RESUMO
The Drosophila columnar genes are key regulators of neural precursor formation and patterning along the dorsal-ventral axis of the developing CNS and include ventral nerve cord defective (vnd), intermediate nerve cord defective (ind), muscle segment homeodomain (msh), and Epidermal growth factor receptor (Egfr). To investigate the evolution of neural pattern formation, we identified and determined the expression patterns of Tribolium vnd, ind, and msh, and found that they are expressed in the medial, intermediate, and lateral columns of the developing CNS, respectively, in patterns similar, but not identical, to their Drosophila orthologs. The pattern of Egfr activity suggests that the genetic regulatory mechanisms that initiate Tc-vnd expression are similar in Drosophila and Tribolium, whereas those that initiate Tc-ind have diverged. RNAi analyses of gene function show that Tc-vnd and Tc-ind promote the formation of medial and intermediate column neural precursors and that vnd-mediated repression of ind establishes the boundary between the medial and intermediate columns. These data suggest that columnar gene expression and function underlie neural pattern formation in Drosophila, Tribolium, and potentially all insects, but that subtle spatiotemporal differences in expression of these genes may produce species-specific morphological differences.
Assuntos
Padronização Corporal/genética , Neurônios/fisiologia , Células-Tronco/fisiologia , Tribolium/embriologia , Tribolium/genética , Sequência de Aminoácidos , Animais , Linhagem da Célula , Sistema Nervoso Central/anatomia & histologia , Sistema Nervoso Central/embriologia , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Receptores ErbB/genética , Receptores ErbB/metabolismo , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Proteínas de Insetos/genética , Proteínas de Insetos/metabolismo , Dados de Sequência Molecular , Morfogênese/fisiologia , Neurônios/citologia , Proteínas Quinases/genética , Proteínas Quinases/metabolismo , Interferência de RNA , Receptores de Peptídeos de Invertebrados/genética , Receptores de Peptídeos de Invertebrados/metabolismo , Alinhamento de Sequência , Células-Tronco/citologia , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
The study of achaete-scute (ac/sc) genes has recently become a paradigm to understand the evolution and development of the arthropod nervous system. We describe the identification and characterization of the ac/sc genes in the coleopteran insect species Tribolium castaneum. We have identified two Tribolium ac/sc genes - achaete-scute homolog (Tc-ASH) a proneural gene and asense (Tc-ase) a neural precursor gene that reside in a gene complex. Focusing on the embryonic central nervous system we find that Tc-ASH is expressed in all neural precursors and the proneural clusters from which they segregate. Through RNAi and misexpression studies we show that Tc-ASH is necessary for neural precursor formation in Tribolium and sufficient for neural precursor formation in Drosophila. Comparison of the function of the Drosophila and Tribolium proneural ac/sc genes suggests that in the Drosophila lineage these genes have maintained their ancestral function in neural precursor formation and have acquired a new role in the fate specification of individual neural precursors. Furthermore, we find that Tc-ase is expressed in all neural precursors suggesting an important and conserved role for asense genes in insect nervous system development. Our analysis of the Tribolium ac/sc genes indicates significant plasticity in gene number, expression and function, and implicates these modifications in the evolution of arthropod neural development.
