Characterization and perturbation of CTCF-mediated chromatin interactions for enhancing myogenic transdifferentiation

Expression of key transcription factors can induce transdifferentiation in somatic cells; however, this conversion is usually incomplete due to undefined intrinsic barriers. Here, we employ MyoD-induced transdifferentiation of fibroblasts as a model to illustrate the chromatin structures that impede the cell-fate transition. Focusing on the three-dimensional (3D) chromatin interactions, we show that MyoD directly establishes chromatin loops to activate myogenic transcriptional program. Similarly, dynamic changes of CTCF-mediated chromatin interactions are favorable for fibroblast-to-myoblast conversion. However, a substantial portion of CTCF-mediated chromatin interactions remain stable, and the associated genes are steady in expression and enriched for fibroblast function that may restrict cell-identity transformation. Temporal CTCF depletion can interrupt the resistant chromatin loops to enhance myogenic transdifferentiation in mice, pig, and chicken fibroblasts. Therefore, during induced transdifferentiation, the transcription factor can directly reorganize the 3D chromatin interactions, and perturbation of CTCF-mediated genome topology may resolve the limitations of cell fate transitions.