Constraint of gene expression by the chromatin remodelling protein CHD4 facilitates lineage specification.

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O'Shaughnessy-Kirwan, Aoife 
Signolet, Jason 
Costello, Ita 
Gharbi, Sarah 

Chromatin remodelling proteins are essential for different aspects of metazoan biology, yet functional details of why these proteins are important are lacking. Although it is possible to describe the biochemistry of how they remodel chromatin, their chromatin-binding profiles in cell lines, and gene expression changes upon loss of a given protein, in very few cases can this easily translate into an understanding of how the function of that protein actually influences a developmental process. Here, we investigate how the chromatin remodelling protein CHD4 facilitates the first lineage decision in mammalian embryogenesis. Embryos lacking CHD4 can form a morphologically normal early blastocyst, but are unable to successfully complete the first lineage decision and form functional trophectoderm (TE). In the absence of a functional TE, Chd4 mutant blastocysts do not implant and are hence not viable. By measuring transcript levels in single cells from early embryos, we show that CHD4 influences the frequency at which unspecified cells in preimplantation stage embryos express lineage markers prior to the execution of this first lineage decision. In the absence of CHD4, this frequency is increased in 16-cell embryos, and by the blastocyst stage cells fail to properly adopt a TE gene expression programme. We propose that CHD4 allows cells to undertake lineage commitment in vivo by modulating the frequency with which lineage-specification genes are expressed. This provides novel insight into both how lineage decisions are made in mammalian cells, and how a chromatin remodelling protein functions to facilitate lineage commitment.

Blastocyst, CHD4, Chromatin remodelling, Lineage commitment, Transcription, Trophectoderm, Animals, Blastocyst, Cell Differentiation, Cell Lineage, Chromatin Assembly and Disassembly, Crosses, Genetic, DNA Helicases, DNA Primers, Fluorescent Antibody Technique, Gene Expression Regulation, Developmental, In Situ Nick-End Labeling, Mice, Mice, Inbred C57BL, Multiplex Polymerase Chain Reaction, Single-Cell Analysis
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The Company of Biologists
Wellcome Trust (098021/Z/11/Z)
Wellcome Trust (097922/Z/11/B)