Expression of retinoic acid receptor genes in fetal and newborn rat lung

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Abstract
Lung differentiation and development are affected by vitamin A and its metabolites. One mechanism through which retinoids might exert their effects is through nuclear retinoic acid receptors (RAR). The gene expression profile of the RAR family (α, β, γ) has previously been determined in both the developing mouse embryo to 14.5 days gestation,28–30 and in the adult The purpose of this study was to determine the expression of the RAR genes during the period of gestation that results in the formation of the saccular lung stage. Total RNA was extracted from fetal lungs of Sprague-Dawley rats at gestational days 17, 19,20, 21, and 22, and from 12-hour-old newborns for Northern hybridization. Two transcripts of RAR α mRNA (3.7 and 2.7 kb) were found at each time point. At day 17, the 2.7 kb RAR α mRNA was increased two-fold or more than at any other time studied. At days 19–22 the levels of the 3.7 kb RAR α species were also lower than day 17 and newborn levels. One RAR p mRNA transcript (3.4 kb), present at all time points, was significantly higher in the newborn than on days 17–22. Expression of RAR γ mRNA could only be demonstrated by reverse transcriptase-polymerase chain reaction. We speculate that the higher RAR (Y species at day 17 indicates a role for RAR α in the maintenance of the columnar epithelial cells of the glandular phase of lung development. The significant rise at birth of RAR β expression, after being low from days 17–22, suggests its relationship to completion of terminal saccule formation and preparation for subsequent alveolarization. Pediatr Pulmonol. 1994; 17:234–238.