RESUMEN
The retinal homeobox (Rx/rax) gene is essential for the development of the eye. Rax is among the earliest genes expressed during eye development, beginning in the prospective eye fields in the anterior neural plate. Additionally Rax expression persists in retinal progenitor cells and in differentiated photoreceptors. We have isolated and characterized a 2.8 kb genomic DNA fragment that regulates expression of Rax in the developing and maturing retina. We have discovered and characterized cis-acting elements that function to specifically control spatial and temporal Rax expression during retinal development. We have found that the regulation of Rax2A promoter activity requires cooperative interactions between positive and negative regulatory elements. Further, a highly conserved genomic element containing SOX, OTX, and POU transcription factor binding sites is necessary but not sufficient for promoter activity in retinal progenitor or stem cells. Finally, a putative binding element for forkhead transcription factors is necessary for promoter activity and can cooperate with other cis-acting elements to drive Rax2A promoter activity.
Asunto(s)
Proteínas del Ojo/genética , Regulación del Desarrollo de la Expresión Génica , Genes Homeobox , Retina/embriología , Proteínas de Xenopus/genética , Xenopus laevis/embriología , Xenopus laevis/genética , Animales , Secuencia de Bases , Sitios de Unión , Secuencia Conservada , Femenino , Masculino , Datos de Secuencia Molecular , Regiones Promotoras Genéticas , Eliminación de Secuencia , Factores de Tiempo , Transcripción GenéticaRESUMEN
The retinal homeobox (Rx) gene product is essential for eye development. However little is known about its molecular function. It has been demonstrated that Rx binds to photoreceptor conserved element (PCE-1), a highly conserved element found in the promoter region of photoreceptor-specific genes such as rhodopsin and red cone opsin. We verify that Rx is co-expressed with rhodopsin and red cone opsin in maturing photoreceptors and demonstrate that Rx binds to the rhodopsin and red cone opsin promoters in vivo. We also find that Rx can cooperate with the Xenopus analogs of Crx and Nrl, otx5b and XLMaf (respectively), to activate a Xenopus opsin promoter-dependent reporter. Finally, we demonstrate that reduction of Rx expression in tadpoles results in decreases in expression of several PCE-1 containing photoreceptor genes, abnormal photoreceptor morphology, and impaired vision. Our data suggests that Rx, in combination with other transcription factors, is necessary for normal photoreceptor gene expression, maintenance, and function. This establishes a direct role for Rx in regulation of genes expressed in a differentiated cell type.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/metabolismo , Células Fotorreceptoras/metabolismo , Rodopsina/genética , Opsinas de Bastones/genética , Proteínas de Xenopus/genética , Animales , Embrión no Mamífero/metabolismo , Proteínas del Ojo/genética , Proteínas del Ojo/metabolismo , Proteínas de Homeodominio/genética , Retinaldehído , Rodopsina/metabolismo , Opsinas de Bastones/metabolismo , Proteínas de Xenopus/metabolismo , Xenopus laevisRESUMEN
Forkhead transcription factors comprise a large family of proteins with diverse functions during development. Recently, there has been accumulating evidence that several members of this family of proteins play an important role in the development of the vertebrate retina. Here, we summarize the cumulative data which demonstrates the integral role that forkhead factors play in cell cycle control of retinal precursors, as well as in cell fate determination, during retinal development. The expression patterns for 14 retinal expressed forkhead transcription factors are presented with an emphasis on comparing the expression profiles across species. The functional data regarding forkhead gene products expressed within the retina are discussed. As presented, these data suggest that forkhead gene products contribute to the complex regulation of proliferation and differentiation of retinal precursors during vertebrate eye development.
Asunto(s)
Ojo/metabolismo , Factores de Transcripción Forkhead/metabolismo , Animales , Ojo/embriología , Factores de Transcripción Forkhead/genética , Regulación del Desarrollo de la Expresión Génica , Humanos , Especificidad de Órganos , Células Madre/metabolismoRESUMEN
Forkhead proteins are involved in gene regulation in a large variety of developmental situations. Several forkhead gene products are expressed in the developing eye and brain. Here we characterize the expression of FoxN4 during Xenopus development. We report that FoxN4 is expressed in the eye from the earliest stages of specification through retinal maturation. FoxN4 is also expressed in the pallium, optic tectum, isthmus, reticular formation, and in cells lining the ventricle of the tadpole brain.
