RESUMEN
Vitamin A is essential for vertebrate embryonic development; dietary carotenoids are the primary source of vitamin A since animals cannot synthesize it de novo. To study the role of beta-carotene during embryonic development, we analyzed in chick embryos the expression of beta,beta-carotene 15,15'-oxygenase (beta-oxy) which cleaves beta-carotene to produce two molecules of retinal. Beta-oxy transcripts were detected in one-and-a-half- to five-day-old embryo homogenates and in situ hybridization in five-day-old embryos, revealing their presence in tissues including the central nervous system, lungs, limbs, and cardiovascular system. Moreover, we detected beta-oxy enzymatic activity in extracts from five-day-old embryos as well as small amounts of beta-carotene in the egg yolk. These results indicate that beta-oxy is present during early developmental stages, raising the possibility that yolk-stored beta-carotene is utilized as a source of vitamin A. Thus, our results suggest that beta-carotene could play an important role in early avian embryonic development as a local source of vitamin A in specific tissues.