Expresión génica diferencial y mapa de destino del prosencéfalo, el área paraneural rostral y la adenohipofisis en estadios de placa neural del embrión pollo / Luisa María Sánchez Arrones; directores, Luis Puelles López, Lucía Rodríguez Gallardo.

Tesis-Universidad de Murcia.Consulte la tesis en: BCA. GENERAL. ARCHIVO UNIVERSITARIO. T.M. 3897

Shh goes multidirectional in axon guidance

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Cdon acts as a Hedgehog decoy receptor during proximal-distal patterning of the optic vesicle

Patterning of the vertebrate optic vesicle into proximal/optic stalk and distal/neural retina involves midline-derived Hedgehog (Hh) signalling, which promotes stalk specification. In the absence of Hh signalling, the stalks are not specified, causing cyclopia. Recent studies showed that the cell adhesion molecule Cdon forms a heteromeric complex with the Hh receptor Patched 1 (Ptc1). This receptor complex binds Hh and enhances signalling activation, indicating that Cdon positively regulates the pathway. Here we show that in the developing zebrafish and chick optic vesicle, in which cdon and ptc1 are expressed with a complementary pattern, Cdon acts as a negative Hh signalling regulator. Cdon predominantly localizes to the basolateral side of neuroepithelial cells, promotes the enlargement of the neuroepithelial basal end-foot and traps Hh protein, thereby limiting its dispersion. This Ptc-independent function protects the retinal primordium from Hh activity, defines the stalk/retina boundary and thus the correct proximo-distal patterning of the eye. © 2014 Macmillan Publishers Limited. All rights reserved.This work was supported by grants from the Spanish Ministerio de Economía y Competitividad (MINECO) (BFU2010-16031), Comunidad Autónoma de Madrid (CAM, CELL-DD S2010/BMD-2315), the Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER) del Instituto Carlos III (ISCIII) to P.B., MINECO (BFU2011-25987) to I.G. and an Institutional Grant from the Fundacion Ramon Areces.Peer Reviewe

Shh/Boc signaling is required for sustained generation of ipsilateral projecting ganglion cells in the mouse retina

Sonic Hedgehog (Shh) signaling is an important determinant of vertebrate retinal ganglion cell (RGC) development. In mice, there are two major RGC populations: (1) the Islet2-expressing contralateral projecting (c)RGCs, which both produce and respond to Shh; and (2) the Zic2-expressing ipsilateral projecting RGCs (iRGCs), which lack Shh expression. In contrast to cRGCs, iRGCs, which are generated in the ventrotemporal crescent (VTC) of the retina, specifically express Boc, a cell adhesion molecule that acts as a high-affinity receptor for Shh. In Boc-/-mutant mice, the ipsilateral projection is significantly decreased. Here, we demonstrate that this phenotype results, at least in part, from the misspecification of a proportion of iRGCs. In Boc-/-VTC, the number of Zic2-positive RGCs is reduced, whereas more Islet2/Shh-positive RGCs are observed, a phenotype also detected in Zic2 and Foxd1 null embryos. Consistent with this observation, organization of retinal projections at the dorsal lateral geniculate nucleus is altered in Boc-/-mice. Analyses of the molecular and cellular consequences of introducing Shh into the developing VTC and Zic2 and Boc into the central retina indicate that Boc expression alone is insufficient to fully activate the ipsilateral program and that Zic2 regulates Shh expression. Taking these data together, we propose that expression of Boc in cells from the VTC is required to sustain Zic2 expression, likely by regulating the levels of Shh signaling from the nearby cRGCs. Zic2, in turn, directly or indirectly, counteracts Shh and Islet2 expression in the VTC and activates the ipsilateral program. © 2013 the authors.Spanish Ministerio de Ciencia e Innovación (Grant BFU2010-16031); Comunidad Autonoma de Madrid (S2010/BMD-2315); a CIBER de Enfermedades Raras; MICINN (BFU2011-16563); CONSOLIDER-Ingenio Program Grant CDS2007-023Peer Reviewe

Sharpening of the anterior neural border in the chick by rostral endoderm signalling

