Mechanism of Retinoic Acid-Induced Neural Tube Defects-The Role of the Retinoic Acid Receptors RAR-Beta and RAR-GammaEPA Grant Number: U915462
Title: Mechanism of Retinoic Acid-Induced Neural Tube Defects-The Role of the Retinoic Acid Receptors RAR-Beta and RAR-Gamma
Investigators: Mao, Gloria
Institution: University of California - Los Angeles
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 1998 through September 1, 2001
Project Amount: $39,178
RFA: STAR Graduate Fellowships (1998) RFA Text | Recipients Lists
Research Category: Fellowship - Toxicology , Health Effects , Academic Fellowships
The objective of this research project is to determine whether: (1) Retinoic Acid Receptor (RAR)-beta or RAR-gamma isoforms are specifically expressed during neurulation; (2) the switch in expression from RAR-gamma in the open neural tube to RAR-beta in the closed neural tube is essential for posterior neural tube closure; and (3) retinoic acid or genetic mutations, which induce neural tube defects, disrupt RAR-beta or RAR-gamma expression. Excess retinoic acid, a metabolite of vitamin A (retinol), causes developmental malformations including the neural tube closure defect spina bifida in the mouse. The effects of retinoic acid are mediated by RARs and Retinoid X Receptors (RXRs) (receptors that act as regulatory gene transcription factors). RAR has three subtypes: alpha, beta, and gamma; additionally, each subtype has several isoforms. Neural tube closure in the posterior neural tube is associated with a change in expression from RAR-gamma in the open neural tube to RAR-beta after closure. Retinoic acid can regulate the expression of RAR-beta and RAR-gamma, which poses the question of whether retinoic acid disrupts neural tube closure by perturbing the normal expression patterns of RAR-beta and RAR-gamma.
RAR-beta and RAR-gamma isoform expression levels have been quantitated by ribonuclease protection assays, and their expression patterns have been determined by whole-mount in situ hybridization in mouse embryos during neurulation. The regulation of RAR-beta and RAR-gamma expression has been examined by similar methods in embryos that have neural tube defects induced by retinoic acid. This research project has shown that in retinoic acid-treated embryos, RAR-gamma downregulation in the closing neural tube and RAR-beta upregulation in the closed neural tube occurred normally, and were not disrupted by retinoic acid. Additionally, the transition from RAR-gamma to RAR-beta expression has been examined in Splotch mutant mice that develop posterior neural tube defects. Identifying genes involved in neural tube closure will be accomplished by using cDNA expression array techniques to determine differences in gene expression before and after neural tube closure or after retinoic acid treatment.