An Unexpected Function of the Prader-Willi Syndrome Imprinting Center in Maternal Imprinting in Mice

Genomic imprinting is a phenomenon that some genes are expressed differentially according to the parent of origin. Prader-Willi syndrome (PWS) and Angelman syndrome (AS) are neurobehavioral disorders caused by deficiency of imprinted gene expression from paternal and maternal chromosome 15q11–q13, respectively. Imprinted genes at the PWS/AS domain are regulated through a bipartite imprinting center, the PWS-IC and AS-IC. The PWS-IC activates paternal-specific gene expression and is responsible for the paternal imprint, whereas the AS-IC functions in the maternal imprint by allele-specific repression of the PWS-IC to prevent the paternal imprinting program. Although mouse chromosome 7C has a conserved PWS/AS imprinted domain, the mouse equivalent of the human AS-IC element has not yet been identified. Here, we suggest another dimension that the PWS-IC also functions in maternal imprinting by negatively regulating the paternally expressed imprinted genes in mice, in contrast to its known function as a positive regulator for paternal-specific gene expression. Using a mouse model carrying a 4.8-kb deletion at the PWS-IC, we demonstrated that maternal transmission of the PWS-IC deletion resulted in a maternal imprinting defect with activation of the paternally expressed imprinted genes and decreased expression of the maternally expressed imprinted gene on the maternal chromosome, accompanied by alteration of the maternal epigenotype toward a paternal state spread over the PWS/AS domain. The functional significance of this acquired paternal pattern of gene expression was demonstrated by the ability to complement PWS phenotypes by maternal inheritance of the PWS-IC deletion, which is in stark contrast to paternal inheritance of the PWS-IC deletion that resulted in the PWS phenotypes. Importantly, low levels of expression of the paternally expressed imprinted genes are sufficient to rescue postnatal lethality and growth retardation in two PWS mouse models. These findings open the opportunity for a novel approach to the treatment of PWS

5-HT2CR pre-RNA editing, alternate splicing and function in a mouse model of Prader-Willi syndrome

Prader–Willi syndrome (PWS) is a complex genetic disorder caused by the loss of paternal gene expression from chromosome 15q11-q13. In addition to a number of coding genes, there are several imprinted small nucleolar (sno)RNAs present in the PWS cluster. Recent research has demonstrated that one of these, HBII-52, has a regulatory function in that it reduces alternate splicing of the RNA-editing region of the serotonin 2C receptor (5-HT2CR) pre-RNA, and that loss of expression of this snoRNA may lead to abnormal molecular processing of 5-HT2CR in the PWS brain. In turn, these molecular modifications of 5-HT2CR pre-RNA lead to a much less functional receptor. Using a mouse model of PWS (PWS-IC+/del) we are investigating the consequences of the loss of mbii-52 (mouse homologue of HBII-52) for 5- HT2CR functioning at a molecular, neurochemical and behavioural level. To achieve this we have examined the brains of adult PWS-IC+/del mice and found altered levels of expression and alternate splicing of 5-HT2CR. We are now examining RNA editing at five key sites of the 5-HT2CR pre-RNA. Behavioural studies, using a cohort of 64 mixed gender mice (28 PWS-IC +/del, 36 Wild Type (WT), weight range 19–65 g) are focussing on those known to be influenced by serotonin. These include spontaneous behaviours, such as marble burying and locomotor activity, and complex cognitive processes. PWS-IC+/del mice are hypoactive, but were no different to WT mice in the marble burying test. Importantly, marble burying behaviour was also not to be affected by dosing with the 5-HT2CR antagonist SB242084, demonstrating a degree of specificity of any 5- HT deficits in the PWS-IC+/del mice. We are now using the 5-choice serial reaction time test (5-csrtt) to examine aspects of attention and impulse control. The specificity of any deficits in the PWS-IC+/del mice and will be tested by examining the effects of pharmacological manipulations with 5-HT2CR and 5-HT2AR drugs. Our findings suggest that abnormalities in 5-HT2CR functioning may underlie aspects of the behavioural phenotype seen in PWS, and that the imprinted snoRNA mbii-52 plays an important role in sculpting brain and behaviour

