Hierarchically Clustering to 1,033 Genes Differentially Expressed in Mouse Superior Colliculus in the Courses of Optic Nerve Development and Injury

Tempo spatially specific expression of many development-related genes is the molecular basis for the formation of the central nervous system (CNS), especially those genes regulating the proliferation, differentiation, migration, axon growth, and orientation of nerve cells. The development-related genes are usually prominent during the embryonic and newborn stages, but rarely express during the adulthood. These genes are believed to be suitable target genes for promoting CNS regeneration, despite majority of which remains unknown. Hence, the aim of this study was to screen development-related genes which might contribute to CNS regeneration. In this study, 1,033 differentially-expressed genes of superior colliculus in the courses of mouse optic nerve development and injury, as previously identified by cDNA microarrays, were hierarchically clustered to display expression pattern of each gene and reveal the relationships among these genes, and infer the functions of some unknown genes based on function-identified genes with the similar expression patterns. Consequently, the expression patterns of 1,033 candidate genes were revealed at eight time points during optic nerve development or injury. According to the similarity among gene expression patterns, 1,033 genes were divided into seven groups. The potential function of genes in each group was inferred on the basis of the dynamic trend for mean gene expression values. Moreover, the expression patterns of six function-unidentified genes were extremely similar to that of the ptn gene which could promote and guide axonal extension. Therefore, these six genes are temporally regarded as candidate genes related to axon growth and guidance. The results may help to better understand the roles of function-identified genes in the stages of CNS development and injury, and offer useful clues to evaluate the functions of hundreds of unidentified genes.