TBX5 drivesAldh1a2expression to regulate a RA-Hedgehog-Wnt gene regulatory network coordinating cardiopulmonary development

Abstract

The gene regulatory networks that coordinate the development of the cardiac and pulmonary systems are essential for terrestrial life but poorly understood. The T-box transcription factor Tbx5 is critical for both pulmonary specification and heart development, but how these activities are mechanistically integrated remains unclear. We show that Tbx5 regulates an evolutionarily conserved retinoic acid (RA)-Hedgehog-Wnt signaling cascade coordinating cardiopulmonary development. We demonstrate that Tbx5 directly maintains expression of the RA-synthesizing enzyme Aldh1a2 in the foregut lateral plate mesoderm via an intronic enhancer that is evolutionarily conserved among terrestrial vertebrates. Tbx5 promotes posterior second heart field identity in a positive feedback loop with RA, antagonizing a Fgf8-Cyp regulatory module and restricting FGF activity to the anterior. Tbx5/Aldh1a2-dependent RA signaling also directly activates Shh transcription in the adjacent foregut endoderm through the conserved MACS1 enhancer. Epithelial Hedgehog then signals back to the mesoderm, where together with Tbx5 it activates expression of Wnt2/2b that ultimately induce pulmonary fate in the foregut endoderm. These results provide mechanistic insight into the interrelationship between heart and lung development informing cardiopulmonary evolution and birth defects.

Retinoic acid signaling in heart development: Application in the differentiation of cardiovascular lineages from human pluripotent stem cells

“…During embryonic development, Raldh2 is co-expressed with Tbx5 in a subset of pSHF progenitors (Hochgreb et al, 2003;Ryckebusch et al, 2008;De Bono et al, 2018), and Raldh2 knockouts display reduced Tbx5 expression (Niederreither et al, 2001;Sirbu et al, 2008). Furthermore, a recent study revealed that Tbx5 promotes pSHF identity through a positive feedback loop with Raldh2 (Rankin et al, 2021). Importantly, Tbx5 regulates the expression of a key pacemaker gene, Shox2…”

“…Interestingly, both in limb and lung development, where Tbx5 plays an important role, the transcription factor interacts with canonical WNT signaling. Whereas in limb development canonical WNT signaling is upstream of Tbx5, in lung development Tbx5 activates the expression of Wnt2 in cardiopulmonary progenitors (Ng et al, 2002;Nishimoto et al, 2015;Steimle et al, 2018;Rankin et al, 2021). WNT signaling has also been identified as a critical cue for pacemaker development (Bressan et al, 2013;Ren et al, 2019).…”