Two Forkhead transcription factors regulate cardiac progenitor specification by controlling the expression of receptors of the fibroblast growth factor and Wnt signaling pathways

Cardiogenesis involves multiple biological processes acting in concert during development, a coordination achieved by the regulation of diverse cardiac genes by a finite set of transcription factors (TFs). Previous work from our laboratory identified the roles of two Forkhead TFs, Checkpoint suppressor homologue (CHES-1-like) and Jumeau (Jumu) in governing cardiac progenitor cell divisions by regulating Polo kinase activity. These TFs were also implicated in the regulation of numerous other cardiac genes. Here we show that these two Forkhead TFs play an additional and mutually redundant role in specifying the cardiac mesoderm (CM): eliminating the functions of both CHES-1-like and jumu in the same embryo results in defective hearts with missing hemisegments. Our observations indicate that this process is mediated by the Forkhead TFs regulating the fibroblast growth factor receptor Heartless (Htl) and the Wnt receptor Frizzled (Fz), both previously known to function in cardiac progenitor specification: CHES-1-like and jumu exhibit synergistic genetic interactions with htl and fz in CM specification, thereby implying function through the same genetic pathways, and transcriptionally activate the expression of both receptor-encoding genes. Furthermore, ectopic overexpression of either htl or fz in the mesoderm partially rescues the defective CM specification phenotype seen in embryos doubly homozygous for mutations in jumu and CHES-1-like. Together, these data emphasize the functional redundancy that leads to robustness in the cardiac progenitor specification process mediated by Forkhead TFs regulating the expression of signaling pathway receptors, and illustrate the pleiotropic functions of this class of TFs in different aspects of cardiogenesis.

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Ahmad SM, Tansey TR, Busser BW, Nolte MT, Jeffries N, Gisselbrecht SS, Rusan NM, Michelson AM