| Metazoan development requires mechanisms to generate cells with diverse functions. Cellular diversity is dictated by complex patterns of molecular expression, originating from dynamic spatiotemporal regulation of transcriptomes. Both gene duplication and alternative splicing have been proposed as a means to expand transcriptomes. Although gene duplication expands genomics, the small number of protein-coding genes in metazoan genomes is insufficient to account for their cellular diversity within organisms. Alternative splicing, producing more than one transcript from a single gene, provides a way to generate complexity with limited amount of genetic materials. Here, we use in silico approaches to show that the arthropod N-Cadherin gene has maintained exactly the same genomic organization, a common promoter and three sets of mutually exclusive alternatively-spliced exons (MEs), for over 400 million years. Furthermore, in vivo studies demonstrated that isoforms derived from these MEs receive separate and evolutionarily conserved spatiotemporal controls critical for the organism's development in both Drosophila melanogaster and in Tribolium castaneum, which are at least 290 million years apart. We propose that alternative splicing fundamentally expands genome's ability to generate complex yet reproducible patterns of molecular expression during development, and its adaptation is tied to evolution of metazoa. |
