RESUMEN

Pax genes are a group of critical developmental transcriptional regulators in both invertebrates and vertebrates, characterized by the presence of a paired DNA-binding domain. Pax proteins also often contain an octapeptide motif and a C-terminal homeodomain. The genome of Nasonia vitripennis (Hymenoptera) has recently become available, and analysis of this genome alongside Apis mellifera allowed us to contribute to the phylogeny of this gene family in insects. Nasonia, a parasitic wasp, has independently evolved a similar mode of development to that of the well-studied Drosophila, making it an excellent model system for comparative studies of developmental gene networks. We report the characterization of the seven Nasonia Pax genes. We describe their genomic organization, and the embryonic expression of three of them, and uncover wider conservation of the octapeptide motif than previously described.

Asunto(s)

Redes Reguladoras de Genes/genética , Proteínas de Insectos/genética , Factores de Transcripción Paired Box/genética , Filogenia , Avispas/genética , Secuencia de Aminoácidos , Animales , Abejas/genética , Embrión no Mamífero/metabolismo , Componentes del Gen , Genómica , Hibridación in Situ , Proteínas de Insectos/metabolismo , Datos de Secuencia Molecular , Factores de Transcripción Paired Box/metabolismo , Péptidos/genética , Alineación de Secuencia , Especificidad de la Especie

RESUMEN

Multiple cell types often differentiate from a pluripotent cell. These cells may then further diversify as distinct subtypes. The visual system provides an ideal model for studying subtype specification as various photoreceptors acquire different functions based on the type of opsin they express. Opsin expression is mostly controlled through transcriptional mechanisms that are evolutionary conserved from Drosophila to humans. In addition, it appears that, from a "default" developmental state, distinct "acquired" photoreceptor states develop upon receiving intrinsic or extrinsic signals. This review discusses factors involved in opsin gene regulation and how their integration may explain how subtype specificity is achieved.

Asunto(s)

Células Fotorreceptoras/embriología , Opsinas de Bastones/genética , Animales , Drosophila/embriología , Drosophila/genética , Regulación de la Expresión Génica , Humanos , Región de Control de Posición/fisiología , Morfogénesis , Células Fotorreceptoras/crecimiento & desarrollo , Células Fotorreceptoras de Vertebrados/fisiología

RESUMEN

The formation of photoreceptor cells (PRCs) in Drosophila serves as a paradigm for understanding neuronal determination and differentiation. During larval stages, a precise series of sequential inductive processes leads to the recruitment of eight distinct PRCs (R1-R8). But, final photoreceptor differentiation, including rhabdomere morphogenesis and opsin expression, is completed four days later, during pupal development. It is thought that photoreceptor cell fate is irreversibly established during larval development, when each photoreceptor expresses a particular set of transcriptional regulators and sends its projection to different layers of the optic lobes. Here, we show that the spalt (sal) gene complex encodes two transcription factors that are required late in pupation for photoreceptor differentiation. In the absence of the sal complex, rhabdomere morphology and expression of opsin genes in the inner PRCs R7 and R8 are changed to become identical to those of outer R1-R6 PRCs. However, these cells maintain their normal projections to the medulla part of the optic lobe, and not to the lamina where outer PRCs project. These data indicate that photoreceptor differentiation occurs as a two-step process. First, during larval development, the photoreceptor neurons become committed and send their axonal projections to their targets in the brain. Second, terminal differentiation is executed during pupal development and the photoreceptors adopt their final cellular properties.

Asunto(s)

Proteínas de Homeodominio/fisiología , Células Fotorreceptoras de Invertebrados/fisiología , Factores de Transcripción/fisiología , Animales , Diferenciación Celular , Drosophila , Proteínas de Drosophila , Femenino , Expresión Génica , Proteínas de Homeodominio/genética , Masculino , Morfogénesis , Células Fotorreceptoras de Invertebrados/citología , Células Fotorreceptoras de Invertebrados/ultraestructura , Rodopsina/biosíntesis , Factores de Transcripción/genética , Dedos de Zinc

Asunto(s)