Loss of the imprinted snoRNA mbii-52 leads to increased 5htr2c pre-RNA editing and altered 5HT2CR-mediated behaviour

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. 5HT2CRs 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+/−), 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 5HT2CR-related behaviours, including impulsive responding, locomotor activity and reactivity to palatable foodstuffs. In a non-5HT2CR-related behaviour, marble burying, loss of mbii-52 was without effect. The specificity of the behavioural effects to changes in 5HT2CR 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

Reduction of nitrate in water over supported nickel catalysts toward purification of polluted groundwater [an abstract of dissertation and a summary of dissertation review]

Prader–Willi syndrome (PWS), a neurodevelopmental disorder caused by loss of paternal gene expression from 15q11–q13, is characterised by growth retardation, hyperphagia and obesity. However, as single gene mutation mouse models for this condition display an incomplete spectrum of the PWS phenotype, we have characterised the metabolic impairment in a mouse model for ‘full’ PWS, in which deletion of the imprinting centre (IC) abolishes paternal gene expression from the entire PWS cluster. We show that PWS-ICdel mice displayed postnatal growth retardation, with reduced body weight, hyperghrelinaemia and marked abdominal leanness; proportionate retroperitoneal, epididymal/omental and inguinal white adipose tissue (WAT) weights being reduced by 82%, 84% and 67%, respectively. PWS-ICdel mice also displayed a 48% reduction in proportionate interscapular brown adipose tissue (isBAT) weight with significant ‘beiging’ of abdominal WAT, and a 2°C increase in interscapular surface body temperature. Maintenance of PWS-ICdel mice under thermoneutral conditions (30°C) suppressed the thermogenic activity in PWS-ICdel males, but failed to elevate the abdominal WAT weight, possibly due to a normalisation of caloric intake. Interestingly, PWS-ICdel mice also showed exaggerated food hoarding behaviour with standard and high-fat diets, but despite becoming hyperphagic when switched to a high-fat diet, PWS-ICdel mice failed to gain weight. This evidence indicates that, unlike humans with PWS, loss of paternal gene expression from the PWS cluster in mice results in abdominal leanness. Although reduced subcutaneous insulation may lead to exaggerated heat loss and thermogenesis, abdominal leanness is likely to arise from a reduced lipid storage capacity rather than increased energy utilisation in BAT

Impact of Serotonin (5-HT)2C Receptors On Executive Control Processes

Although the serotonin (5-hydroxytryptamine, 5-HT) neurotransmitter system has been implicated in modulating executive control processes such as attention, response inhibition, and behavioral flexibility, the contributions of particular serotonin receptors remain unclear. Here, using operant-based behavioral paradigms, we demonstrate that mice with genetically ablated 5-HT(2C) receptors (2CKO mice) display deficits in executive functions. 2CKO mice were impaired in the acquisition of a visuospatial attention task as assessed in the 5-choice serial reaction time task (5-CSRTT). In this task, 2CKO mice exhibited marked impairment of attentional processes, with normal response inhibition. We assessed dynamic changes in neurotransmitter levels within the nucleus accumbens (NAc) by in vivo microdialysis in task-performing animals. Extracellular dopamine concentrations were elevated in the NAc of 2CKO mice during task performance, indicating that 5-HT(2C) receptors impact dopamine homeostasis during a visuospatial attention task. These findings raise the possibility that disinhibition of mesolimbic dopamine pathways contributes to impaired attention and perturbed task performance in 2CKO mice. Additionally, in a spatial reversal learning task, 2CKO mice failed to improve their performance over a series of reversals, indicating that intact 5-HT(2C) receptor signaling is required to accurately respond to repeated changes in reward contingencies. In contrast to the 2CKO phenotype in the 5-CSRTT, wild-type mice treated with the 5-HT(2C) receptor antagonist SB242084 exhibited diminished response inhibition, suggesting differing effects of acute pharmacological blockade and constitutive loss of 5-HT(2C) receptor activity. Altogether, these findings provide insights into the serotonergic regulation of executive control processes and suggest that impaired 5-HT(2C) receptor signaling during development may predispose to executive function disorders