RESUMEN
Gene duplication is a major driver of evolutionary divergence. In most vertebrates a single PAX6 gene encodes a transcription factor required for eye, brain, olfactory system, and pancreas development. In zebrafish, following a postulated whole-genome duplication event in an ancestral teleost, duplicates pax6a and pax6b jointly fulfill these roles. Mapping of the homozygously viable eye mutant sunrise identified a homeodomain missense change in pax6b, leading to loss of target binding. The mild phenotype emphasizes role-sharing between the co-orthologues. Meticulous mapping of isolated BACs identified perturbed synteny relationships around the duplicates. This highlights the functional conservation of pax6 downstream (3') control sequences, which in most vertebrates reside within the introns of a ubiquitously expressed neighbour gene, ELP4, whose pax6a-linked exons have been lost in zebrafish. Reporter transgenic studies in both mouse and zebrafish, combined with analysis of vertebrate sequence conservation, reveal loss and retention of specific cis-regulatory elements, correlating strongly with the diverged expression of co-orthologues, and providing clear evidence for evolution by subfunctionalization.
Asunto(s)
Proteínas del Ojo/genética , Duplicación de Gen , Proteínas de Homeodominio/genética , Factores de Transcripción Paired Box/genética , Proteínas Represoras/genética , Proteínas de Pez Cebra/genética , Pez Cebra/genética , Animales , Animales Modificados Genéticamente , Secuencia de Bases , Cromosomas Artificiales Bacterianos/genética , Biología Computacional , Cartilla de ADN/genética , Elementos de Facilitación Genéticos , Evolución Molecular , Anomalías del Ojo/embriología , Anomalías del Ojo/genética , Regulación del Desarrollo de la Expresión Génica , Genes Homeobox , Genes Reporteros , Prueba de Complementación Genética , Ligamiento Genético , Ratones , Ratones Transgénicos , Modelos Genéticos , Datos de Secuencia Molecular , Mutación Missense , Factor de Transcripción PAX6 , Fenotipo , Homología de Secuencia de Ácido Nucleico , Pez Cebra/anomalías , Pez Cebra/embriologíaRESUMEN
Compromised heat shock protein 90 (Hsp90) function reveals cryptic phenotypes in flies and plants. These observations were interpreted to suggest that this molecular stress-response chaperone has a capacity to buffer underlying genetic variation. Conversely, the protective role of Hsp90 could account for the variable penetrance or severity of some heritable developmental malformations in vertebrates. Using zebrafish as a model, we defined Hsp90 inhibitor levels that did not induce a heat shock response or perturb phenotype in wild-type strains. Under these conditions the severity of the recessive eye phenotype in sunrise, caused by a pax6b mutation, was increased, while in dreumes, caused by a sufu mutation, it was decreased. In another strain, a previously unobserved spectrum of severe structural eye malformations, reminiscent of anophthalmia, microphthalmia, and nanophthalmia complex in humans, was uncovered by this limited inhibition of Hsp90 function. Inbreeding of offspring from selected unaffected carrier parents led to significantly elevated malformation frequencies and revealed the oligogenic nature of this phenotype. Unlike in Drosophila, Hsp90 inhibition can decrease developmental stability in zebrafish, as indicated by increased asymmetric presentation of anophthalmia, microphthalmia, and nanophthalmia and sunrise phenotypes. Analysis of the sunrise pax6b mutation suggests a molecular mechanism for the buffering of mutations by Hsp90. The zebrafish studies imply that mild perturbation of Hsp90 function at critical developmental stages may underpin the variable penetrance and expressivity of many developmental anomalies where the interaction between genotype and environment plays a major role.