Distribution of retinoids in the chick limb bud: analysis with monoclonal antibody.

Retinoic acid induces anteroposterior duplicate formation in developing chick limb bud, and it may be a natural morphogen involved in limb pattern formation. Retinoic acid is produced from retinol locally in the limb bud via retinal, and thus, to elucidate the distribution of these retinoids in the limb bud seems to be important for the understanding of the morphogen formation. We produced a monoclonal antibody against the retinoids with BSA-RA (bovine serum albumin-retinoic acid) conjugate for antigen, and investigated the distribution of retinoids in the chick limb bud. The antibody predominantly bound to retinoic acid, but weakly to retinol and retinal. Retinoids appeared in the limb bud at stage 18 and were distributed through stages 20-24, when the pattern formation in distal mesoderm was in progress. Initially they were found evenly in the whole mesoderm, but disappeared gradually from core mesoderm and remained only in the region of peripheral mesoderm at stage 24. At stage 26, retinoids were detected only in ectoderm. These results support the idea that the retinoids actually play roles in limb pattern formation and suggest that the retinoids in the peripheral mesoderm are important for pattern formation. Further, the role of retinoids in epidermis development at later limb bud stages is also suggested.