Alternative splicing increases complexity of stem cell transcriptome

Development of highly anticipated stem cell-based therapies requires a detailed understanding of mechanisms regulating biological properties of these cells. Comprehensive identification of all biological molecules produced in stem cells is an important step toward this goal. During the past several years, microarray studies have essentially identified genes that are transcriptionally activated in various embryonic and adult stem cell populations. However, the extent of post-transcriptional modifications within the stem cell transcriptome remained undetermined. Recently, we presented evidence that thousands of genes expressed in hematopoietic and embryonic stem cells undergo alternative splicing. Using combined computational and experimental analyses, we found that the frequency of alternative splicing is especially high in tissue-specific genes, as compared to ubiquitous genes. Our results also indicate that negative regulation of constitutively active splicing sites can be a prevalent mode for generation of splicing variants, and that alternative splicing is generally not conserved between orthologous genes in human and mouse. Here, we discuss the implications of our findings for stem cell biology, and present possible approaches toward genome-wide identification and characterization of splice variants.