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. 2017 Aug 16;7(1):8451.
doi: 10.1038/s41598-017-08825-x.

Strain-dependence of the Angelman Syndrome Phenotypes in Ube3a Maternal Deficiency Mice

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Free PMC article

Strain-dependence of the Angelman Syndrome Phenotypes in Ube3a Maternal Deficiency Mice

Heather A Born et al. Sci Rep. .
Free PMC article

Abstract

Angelman syndrome (AS) is a genetic neurodevelopmental disorder, most commonly caused by deletion or mutation of the maternal allele of the UBE3A gene, with behavioral phenotypes and seizures as key features. Currently no treatment is available, and therapeutics are often ineffective in controlling AS-associated seizures. Previous publications using the Ube3a maternal deletion model have shown behavioral and seizure susceptibility phenotypes, however findings have been variable and merit characterization of electroencephalographic (EEG) activity. In this study, we extend previous studies comparing the effect of genetic background on the AS phenotype by investigating the behavioral profile, EEG activity, and seizure threshold. AS C57BL/6J mice displayed robust behavioral impairments, spontaneous EEG polyspikes, and increased cortical and hippocampal power primarily driven by delta and theta frequencies. AS 129 mice performed poorly on wire hang and contextual fear conditioning and exhibited a lower seizure threshold and altered spectral power. AS F1 hybrid mice (C57BL/6J × 129) showed milder behavioral impairments, infrequent EEG polyspikes, and fewer spectral power alterations. These findings indicate the effect of common genetic backgrounds on the Ube3a maternal deletion behavioral, EEG, and seizure threshold phenotypes. Our results will inform future studies on the optimal strain for evaluating therapeutics with different AS-like phenotypes.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Timeline for behavioral battery of activity, anxiety, motor, and learning and memory tests.
Figure 2
Figure 2
Strain dependent changes in activity, anxiety, and marble burying found in AS mice. Open field assessment (OFA), elevated plus maze (EPM), and marble burying tests highlighted differences between Wt and AS mice, as well as differences in activity levels between background strains. (a,b) Both B6 and F1 hybrid AS mice showed significant hypoactivity in the open field through distance travelled and number of rearing episodes (vertical activity). (c) No differences were found between Wt and AS mice in the OFA measure of anxiety, % distance travelled in center zone. (d) B6 AS mice spent significantly less time in the closed arms of the EPM. (e) B6 and F1 hybrid AS mice buried significantly less marbles than Wt mice. The 129 mice showed low amounts of locomotor activity and marble burying compared to the B6 and F1 hybrid mice. For each strain, AS and Wt mice were compared with a Student’s t-test and data are shown as the mean ± SEM, *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.
Figure 3
Figure 3
AS mice from all three backgrounds performed poorly on motor testing. (a) Adult AS mice from all three backgrounds performed normally on the inverted screen test. (b) AS mice from the B6 and 129 backgrounds spent significantly less time on the wire hang test before fall compared to Wt mice. For each strain, AS and Wt mice were compared with a Student’s t-test and data are shown as the mean ± SEM, *p < 0.05, ***p < 0.001. (c–e) When tested with the accelerating rotarod protocol, B6 and F1 hybrid mice performed significantly worse than Wt mice. Rotarod results were analyzed with 2-way ANOVA and Bonferroni posttest; n = 15–16 mice/group; *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.
Figure 4
Figure 4
AS mice showed strain-dependent learning and memory deficits. (a) The B6 Wt mice spent significantly more time with the novel object and were successful in the NOR task, while the B6 AS mice showed a similar preference for both objects. (b) Both the 129 AS and Wt mice performed poorly on NOR. (c) The F1 hybrid AS and Wt mice both showed a significant preference for the novel object. (d) The 129 AS mice showed a significant decrease in freezing behavior compared to Wt mice during the 24 hour context test indicating decreased fear memory. No significant difference in % time freezing was seen during the fear conditioning context test for the B6 and F1 hybrid mice. (e) Mice from all three backgrounds showed no difference in freezing behavior during cue testing 26 hours after fear conditioning training. For each strain, AS and Wt mice were compared with a Student’s t-test and data are shown as the mean ± SEM; n = 15–16 mice/group; *p < 0.05.
Figure 5
Figure 5
Analysis of spontaneous epileptiform activity. (a) Representative traces of spontaneous polyspike burst activity were identified in AS mice of all three background strains. The B6 and F1 hybrid AS mice typically exhibited more pronounced and frequent polyspike events compared with 129 AS mice. The Wt mice of all backgrounds did not show abnormal EEG activity. (b) Quantification of polyspike activity in all three strains during continuous vEEG recording (24 hrs for 5 days). Both B6 and F1 AS mice exhibited more polyspike events in cortical and hippocampal EEG traces compared with 129 AS mice. The B6 AS mice showed the most pronounced and frequent polyspikes. For each strain, AS and Wt mice were compared with a Student’s t-test with Welch’s correction where variances were significantly different and data are shown as the mean ± SEM; n = 3–7 mice/group; *p < 0.05. CTX: cortex, HC: hippocampus.