Ojo/embriología , Animales , Tipificación del Cuerpo , Diferenciación Celular/genética , Drosophila , Inducción Embrionaria , Evolución Molecular , Ojo/crecimiento & desarrollo , Ojo/metabolismo , Proteínas del Ojo , Regulación del Desarrollo de la Expresión Génica , Genes Reguladores , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Morfogénesis , Factor de Transcripción PAX6 , Factores de Transcripción Paired Box , Células Fotorreceptoras/metabolismo , Proteínas Represoras , Vertebrados

RESUMEN

The Drosophila rhodopsin genes (rh's) represent a unique family of highly regulated cell-specific genes, where each member has its own expression pattern in the visual system. Extensive analysis of the rh's has revealed several functional elements that are involved in cell-specificity. We have investigated the functional role of the RCSI/P3 site that is found in the proximal promoter of all Drosophila rh genes. This sequence is remarkably conserved in evolution and is located 15-30 bp upstream of the TATA box. We have previously shown that, in the context of the rh1 promoter, this element is recognized in vivo by a Pax6 protein, the master regulator of eye development. Thus, rh regulation might represent the ancestral function of Pax6. Here, we investigated the role of the RCSI/P3 sequence in the other rh genes and show that they also mediate Pax6 function. We also tested the potential impact of the various RCSI/P3 sequences on the precise cell-specific expression of rh genes. Our results demonstrate that, even though all RCSI/P3 sequences bind Pax6, they are clearly distinct in various rh promoters and these differences are conserved throughout evolution: RCSI/P3 appears to participate in the fine-tuning of cell-specificity. We also show that Pax6 or a related Pax protein may be involved in the regulation of olfactory genes. Therefore, in addition to performing a global photoreceptor-specific function, RCSI also appears to mediate the combined action of Pax6 and other factors and to contribute to rh regulation in subsets of photoreceptors.

Asunto(s)

Drosophila/embriología , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/genética , Rodopsina/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Secuencia Conservada , Drosophila/genética , Proteínas del Ojo , Modelos Genéticos , Datos de Secuencia Molecular , Mutagénesis , Factor de Transcripción PAX6 , Factores de Transcripción Paired Box , Filogenia , Reacción en Cadena de la Polimerasa , Regiones Promotoras Genéticas , Unión Proteica , Proteínas Represoras , Rodopsina/biosíntesis , Homología de Secuencia de Aminoácido , Transgenes

RESUMEN

The Drosophila eye is widely used as a model system to study neuronal differentiation, survival and axon projection. Photoreceptor differentiation starts with the specification of a founder cell R8, which sequentially recruits other photoreceptor neurons to the ommatidium. The eight photoreceptors that compose each ommatidium exist in two chiral forms organized along two axes of symmetry and this pattern represents a paradigm to study tissue polarity. We have developed a method of fluoroscopy to visualize the different types of photoreceptors and the organization of the ommatidia in living animals. This allowed us to perform an F(1) genetic screen to isolate mutants affecting photoreceptor differentiation, survival or planar polarity. We illustrate the power of this detection system using known genetic backgrounds and new mutations that affect ommatidial differentiation, morphology or chirality.

Asunto(s)

Drosophila/embriología , Drosophila/genética , Ojo/embriología , Neuronas/citología , Animales , Animales Modificados Genéticamente , Tipificación del Cuerpo , Diferenciación Celular , Córnea/citología , Córnea/embriología , Cruzamientos Genéticos , Embrión no Mamífero/fisiología , Metanosulfonato de Etilo , Ojo/citología , Femenino , Proteínas Fluorescentes Verdes , Proteínas Luminiscentes/genética , Masculino , Modelos Neurológicos , Mutagénesis , Neuronas/fisiología , Células Fotorreceptoras de Invertebrados/citología , Células Fotorreceptoras de Invertebrados/embriología

RESUMEN

In Drosophila, the gradient of the Bicoid (Bcd) morphogen organizes the anteroposterior axis while the ends of the embryo are patterned by the maternal terminal system. At the posterior pole, expression of terminal gap genes is mediated by the local activation of the Torso receptor tyrosine kinase (Tor). At the anterior, terminal gap genes are also activated by the Tor pathway but Bcd contributes to their activation. Here we present evidence that Tor and Bcd act independently on common target genes in an additive manner. Furthermore, we show that the terminal maternal system is not required for proper head development, since high levels of Bcd activity can functionally rescue the lack of terminal system activity at the anterior pole. This observation is consistent with a recent evolution of an anterior morphogenetic center consisting of Bcd and anterior Tor function.

