Retinoic Acid Synthesis in the Developing Spinal Cord

Abstract

The lipid retinoic acid is the activating ligand for a diverse group of transcription factors, the retinoic acid receptors, which are members of the superfamily of nuclear receptors that include, in addition, the receptors for thyroid hormone, steroids and vitamin D (Chambon et al. 1991; Mangelsdorf 1993). Expression of more than 100 proteins is known to be regulated by retinoic acid (Chytil and ul-Haq 1990). While much has been learned in recent years about the mechanisms of retinoic-acid mediated transcriptional regulation, relatively little was known about the enzymes that catalyze the oxidation of retinaldehyde to retinoic acid in the developing embryo. We previously developed a technique for the detection of such enzymes based on retinoic acid reporter cells (Wagner, Han, and Jessell 1992): tissue extracts are separated by isoelectric focussing gel electrophoresis, the gel is cut into thin consecutive slices, from which the proteins are eluted and assayed for capacity to synthesize retinoic acid from added retinaldehyde (McCaffery et al. 1992). This technique requires only minute amounts of tissue, and it makes it possible to analyze detailed patterns of retinoic acid synthesis in the developing embryo.