Retinoic acid (RA), a putative morphogen in vertebrates, has profound effects on development during embryogenesis, chondrogenesis and differentiation of squamous epithelia. The distribution of the transcripts of the retinoic acid receptor gamma (RAR-gamma) gene has been studied here by in situ hybridization during mouse development from days 6.5 to 15.5 post-coitum (p.c.). RAR-gamma transcripts are detected as early as day 8 p.c. in the presomitic posterior region. Between days 9.5 and 11.5 p.c., the transcripts are uniformly distributed in the mesenchyme of the frontonasal region, pharyngeal arches, limb buds and sclerotomes. At day 12.5 p.c., RAR-gamma transcripts are found in all precartilaginous mesenchymal condensations. From day 13.5 p.c., the transcripts are specifically localized in all cartilages and differentiating squamous keratinizing epithelia, irrespective of their embryological origin. RAR-gamma transcripts are also found in the developing teeth and whisker follicles. The developmental pattern of expression of the RAR-gamma gene suggests that RAR-gamma plays a crucial role for transducing RA signals at the level of gene expression during morphogenesis, chondrogenesis and differentiation of squamous epithelia.

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