Asunto(s)

Tipificación del Cuerpo , Proteínas de Drosophila , Drosophila melanogaster/embriología , Cabeza/embriología , Proteínas de Homeodominio/metabolismo , Proteínas de Insectos/metabolismo , Proteínas Tirosina Quinasas Receptoras/metabolismo , Transactivadores/metabolismo , Animales , Animales Modificados Genéticamente , Tipificación del Cuerpo/genética , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Drosophila melanogaster/enzimología , Drosophila melanogaster/genética , Evolución Molecular , Femenino , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/genética , Inmunohistoquímica , Hibridación in Situ , Proteínas de Insectos/genética , Mutación , Fenotipo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Proteínas Tirosina Quinasas Receptoras/genética , Transactivadores/genética , Transgenes/genética

RESUMEN

The Drosophila ommatidia contain two classes of photoreceptor cells (PR's), the outer and the inner PR's. We performed an enhancer trap screen in order to target genes specifically expressed in PR's. Using the UAS/GAL4 method with enhanced green fluorescent protein (eGFP) as a vital marker, we screened 180000 flies. Out of 2730 lines exhibiting new eGFP patterns, we focused on 16 lines expressing eGFP in particular subsets of PR's. In particular, we describe three lines inserted near the spalt major, m-spondin and furrowed genes, whose respective expression patterns resemble those genes. These genes had not been reported to be expressed in the adult eye. These examples clearly show the ability of our screen to target genes expressed in the adult Drosophila eye.

Asunto(s)

Proteínas de Drosophila , Drosophila melanogaster/genética , Genes de Insecto , Proteínas Luminiscentes , Células Fotorreceptoras de Invertebrados , Animales , Proteínas de la Matriz Extracelular/genética , Ojo , Femenino , Expresión Génica , Proteínas Fluorescentes Verdes , Proteínas de Homeodominio/genética , Proteínas de Insectos/genética , Operón Lac , Proteínas Luminiscentes/genética , Masculino , Selectinas/genética , Factores de Transcripción/genética

RESUMEN

The maternal determinant Bicoid (Bcd) represents the paradigm of a morphogen that provides positional information for pattern formation. However, as bicoid seems to be a recently acquired gene in flies, the question was raised as to how embryonic patterning is achieved in organisms with more ancestral modes of development. Because the phylogenetically conserved Hunchback (Hb) protein had previously been shown to act as a morphogen in abdominal patterning, we asked which functions of Bcd could be performed by Hb. By reestablishing a proposed ancient regulatory circuitry in which maternal Hb controls zygotic hunchback expression, we show that Hb is able to form thoracic segments in the absence of Bcd.

Asunto(s)

Tipificación del Cuerpo , Proteínas de Unión al ADN/fisiología , Proteínas de Drosophila , Drosophila/embriología , Proteínas de Homeodominio/fisiología , Proteínas de Insectos/fisiología , Transactivadores/fisiología , Factores de Transcripción/fisiología , Animales , Proteínas de Unión al ADN/genética , Drosophila/genética , Desarrollo Embrionario , Femenino , Regulación del Desarrollo de la Expresión Génica , Genes de Insecto , Proteínas de Homeodominio/genética , Proteínas de Insectos/genética , Masculino , Mutación , Fenotipo , Regiones Promotoras Genéticas , Tórax/embriología , Transactivadores/genética , Factores de Transcripción/genética , Transgenes , Dedos de Zinc , Cigoto/fisiología

RESUMEN

The Torso signal transduction pathway exhibits two opposite effects on the activity of the Bicoid (Bcd) morphogen: (i) Bcd function is repressed by Torso (Tor) at the anterior pole of the embryo leading to a retraction of the expression of many Bcd targets from the most anterior region of the embryo, where the Tor tyrosine kinase receptor is activated, and (ii) Bcd function is strengthened by Tor in a broader anterior region, as indicated by a shift of the posterior border of Bcd targets towards the anterior pole in embryos deprived from Tor activity. Anterior repression of Bcd targets was not observed in embryos lacking maternal contribution of D-sor, which acts downstream of Tor and encodes a MAP-kinase kinase. This indicates that the Ras signalling cascade is directly involved in this process, although the known transcriptional effectors of the Tor pathway, tll and hkb, are not (Ronchi, E., Treisman, J., Dostatni, N., Struhl, G. and Desplan, C. (1993) Cell 74, 347-355). Bcd is a good in vitro substrate for phosphorylation by MAP-kinase and phosphorylation of the protein occur in vivo on MAP-kinase sites. In the presence of a Bcd mutant that could no longer be phosphorylated by MAP-kinase, expression of Bcd targets remained repressed by Tor at the pole while strengthening of Bcd activity was reduced. These experiments indicate that phosphorylation of Bcd by MAP-kinase is likely to be required for the Tor pathway to induce its full positive effect on Bcd. This suggests that Tor signalling acts at a distance from the anterior pole by direct modification of the diffusing Bcd morphogen.

