Mesp1 and Hes1 interplay controls early cardiac progenitor cell specification

Introduction

Cardiac progenitors (CPs) arise early during gastrulation. CPs express transcription factor Mesp1 and contribute to all cardiac territories. Alteration in CP specification or migration leads to congenital heart defects (CHDs) affecting 1% of live births. We uncovered Mesp1 as a master regulator of early cardiovascular specification and differentiation (Lescroart et al., Science 2018; Lin et al., Nat Cell Biol 2022), and recently identified a crucial role for transcriptional repressor Hes1 in CP deployment (Rammah et al., Circ Res 2022). Indeed, Hes1 deletion results in embryonic lethality due to CHDs. Interestingly, Hes1 conditional deletion in Mesp1 lineage recapitulates the heart defects observed in Hes1 null embryos.

Objective

To investigate the mechanism of early CP specification by exploring Mesp1 and Hes1 possible interplay.

Method

In vitro mouse gastrulation model, gastruloid and mouse embryos were used to reveal expression levels and patterns of Mesp1 and Hes1 using fluorescent in situ hybridization technique, RNAscope. RNAseq and Chip-seq experiments were performed on Mesp1 gain-of-function (GOF) mESC line. ScRNAseq analysis was performed during gastruloid culture.

Results

RNAscope on mouse embryos revealed differential Hes1 expression during gastrulation. While Hes1 expression is high in FHF progenitors, starts to decline in SHF progenitors. RNAseq and Chip-seq data using Mesp1 GOF mESCs has shown downregulation of Hes1 by Mesp1. Using Mesp1 mutant embryos, we showed increased Hes1 expression in mesoderm supporting the previous data. ScRNAseq on gastruloids revealed coexpression of Mesp1 and Hes1 in CP subpopulations. We reproduced these results with RNAscope and uncovered similar expression patterns in different CPs that of embryos. Hes1 expression is detected in Hand1+ FHF progenitors and downregulated in Foxc2+ SHF progenitors. These results validate our in vivo and in vitro models and point out a role for Hes1 in early heart development that has not been reported.

Conclusion

Our data strongly support a role for Mesp1-Hes1 interplay in the regulation of early CP specification.