Triggering neural differentiation of ES cells by subtype switching of importin-α

Nuclear proteins are selectively imported into the nucleus by transport factors such as importin-α and importin-β1,2. Here, we show that the expression of importin-α subtypes is strictly regulated during neural differentiation of mouse embryonic stem (ES) cells, and that the switching of importin-α subtype expression is critical for neural differentiation. Moreover, reproducing the switching of importin-α subtype expression in undifferentiated ES cells induced neural differentiation in the presence of leukaemia inhibitory factor (LIF) and serum, coordinated with the regulated expression of Oct3/4, Brn2 and SOX2, which are involved in ES–neural identity determination. These transcription factors were selectively imported into the nucleus by specific subtypes of importin-α. Thus, importin-α subtype switching has a major impact on cell differentiation through the regulated nuclear import of a specific set of transcription factors. This is the first study to propose that transport factors should be considered as major players in cell-fate determination.