RESUMO
The early axon scaffolding in the embryonic vertebrate brain consists of a series of ventrally projecting axon tracts that grow into a single major longitudinal pathway connected across the midline by commissures. We have investigated the role of Brother of CDO (BOC), an immunoglobulin (Ig) superfamily member distantly related to the Roundabout (Robo) family of axon-guidance receptors, in the development of this embryonic template of axon tracts in the zebrafish brain. A zebrafish homologue of BOC was isolated and shown to be expressed predominantly in the developing neural plate and later in the neural tube and developing brain. Zebrafish boc was initially highly localized to discrete bands in the mid- and hindbrain, but, as the major brain subdivisions emerged, it became more evenly expressed along the rostrocaudal axis, particularly in dorsal regions. The function of zebrafish boc was examined by a loss-of-function approach. Analysis of embryos injected with antisense morpholinos designed against boc revealed highly selective defects in the development of dorsoventrally projecting axon tracts. Loss of boc caused ventrally projecting axons, particularly those arising from the presumptive telencephalon, to follow aberrant trajectories. These data indicate that boc is an axon-guidance molecule playing a fundamental role in pathfinding during the early patterning of the axon scaffold in the embryonic vertebrate brain.
Assuntos
Axônios/fisiologia , Encéfalo/embriologia , Encéfalo/metabolismo , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Imunoglobulina G/fisiologia , Moléculas de Adesão de Célula Nervosa/metabolismo , Receptores de Superfície Celular/fisiologia , Proteínas de Peixe-Zebra/metabolismo , Animais , Animais Geneticamente Modificados , Antígenos CD57/genética , Antígenos CD57/metabolismo , Clonagem Molecular/métodos , Embrião não Mamífero , Indução Embrionária/efeitos dos fármacos , Indução Embrionária/fisiologia , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Humanos , Imuno-Histoquímica/métodos , Hibridização In Situ/métodos , Camundongos , Microinjeções/métodos , Microscopia Confocal/métodos , Modelos Moleculares , Morfolinas/farmacologia , Moléculas de Adesão de Célula Nervosa/genética , Redes Neurais de Computação , RNA Complementar/metabolismo , RNA Mensageiro/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Peixe-Zebra , Proteínas de Peixe-Zebra/genéticaRESUMO
hlx1 is a related homeobox gene expressed in a dynamic spatiotemporal expression pattern during development of the zebrafish brain. The homologues of hlx1, mouse dbx1 and Xenopus Xdbx, are known to play a role in the specification of neurons in the spinal cord. However, the role of these molecules in the brain is less well known. We have used two different approaches to elucidate a putative function for hlx1 in the developing zebrafish brain. Blastomeres were injected with either synthetic hlx1 mRNA in gain-of-function experiments or with antisense morpholino oligonucleotides directed against hlx1 in loss-of-function experiments. Mis-expression of hlx1 produced severe defects in brain morphogenesis as a result of abnormal ventricle formation, a phenotype we referred to as "fused-brain". These animals also showed a reduction in the size of forebrain neuronal clusters as well as abnormal axon pathfinding. hlx1 antisense morpholinos specifically perturbed hindbrain morphogenesis leading to defects in the integrity of the neuroepithelium. While hindbrain patterning was in the most part unaffected there were select disruptions to the expression pattern of the neurogenic gene Zash1B in specific rhombomeres. Our results indicate multiple roles for hlx1 during zebrafish brain morphogenesis.
