SMAD1/5-mediated recruitment of the histone demethylase KDM1A controls cell fate programs in embryonic stem cells.

Bone morphogenetic proteins (BMPs) play diverse roles in mouse embryonic stem cell (mESC) biology. Recent studies suggest that BMPs induce multiple cell fates and enhance mESC heterogeneity by cross-activating multiple signaling pathways. Although BMPs primarily signal through SMAD1 and SMAD5 in mESCs, their roles remain incompletely defined. Here, we investigated the SMAD signaling pathway using Smad1/5 double knockout (S1/5 dKO) mESCs. While SMAD1/5 depletion may influence mESC heterogeneity, single-cell RNA sequencing (scRNA-seq) revealed only minor differences between S1/5 dKO and WT cells, suggesting that the observed changes are not because of altered cell states. Chromatin immunoprecipitation sequencing (ChIP-seq) demonstrated that SMAD1/5 recruit the histone demethylase KDM1A/LSD1 to specific genomic regions, where it removes H3K4me1/2 marks associated with enhancers. Published scRNA-seq data from Kdm1a-deficient mESCs during embryoid body differentiation further supported this mechanism. This study reveals a transcriptional repression mechanism of SMAD1/5, involving KDM1A-dependent H3K4me1/2 depletion and the regulation of cell type-specific gene expression programs.