TGF-beta receptor type I (TGFR1) forms a receptor comple, Xenopus/Amphibian, consisting of two type II and two type I transmembrane serine/threonine kinases. Type II receptors phosphorylate and activate type I receptors that autophosphorylate and activate SMAD transcriptional regulators. Although TGFR1 is ubiquitously e, Xenopus/Amphibian,pressed, it is found most abundant in placenta and least abundant in brain and heart. Defects in TGFBR1 are the cause of Loeys-Dietz syndrome type 1 and 2 (aortic aneurysm syndromes).