Asunto(s)

Proteínas de Drosophila , Drosophila/embriología , Proteínas de Homeodominio/metabolismo , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Proteínas Tirosina Quinasas Receptoras/metabolismo , Transactivadores/metabolismo , Secuencia de Aminoácidos , Animales , Animales Modificados Genéticamente , Células Cultivadas , Drosophila/metabolismo , Hibridación in Situ , Quinasas de Proteína Quinasa Activadas por Mitógenos/metabolismo , Datos de Secuencia Molecular , Mutación , Oligonucleótidos Antisentido , Fenotipo , Fosforilación , ARN Mensajero/metabolismo , Proteínas Represoras/metabolismo , Transducción de Señal

RESUMEN

Munster (Mu) is a homeobox-containing gene of the Paired-class which is specifically expressed in the developing Bolwig organs, the Drosophila larval eyes. This expression is first detected during early germ band retraction stage (stage 12 from 7 h 20 at 25 degrees C) and persists until the end of embryogenesis. Mu homeodomain is most similar to that of Aristaless and D-Goosecoid. Strikingly, the Munster gene maps within 6 kb of D-goosecoid, in the same genomic region as aristaless, suggesting that these genes are part of a homeobox gene cluster.

Asunto(s)

Proteínas de Drosophila , Drosophila/crecimiento & desarrollo , Drosophila/genética , Ojo/crecimiento & desarrollo , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Proteínas de Insectos/genética , Proteínas Represoras , Factores de Transcripción , Secuencia de Aminoácidos , Animales , Mapeo Cromosómico , Clonación Molecular , Drosophila/embriología , Embrión no Mamífero , Ojo/embriología , Ojo/metabolismo , Regulación del Desarrollo de la Expresión Génica , Proteína Goosecoide , Proteínas de Insectos/metabolismo , Larva , Datos de Secuencia Molecular , Análisis de Secuencia , Homología de Secuencia de Aminoácido

RESUMEN

Color vision is achieved by comparing the inputs from retinal photoreceptor neurons that differ in their wavelength sensitivity. Recent studies have elucidated the distribution and phylogeny of opsins, the family of light-sensitive molecules involved in this process. Interesting new findings suggest that animals have evolved a strategy to achieve specific sensitivity through the mutually exclusive expression of different opsin genes in photoreceptors.

Asunto(s)

Evolución Biológica , Percepción de Color/fisiología , Animales , Humanos , Insectos/fisiología , Filogenia , Retina/fisiología , Opsinas de Bastones/fisiología , Vertebrados/fisiología , Visión Ocular/fisiología

Asunto(s)

Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/metabolismo , Proteínas de Homeodominio/química , Proteínas de Homeodominio/metabolismo , Proteínas Proto-Oncogénicas/química , Proteínas Proto-Oncogénicas/metabolismo , Dimerización , Proteínas de Homeodominio/clasificación , Modelos Moleculares , Factor de Transcripción 1 de la Leucemia de Células Pre-B , Conformación Proteica , Especificidad por Sustrato

RESUMEN

Four maternal systems are known to pattern the early Drosophila embryo. The key component of the anterior system is the homeodomain protein Bicoid (Bcd). Bcd needs the contribution of another anterior morphogen, Hunchback (Hb), to function properly: Bcd and Hb synergize to organize anterior development. A molecular mechanism for this synergy has been proposed to involve specific interactions of Bcd and Hb with TATA-binding protein-associated factors (TAFIIs) that are components of the general transcription machinery. Bcd contains three putative activation domains: a glutamine-rich region, which interacts in vitro with TAFII110; an alanine-rich domain, which targets TAFII60; and a C-terminal acidic region, which has an unknown role. We have generated flies carrying bcd transgenes lacking one or several of these domains to test their function in vivo. Surprisingly, a bcd transgene that lacks all three putative activation domains is able to rescue the bcdE1 null phenotype to viability. Moreover, the development of these embryos is not affected by the presence of dominant negative mutations in TAFII110 or TAFII60. This means that the interactions observed in vitro between Bcd and TAFII60 or TAFII110 aid transcriptional activation but are dispensable for normal development.