The anterior border of the neural plate, presumed to contain the prospective peripheral portion (roof) of the prospective telencephalon, emerges within a vaguely defined proneural ectodermal region. Fate maps carried out at HH4 in the chick reveal that this region still produces indistinctly neural, placodal and non-neural derivatives; it does not express neural markers. We examined how the definitive anterior border domain of the rostral forebrain becomes established and comes to display a neural molecular profile, whereas local non-neural derivatives become separated. The process, interpreted as a border sharpening mechanism via intercalatory cell movements, was studied using fate mapping, time-lapse microscopy and in situ hybridization. Separation of neural and non-neural domains proceeds along stages HH4-HH4+, is well advanced at HH5, and is accompanied by a novel dorsoventral intercalation, oriented orthogonal to the border, that distributes transitional cells into molecularly distinct neural and non-neural fields. Meanwhile, neuroectodermal Sox2 expression spreads peripherally from the neighbourhood of the node, reaching the nascent anterior border domain at HH5. We also show that concurrent signals from the endodermal layer are necessary to position and sharpen the neural border, and suggest that FGF8 might be a component of this signalling. © 2012. Published by The Company of Biologists Ltd.Spanish Ministry of Science and Innovation (BFU2005-09378-C02-01, BFU2008-04156);Fundación SENECAPeer Reviewe

Cdon and Boc: Two transmembrane proteins implicated in cell-cell communication

Cdon and Boc, and their Drosophila homologues Ihog and Boi, are evolutionary conserved transmembrane glycoproteins belonging to a subgroup of the Immunoglobulin superfamily of cell adhesion molecules (CAMs). Initially isolated in vertebrates as CAMs that link cadherin function with MAPK signaling in myoblast differentiation, they have thereafter been shown to act as essential receptors for the Hedgehog (Hh) family of secreted proteins. They associate with both ligand and other Hh receptor components, including Ptch and Gas1, thus forming homo- and heteromeric complexes. In Drosophila, they are also involved in ligand processing and release from Hh producing cells. Cdon/Boc and Ihog/Boi can substitute one another and play redundant functions is some contexts. In addition, Boc, but not Cdon, mediates axon guidance information provided by Hh in specific neuronal populations, whereas mutations in the CDON cause holoprosencephaly, a human congenital anomaly defined by forebrain midline defects prominently associated with diminished Hh pathway activity. © 2012 Elsevier Ltd. All rights reserved.Spanish MICINN; Comunidad Autónoma de Madrid; Fundación ONCE; Fundaluce; CIBERER; Fundación Ramón ArecesPeer Reviewe

Adenohypophysis placodal precursors exhibit distinctive features within the rostral preplacodal ectoderm

Placodes are discrete thickenings of the vertebrate cranial ectoderm that generate morpho-functionally distinct structures, such as the adenohypophysis, olfactory epithelium and lens. All placodes arise from a horseshoe-shaped preplacodal ectoderm in which the precursors of individual placodes are intermingled. However, fatemap studies indicated that cells positioned at the preplacodal midline give rise to only the adenohypophyseal placode, suggesting a unique organization of these precursors within the preplacode. To test this possibility, we combined embryological and molecular approaches in chick embryos to show that, at gastrula stage, adenohypophyseal precursors are clustered in the median preplacodal ectoderm, largely segregated from those of the adjacent olfactory placode. Median precursors are elongated, densely packed and, at neurula stage, express a molecular signature that distinguishes them from the remaining preplacodal cells. Olfactory placode precursors and midline neural cells can replace ablated adenohypophyseal precursors up to head-fold stage, although with a more plastic organization. We thus propose that adenohypophyseal placode precursors are unique within the preplacodal ectoderm possibly because they originate the only single placode and the only one with an endocrine character.Secretarıía de Estado de Investigación, Desarrollo e Innovación(MINECO), Spain (BFU2013-43213-P, BFU2016-75412-R and BFU2014-55738-REDT); the Comunidad Autonoma de Madrid (S2010/BMD-2315) and the Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER) del Instituto de Salud Carlos III (ISCIII) to P.B. and by an institutional grant from the Fundación Ramón arecesPeer Reviewe

Origin and early development of the chicken adenohypophysis.

