The Prader -Willi syndrome (PWS) genetic interval contains several brain-expressed small nucleolar (sno)RNA species that are subject to genomic imprinting. In vitro studies have shown that one of these snoRNA molecules, h/mbii-52, negatively regulates editing and alternative splicing of the serotonin 2C receptor (5htr2c) pre-RNA. However, the functional consequences of loss of h/mbii-52 and subsequent increased post-transcriptional modification of 5htr2c are unknown. 5HT 2C Rs are important in controlling aspects of cognition and the cessation of feeding, and disruption of their function may underlie some of the psychiatric and feeding abnormalities seen in PWS. In a mouse model for PWS lacking expression of mbii-52 (PWS-IC 1/2 ), we show an increase in editing, but not alternative splicing, of the 5htr2c pre-RNA. This change in post-transcriptional modification is associated with alterations in a number of 5HT 2C R-related behaviours, including impulsive responding, locomotor activity and reactivity to palatable foodstuffs. In a non-5HT 2C Rrelated behaviour, marble burying, loss of mbii-52 was without effect. The specificity of the behavioural effects to changes in 5HT 2C R function was further confirmed using drug challenges. These data illustrate, for the first time, the physiological consequences of altered RNA editing of 5htr2c linked to mbii-52 loss that may underlie specific aspects of the complex PWS phenotype and point to an important functional role for this imprinted snoRNA.

The genes in the imprinted cluster on human chromosome 15q11-q13 are known to contribute to psychiatric conditions such as schizophrenia and autism. Major disruptions of this interval leading to a lack of paternal allele expression give rise to Prader-Willi syndrome (PWS), a neurodevelopmental disorder with core symptoms of a failure to thrive in infancy and, on emergence from infancy, learning disabilities and over-eating. Individuals with PWS also display a number of behavioural problems and an increased incidence of neuropsychiatric abnormalities, which recent work indicates involve aspects of frontal dysfunction. To begin to examine the contribution of genes in this interval to relevant psychological and behavioural phenotypes, we exploited the imprinting centre (IC) deletion mouse model for PWS (PWS-IC(+/-)) and the five-choice serial reaction time task (5-CSRTT), which is primarily an assay of visuospatial attention and response control that is highly sensitive to frontal manipulations. Locomotor activity, open-field behaviour and sensorimotor gating were also assessed. PWS-IC(+/-) mice displayed reduced locomotor activity, increased acoustic startle responses and decreased prepulse inhibition of startle responses. In the 5-CSRTT, the PWS-IC(+/-) mice showed deficits in discriminative response accuracy, increased correct reaction times and increased omissions. Task manipulations confirmed that these differences were likely to be due to impaired attention. Our data recapitulate several aspects of the PWS clinical condition, including findings consistent with frontal abnormalities, and may indicate novel contributions of the imprinted genes found in 15q11-q13 to behavioural and cognitive function generally.