Cells transit through a quiescent-like state to convert to neurons at high rates

While transcription factors (TFs) provide essential cues for directing and redirecting cell fate, TFs alone are insufficient to drive cells to adopt alternative fates. Rather, transcription factors rely on receptive cell states to induce novel identities. Cell state emerges from and is shaped by cellular history and the activity of diverse processes. Here, we define the cellular and molecular properties of a highly receptive state amenable to transcription factor-mediated direct conversion from fibroblasts to induced motor neurons. Using a well-defined model of direct conversion to a post-mitotic fate, we identify the highly proliferative, receptive state that transiently emerges during conversion. Through examining chromatin accessibility, histone marks, and nuclear features, we find that cells reprogram from a state characterized by global reductions in nuclear size and transcriptional activity. Supported by globally increased levels of H3K27me3, cells enter a quiescent-like state of reduced RNA metabolism and elevated expression of REST and p27, markers of quiescent neural stem cells. From this transient state, cells convert to neurons at high rates. Inhibition of Ezh2, the catalytic subunit of PRC2 that deposits H3K27me3, abolishes conversion. Our work offers a roadmap to identify global changes in cellular processes that define cells with different conversion potentials that may generalize to other cell-fate transitions. HighlightsO_LIProliferation drives cells to a compact nuclear state that is receptive to TF-mediated conversion. C_LIO_LIIncreased receptivity to TFs corresponds to reduced nuclear volumes. C_LIO_LIReprogrammable cells display global, genome-wide increases in H3K27me3. C_LIO_LIHigh levels of H3K27me3 support cells transits through a state of altered RNA metabolism. C_LIO_LIInhibition of Ezh2 increases nuclear size, reduces the expression of the quiescence marker p27. C_LIO_LIAcute inhibition of Ezh2 abolishes motor neuron conversion. C_LI One Sentence SummaryCells transit through a quiescent-like state characterized by global reductions in nuclear size and transcriptional activity to convert to neurons at high rates. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/624928v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@ee2127org.highwire.dtl.DTLVardef@1c2a39dorg.highwire.dtl.DTLVardef@183bf46org.highwire.dtl.DTLVardef@82b98d_HPS_FORMAT_FIGEXP M_FIG C_FIG