Role of retinoic acid (RA) in vertebrate somitogenesis

Determine the functional role of retinoic acid in vertebrate somitogenesis, specifically whether RA is necessary for somite formation and how RA interacts with FGF signaling and left–right asymmetry to influence the determination front and anterior–posterior polarity within somites.

Background

The authors discuss RA forming an anteroposterior gradient opposite to FGF and note phenotypes in RA mutants, including smaller somites and dynamic left–right asymmetries. Yet, RA-null embryos can still form somites, complicating RA’s proposed role in the wavefront and segmentation.

Clarifying whether RA is essential, buffering, or redundant—possibly operating through mutual repression with FGF or via coordination with clock outputs—remains a central unresolved issue for mechanistic models.