Figure 6
Figure 6
129 AS mice were vulnerable to audiogenic seizures and exhibited wild running and tonic-clonic seizures when exposed to 140 dB sound in an enclosed chamber. The AGS phenotype affected a greater percentage of mice in the 7 mo old age group when compared with younger 3 mo old mice (n = 11–13 / group). Fisher’s test was used for analysis of seizure percentage at each designated age; n = 11–12 mice/group; *p < 0.05, ***p < 0.001.
Figure 7
Figure 7
Seizure induction with KA. (a,b) KA induction (25 mg/kg) in Wt and AS mice in the B6 background (n = 12–13 / group). No significant difference was found between B6 Wt and AS mice for time to reach the first clonus (tail/head/limbs) (a) or time to reach stage 4 or greater seizure (b). (c,d) KA induction (40 mg/kg) in Wt and AS mice in the 129 background (n = 11–12 / group). 129 AS mice exhibited a significantly lower latency to reach the first visible clonus of tail/head/limb (c) and stage 4 or greater seizure (d) compared to Wt littermates. (e,f) KA induction (35 mg/kg) in Wt and AS mice in the F1 background (n = 11–12 / group). F1 AS mice exhibited a significantly lower latency to reach the first visible clonus of tail/head/limb (e) compared to their Wt littermates. No significant difference was found between F1 Wt and AS mice for latency to stage 4 or greater seizure (f). Data are presented as the mean ± SEM; Student’s t-test was used to compare between AS and Wt mice; n = 11–13 mice/group; *p < 0.05.
Figure 8
Figure 8
Total EEG spectral power in the cortex and hippocampus of Wt and AS mice on B6, 129, or F1 hybrid backgrounds. (a,c) Total EEG spectral power in cortex during the light (a) and dark (c) cycle was significantly increased in B6 AS mice compared to Wt controls (n = 9–11/group). No differences in total EEG spectral power between genotypes were observed in the recordings from cortex with 129 (n = 8–10/group) and F1 hybrid (n = 3–6/group) backgrounds. (b,d) Total EEG spectral power in hippocampus during the light (b) and dark (d) cycle was not significantly different in AS mice compared to the Wt controls for any strain. For each strain and time of day, Student’s t-test was used for analysis and data are presented as the mean ± SEM; *p < 0.5.
Figure 9
Figure 9
Detailed analysis of EEG spectral cortical power during a representative hour of the light cycle (a–c) and dark cycle (d,e,f) from AS mice compared to Wt mice. (a,d) There was an upward shift of the B6 AS spectral cortical power compared to the B6 Wt mice during both dark and light cycle. This shift was primarily driven by increased power in the delta and theta frequency range (n = 9–11/group). During the dark cycle (d), significant increases were also seen in the summed alpha and beta spectral bands in B6 AS mice. (b,e) An upward shift in power was also seen in 129 AS compared to 129 Wt mice, driven by increased power in the 1–7 Hz range, although no significant differences were seen in the summed frequency bands (n = 8–10/group). (c,f) No significant changes were seen between F1 AS and Wt mice during the light cycle, however increased power was seen in the delta frequency range in F1 AS mice during the dark cycle when compared to F1 Wt mice (n = 3–6 / group). 2-way ANOVA was used to compare the individual frequencies across the spectrum. Student’s t-test was used to compare between individual frequency bands and data are presented as the mean ± SEM; *p < 0.05, **p < 0.01, ***p < 0.001.
Figure 10
Figure 10
Detailed analysis of EEG spectral hippocampal power during a representative hour of the light cycle (a–c) and dark cycle (d–f) from AS mice compared to Wt mice. (a,d) There was an upward shift of the B6 AS mice spectral hippocampal power compared to the B6 Wt mice during both dark and light cycle. Increased power was seen in individual frequencies in the delta range and the summed theta bands (n = 9–11/group). (b,e) An upward shift in power was also seen in 129 AS compared to 129 Wt mice during the light cycle (B), driven by increased power in individual frequencies in the delta range, although no significant differences were seen in the summed frequency bands (n = 8–10/group). Hippocampal EEG activity during the dark cycle (e) was similar for 129 Wt and AS mice. (c,f) A significant increase in power at 1 Hz was seen during both light (c) and dark (f) cycles, while a significant decrease in the summed gamma spectral band was found in F1 AS mice only during the dark cycle (f) (n = 3–6 / group). 2-way ANOVA was used to compare the individual frequencies across the spectrum. Student’s t-test was used to compare between individual frequency bands and data are presented as the mean ± SEM; *p < 0.05, **p < 0.01, ***p < 0.001.

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