RESUMO
As growing retinotectal axons navigate from the eye to the tectum, they sense guidance molecules distributed along the optic pathway. Mutations in the zebrafish astray gene severely disrupt retinal axon guidance, causing anterior-posterior pathfinding defects, excessive midline crossing, and defasciculation of the retinal projection. Eye transplantation experiments show that astray function is required in the eye. We identify astray as zebrafish robo2, a member of the Roundabout family of axon guidance receptors. Retinal ganglion cells express robo2 as they extend axons. Thus, robo2 is required for multiple axon guidance decisions during establishment of the vertebrate visual projection.
Assuntos
Axônios/fisiologia , Proteínas do Tecido Nervoso/genética , Receptores Imunológicos/genética , Receptores Imunológicos/fisiologia , Células Ganglionares da Retina/fisiologia , Colículos Superiores/embriologia , Alelos , Animais , Padronização Corporal , Mapeamento Cromossômico , Cruzamentos Genéticos , Olho/embriologia , Olho/transplante , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Genes , Hibridização In Situ , Masculino , Mutação , Proteínas do Tecido Nervoso/fisiologia , Fenótipo , Retina/embriologia , Retina/metabolismo , Células Ganglionares da Retina/metabolismo , Colículos Superiores/citologia , Vias Visuais/embriologia , Peixe-Zebra/embriologia , Peixe-Zebra/genética , Proteínas de Peixe-ZebraRESUMO
Recent large-scale mutagenesis screens have made the zebrafish the first vertebrate organism to allow a forward genetic approach to the discovery of developmental control genes. Mutations can be cloned positionally, or placed on a simple sequence length polymorphism (SSLP) map to match them with mapped candidate genes and expressed sequence tags (ESTs). To facilitate the mapping of candidate genes and to increase the density of markers available for positional cloning, we have created a radiation hybrid (RH) map of the zebrafish genome. This technique is based on somatic cell hybrid lines produced by fusion of lethally irradiated cells of the species of interest with a rodent cell line. Random fragments of the donor chromosomes are integrated into recipient chromosomes or retained as separate minichromosomes. The radiation-induced breakpoints can be used for mapping in a manner analogous to genetic mapping, but at higher resolution and without a need for polymorphism. Genome-wide maps exist for the human, based on three RH panels of different resolutions, as well as for the dog, rat and mouse. For our map of the zebrafish genome, we used an existing RH panel and 1,451 sequence tagged site (STS) markers, including SSLPs, cloned candidate genes and ESTs. Of these, 1,275 (87.9%) have significant linkage to at least one other marker. The fraction of ESTs with significant linkage, which can be used as an estimate of map coverage, is 81.9%. We found the average marker retention frequency to be 18.4%. One cR3000 is equivalent to 61 kb, resulting in a potential resolution of approximately 350 kb.
