An Alternative Splicing Switch Regulates Embryonic Stem Cell Pluripotency and Reprogramming [RNA-Seq]

Alternative splicing (AS) is a key process underlying the expansion of proteomic diversity and the regulation of gene expression. However, the contribution of AS to the control of embryonic stem cell (ESC) pluripotency is not well understood. Here, we identify an evolutionarily conserved 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. Remarkably, this isoform also promotes the maintenance of ESC pluripotency and the efficient reprogramming of somatic cells to induced pluripotent stem cells. These results thus reveal that an AS switch plays a pivotal role in the regulation of pluripotency and functions by controlling critical ESC-specific transcriptional programs. Exons 18 and 18b form a mutually exclusive splicing event. The FOXP1 (non-ES) isoform contains only exon 18 and not 18b, while the FOXP1-ES isoform contains only exon 18b and not 18. To investigate whether FOXP1 and FOXP1-ES control different sets of genes, we performed knockdowns using custom siRNA pools targeting FOXP1 exons 18 or 18b in undifferentiated H9 cells, followed by RNA-Seq profiling.