The adenohypophysis (ADH) is an important endocrine organ involved in the regulation of many physiological processes. The late morphogenesis of this organ at neural tube stages is well known: the epithelial ADH primordium is recognized as an invagination of the stomodeal roof (Rathke’s pouch), whose walls later thicken and differentiate as the primordium becomes pediculated, and then fully separated from the stomodeum. The primordium attaches to the pial surface of the basal hypothalamus, next to the neurohypophyseal field (NH; future posterior pituitary), from which it was previously separated by migrating prechordal plate cells. Once the NH evaginates, the ADH surrounds it and jointly forms with it the pituitary gland. In contrast, little is known about the precise origin of the ADH precursors at neural plate stages and how the primordium reaches the stomodeum. For that reason, we produced in the chicken a specific ADH fate map at early neural plate stages, which was amplified with gene markers. By means of experiments labelling the mapped presumptive ADH, we were able to follow the initial anlage into its transformation into Rathke’s pouch. The ADH origin was corroborated to be strictly extraneural, i.e., to lie at stage HH4/5 outside of the anterior neural plate within the pre-placodal field. The ADH primordium is fully segregated from the anterior neural border cells and the neighboring olfactory placodes both in terms of precursor cells and molecular profile from head fold stages onwards. The placode becomes visible as a molecularly characteristic ectodermal thickening from stage HH10 onwards. The onset of ADH genoarchitectonic regionalization into intermediate and anterior lobes occurs at closed neural tube stages

Origin and early development of the chicken adenohypophysis

La adenohipófisis (ADH) es un importante órgano endocrino implicado en la regulación de muchos procesos fisiológicos. La morfogénesis tardía de este órgano en las etapas del tubo neural es bien conocida: el primordio de ADH epitelial es reconocido como una invaginación del techo estomodeo (bolsa de Rathke), cuyas paredes después espesar y diferenciar, como sucede con el primordio, se convierten en pediculado, y luego se separan del estomodeo. El primordio se asocia a la superficie pial del hipotálamo basal, junto al campo neurohipofísico (NH; futura pituitaria posterior), desde la cual se separa para migrar a la placa precordal de las células (PP). Una vez que se envaina el NH, el ADH rodea e integra con la glándula pituitaria. En cambio, poco se sabe sobre el origen exacto de los precursores de la ADH en la placa neural y cómo el primordio alcanza el estomodeo. Por ese motivo, hemos producido en el pollo una suerte de ADH en etapas tempranas de la placa neural, que fue amplificado con marcadores de genes. Por medio de experimentos de etiquetado, asignado la presunción de ADH, pudimos seguir el enlace inicial en su transformación en bolsa de Rathke. El origen de la ADH fue corroborado por ser estrictamente extraneural, es decir, radica en la etapa HH4/5 anterior de la placa neural (ANP) en el campo Pre-placodal. El primordio de la ADH está completamente separado del límite anterior de las células neuronales y de la cercana placodes olfativa tanto en las células precursoras como en el perfil molecular de plegado del cabezal de las etapas posteriores. La placode se hace visible como una característica molecular a partir del engrosamiento ectodérmico desde la etapa HH10 en adelante. La aparición de la geno-arquitectura de la ADH se produce gradualmente en la zona intermedia y en los lóbulos anterior del tubo neural.The adenohypophysis (ADH) is an important endocrine organ involved in the regulation of many physiological processes. The late morphogenesis of this organ at neural tube stages is well known: the epithelial ADH primordium is recognized as an invagination of the stomodeal roof (Rathke’s pouch), whose walls later thicken and differentiate as the primordium becomes pediculated, and then fully separated from the stomodeum. The primordium attaches to the pial surface of the basal hypothalamus, next to the neurohypophyseal field (NH; future posterior pituitary), from which it was previously separated by migrating prechordal plate (pp) cells. Once the NH evaginates, the ADH surrounds it and jointly forms with it the pituitary gland. In contrast, little is known about the precise origin of the ADH precursors at neural plate stages and how the primordium reaches the stomodeum. For that reason, we produced in the chicken a specific ADH fate map at early neural plate stages, which was amplified with gene markers. By means of experiments labeling the mapped presumptive ADH, we were able to follow the initial anlage into its transformation into Rathke’s pouch. The ADH origin was corroborated to be strictly extraneural, i.e., to lie at stage HH4/5 outside of the anterior neural plate (anp) within the pre-placodal field. The ADH primordium is fully segregated from the anterior neural border cells and the neighboring olfactory placodes both in terms of precursor cells and molecular profile from head fold stages onwards. The placode becomes visible as a molecularly characteristic ectodermal thickening from stage HH10 onwards. The onset of ADH genoarchitectonic regionalization into intermediate and anterior lobes occurs at closed neural tube stages.Trabajo patrocinado por: Ministerio de Economía y competitividad. Beca BFU2008-04156 Fundación Séneca. Ayuda 04548/06 (Nº10891), para Luis Puelles LópezpeerReviewe