Ontogeny of ependymoglial cells lining the third ventricle in mice.

During hypothalamic development, the germinative neuroepithelium gives birth to diverse neural cells that regulate numerous physiological functions in adulthood. Here, we studied the ontogeny of ependymal cells in the mouse mediobasal hypothalamus using the BrdU approach and publicly available single-cell RNAseq datasets. We observed that while typical ependymal cells are mainly produced at E13, tanycyte birth depends on time and subtypes and lasts up to P8. Typical ependymocytes and β tanycytes are the first to arise at the top and bottom of the dorsoventral axis around E13, whereas α tanycytes emerge later in development, generating an outside-in dorsoventral gradient along the third ventricle. Additionally, α tanycyte generation displayed a rostral-to-caudal pattern. Finally, tanycytes mature progressively until they reach transcriptional maturity between P4 and P14. Altogether, this data shows that ependyma generation differs in time and distribution, highlighting the heterogeneity of the third ventricle

Fgf15 Neurons of the Dorsomedial Hypothalamus Control Glucagon Secretion and Hepatic Gluconeogenesis.

The counterregulatory response to hypoglycemia is an essential survival function. It is controlled by an integrated network of glucose-responsive neurons, which trigger endogenous glucose production to restore normoglycemia. The complexity of this glucoregulatory network is, however, only partly characterized. In a genetic screen of a panel of recombinant inbred mice we previously identified Fgf15, expressed in neurons of the dorsomedial hypothalamus (DMH), as a negative regulator of glucagon secretion. Here, we report on the generation of Fgf15 <sup>CretdTomato</sup> mice and their use to further characterize these neurons. We show that they were glutamatergic and comprised glucose-inhibited and glucose-excited neurons. When activated by chemogenetics, Fgf15 neurons prevented the increase in vagal nerve firing and the secretion of glucagon normally triggered by insulin-induced hypoglycemia. On the other hand, they increased the activity of the sympathetic nerve in the basal state and prevented its silencing by glucose overload. Higher sympathetic tone increased hepatic Creb1 phosphorylation, Pck1 mRNA expression, and hepatic glucose production leading to glucose intolerance. Thus, Fgf15 neurons of the DMH participate in the counterregulatory response to hypoglycemia by a direct adrenergic stimulation of hepatic glucose production while suppressing vagally induced glucagon secretion. This study provides new insights into the complex neuronal network that prevents the development of hypoglycemia

Establishment of a cell line derived from embryos of the potato tuber moth Phthorimaea operculella (Zeller)

Une lignée cellulaire a été obtenue à partir d'embryocultures de #Phthorimaea operculella (Zeller), le principal ravageur de la pomme de terre dans les régions tropicales et sub-tropicales. La lignée cellulaire, nommée ORS-Pop-93, cultivée en milieu Grace modifié, a une population hétérogène de cellules arrondies et allongées très adhérentes. Le temps de doublement des cellules est de 40 h. La lignée a été subcultivée plus de 40 fois. Le profil polypeptidique est différent de celui d'autres lignées de lépidoptères. La lignée est permissive à la polyhédrose nucléaire de #Autographa californica. (Résumé d'auteur

Central Dicer-miR-103/107 controls developmental switch of POMC progenitors into NPY neurons and impacts glucose homeostasis.

Proopiomelanocortin (POMC) neurons are major negative regulators of energy balance. A distinct developmental property of POMC neurons is that they can adopt an orexigenic neuropeptide Y (NPY) phenotype. However, the mechanisms underlying the differentiation of <i>Pomc</i> progenitors remain unknown. Here, we show that the loss of the microRNA (miRNA)-processing enzyme <i>Dicer</i> in POMC neurons causes metabolic defects, an age-dependent decline in the number of <i>Pomc</i> mRNA-expressing cells, and an increased proportion of <i>Pomc</i> progenitors acquiring a NPY phenotype. miRNome microarray screening further identified miR-103/107 as candidates that may be involved in the maturation of <i>Pomc</i> progenitors. In vitro inhibition of miR-103/107 causes a reduction in the number of <i>Pomc</i> -expressing cells and increases the proportion of <i>Pomc</i> progenitors differentiating into NPY neurons. Moreover, in utero silencing of miR-103/107 causes perturbations in glucose homeostasis. Together, these data suggest a role for prenatal miR-103/107 in the maturation of <i>Pomc</i> progenitors and glucose homeostasis

A Comparative Analysis Shows Morphofunctional Differences between the Rat and Mouse Melanin-Concentrating Hormone Systems

Sub-populations of neurons producing melanin-concentrating hormone (MCH) are characterized by distinct projection patterns, birthdates and CART/NK3 expression in rat. Evidence for such sub-populations has not been reported in other species. However, given that genetically engineered mouse lines are now commonly used as experimental models, a better characterization of the anatomy and morphofunctionnal organization of MCH system in this species is then necessary. Combining multiple immunohistochemistry experiments with in situ hybridization, tract tracing or BrdU injections, evidence supporting the hypothesis that rat and mouse MCH systems are not identical was obtained: sub-populations of MCH neurons also exist in mouse, but their relative abundance is different. Furthermore, divergences in the distribution of MCH axons were observed, in particular in the ventromedial hypothalamus. These differences suggest that rat and mouse MCH neurons are differentially involved in anatomical networks that control feeding and the sleep/wake cycle

The Melanin-Concentrating Hormone (MCH) System Modulates Behaviors Associated with Psychiatric Disorders

