Heterozygous mutation or deletion of the retinoic acid induced 1 (RAI1) gene results in Smith-Magenis syndrome while duplication of the genomic region containing RAI1 results in the dup(17)(p11.2) syndrome. SMS is a complex syndrome that encompasses developmental, physical, and behavioral abnormalities. Persons with SMS have variable developmental delays, mild craniofacial anomalies, obesity, and significant abnormalities in sleep, circadian rhythm, attention, and self-control. Individuals with RAI1 mutations exhibit overgrowth, with all reported cases at >90th percentile for height and weight. Interestingly, individuals with dup(17)(p11.2) display developmental delays, behavioral problems, and autism spectrum disorder, in addition to significant pre- and post-natal growth delays. Further supporting the human data, mice overexpressing Rai1 are growth delayed, while those with a heterozygous targeted knockout of Rai1 are obese, and both mouse models have neurological deficits. Taken together, these findings strongly suggest that gene dosage of RAI1 is critical for normal development, behavior, and growth. The overall goal of this application is to determine the biological role of RAI1 in the cell. The studies proposed seek to develop zebrafish as model for studying gene dosage requirements for rai1. The following studies are proposed: 1) Determine spatial and temporal expression of rai1 in zebrafish embryos by RNA in situ hybridization and assess the effect of retinoic acid (presence or absence) on this expression. 2) Develop zebrafish models to assess rai1 dosage threshold requirements and the primary developmental defects associated with reduced, absent, or increased expression of rai1. 3) Evaluate the functional consequences of rai1 knockdown or overexpression on the expression of putative RAI1-regulated genes. Thus, the studies proposed here will: 1) investigate the hypothesis that RAI1 is regulated by retinoic acid;2) create an rai1 antisense morpholino model to evaluate the effects of rai1 knockdown and an rai1 overexpression transgenic model to assess dosage effects;and 3) investigate putative RAI1-interacting genes utilizing the rai1 morpholino and transgenic models. Understanding the developmental and behavioral effects of rai1 gene dosage is critical. Disorders involving gene dosage, such as Smith-Magenis and dup(17)(p11.2) syndromes, together function as an ideal model in which to study a gene that has significant broader implications for common human phenotypes, including disorders involving sleep, mental illness, behavior disorders, and obesity. Thus, the investigators'studies will show that RAI1 regulates genes involved in development, obesity, sleep, and behavior, and that retinoic acid is a tissue-specific regulator for normal RAI1 function. PROJECT NARRATIVE: The proposed studies focus on a gene called RAI1 that plays a role in normal development. The project is focused toward developing a zebrafish model in which to study this gene.
Development, behavior, and growth involve complex processes encompassing many genes and pathways. Understanding these pathways is important for continued advances in healthcare for the general population. The proposed studies focus on a gene called RAI1 that when deleted or mutated causes obesity, behavior and learning problems, sleep dysfunction, and other anomalies. When this same gene is duplicated, individuals also have learning and behavior problems such as attention-deficit, hyperactivity, and autism- spectrum disorder;however, these individuals are instead growth-delayed. These findings support a role for RAI1 in normal development, growth, and behavior. Thus, understanding the role this protein plays in the cell and the pathways in which it functions is crucial to our knowledge of common, often chronic, debilitating disorders such as obesity, sleep disturbance, autism, and mental illness, commonly seen in the general population. This project is focused toward developing a zebrafish model in which to study rai1. The zebrafish offers an excellent system in which to study normal gene expression, gene expression related to environmental changes, and gene:gene interactions which are not easily evaluated in any other vertebrate system. Development of a genetic model for rai1 wherein gene dosage can be easily manipulated further supports the use of zebrafish for the proposed studies.
