Elsevier

Behavioural Brain Research

Volume 243, 15 April 2013, Pages 79-90
Behavioural Brain Research

Research report
Behavioral deficits in an Angelman syndrome model: Effects of genetic background and age

https://doi.org/10.1016/j.bbr.2012.12.052Get rights and content

Abstract

Angelman syndrome (AS) is a severe neurodevelopmental disorder associated with disruption of maternally inherited UBE3A (ubiquitin protein ligase E3A) expression. At the present time, there is no effective treatment for AS. Mouse lines with loss of maternal Ube3a (Ube3am−/p+) recapitulate multiple aspects of the clinical AS profile, including impaired motor coordination, learning deficits, and seizures. Thus, these genetic mouse models could serve as behavioral screens for preclinical efficacy testing, a critical component of drug discovery for AS intervention. However, the severity and consistency of abnormal phenotypes reported in Ube3am−/p+ mice can vary, dependent upon age and background strain, which is problematic for the detection of beneficial drug effects. As part of an ongoing AS drug discovery initiative, we characterized Ube3am−/p+ mice on either a 129S7/SvEvBrd-Hprtb-m2 (129) or C57BL/6J (B6) background across a range of functional domains and ages to identify reproducible and sufficiently large phenotypes suitable for screening therapeutic compounds. The results from the study showed that Ube3am−/p+ mice have significant deficits in acquisition and reversal learning in the Morris water maze. The findings also demonstrated that Ube3am−/p+ mice exhibit motor impairment in a rotarod task, hypoactivity, reduced rearing and marble-burying, and deficient fear conditioning. Overall, these profiles of abnormal phenotypes can provide behavioral targets for evaluating effects of novel therapeutic strategies relevant to AS.

Highlights

Ube3am−/p+ mice had impaired reversal learning in the Morris water maze. ► Deficient acquisition of spatial learning varied across background strain and age. ► Aberrant phenotypes included deficits in rearing, rotarod ability, and marble-burying. ► The C57BL/6J background conferred susceptibility to a range of abnormal behaviors.

Introduction

Angelman syndrome (AS) is a severe genomic imprinting disorder with phenotypes that typically manifest early in childhood. AS is characterized by intellectual disability, speech impairment, motor dysfunction, sleep disturbances, epilepsy, inappropriate laughter, and an unusually happy demeanor [1], [2]. In most cases, AS arises from the deletion or mutation of maternal UBE3A [3], [4], which encodes ubiquitin protein ligase E3A. In neurons, only the maternal copy of UBE3A is active, while the paternally inherited UBE3A allele is silenced [5], [6]. Evidence from mouse lines with targeted disruption of the maternal Ube3a allele supports an important role for UBE3A in neuronal morphology, synaptic function, and the maturation of neocortical circuits in the brain [7], [8], [9], [10]. Maternal Ube3a-deficient mice (Ube3am−/p+ mice) have abnormal phenotypes that resemble many of the clinical symptoms observed in AS, including motor dysfunction, cognitive deficits, and enhanced susceptibility to seizures [11]. Ube3am−/p+ mice also have overt deficiencies in hippocampal long-term potentiation and dendritic spine density, in line with deficits in behavioral tasks, such as contextual fear conditioning and spatial learning in the Morris water maze, which are mediated by the hippocampus [9], [11], [12], [13], [14].