Asunto(s)
Encéfalo/embriología , Factores de Transcripción Forkhead/genética , Regulación del Desarrollo de la Expresión Génica , Retina/embriología , Células Madre/metabolismo , Proteínas de Xenopus/genética , Xenopus laevis/embriología , Secuencia de Aminoácidos , Animales , Encéfalo/citología , Embrión no Mamífero/metabolismo , Factores de Transcripción Forkhead/química , Datos de Secuencia Molecular , Retina/citología , Alineación de Secuencia , Proteínas de Xenopus/química , Xenopus laevis/genética , Xenopus laevis/metabolismoRESUMEN
PURPOSE: The retinal homeobox (Rx) gene plays an essential role in retinal development. An Rx-like (Rx-L) gene from Xenopus laevis has been identified. The purpose of this study was to analyze the function of Rx-L in the developing retina. METHODS: DNA-binding properties of Rx-L were analyzed by electrophoretic mobility shift assay (EMSA), with in vitro-translated proteins and radiolabeled oligonucleotide probe. The Rx-L expression pattern was analyzed by in situ hybridization using whole or sectioned embryos and digoxigenin-labeled antisense riboprobes. Rx-L loss of function was studied by using antisense morpholino oligonucleotides targeted to the Rx-L translation initiation site. Embryos injected with control or Rx-L morpholinos were analyzed at stage 41 or 45. RESULTS: Rx-L shares homology with Rx at the homeo-, OAR, and Rx domains, but lacks an octapeptide motif. Rx-L is expressed in the developing retina beginning in the early tailbud stage. In the maturing retina, Rx-L expression is restricted primarily to the developing photoreceptor layer and the ciliary marginal zone. Rx-L can bind a photoreceptor conserved element-1 (PCE-1) oligonucleotide, an element conserved among all known photoreceptor gene promoters. In a promoter activity assay, Rx-L functions as a stronger transcriptional activator than Rx. Antisense morpholino-mediated knockdown of Rx-L expression resulted in a decrease in rhodopsin and red cone opsin expression levels in Xenopus retinas. Injection of the Rx-L antisense morpholino oligonucleotide also resulted in a decrease in the length of both rod and cone outer segments. CONCLUSIONS: The results suggest that Rx-L functions to regulate rod and cone development by activating photoreceptor-specific gene expression.
Asunto(s)
Proteínas del Ojo/genética , Regulación del Desarrollo de la Expresión Génica/fisiología , Proteínas de Homeodominio/genética , Células Fotorreceptoras de Vertebrados/fisiología , Retina/embriología , Factores de Transcripción/genética , Secuencia de Aminoácidos , Animales , Ensayo de Cambio de Movilidad Electroforética , Inmunohistoquímica , Hibridación in Situ , Datos de Secuencia Molecular , Sondas de Oligonucleótidos/química , Células Fotorreceptoras de Vertebrados/citología , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de Aminoácido , Xenopus laevisRESUMEN
Members of the Ski/Sno family of gene products contain a characteristic peptide domain involved in protein-protein or protein-DNA interaction. Here, we characterize the developmental expression of xDawg, in Xenopus laevis, of a new gene, related to the Ski/Sno family of transcription regulators. The Ski/Sno domain of xDawg is predicted to present an electropositive surface, consistent with a role in DNA binding. This gene is expressed in the marginal zone of early gastrulae, and in the brain, sensory vesicles, and cranial neural crest of neurula and tailbud embryos.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica , Factores de Transcripción/genética , Proteínas de Xenopus/genética , Xenopus laevis/embriología , Secuencia de Aminoácidos , Animales , Embrión no Mamífero/química , Embrión no Mamífero/metabolismo , Expresión Génica , Hibridación in Situ , Datos de Secuencia Molecular , Ribonucleoproteínas/análisis , Ribonucleoproteínas/metabolismo , Xenopus laevis/genéticaRESUMEN
The members of the FoxE subfamily of Fox (forkhead) genes are expressed in the developing pituitary, thyroid and lens. Mammalian Foxe1 is expressed primarily in the developing pituitary and thyroid gland, Foxe3 is expressed in the developing lens, while Xenopus FoxE4 is expressed in the developing lens and thyroid. Here we report the identification of Xenopus FoxE1, a gene that is primarily expressed in the developing pituitary and thyroid.