Asunto(s)

Proteínas de Unión al ADN/metabolismo , Proteínas de Drosophila , Drosophila/embriología , Proteínas de Homeodominio/metabolismo , Factores Asociados con la Proteína de Unión a TATA , Transactivadores/metabolismo , Factor de Transcripción TFIID , Factores de Transcripción/metabolismo , Animales , Animales Modificados Genéticamente , Tipificación del Cuerpo , Proteínas de Unión al ADN/química , Embrión no Mamífero/fisiología , Femenino , Eliminación de Gen , Impresión Genómica , Proteínas de Homeodominio/química , Proteínas de Homeodominio/genética , Homocigoto , Técnicas In Vitro , Proteínas de Insectos/metabolismo , Recombinación Genética , Transactivadores/química , Transactivadores/genética , Transcripción Genética

RESUMEN

Pax proteins, characterized by the presence of a paired domain, play key regulatory roles during development. The paired domain is a bipartite DNA-binding domain that contains two helix-turn-helix domains joined by a linker region. Each of the subdomains, the PAI and RED domains, has been shown to be a distinct DNA-binding domain. The PAI domain is the most critical, but in specific circumstances, the RED domain is involved in DNA recognition. We describe a Pax protein, originally called Lune, that is the product of the Drosophila eye gone gene (eyg). It is unique among Pax proteins, because it contains only the RED domain. eyg seems to play a role both in the organogenesis of the salivary gland during embryogenesis and in the development of the eye. A high-affinity binding site for the Eyg RED domain was identified by using systematic evolution of ligands by exponential enrichment techniques. This binding site is related to a binding site previously identified for the RED domain of the Pax-6 5a isoform. Eyg also contains another DNA-binding domain, a Prd-class homeodomain (HD), whose palindromic binding site is similar to other Prd-class HDs. The ability of Pax proteins to use the PAI, RED, and HD, or combinations thereof, may be one mechanism that allows them to be used at different stages of development to regulate various developmental processes through the activation of specific target genes.

Asunto(s)

Proteínas de Unión al ADN/genética , ADN/genética , Drosophila/genética , Genes de Insecto , Proteínas Nucleares/genética , Factores de Transcripción , Secuencia de Aminoácidos , Animales , Sitios de Unión/genética , ADN/metabolismo , Proteínas de Unión al ADN/metabolismo , Drosophila/embriología , Embrión no Mamífero/embriología , Proteínas del Ojo/genética , Proteínas del Ojo/metabolismo , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Datos de Secuencia Molecular , Proteínas Nucleares/metabolismo , Factor de Transcripción PAX5 , Factor de Transcripción PAX6 , Factores de Transcripción Paired Box , Unión Proteica , Proteínas Represoras , Alineación de Secuencia

RESUMEN

Goosecoid (Gsc) is a homeodomain protein expressed in the organizer region of vertebrate embryos. Its Drosophila homologue, D-Gsc, has been implicated in the formation of the Stomatogastric Nervous System. Although there are no apparent similarities between the phenotypes of mutations in the gsc gene in flies and mice, all known Gsc proteins can rescue dorsoanterior structures in ventralized Xenopus embryos. We describe how D-Gsc behaves as a transcriptional repressor in Drosophila cells, acting through specific palindromic HD binding sites (P3K). D-Gsc is a 'passive repressor' of activator homeoproteins binding to the same sites and an 'active repressor' of activators binding to distinct sites. In addition, D-Gsc is able to strongly repress transcription activated by Paired-class homeoproteins through P3K, via specific protein-protein interactions in what we define as 'interactive repression'. This form of repression requires the short conserved GEH/eh-1 domain, also present in the Engrailed repressor. Although the GEH/eh-1 domain is necessary for rescue of UV-ventralized Xenopus embryos, it is dispensable for ectopic induction of Xlim-1 expression, demonstrating that this domain is not required for all Gsc functions in vivo. Interactive repression may represent specific interactions among Prd-class homeoproteins, several of which act early during development of invertebrate and vertebrate embryos.