Deficits in sensorimotor gating measured by prepulse inhibition (PPI) of the startle have been known as characteristics of patients with schizophrenia and related neuropsychiatric disorders. PPI disruption is thought to rely on the activity of the mesocorticolimbic dopaminergic system and is inhibited by most antipsychotic drugs. These drugs however act also at the nigrostriatal dopaminergic pathway and exert adverse locomotor responses. Finding a way to inhibit the mesocorticolimbic- without affecting the nigrostriatal-dopaminergic pathway may thus be beneficial to antipsychotic therapies. The melanin-concentrating hormone (MCH) system has been shown to modulate dopamine-related responses. Its receptor (MCH1R) is expressed at high levels in the mesocorticolimbic and not in the nigrostriatal dopaminergic pathways. Interestingly a genomic linkage study revealed significant associations between schizophrenia and markers located in the MCH1R gene locus. We hypothesize that the MCH system can selectively modulate the behavior associated with the mesocorticolimbic dopamine pathway. Using mice, we found that central administration of MCH potentiates apomorphine-induced PPI deficits. Using congenic rat lines that differ in their responses to PPI, we found that the rats that are susceptible to apomorphine (APO-SUS rats) and exhibit PPI deficits display higher MCH mRNA expression in the lateral hypothalamic region and that blocking the MCH system reverses their PPI deficits. On the other hand, in mice and rats, activation or inactivation of the MCH system does not affect stereotyped behaviors, dopamine-related responses that depend on the activity of the nigrostriatal pathway. Furthermore MCH does not affect dizocilpine-induced PPI deficit, a glutamate related response. Thus, our data present the MCH system as a regulator of sensorimotor gating, and provide a new rationale to understand the etiologies of schizophrenia and related psychiatric disorders

Molecular control of the development of hypothalamic neurons involved in metabolic regulation.

The hypothalamus is a large brain region made of nuclei and areas involved in the control of behaviors and physiological regulations. Among them, the arcuate nucleus (ARH) and the lateral hypothalamic area (LHA) contain key neuronal populations expressing the pro-opiomelanocortin (POMC), the agouti-related peptide (AgRP), and the melanin-concentrating hormone (MCH), respectively, that are involved in goal-oriented behaviors (such as feeding behavior) and glucose homeostasis. These neuronal populations are generated from distinct parts of the germinative neuroepithelium during embryonic life, and acquire their cell fate under the influence of morphogen proteins, specific transcription factors, and epigenetic modulators. POMC and MCH neuronal development continues by sending long descending axonal projections before birth under the control of axon guidance molecules such as Netrin1 and Slit2. Later, during the postnatal period, POMC and AgRP neurons develop intra-hypothalamic projections notably to the paraventricular nucleus of the hypothalamus through the influence of other axon guidance cues such as the class3 Semaphorins. Other cellular processes, such as autophagy and primary cilia function, and hormonal cues also appear critical for the proper development of POMC neurons

Ontogeny of the Projections From the Dorsomedial Division of the Anterior Bed Nucleus of the Stria Terminalis to Hypothalamic Nuclei.

The bed nucleus of the stria terminalis (BNST) is a telencephalic structure well-connected to hypothalamic regions known to control goal-oriented behaviors such as feeding. In particular, we showed that the dorsomedial division of the anterior BNST innervate neurons of the paraventricular (PVH), dorsomedial (DMH), and arcuate (ARH) hypothalamic nuclei as well as the lateral hypothalamic area (LHA). While the anatomy of these projections has been characterized in mice, their ontogeny has not been studied. In this study, we used the DiI-based tract tracing approach to study the development of BNST projections innervating several hypothalamic areas including the PVH, DMH, ARH, and LHA. These results indicate that projections from the dorsomedial division of the anterior BNST to hypothalamic nuclei are immature at birth and substantially reach the PVH, DMH, and the LHA at P10. In the ARH, only sparse fibers are observed at P10, but their density increased markedly between P12 and P14. Collectively, these findings provide new insight into the ontogeny of hypothalamic circuits, and highlight the importance of considering the developmental context as a direct modulator in their proper formation

EphrinB1 modulates glutamatergic inputs into POMC-expressing progenitors and controls glucose homeostasis.

Proopiomelanocortin (POMC) neurons are major regulators of energy balance and glucose homeostasis. In addition to being regulated by hormones and nutrients, POMC neurons are controlled by glutamatergic input originating from multiple brain regions. However, the factors involved in the formation of glutamatergic inputs and how they contribute to bodily functions remain largely unknown. Here, we show that during the development of glutamatergic inputs, POMC neurons exhibit enriched expression of the Efnb1 (EphrinB1) and Efnb2 (EphrinB2) genes, which are known to control excitatory synapse formation. In vivo loss of Efnb1 in POMC-expressing progenitors decreases the amount of glutamatergic inputs, associated with a reduced number of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor subunits and excitability of these cells. We found that mice lacking Efnb1 in POMC-expressing progenitors display impaired glucose tolerance due to blunted vagus nerve activity and decreased insulin secretion. However, despite reduced excitatory inputs, mice lacking Efnb2 in POMC-expressing progenitors showed no deregulation of insulin secretion and only mild alterations in feeding behavior and gluconeogenesis. Collectively, our data demonstrate the role of ephrins in controlling excitatory input amount into POMC-expressing progenitors and show an isotype-specific role of ephrins on the regulation of glucose homeostasis and feeding