CTCF is an essential DNA binding protein whose absence leads to embryonic lethality. CTCF is primarily known for its role in 3D genome organization where its N-terminal domain interacts with cohesin to anchor chromatin loops. How CTCF facilitates proper embryonic development remains unclear, necessitating temporal control to resolve its stage-specific functions. By combining gastruloids, an in vitro model of embryonic development, with a degron system to rapidly deplete CTCF at defined timepoints, we show that early CTCF depletion impairs early gastruloid morphogenesis. Surprisingly, ATAC-seq and time-resolved RNA-seq revealed that differentiation was unaffected. CTCF binding is strongly enriched at promoters of downregulated genes. Re-expression of a CTCF variant with an N-terminal truncation, incapable of looping, was sufficient to rescue the expression of CTCF-promoter bound genes and the defects in morphogenesis. However, extended culture (up to 168 hours) of gastruloids reconstituted with N-terminal truncated CTCF led to their collapse. Our work shows that CTCF has a dual function in early mammalian development: at early stages CTCF regulates developmentally important genes through promoter binding, while at later stages its looping function is required for correct development. ### Competing Interest Statement The authors have declared no competing interest. European Research Council, https://ror.org/0472cxd90, 637587, 865459 Dutch Research Council, https://ror.org/04jsz6e67, 016.161.316, VI.C.222.049 Dutch Cancer Society, https://ror.org/0368jnd28, N/A

Although IWS1 has been implicated in transcription-coupled processes, its direct role in RNA polymerase II function remained undefined. Here, the authors demonstrate that IWS1 enhances Pol II elongati...

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Using cryo-electron microscopy and biochemistry, Zhang et al. reveal that the DNA helicase RECQL5 and the transcription-coupled DNA repair complex coordinate to regulate transcription elongation rates...