ESRP1-Induced CD44 v3 Is Important for Controlling Pluripotency in Human Pluripotent Stem Cells : ESRP1 as a Key Regulator of Human Pluripotency

The elucidation of a code for regulated splicing has been a long-standing goal in understanding the control of post-transcriptional gene expression events that are crucial for cell survival, differentiation and development. We decoded functional RNA elements in vivo by constructing an RNA map for the cell type-specific splicing regulator FOX2 (also known as RBM9) via cross-linking immunoprecipitation coupled with high-throughput sequencing (CLIP-seq) in human embryonic stem cells. The map identified a large cohort of specific FOX2 targets, many of which are themselves splicing regulators, and comparison between the FOX2 binding profile and validated splicing events revealed a general rule for FOX2-regulated exon inclusion or skipping in a position-dependent manner. These findings suggest that FOX2 functions as a critical regulator of a splicing network, and we further show that FOX2 is important for the survival of human embryonic stem cells.

Alternative splicing achieves coordinated changes in post-transcriptional gene expression programmes through the activities of diverse RNA-binding proteins. Epithelial splicing regulatory proteins 1 and 2 (ESRP1 and ESRP2) are cell-type-specific regulators of transcripts that switch splicing during the epithelial-mesenchymal transition (EMT). To define a comprehensive programme of alternative splicing that is regulated during the EMT, we identified an extensive ESRP-regulated splicing network of hundreds of alternative splicing events within numerous genes with functions in cell-cell adhesion, polarity, and migration. Loss of this global ESRP-regulated epithelial splicing programme induces the phenotypic changes in cell morphology that are observed during the EMT. Components of this splicing signature provide novel molecular markers that can be used to characterize the EMT. Bioinformatics and experimental approaches revealed a high-affinity ESRP-binding motif and a predictive RNA map that governs their activity. This work establishes the ESRPs as coordinators of a complex alternative splicing network that adds an important post-transcriptional layer to the changes in gene expression that underlie epithelial-mesenchymal transitions during development and disease.

Alternative splicing (AS) is a key process underlying the expansion of proteomic diversity and the regulation of gene expression. Here, we identify an evolutionarily conserved embryonic stem cell (ESC)-specific AS event that changes the DNA-binding preference of the forkhead family transcription factor FOXP1. We show that the ESC-specific isoform of FOXP1 stimulates the expression of transcription factor genes required for pluripotency, including OCT4, NANOG, NR5A2, and GDF3, while concomitantly repressing genes required for ESC differentiation. This isoform also promotes the maintenance of ESC pluripotency and contributes to efficient reprogramming of somatic cells into induced pluripotent stem cells. These results reveal a pivotal role for an AS event in the regulation of pluripotency through the control of critical ESC-specific transcriptional programs. Copyright © 2011 Elsevier Inc. All rights reserved.