Developmental analysis of the retinoic acid-inducible RAR-βJ2 promoter in transgenic animals

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Abstract
Retinoic acid (RA) is a signalling molecule important for pattern formation during development. There are three known types of nuclear receptors for RA in mammals, RAR-α, RAR-β and RAR-γ, which transduce the RA signal by inducing or repressing the transcription of target genes. Here we describe the developmental expression pattern of the mouse RAR-β2 promoter. Independent lines of transgenic animals expressing RAR-β2 promoter sequences fused to the E. coil β- galactosidase gene were examined throughout the course of embryogenesis and found to exhibit reproducible and specific patterns of β-galactosidase expression in a majority of sites that have been shown previously to contain mRAR-β transcripts. In the limbs, mRAR-β2 promoter activity and mRAR-β transcripts were both excluded from precartilagenous condensations; interestingly, mRAR-β2 promoter activity was observed in the apical ectodermal ridge (AER) where mRAR-β transcripts could not be detected, while no mRAR-β2 promoter activity or mRAR-β transcripts were associated with the limb region that contains the zone of polarizing activity (ZPA). Analysis of the lacZ expression pattern in embryos from mothers treated with teratogenic doses of RA, indicated that mRAR-β2 promoter is selectively induced in a manner suggesting that overexpression of the mRAR-β2 isoform is involved in RA-generated malformations. The normal and induced expression pattern of the mRAR-β2 promoter suggests several possible roles for mRAR-β2 in development of the limbs, as an inhibitor of cartilage formation, in programmed cell death and in the formation of loose connective tissue.