RESUMEN
We have constructed a zebrafish genetic linkage map consisting of 705 simple sequence-length polymorphism markers (SSLPs). The map covers 2350 centimorgans (cM) of the zebrafish genome with an average resolution of 3.3 cM. It is a complete map in genetic mapping terms (there is one linkage group for each of the 25 chromosomes), and it has been confirmed by somatic-cell hybrids and centromere-mapping using half-tetrad analysis. The markers are highly polymorphic in the zebrafish strains used for genetic crosses and provide a means to compare genetic segregation of developmental mutations between laboratories. These markers will provide an initial infrastructure for the positional cloning of the nearly 600 zebrafish genes identified as crucial to vertebrate development,and will become the anchor for the physical map of the zebrafish genome.
Asunto(s)
Repeticiones de Microsatélite/genética , Pez Cebra/genética , Animales , Mapeo Cromosómico , Genes/genética , Ligamiento Genético , Marcadores Genéticos/genética , Genoma , Análisis de Secuencia de ADNRESUMEN
In chordate phylogeny, changes in the nervous system, jaws, and appendages transformed meek filter feeders into fearsome predators. Gene duplication is thought to promote such innovation. Vertebrate ancestors probably had single copies of genes now found in multiple copies in vertebrates and gene maps suggest that this occurred by polyploidization. It has been suggested that one genome duplication event occurred before, and one after the divergence of ray-finned and lobe-finned fishes. Holland et al., however, have argued that because various vertebrates have several HOX clusters, two rounds of duplication occurred before the origin of jawed fishes. Such gene-number data, however, do not distinguish between tandem duplications and polyploidization events, nor whether independent duplications occurred in different lineages. To investigate these matters, we mapped 144 zebrafish genes and compared the resulting map with mammalian maps. Comparison revealed large conserved chromosome segments. Because duplicated chromosome segments in zebrafish often correspond with specific chromosome segments in mammals, it is likely that two polyploidization events occurred prior to the divergence of fish and mammal lineages. This zebrafish gene map will facilitate molecular identification of mutated zebrafish genes, which can suggest functions for human genes known only by sequence.
Asunto(s)
Vertebrados/genética , Vertebrados/fisiología , Pez Cebra/genética , Animales , Mapeo Cromosómico , Evolución Molecular , Genes/genética , Genoma , Familia de Multigenes , PoliploidíaRESUMEN
Chondromodulin-I (ChM-I) is suggested in higher vertebrate systems to function as a key regulatory protein for cartilage development. To further understand the process of chondrogenesis and the function of ChM-I, we have cloned the zebrafish cDNA for chondromodulin-1 (chm1) and have mapped the chm1 gene locus. The expression profile of chm1 was determined during zebrafish embryonic development and compared to that of type II collagen (col2a1). Maternal chm1 transcripts were detected before midblastula transition and zygotic expression of chm1 was first observed in the notochord at the 10-somite stage. At later developmental stages, chm1 expression was detected in areas surrounding the otic vesicles, in the developing craniofacial cartilage elements, and in the chondrogenic region of the pectoral fins.
Asunto(s)
Cartílago/embriología , Sustancias de Crecimiento/biosíntesis , Sustancias de Crecimiento/genética , Péptidos y Proteínas de Señalización Intercelular , Proteínas de la Membrana , Notocorda/metabolismo , Secuencia de Aminoácidos , Animales , Bovinos , ADN Complementario/metabolismo , Humanos , Hibridación in Situ , Datos de Secuencia Molecular , Filogenia , Mapeo de Híbrido por Radiación , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Factores de Tiempo , Distribución Tisular , Pez Cebra , Cigoto/metabolismoRESUMEN
The expression of the murine paired-box-containing gene, Pax2, is examined in the developing central nervous system by in situ hybridization. Pax2 expression is detected along the boundaries of primary divisions of the neural tube. Initially, Pax2 is expressed in the ventricular zone in two compartments of cells on either side of the sulcus limitans and along the entire rhombencephalon and spinal cord. At later times, Pax2 is restricted to progeny cells that have migrated to specific regions of the intermediate zone. In the eye, Pax2 expression is restricted to the ventral half of the optic cup and stalk and later to the optic disc and nerve. In the ear, expression is restricted to regions of the otic vesicle that form neuronal components. The transient and restricted nature of Pax2 expression suggests that this murine segmentation gene homologue may also establish compartmental boundaries and contribute to the specification of neuronal identity, as do certain Drosophila segmentation genes.
