SUMMARYThe hypothalamic arcuate nucleus (Arc), containing pro-opoiomelanocortin (POMC), neuropeptide Y (NPY) and growth hormone releasing hormone (GHRH) neurons, regulates feeding, energy balance and body size. Dysregulation of this homeostatic mediator underlies diseases ranging from growth failure to obesity. Despite considerable investigation regarding the function of Arc neurons, mechanisms governing their development remain unclear. Notch signaling factors such as Hes1 and Mash1 are present in hypothalamic progenitors that give rise to Arc neurons. However, how Notch signaling controls these progenitor populations is unknown. To elucidate the role of Notch signaling in Arc development, we analyzed conditional loss-of-function mice lacking a necessary Notch co-factor, Rbpjκ, in Nkx2.1-cre-expressing cells (Rbpjκ cKO), as well as mice with expression of the constitutively active Notch1 intracellular domain (NICD) in Nkx2.1-cre-expressing cells (NICD Tg). We found that loss of Rbpjκ results in absence of Hes1 but not of Hes5 within the primordial Arc at E13.5. Additionally, Mash1 expression is increased, coincident with increased proliferation and accumulation of Arc neurons at E13.5. At E18.5, Rbpjκ cKO mice have few progenitors and show increased numbers of differentiated Pomc, NPY and Ghrh neurons. By contrast, NICD Tg mice have increased hypothalamic progenitors, show an absence of differentiated Arc neurons and aberrant glial differentiation at E18.5. Subsequently, both Rbpjκ cKO and NICD Tg mice have changes in growth and body size during postnatal development. Taken together, our results demonstrate that Notch/Rbpjκ signaling regulates the generation and differentiation of Arc neurons, which contribute to homeostatic regulation of body size. KEY WORDS: Arcuate, Notch, POMC, NPY, Hypothalamus, MouseNotch/Rbpjκ signaling regulates progenitor maintenance and differentiation of hypothalamic arcuate neurons Paven K. Aujla, George T. Naratadam, Liwen Xu and Lori T. Raetzman* DEVELOPMENT 3512During embryonic development, cells migrate from the hypothalamic ventricular zone (HVZ) surrounding the ventral region of the third ventricle in order to form the Arc by E16.5 (Bayer and Altman, 1987;Ishii and Bouret, 2012;Shimada and Nakamura, 1973). One of the major functions of the Arc is to respond to food intake and energy expenditure. Energy-related hormone signals such as leptin are sensed by anorexic proopoiomelanocortin (POMC)/cocaine and amphetamine-regulated transcript (CART) neurons and orexic neuropeptide Y (NPY)/Agouti-related peptide (AgRP) neurons. POMC and NPY neurons regulate feeding behavior and are crucial to maintaining proper energy balance and homeostasis (Broberger, 2005;Morton et al., 2006;Srinivas et al., 2001). An additional subtype of neurons, growth hormone-releasing hormone (GHRH) neurons, are present in the Arc and regulate body size and growth by controlling release of growth hormone from the pituitary gland (Bouyer et al., 2007; Grossman et al., 1986).Despite the functional importance of ...

Background As the pituitary gland develops, signals from the hypothalamus are necessary for pituitary induction and expansion. Little is known about the control of cues that regulate early signaling between the two structures. Ligands and receptors of the Notch signaling pathway are found in both the hypothalamus and Rathke’s pouch. The downstream Notch effector gene Hes1 is required for proper pituitary formation, however these effects could be due to the action of Hes1 in the hypothalamus, Rathke’s pouch or both. To determine the contribution of hypothalamic Notch signaling to pituitary organogenesis, we used mice with loss and gain of Notch function within the developing hypothalamus. Results We demonstrate that loss of Notch signaling by conditional deletion of Rbpj in the hypothalamus does not affect expression of Hes1 within the posterior hypothalamus or expression of Hes5. In contrast, expression of activated Notch within the hypothalamus results in ectopic Hes5 expression and increased Hes1 expression, which is sufficient to disrupt pituitary development and postnatal expansion. Conclusions Taken together, our results indicate that Rbpjdependent Notch signaling within the developing hypothalamus is not necessary for pituitary development, but persistent Notch signaling and ectopic Hes5 expression in hypothalamic progenitors affects pituitary induction and expansion.

Background: As the pituitary gland develops, signals from the hypothalamus are necessary for pituitary induction and expansion. Little is known about the control of cues that regulate early signaling between the two structures. Ligands and receptors of the Notch signaling pathway are found in both the hypothalamus and Rathke's pouch. The downstream Notch effector gene Hes1 is required for proper pituitary formation; however, these effects could be due to the action of Hes1 in the hypothalamus, Rathke's pouch, or both. To determine the contribution of hypothalamic Notch signaling to pituitary organogenesis, we used mice with loss and gain of Notch function within the developing hypothalamus. Results: We demonstrate that loss of Notch signaling by conditional deletion of Rbpj in the hypothalamus does not affect expression of Hes1 within the posterior hypothalamus or expression of Hes5. In contrast, expression of activated Notch within the hypothalamus results in ectopic Hes5 expression and increased Hes1 expression, which is sufficient to disrupt pituitary development and postnatal expansion. Conclusions: Taken together, our results indicate that Rbpj‐dependent Notch signaling within the developing hypothalamus is not necessary for pituitary development, but persistent Notch signaling and ectopic Hes5 expression in hypothalamic progenitors affects pituitary induction and expansion. Developmental Dynamics 244:921–934, 2015. © 2015 Wiley Periodicals, Inc.

Key clinical messageHereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disease. Conjunctival telangiectasias and retinal vascular malformations are known ocular manifestations. We report here the first case of open angle glaucoma in a patient with HHT caused by a nonsense mutation, C471X in the ACVRL1 gene.

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