A tale of signalling and chromatin – how GSK3/WNT pathway controls cell fate decision through CHD4 regulation in stem cells

When WNT signalling is activated, Glycogen Synthase Kinase 3 (GSK3) is inhibited, leading to dephosphorylation and nuclear accumulation of β-catenin, where it regulates WNT-target genes. However, GSK3 is a major kinase with multiple client proteins, and how phosphorylation of additional chromatin proteins downstream of GSK3 regulates stem cell identity remains poorly understood.

Using phospho-proteomic approaches we found that CHD4, a chromatin repressor important in lineage differentiation, is de-phosphorylated downstream of WNT-signalling in mouse embryonic stem cells (mESCs). To unravel the overall CHD4 function, we generated Chd4-knockout mESCs and observed profound upregulation of primitive endoderm markers, implying a repressive role of CHD4 for endoderm lineage specification. To address how differential phosphorylation of CHD4 downstream of WNT signalling is involved in chromatin and stem cell biology, we used gene editing and engineered mESCs expressing different CHD4 phospho-variants.