Michael V. Morabito¹, Atheir I. Abbas³, Jennifer L. Veale¹, Robert A. Kesterson⁴, Michelle M. Jacobs¹, David S. Kump⁴, James L. Resnick⁵, Bryan L. Roth⁶ & Ronald B. Emeson^1,2 

Center for Molecular Neuroscience¹ and Department of Pharmacology², Vanderbilt Uni­vers­i­ty; Depart­ment of Biochemistry³, Case Western Reserve Univers­ity School of Medicine; Department of Genetics⁴, University of Alabama at Birmingham; Department of Molecular Genetics and Microbiology⁵, University of Florida; Department of Pharma­cology⁶, University of North Carolina, Chapel Hill 

Introduction: RNA transcripts encoding the 2C-subtype of serotonin receptor (5HT_2CR) undergo up to five A-to-I editing events to generate as many as 24 distinct 5HT_2CR iso­forms. These editing events can alter the identity of three amino acids within the second intra­cellular loop of the receptor to reduce the efficacy of receptor:G-protein interactions and silence the constitutive activity of edited 5HT_2C receptors. Sequence analysis of cDNAs isolated from dissected rat, mouse and human brains have predicted the reg­ion-specific expression of diverse 5HT_2CR isoforms, suggesting that differentially edited 5HT_2C receptors may serve distinct biological functions in those regions in which they are expressed. 

Methods: To assess the physiologic importance for generating multiple, edited 5HT_2C receptors in the central nervous system, we have created mutant mice that solely express the fully-edited (VGV) isoform of the receptor. 

Results: Mutant animals solely expressing the fully-edited isoform of the 5HT_2CR pre­sent phenotypic charac­teristics of Prader-Willi Syndrome (PWS), an imprinted human disor­der resulting from a loss of paternal gene expression on chromosome 15q11-13, including a failure to thrive, decreased somatic growth and neonatal muscular hypotonia, followed by post-weaning hyperphagia. The changes in food consumption in mutant animals are con­sis­tent with alterations in the expression of hypothalamic transcripts encoding neuropep­tide Y (NPY) and proopio­mel­an­o­cort­in (POMC). The observed pheno­typic altera­tions share fur­ther similar­i­ties with other mouse models of PWS where deletions within the syntenic por­tion of the imprint­ing center on chromosome 7 also resulted in neonatal lethal­ity on a C57BL/6 back­ground. While steady-state 5HT_2CR mRNA levels are unchanged in mutant mice, alter­na­tive 5HT_2CR splicing patterns are affected in a manner consistent with decreased inter­ac­tion be­tween MBII-52 transcripts, small nucleolar RNAs encoded in the PWS critical region, and 5HT_2CR pre-mRNAs. 5HT_2CR protein levels are increased 40-to-70-fold in dis­tinct brain reg­ions of mutant mice, indicating important post-tran­scrip­tional mechanisms for modulat­ing 5HT_2CR pro­tein expression.  

Conclusion: The 5HT_2CR gene is the first locus outside the PWS critical region in which mutations can recapitulate multiple aspects of this human genetic disorder, implicating serotonergic dysfunction in the etiology of PWS and demonstrating the physiologic import­ance of normal pat­terns of 5HT_2CR editing in vivo.

Edited: 02/09/2012