Evolution and Diversity in the system of development and differentiation

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(1) Evolution and Developmental mechanism in Nervous systemTo understand when and how the structural brain emerged, we analyzed the central nervous system of a lower invertebrate, planarian. We conducted a large-scale screening of the head part-specific genes in the planarian by constructing a cDNA microarray. As a result, 205 genes with head part-specific spikes were found, which included some essential genes in the vertebrate nervous system. The expression patterns of the top 30 genes showing the strongest spikes implied that the planarian brain has undergone functional regionalization.As a result of homology searches, we found that 116 clones had significant similarity to known genes related to the nervous system. Interestingly, we found that 〜30% of planarian nervous system-related genes had homologous sequences in Arabidopsis and yeast, which do not possess a nervous system. This implies that the origin of nervous system-related genes greatly predated the emergence of the nervous system, and that these genes might have been recruited toward the nervous system.(2) Evolution and Diversity in the system of development and differentiationTo investigate the diversification of cichlid jaw morphology at the genetic level, we used a DNA chip to compare gene expression levels between closely related cichlid fishes. This analysis indicated that the expression of some genes differed in the larvae of two cichlid species. One such clone encodes a new astacin family metalloproteinase. Because some astacin family proteins contribute to morphogenesis in animals, CiMP1 is expected to participate in species-specific head morphogenesis in cichlids.In Cichlids, here, we provide an example in which alternative splicing may play a role in mate choice, leading to cichlid speciation through diversification of gene function by production of multiple mRNAs from a single gene.