Qun Pan

How species with similar repertoires of protein-coding genes differ so markedly at the phenotypic level is poorly understood. By comparing organ transcriptomes from vertebrate species spanning ~350 million years of evolution, we observed significant differences in alternative splicing complexity between vertebrate lineages, with the highest complexity in primates. Within 6 million years, the splicing profiles of physiologically equivalent organs diverged such that they are more strongly related to the identity of a species than they are to organ type. Most vertebrate species-specific splicing patterns are cis-directed. However, a subset of pronounced splicing changes are predicted to remodel protein interactions involving trans-acting regulators. These events likely further contributed to the diversification of splicing and other transcriptomic changes that underlie phenotypic differences among vertebrate species.

Histones and Alternative Splicing Alternative splicing—the inclusion of different combinations of gene exons within a messenger RNA transcript—occurs in the majority of human genes and is regulated by basal and tissue-specific splicing factors, by transcription kinetics, and by chromatin structure. Luco et al. (p. 996 , published online 4 February) analyzed the alternative splicing of the human fibroblast growth factor receptor 2 gene in tissue culture cells and found that inclusion of exon IIIb or IIIc was modulated by the levels of histone H3 lysine 36 trimethylation (H3-K36me3) and H3-K4me3. Histone H3-K36me3 enrichment correlated with binding of the chromatin protein, MRG15. The MRG15 protein in turn recruited the polypyrimidine tract–binding protein (PTB) splicing factor, which acts to repress alternative exon inclusion, thus establishing a direct link between histone modifications and the splicing machinery.