OVEX1, a novel chicken endogenous retrovirus with sex-specific and left-right asymmetrical expression in gonads

<p>Abstract</p> <p>Background</p> <p>In chickens, as in most birds, female gonad morphogenesis is asymmetrical. Gonads appear first rather similarly, but only the left one undergoes full differentiation and gives rise to a functional ovary. The right gonad, in which the cortex does not develop, remains restricted to the medulla and finally regresses. Opportunity was taken of this left-right asymmetry to perform a suppression subtractive hybridization screening to select for transcripts preferentially expressed in the developing left ovary as compared to the right one, and thus identify genes that are potentially involved in the process of ovarian differentiation.</p> <p>Results</p> <p>One of these transcripts, named <it>Ovex1 </it>according to its expression profile, corresponds to an endogenous retrovirus that has not been previously characterized. It is transcribed as full-length and singly spliced mRNAs and contains three uninterrupted open reading frames coding potentially for proteins with homology to Gag and Pro-Pol retroviral polyproteins and a third protein showing only a weak similarity with Env glycoproteins. <it>Ovex1 </it>is severely degenerated; it is devoid of typical long terminal repeats and displays some evidence of recombination. An orthologous <it>Ovex1 </it>locus was identified in the genome of zebra finch, a member of a different bird order, and similar sequences were detected in turkey, guinea fowl, and duck DNA. The relationship between these sequences follows the bird phylogeny, suggesting vertical transmission of the endogenous retrovirus for more than 100 million years.</p> <p><it>Ovex1 </it>is transcribed in chicken gonads with a sex-dependent and left-right asymmetrical pattern. It is first expressed in the cortex of the left indifferent gonads of both sexes. Expression is transient in the left testis and absent in the right one. In developing ovaries, <it>Ovex1 </it>transcription increases sharply in the left cortex and is weakly detected in the medulla. After folliculogenesis, <it>Ovex1</it>-expressing cells constitute the follicular granulosa cell layer. <it>Ovex1 </it>expression highlights a striking desquamation process that leads to profound cortical remodeling associated with follicle morphogenesis.</p> <p>Conclusion</p> <p>Evidence for a selection pressure at the protein level suggests that this endogenous retrovirus, expressed in the ovarian supporting cell lineage, might play an active role in bird ovarian physiology.</p

The GnRH receptor and the response of gonadotrope cells to GnRH pulse frequency code. A story of an atypical adaptation of cell function relying on a lack of receptor homologous desensitization.

Brain control of the reproductive system is mediated through hypothalamic gonadotropin-releasing hormone (GnRH) which activates specific receptors (GnRHR) present at the surface of the pituitary gonadotropes to trigger secretion of the two gonadotropins LH and FSH. A unique feature of this system is the high dependence on the secretion mode of GnRH, which is basically pulsatile but undergoes considerable fluctuations in pulse frequency pattern in response to endogenous or external factors. How the physiological fluctuations of GnRH secretion that orchestrate normal reproduction are decoded by the gonadotrope cell machinery to ultimately control gonadotropin release and/or subunit gene transcription has been the subject of intensive studies during the past decades. Surprisingly, the mammalian GnRHR is unique among G protein-coupled receptor family as it lacks the carboxy-terminal tail usually involved in classical endocytotic process. Accordingly, it does not desensitize properly and internalizes very poorly. Both this atypical intrinsic property and post-receptor events may thus contribute to decode the GnRH signal. This includes the participation of a network of signaling pathways that differently respond to GnRH together with a growing amount of genes differentially sensitive to pulse frequency. Among these are two pairs of genes, the transcription factors EGR-1 and NAB, and the regulatory factors activin and follistatin, that function as intracellular autoregulatory feedback loops controlling respectively LHbeta and FSHbeta gene expression and hence, LH and FSH synthesis. Pituitary gonadotropes thus represent a unique model of cells functionally adapted to respond to a considerably fluctuating neuroendocrine stimulation, from short individual pulses to sustained GnRH as observed at the proestrus of ovarian cycle. Altogether, the data emphasize the adaptative reciprocal complementarity of hypothalamic GnRH neurones and pituitary gonadotropes to function as an original unit

MANIFESTO DOS PIONEIROS DA EDUCAÇÃO NOVA DE 1932: RELAÇÃO ENTRE CONHECIMENTO, INDIVÍDUO E SOCIEDADE

This article is designated to analyze the educational proposal contained in the Manifest of the Pioneers of the new education in 1932. This document was written during a moment in which the national education was suffering hard critics concerning to its organization, its structure and its pedagogical procedures. Along the last decades a great number of educators were instigated to take it once again as a theme of reflection in their researches, and it resulted in some consensual positions concerning certain aspects of the document but also in controversial ones concerning some other points. In the intuition to contribute in the debates about this thematic we decided to analyze the proposal of a reform in the educational system that is assigned in this document by their authors. In this way we give particular attention to the importance they attributed to the scientifically knowledge in order to solve the problems faced by the individual as an evidence of the new demands generated by the modernization of the society. We intend to analyze such a proposal considering its relations to the historical circumstances in which it was produced as well as to point out the importance of this study in our days.O artigo &eacute; destinado a uma an&aacute;lise da proposta educacional contida no Manifesto dos Pioneiros da Educa&ccedil;&atilde;o Nova de 1932. Esse documento foi escrito num momento em que a educa&ccedil;&atilde;o nacional sofria duras criticas no que se refere &agrave; organiza&ccedil;&atilde;o, &agrave; estrutura e &agrave; pedagogia. Ao longo das &uacute;ltimas d&eacute;cadas, muitos estudiosos da educa&ccedil;&atilde;o foram instigados a tom&aacute;-lo como tema de reflex&atilde;o em suas pesquisas, o que resultou em posi&ccedil;&otilde;es consensuais em rela&ccedil;&atilde;o a alguns aspectos, mas discord&acirc;ncias em rela&ccedil;&atilde;o a outros. &nbsp;No intuito de contribuir para esse debate, ser&aacute; analisada a proposta de reforma da educa&ccedil;&atilde;o pleiteada pelos signat&aacute;rios do documento, particularmente a import&acirc;ncia que atribu&iacute;am ao conhecimento cient&iacute;fico na solu&ccedil;&atilde;o dos problemas enfrentados pelos indiv&iacute;duos em decorr&ecirc;ncia das novas demandas geradas pela moderniza&ccedil;&atilde;o da sociedade. Procura-se analisar a quest&atilde;o proposta relacionando-a &agrave;s circunst&acirc;ncias hist&oacute;ricas em que o documento foi produzido bem como apontar a import&acirc;ncia de tal estudo para a atualidade

Etude de la lignée épithéliale de l'ovaire normal et pathologique.Développement du modèle expérimental de l'ovaire de ratte irradiée in utero

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Effects of caffeine and its reactive metabolites theophylline and theobromine on the differentiating testis

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