RARβ2 is required for vertebrate somitogenesis
Abstract
During vertebrate somitogenesis, retinoic acid determines where new somites can form along the body’s anteroposterior axis by establishing the position of the determination wavefront. However, the role of RAR in somite patterning, rostral-caudal boundary setting, myotome subdivision specialization, and the specific RAR subtype involved remains less clear. Investigating RARβ has been difficult due to a lack of distinct embryonic phenotypes in murine loss-of-function studies. Using the Xenopus model, we demonstrate that RARβ2 is crucial for regulating somite number and size, the restriction of the presomitic mesoderm’s anterior border, somite chevron shape, and hypaxial myoblast migration. RARβ2 is the RAR subtype most responsive to ligand expression, and its localization in trunk somites allows it to effectively respond to retinoid levels during somitogenesis. It positively regulates Tbx3, a marker of hypaxial muscle, and negatively regulates Tbx6 through Ripply2 to control the anterior boundaries of the presomitic mesoderm and caudal progenitor pool. These findings reveal a novel and essential role for RARβ2 in vertebrate somitogenesis.