Evolutionarily conserved Tbx5 – Wnt2/2b pathway orchestrates cardiopulmonary development

Abstract

Codevelopment of the lungs and heart underlies key evolutionary innovations in the transition to terrestrial life. Cardiac specializations that support pulmonary circulation, including the atrial septum, are generated by second heart field (SHF) cardiopulmonary progenitors (CPPs). It has been presumed that transcription factors required in the SHF for cardiac septation, e.g., Tbx5, directly drive a cardiac morphogenesis gene-regulatory network. Here, we report instead that TBX5 directly drives Wnt ligands to initiate a bidirectional signaling loop between cardiopulmonary mesoderm and the foregut endoderm for endodermal pulmonary specification and, subsequently, atrial septation. We show that Tbx5 is required for pulmonary specification in mice and amphibians but not for swim bladder development in zebrafish. TBX5 is non-cell-autonomously required for pulmonary endoderm specification by directly driving Wnt2 and Wnt2b expression in cardiopulmonary mesoderm. TBX5 ChIPsequencing identified cis-regulatory elements at Wnt2 sufficient for endogenous Wnt2 expression domains in vivo and required for Wnt2 expression in precardiac mesoderm in vitro. Tbx5 cooperated with Shh signaling to drive Wnt2b expression for lung morphogenesis. Tbx5 haploinsufficiency in mice, a model of Holt-Oram syndrome, caused a quantitative decrement of mesodermal-to-endodermal Wnt signaling and subsequent endodermal-to-mesodermal Shh signaling required for cardiac morphogenesis. Thus, Tbx5 initiates a mesodermendoderm-mesoderm signaling loop in lunged vertebrates that provides a molecular basis for the coevolution of pulmonary and cardiac structures required for terrestrial life. lung development | heart development | TBX5 | Wnt signaling | Hedgehog signaling

Development and evolution of the metazoan heart

“…It has been observed that the DMP is not as developed and the mesenchymal cap is very diminutive. [216][217][218][219] Genes involved in the tool kit acting in normal and, when corrupt, in abnormal development include Tbx5, 72 PDGFRα, 171,218 and Sonic hedgehog. 216 It is interesting to note that disturbance of podoplanin can also lead to abnormal pulmonary vein connections, which normally are guided to the left atrium by the DMP.…”

Retinoic acid signaling in heart development

“…In the amphibian heart, the sinus venosus moves more anteriorly, and the pulmonary vein connects with the atrium through the dorsal mesocardium (Romer, 1971). The atrial septum is present in vertebrates with pulmonary respiration including lungfishes, amphibians, and amniotes (Lewis & Hanken, 2017;Moorman & Christoffels, 2003;Steimle et al, 2018). The atrial septum is present in vertebrates with pulmonary respiration including lungfishes, amphibians, and amniotes (Lewis & Hanken, 2017;Moorman & Christoffels, 2003;Steimle et al, 2018).…”

“…The orifice of the pulmonary vein is demarcated by DMP, part of the atrial septum originating from the posterior SHF; therefore, the pulmonary vein drains into the left side of the atrium (Tasaka et al, 1996). The atrial septum is present in vertebrates with pulmonary respiration including lungfishes, amphibians, and amniotes (Lewis & Hanken, 2017;Moorman & Christoffels, 2003;Steimle et al, 2018).…”

“…Gata4 also promotes cell cycle progression of the cardiogenic progenitors in the posterior SHF (Zhou et al, 2017). The RA-Shh pathway in associated with Tbx5 is conserved in the development of the atrial septum and lung in Xenopus and mouse (Rankin et al, 2016;Steimle et al, 2018).…”

“…At the same stage, RA acts on the posterior SHF, containing the cardiopulmonary progenitors, to induce Tbx5 expression. The RA-Shh pathway in associated with Tbx5 is conserved in the development of the atrial septum and lung in Xenopus and mouse(Rankin et al, 2016;Steimle et al, 2018). Foregut endoderm-secreted Shh also acts on the posterior SHF and induces the expression of Wnt2/2b and Bmp4, lunginducing growth factors.…”