Asunto(s)

Proteínas de Unión al ADN/genética , Proteínas de Drosophila , Drosophila/genética , Proteínas de Insectos/genética , Proteínas Represoras , Factores de Transcripción , Proteínas de Xenopus , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Sitios de Unión/genética , Secuencia Conservada , ADN/genética , Cartilla de ADN/genética , Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/metabolismo , Dimerización , Drosophila/embriología , Femenino , Regulación del Desarrollo de la Expresión Génica , Proteína Goosecoide , Proteínas de Homeodominio/química , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Proteínas de Insectos/química , Proteínas de Insectos/metabolismo , Ratones , Mutagénesis Sitio-Dirigida , Fenotipo , Xenopus laevis

RESUMEN

Specificity in transcriptional regulation lies in a large part in the specificity of DNA binding by transcription factors. One group of transcription factors which are of great interest for studying transcriptional specificity is the Pax/Homeodomain (Pax/HD) proteins which contain two conserved DNA binding domains, a paired domain (PD) and a Paired-class homeodomain (HD). The Pax/HD proteins can bind to at least three types of specific DNA sequences: the PD binding sites, the dimeric HD binding sites and a composite HD and PD binding site. We propose that Pax/HD proteins regulate different subsets of their target genes through modular binding to one of these three specific sequences. We show that, in a tissue culture system, a member of the Pax/HD family, Paired, is able to activate transcription after binding through either its PD or its HD. The transactivation mediated by one domain does not require DNA binding of the other domain. Furthermore, binding sites specific for the PD of Paired are sufficient to mediate embryonic expression of a reporter gene in a paired-like pattern. The expression of the reporter gene is dependent on wild type paired function and, in a prd mutant background, it can be rescued by an exogenous paired gene encoding a protein whose HD is not able to bind to DNA. Finally, we show that the Paired protein uses differently its C-terminal activation domain when transactivation is mediated through its PD or its HD. These results and recent evidence from other Pax/HD proteins strongly suggest that this class of proteins is able to achieve specific and modular transcriptional regulation through its multiple DNA binding domains.

Asunto(s)

Proteínas de Unión al ADN/genética , Regulación de la Expresión Génica/fisiología , Proteínas de Homeodominio/genética , Factores de Transcripción/genética , Transcripción Genética/fisiología , Animales , Secuencia de Bases , Células Cultivadas , Clonación Molecular , Proteínas de Unión al ADN/biosíntesis , Drosophila , Eliminación de Gen , Genes Reporteros , Proteínas de Homeodominio/biosíntesis , Datos de Secuencia Molecular , Mutagénesis , Factores de Transcripción Paired Box , Factores de Transcripción/biosíntesis , Transgenes

RESUMEN

The photoreceptor cells of the Drosophila compound eye are precisely organized in elementary units called ommatidia. The outer (R1-R6) and inner (R7, R8) photoreceptors represent two physiologically distinct systems with two different projection targets in the brain (for review see Hardie, 1985). All cells of the primary system, R1-R6, express the same rhodopsin and are functionally identical. In contrast, the R7 and R8 photoreceptors are different from each other. They occupy anatomically precise positions, with R7 on top of R8. In fact, there are several classes of R7/R8 pairs, which differ morphologically and functionally and are characterized by the expression of one of two R7-specific opsins, rh3 or rh4. Here, we describe the identification of a new opsin gene, rhodopsin 5, expressed in one subclass of R8 cells. Interestingly, this subclass represents R8 cells that are directly underneath the R7 photoreceptors expressing rh3, but are never under those expressing rh4. These results confirm the existence of two subpopulations of R7 and R8 cells, which coordinate the expression of their respective rh genes. Thus, developmental signaling pathways between R7 and R8 lead to the exclusive expression of a single rhodopsin gene per cell and to the coordinate expression of another one in the neighboring cell. Consistent with this, rh5 expression in R8 disappears when R7 cells are absent (in sevenless mutant). We propose a model for the concerted evolution of opsin genes and the elaboration of the architecture of the retina.

