roles of this orphan nuclear receptor in reproductive function.