RETINOIC ACID AND RETINOIC ACID RECEPTORS IN DEVELOPMENT

The vitamin A derivative retinoic acid (RA) and related compounds (ret inoids) are utilized as signaling molecules in a diverse array of deve lopmental and physiological regulatory professes, including many impor tant in the developing and mature nervous system. Retinoids function b y interaction with high affinity receptors of the nuclear receptor fam ily, which also mediate the effects of steroid and thyroid hormones an d which act in the nucleus as transcription factors. This review summa rizes current knowledge of the molecular mechanisms of retinoid action , the complex role of retinoid receptors in a variety of hormonal sign aling processes, and illustrates current efforts to more fully underst and the biological functions of retinoid receptors through analysis of downstream gene regulatory networks and studies of mouse gene knockou t systems.