Experimental Evidence for an Early Commitment of Gonadotropin-Releasing Hormone Neurons, with Special Regard to Their Origin from the Ectoderm of Nasal Cavity Presumptive Territory

El-Amraoui, Aziz; Dubois, Paul

doi:10.1159/000126490

Cited by 75 publications

(49 citation statements)

References 14 publications

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Section: Origin Of Gnrh Neuroendocrine Cellsmentioning

confidence: 99%

“…Additional evidence in support of an olfactory placode origin has come from analysis of the Sey mutant, which lacks olfactory placodes and has no GnRH neurons (Dellovade et al, 1998;Skynner et al, 1999). Contrary to these studies, unilateral ablation of ectoderm immediately adjacent to, but not including, the olfactory placode at an early stage resulted in loss of forebrain-localized GnRH neurons (el Amraoui and Dubois, 1993).Advanced teleost fishes (atherinomorpha, percomorpha), including zebrafish, have two distinct types of forebrain GnRH neurons: terminal nerve ganglia GnRH neurons and hypothalamic GnRH neurons (Parhar, 2002;Whitlock et al, 2003). Of these, the terminal nerve ganglia GnRH neurons were considered to originate from olfactory placode (von Bartheld and Baker, 2004).…”

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confidence: 99%

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Competence, specification and commitment to an olfactory placode fate

Bhattacharyya

Bronner‐Fraser

2008

Development

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Cranial sensory placodes arise as transient thickenings of embryonic head ectoderm (van Wijhe, 1883;von Kupffer, 1891) and invaginate/ingress to form components of the nose, lens and inner ear (Bailey and Streit, 2006; Baker and Bronner-Fraser, 2001;Schlosser, 2006). Of the three sensory placodes, the lens and otic are relatively easy to distinguish and manipulate early in development. Therefore, tissue interactions and signals guiding their induction have been studied extensively (reviewed by Brown et al., 2003;Chow and Lang, 2001;Donner et al., 2006;Grainger, 1992;Noramly and Grainger, 2002;Riley and Phillips, 2003;Saha et al., 1989;Streit, 2001;Torres and Giraldez, 1998).By contrast, development of the olfactory sensory system has been primarily investigated at later stages. An attractive model for studying neurogenesis, its myriad of derivatives include the regenerative odorant sensing olfactory neurons in the olfactory epithelium (Calof et al., 1998;Graziadei and Graziadei, 1979;Graziadei and Metcalf, 1971;Graziadei and Monti Graziadei, 1983), the ingressing gonadotropin-releasing hormone neurons (reviewed by Parhar, 2002;Wray, 2002) [for a contrary view see Whitlock (Whitlock, 2005)], the pheromone-detecting vomeronasal organ (Dulac, 1997) and other neuromodulatory and neuroendocrine cells (Northcutt and Muske, 1994;Tarozzo et al., 1995;Yamamoto et al., 1996). It is the only placode to give rise to glial cells that ingress and migrate along the olfactory nerve towards the brain (Chuah and West, 2002;Ramon-Cueto and Avila, 1998). Cues that guide differentiation along these different pathways and the molecular mechanisms underlying the patterned wiring of olfactory sensory neurons have been examined extensively (reviewed by Baker and Margolis, 2002; Balmer and LaMantia, 2005).Contrasting with this wealth of data, inductive events that initiate olfactory development remain ambiguous, partially because the placode is morphologically invisible until relatively late (HH13+ in birds). Transplantation studies show that precursors straddle the lateral anterior neural folds and adjacent ectoderm in the neurula (Couly and Le Douarin, 1985), but their exact location at intervening stages was unclear. Recent cell marking studies in zebrafish and chick have examined the origin of the olfactory placode at higher resolution and at intervening stages (Bhattacharyya et al., 2004;Whitlock and Westerfield, 2000). Olfactory precursors are initially distributed in a broad region spanning the anterior neural folds and overlapping with lens precursors. Over time, they become progressively restricted to the most anterior ectoderm, finally resolving to a discrete olfactory pit. Knowledge of the location of precursors at different stages has facilitated manipulation of their development.To understand how and when the nasal epithelium is first induced, we examined competence, specification and commitment of ectoderm toward an olfactory fate. This information is a necessary prerequisite for interpreting results of functional perturba...