Asunto(s)

Mapeo Cromosómico , Drosophila melanogaster/genética , Regulación del Desarrollo de la Expresión Génica , Células Fotorreceptoras de Invertebrados/fisiología , Regiones Promotoras Genéticas , Rodopsina/biosíntesis , Opsinas de Bastones/biosíntesis , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Evolución Biológica , Secuencia Conservada , Cartilla de ADN , ADN Complementario , Genes de Insecto , Biblioteca Genómica , Datos de Secuencia Molecular , Células Fotorreceptoras de Invertebrados/citología , Reacción en Cadena de la Polimerasa , Estructura Secundaria de Proteína , Rodopsina/química , Rodopsina/genética , Opsinas de Bastones/química , Opsinas de Bastones/genética , Homología de Secuencia de Aminoácido

RESUMEN

Pax-6 is a transcription factor containing both a homeodomain (HD) and a Paired domain (PD). It functions as an essential regulator of eye development in both Drosophila and vertebrates, suggesting an evolutionarily conserved origin for different types of metazoan eyes. Classical morphological and phylogenetic studies, however, have concluded that metazoan eyes have evolved many times independently. These apparently contradictory findings may be reconciled if the evolutionarily ancient role of Pax-6 was to regulate structural genes (e.g., rhodopsin) in primitive photoreceptors, and only later did it expand its function to regulate the morphogenesis of divergent and complex eye structures. In support of this, we present evidence that eyeless (ey), which encodes the Drosophila homolog of Pax-6, directly regulates rhodopsin 1 (rh1) expression in the photoreceptor cells. We detect ey expression in both larval and adult terminally differentiated photoreceptor cells. We show that the HD of Ey binds to a palindromic HD binding site P3/RCS1 in the rh1 promoter, which is essential for rh1 expression. We further demonstrate that, in vivo, P3/RCS1 can be replaced by binding sites specific for the PD of Ey. P3/RCS1 is conserved in the promoters of all Drosophila rhodopsin genes as well as in many opsin genes in vertebrates. Mutimerized P3 sites in front of a basal promoter are able to drive the expression of a reporter gene in all photoreceptors. These results suggest that Pax-6/Ey directly regulates rhodopsin 1 gene expression by binding to the conserved P3/RCS1 element in the promoter.

Asunto(s)

Proteínas de Unión al ADN/metabolismo , Drosophila/genética , Drosophila/fisiología , Proteínas de Homeodominio , Células Fotorreceptoras de Invertebrados/fisiología , Rodopsina/genética , Animales , Secuencia de Bases , Sitios de Unión , Evolución Biológica , Cartilla de ADN/genética , Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/genética , Drosophila/crecimiento & desarrollo , Proteínas del Ojo , Regulación del Desarrollo de la Expresión Génica , Genes de Insecto , Modelos Biológicos , Factor de Transcripción PAX6 , Factores de Transcripción Paired Box , Células Fotorreceptoras de Invertebrados/citología , Células Fotorreceptoras de Invertebrados/crecimiento & desarrollo , Reacción en Cadena de la Polimerasa , Regiones Promotoras Genéticas , Proteínas Represoras

RESUMEN

The Drosophila gap-like segmentation genes orthodenticle, empty spiracles and buttonhead (btd) are expressed and required in overlapping domains in the head region of the blastoderm stage embryo. Their expression domains correspond to two or three segment anlagen that fail to develop in each mutant. It has been proposed that these overlapping expression domains mediate head metamerization and could generate a combinatorial code to specify segment identity. To test this model, we developed a system for targeted gene expression in the early embryo, based on region specific promoters and the flp-out system. Misexpression of btd in the anterior half of the blastoderm embryo directed by the hunchback proximal promoter rescues the btd mutant head phenotype to wild-type. This indicates that, while btd activity is required for the formation of specific head segments, its ectopic expression does not disturb head development. We conclude that the spatial limits of btd expression are not instructive for metamerization of the head region and that btd activity does not contribute to a combinatorial code for specification of segment identity.

Asunto(s)

Proteínas de Unión al ADN/fisiología , Proteínas de Drosophila , Drosophila melanogaster/embriología , Regulación del Desarrollo de la Expresión Génica , Factores de Transcripción/fisiología , Animales , Animales Modificados Genéticamente , Blastodermo , Vectores Genéticos , Cabeza/embriología , Morfogénesis