Although no effective treatment currently exists for AS, recent findings utilizing genetic mouse models for the disorder have suggested that abnormal phenotypes can be rescued [12], [14], [15]. For example, van Woerden et al. [14] were able to genetically rescue the deficits in rotarod performance, quadrant selectivity in the water maze, and contextual fear conditioning that characterize Ube3am−/p+ mice. Our research group recently demonstrated that topoisomerase inhibitors can unsilence paternally inherited Ube3a [16], but the possible beneficial effects of these drugs on abnormal behaviors relevant to AS have not yet been established. While the Ube3am−/p+ mice provide a well-validated model for preclinical efficacy testing, there is a critical need to identify the optimal phenotypes to target for reversal in drug discovery studies. Importantly, there are known strain-specific differences in behavioral phenotypes [11]. Moreover, even in the most carefully controlled studies, it can be difficult to find behavioral phenotypes sufficiently penetrant for inter-species, inter-laboratory, and intra-laboratory reproducibility [17]. We therefore sought to identify AS phenotypes of sufficient magnitude and consistency to be suitable for screening potential therapeutics. Toward this goal, the present studies evaluated Ube3am−/p+ mice on two different genetic backgrounds, either 129S7/SvEvBrd-Hprtb-m2 (129) or C57BL/6J (B6), using multi-component phenotyping regimens and testing at different ages. Because clinical studies have linked genotype to differential developmental trajectories in AS [18], separate cohorts of B6 mice were evaluated, beginning from either adolescence or adulthood, to examine both phenotypic trajectories and reproducibility.

Section snippets

Animals

Subjects were heterozygous mice with maternal deficiency of Ube3a (Ube3am−/p+) and wild type (Ube3am+/p+) littermates, on two different background strains: 129S7/SvEvBrd-Hprtb-m2 (129) and C57BL/6J (B6) [11]. The Ube3am+/p− mice on a 129 strain background were developed by the Beaudet laboratory [11] and were obtained from Jackson Laboratory (Bar Harbor, ME). The Ube3am−/p+ mice on a B6 background were originally developed by the Beaudet laboratory [11] and were backcrossed at least 10

Weight

In line with previous reports [14], maternal-deficiency of Ube3a led to significantly increased body weight in almost all of the Ube3am−/p+ groups (Fig. 1). Higher body weights were most pronounced in the female mice on a 129 background [repeated measures ANOVA; genotype main effect, F(1,10) = 7.33, p = 0.0221], and on a B6 background [genotype × age interaction, F(4,44) = 13.25, p < 0.0001]. The increased body weights were also observed in the male mice on a B6 background [B6 males, cohort 1; genotype × 

Discussion

The present studies demonstrate that AS-like behavioral phenotypes in Ube3am−/p+ mice can vary across genetic background, age at testing, and cohort group. In particular, Ube3am−/p+ mice on the B6 background exhibited motor deficits and impaired acquisition of spatial learning, dependent on age and cohort. Marked deficits in spatial learning acquisition were found in B6 mice at 16 weeks of age, but not at 8 weeks of age, suggesting progressive loss of cognitive function across time. In

Acknowledgments

The authors wish to thank Dr. Yong-hui Jiang for his kind generosity in providing Ube3a breeding pairs for our colony. This work was supported by the Simons Foundation, the Angelman Syndrome Foundation, NIMH grant 1R01MH093372 to BDP, and NICHD grant P30HD03110 to Dr. Joe Piven. These sponsors did not have involvement in study design, data collection, analysis, or interpretation, writing the report, or decision to submit the article for publication.

References (34)

  • W. Paradee et al.

    Fragile X mouse: strain effects of knockout phenotype and evidence suggesting deficient amygdala function

    Neuroscience

    (1999)
  • D. Van Dam et al.

    Spatial learning, contextual fear conditioning and conditioned emotional response in Fmr1 knockout mice

    Behavioural Brain Research

    (2000)
  • H. Angelman

    “Puppet” children. A report on three cases

    Developmental Medicine and Child Neurology

    (1965)
  • T. Matsuura et al.

    De novo truncating mutations in E6-AP ubiquitin-protein ligase gene (UBE3A) in Angelman syndrome

    Nature Genetics

    (1997)
  • T. Kishino et al.

    UBE3A/E6-AP mutations cause Angelman syndrome

    Nature Genetics

    (1997)
  • U. Albrecht et al.

    Imprinted expression of the murine Angelman syndrome gene, Ube3a, in hippocampal and Purkinje neurons

    Nature Genetics

    (1997)
  • C. Rougeulle et al.

    The Angelman syndrome candidate gene, UBE3A/E6-AP, is imprinted in brain

    Nature Genetics

    (1997)
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