Stem cells take the stairs.

Human embryonic stem cells progress through multiple stages in their path to neural differentiation, but the steps taken along the way are difficult to distinguish, limiting our understanding of this important process. Jing and colleagues (2) now report comprehensive analyses of transcriptome dynamics during this process that reveal five discrete stages, defined in part by highly connected transcription factor networks that link progressive stages. Surprisingly, the third stage, which appears to be critical for neural fate commitment, depends almost entirely on intracellular signaling.