Asunto(s)
Sistema Nervioso Central/embriología , Regulación de la Expresión Génica/genética , Genes Homeobox/genética , Animales , Oído/embriología , Ojo/embriología , Ratones , Hibridación de Ácido Nucleico , Médula Espinal/embriología , Factores de TiempoRESUMEN
Several class A basic helix-loop-helix (bHLH) transcription factors have been cloned from the developing mouse and chick nervous system. The cloned cDNAs (ME1, ME2, ME3, ME4, in the mouse and GE1, GE2 in the chick) have HLH coding regions highly homologous to other known class A bHLH genes. The genes corresponding to ME1 and GE1 are abundantly expressed during development of the central nervous system. ME1 and GE1 are expressed in proliferating neuroblasts and in cells at the initial stages of differentiation (for example in the external granule cell layer of the cerebellum and in the lateral region of the ventricular zone in the developing neural tube and cortex). They are also expressed at high levels in morphogenetically active regions such as limb buds, somites and mesonephric tubules. The expression of ME1 and GE1 decreases once cellular differentiation is over. Based on the expression of ME1 and GE1 in regions of active cellular proliferation and differentiation and on the known role of other bHLH factors in development, we suggest that ME1 and GE1 play important roles during development of the nervous system as well as in other organ systems.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Sistema Nervioso/metabolismo , Factores de Transcripción , Secuencia de Aminoácidos , Animales , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico , Northern Blotting , Embrión de Pollo , ADN Complementario/genética , Hibridación in Situ , Ratones , Sondas Moleculares/genética , Datos de Secuencia Molecular , Sistema Nervioso/crecimiento & desarrollo , Reacción en Cadena de la Polimerasa , RibonucleasasRESUMEN
We have characterized a collection of zebrafish/mouse somatic cell hybrids with 211 genes and markers chosen from the 25 zebrafish linkage groups. Most of the zebrafish genome is represented in this collection with 88% of genes/markers present in at least one hybrid cell line. Although most hybrids contain chromosomal fragments, there are a few instances where a complete or nearly complete zebrafish chromosome has been maintained in a mouse background, based on multiple markers covering the entire chromosome. In addition to their use in mapping studies, this collection of somatic cell hybrids should constitute an important tool as a source of specific chromosome fragments and for assessing the function of genome regions.
Asunto(s)
Pez Cebra/genética , Animales , Línea Celular , Ligamiento Genético , Marcadores Genéticos , Células Híbridas , Hibridación Fluorescente in Situ , Ratones , Repeticiones de Microsatélite , Reacción en Cadena de la PolimerasaRESUMEN
To exploit fully the power of the zebrafish system as a model for vertebrate development, it will be necessary to develop efficient tools for genomic analysis. In this report we have tested whether single-strand conformation polymorphism analysis (SSCP) can be utilized for gene mapping in zebrafish. Over 100 primer pairs derived from noncoding regions of known genes and partially characterized cDNAs were analyzed, and a polymorphism frequency of approximately 50% was detected in zebrafish strains used for genetic mapping studies. A subset of these polymorphic cDNAs was localized on the zebrafish map. SSCP thus represents an efficient strategy for mapping transcribed sequences with a high resolution in the zebrafish genome, which will facilitate the integration of existing zebrafish framework maps, the generation of a zebrafish EST map, and the application of alternative gene localization strategies such as comparative mapping.
Asunto(s)
Mapeo Físico de Cromosoma/métodos , Polimorfismo Conformacional Retorcido-Simple , Pez Cebra/genética , Regiones no Traducidas 3' , Animales , Cruzamientos Genéticos , Cartilla de ADN , ADN Complementario/genética , Etiquetas de Secuencia Expresada , Sensibilidad y EspecificidadRESUMEN
The zebrafish is the first vertebrate organism used for large-scale genetic screens seeking genes critical to development. These screens have been quite successful, with more than 1800 recessive mutations discovered that speak to morphogenesis of the vertebrate embryo. The cloning of the mutant genes depends on a dense genetic map. The 2000 markers we present here, using microsatellite (CA) repeats, provides 1.2-cM average resolution. One centimorgan in zebrafish is about 0. 74 megabase, so, for many mutations, these markers are close enough to begin positional cloning by YAC walks.
Asunto(s)
Repeticiones de Microsatélite/genética , Pez Cebra/genética , Animales , Clonación Molecular , Femenino , Biblioteca de Genes , Ligamiento Genético , Genoma , Masculino , Mutación , Mapeo Físico de CromosomaRESUMEN
The ultimate informativeness of the zebrafish mutations described in this issue will rest in part on the ability to clone these genes. However, the genetic infrastructure required for the positional cloning in zebrafish is still in its infancy. Here we report a reference cross panel of DNA, consisting of 520 F2 progeny (1040 meioses) that has been anchored to a zebrafish genetic linkage map by 102 simple sequence length polymorphisms. This reference cross DNA provides: (1) a panel of DNA from the cross that was used to construct the genetic linkage map, upon which polymorphic gene(s) and genetic markers can be mapped; (2) a fine order mapping tool, with a maximum resolution of 0.1 cM; and (3) a foundation for the development of a physical map (an ordered array of clones each containing a known portion of the genome). This reference cross DNA will serve as a resource enabling investigators to relate genes or genetic markers directly to a single genetic linkage map and avoid the problem of integrating different maps with different genetic markers, as must be currently done when using randomly amplified polymorphic DNA markers, or as has occurred with human genetic linkage maps.