Coordinated regulation of striatum-enriched molecules by retinoic acid in the developing striatum

• Main Authors: Hsiao-Fang Wang, 王小芳
• Other Authors: Fu-Chin Liu
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/75068373750473612095

碩士 === 國立陽明大學 === 神經科學研究所 === 87 === Retinoic acid (RA), a derivative of vitamin A, is essential for the normal development of the hindbrain. The developmental effects of RA are mediated by activation of retinoid receptors which are ligand-dependent transcription factors. Although RA has been shown to play an important role in the hindbrain development, its developmental regulation in the forebrain remains elusive. Several RA-related molecules, including the cellular retinol binding protein type I, the cellular retinoic acid binding proteins type I and II, RARb and RXRg were found to be highly expressed in the developing striatum. The preferential expression of these RA signaling molecules in the developing striatum raised the possibility that activation of RA signaling pathways may selectively regulate the development of striatal phenotype, which is characterized by expression of striatum-enriched molecules. We thus hypothesized that activation of RARb and RXRg may regulate the expression of striatum-enriched genes. To test this hypothesis, my first line of study was focused on screening of striatum-enriched signal transduction molecules that may respond to RA regulation. We cultured embryonic day 15 striatal explant in the presence of all-trans RA (1 mM) or 9-cis RA (1 mM) for 1 or 3 days in vitro. We also cultured cortical explants for comparison. The expression levels of striatum-enriched genes were quantified by the RNase protection assay. We found that RA could up-regulate the expression of a set of dopamine signaling transduction molecules, including D1R, Golf, ACV, DARPP-32, STEP and CaMPDE-63kD. By contrast, the expression of these dopamine signaling molecules was not affected in the cortical culture. Neither all-trans nor 9-cis RA altered the mRNA levels of MAP-2, a neuronal marker. Thus the up-regulation expression of dopamine signaling molecules by RA was not due to general enhancement of neuronal differentiation, and moreover, the effects appear to be region-specific. The second line of my study was focused on transcription factors that may respond to RA regulation. We found that RA could reduce in striatal explants the mRNA level of Islet-1, a LIM homeodomain transcription factor that is primarily expressed in the basal part of the nervous system. Reduction of Islet-1/2 mRNA expression also was found in the postnatal development of striatum in vivo. We immunocytochemically studied the distribution of Islet-1/2 protein expression in the developing striatum. The results indicated that the Islet-1/2 expression was already highly expressed in the E15 striatal primordium, but was dramatically reduced in the striatum during postnatal development. The remained Islet-1/2-expressed cells in the postnatal striatum were found to co-express choline acetyltransferase, a synthetic enzyme for acetylcholine, by double immunocytochemistry. These data suggest that RA may be involved in regulating development of striatal cholinergic neurons. Collectively, our findings suggest that RA may play an important role in development of striatum by coordinately regulating striatum-enriched genes.