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Section: Origin Of Gnrh Neuroendocrine Cellsmentioning

confidence: 99%

mentioning

confidence: 99%

Competence, specification and commitment to an olfactory placode fate

Bhattacharyya

Bronner‐Fraser

2008

Development

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“…These investigations were done using tissue fixed after the formation of the olfactory placode, thus after the completion of cell movements necessary for the development of the olfactory sensory system, pituitary and hypothalamus. In contrast, experiments in chick and zebrafish [12,59], done well before the appearance of the olfactory placodes, suggest the olfactory sensory system does not generate GnRH cells. Both physical (axolotl [35]) and genetic (mouse [8]) ablation have been used to remove the olfactory placodes during development.…”

Section: Gnrh Cellsmentioning

confidence: 99%

Developing a sense of scents: Plasticity in olfactory placode formation

Whitlock

2008

Brain Research Bulletin

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The sense organs of the vertebrate head arise predominantly from sensory placodes. The sensory placodes have traditionally been grouped as structures that share common developmental and evolutionary characteristics. In attempts to build a coherent model for development of all placodes, the fascinating differences that make placodes unique are often overlooked. Here I review olfactory placode development with special attention to the origin and cell movements that generate the olfactory placode, the derivatives of this sensory placode, and the degree to which it shows plasticity during development. Next, through comparison with adenohypophyseal, and lens placodes I suggest we revise our thinking and terminology for these anterior placodes, specifically by: 1) referring to the peripheral olfactory sensory system as neural ectoderm because it expresses the same series of genes involved in neural differentiation and differentiates in tandem with the olfactory bulb, 2) grouping the anterior placodes with their corresponding central nervous system structures and emphasizing patterning mechanisms shared between placodes and these targets. Sensory systems did not arise independent of the central nervous system; they are part of a functional unit composed of peripheral sensory structures and their targets. By expanding our analyses of sensory system development to also include cell movements, gene expression and morphological changes observed in this functional unit, we will better understand the evolution of sensory structures.

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“…We have shown through lineage tracing that the GnRH cells of nervus terminalis arise from neural crest, but GnRH cells of the hypothalamus appear to have a separate embryonic origin [Whitlock et al, 2003]. From work in chick [el Amraoui and Dubois, 1993] it appears that GnRH cells might arise from the most anterior limits of the neural fold, which gives rise not only to respiratory epithelium but also to the precursors of the anterior pituitary placode.…”

Section: Adenohypophysis and Gnrh Cellsmentioning

confidence: 99%

A New Model for Olfactory Placode Development

Whitlock

2004

Brain Behav Evol

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The peripheral nervous system of vertebrate animals arises primarily from the interaction of cranial neural crest and sensory placodes. Placodes are described as thickenings of ectoderm that arise through cell division during neural tube formation. The olfactory sensory system is one component of the peripheral nervous system that arises from paired sensory placodes during development. The olfactory placodes give rise to the primary sensory neurons, support cells and basal cells of the olfactory epithelium. Recent evidence from work in zebrafish and chick suggests that the olfactory and auditory placodes arise from large fields of cells that converge to form the sensory placode. The olfactory placodes arise from within the neural plate, and cell division is apparent only after the sensory placodes are morphologically distinct. As the olfactory placode is forming, its precursors must segregate from their neighboring fields which will give rise to the adenohypophyseal placode, cranial neural crest, and telencephalon. Analysis has shown that the endocrine cells thought to arise from the olfactory placode originate in the neighboring adenohypophyseal and cranial neural crest domains. The borders separating the domains are plastic, where cells sort as they move, and cell fate is dependent on the identity of neighbors once the cells have converged to form the sensory placode. Thus there is degeneracy built into the system such that cells accommodate changes in the environment until cell migrations controlling the formation of the sensory placodes are complete.

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Experimental Evidence for an Early Commitment of Gonadotropin-Releasing Hormone Neurons, with Special Regard to Their Origin from the Ectoderm of Nasal Cavity Presumptive Territory

Cited by 75 publications

References 14 publications

Competence, specification and commitment to an olfactory placode fate

Competence, specification and commitment to an olfactory placode fate

Developing a sense of scents: Plasticity in olfactory placode formation

A New Model for Olfactory Placode Development

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