(A,B) Detection of RALDH2 expression in E7.0 and E8.0 embryos by whole mount in situ hybridization. RALDH2 is expressed more strongly in neck skin than in body skin and is also detected in the neural tube (midline). (C,D) RALDH3 is expressed broadly in neck skin at E7.0 and moves laterally by E8.0. (E) Expression of the RA target gene DHRS3 in skin cultured from E7.0 for 2 d in the presence or absence of 5 µM RA. Both neck and body skin respond to RA. (F,G) In vivo DHRS3 is expressed on the neck, but not the feather tract of the body. (H) Quantitative RT-PCR detecting RALDH2, RALDH3, and DHRS3 expression in neck and body skin from E6 to E10. The disparity between neck and body skin is greatest at E7 and E8, when feather patterning is taking place. DHRS3 levels track RALDH2 expression dynamics more closely than those of RALDH3. (I) Quantitative RT-PCR detection of RALDH2, RALDH3, and DHRS3 expression in separated epidermis (Epi) and dermis (Derm) at E7.0. The RA producing enzymes are expressed in the dermis, while RA target gene expression is activated in the epidermis.