Evolution of the vertebrate central nervous system through novel expression changes of duplicated genes and gene expression profiling of amphioxus development
During the transition from invertebrates to vertebrates, the central nervous system has undergone a series of striking changes including the dramatic increase of neuron number, and the emergence of the tripartite brain with telencephalon, mid-hindbrain boundary. Gene duplication is a fundamental evolutionary process which can provide genetic materials for creating novel genes. To study the contribution of gene duplications in CNS evolution, we identified a group of CNS-biased genes that have experienced duplication during vertebrate origin. Their expression patterns in the vertebrate species, Xenopus, were investigated by whole mount in situ hybridization and compared with those of the ancestral genes in amphioxus, the invertebrate species most closely related to the vertebrates. Interestingly, we found that only a part of the CNS-biased duplicate genes exhibit relatively conserved expression patterns between Xenopus and amphioxus. A large proportion of vertebrate CNSbiased duplicate genes arise from non-CNS genes in invertebrates, via shifts or expansions of expression domains. In addition, although the genes identified are substantially expressed in the CNS, nearly all the Xenopus genes have evolved divergent expression patterns between the duplicates. All the changes of these genes could be the driven force of brain evolution. Amphioxus the invertebrate species most closely related to the vertebrates. The study of the regulatory genes and networks of the early developmental stages of amphioxus is important for developmental and evolutionary biology. In our study, we used digital gene expression-tag sequencing (DSAGE) sequenced 13 samples of mRNA from male and female adults and 11 early developmental stages embryos. And we also made a mixed-stages normalized cDNA library with were sequenced by new generation sequencing technology,454 and Solexa. All these data will be used for the further research of the genes and mechanisms of early embryo development.
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