Behavioural abnormalities in a novel mouse model for Silver Russell Syndrome

Abstract

Silver Russell Syndrome (SRS) syndrome is an imprinting disorder involving low birth weight with complex genetics and diagnostics. Some rare SRS patients carry maternally inherited microduplications spanning the imprinted genes CDKN1C, PHLDA2, SLC22A18 and KCNQ1, suggesting that overexpression of one of more of these genes contributes to the SRS phenotype. While this molecular alteration is very rare, feeding difficulties are a very common feature of this condition. Given that SRS children also have very low body mass index, understanding the underpinning biology of the eating disorder is important, as well as potential co-occurring behavioural alterations. Here, we report that a mouse model of this microduplication exhibits a number of behavioural deficits. The mice had a blunted perception of the palatability of a given foodstuff. This perception may underpin the fussiness with food. We additionally report hypoactivity, unrelated to anxiety or motoric function, and a deficit in the appropriate integration of incoming sensory information. Importantly, using a second genetic model, we were able to attribute all altered behaviours to elevated expression of a single gene, Cdkn1c. This is the first report linking elevated Cdkn1c to altered behaviour in mice. Importantly, the findings from our study may have relevance for SRS and highlight a potentially underreported aspect of this disorder.

Figure 1.

Cdkn1c^BACx1 animals display hypoactivity unrelated to any motoric function deficits. (A) Locomotor activity data on the first day of testing broken down into 5-minute bins shows consistent reduced activity of Cdkn1c^BACx1 mice relative to WT littermates throughout the session. (B) Cdkn1c^BACx1 also displayed consistent hypoactivity across three consecutive test days. (C) All animals showed the expected increase in activity after amphetamine administration. (D) Reduced activity in Cdkn1c^BACx1 mice was not related to motoric function deficits as all animals increase time before first fall following successive rotatod training session. (E) Similarly, there was no effect of genotype on latency to fall from an accelerating rotarod across a range of test speeds. Data shown is ± SEM. Main effect of GENOTYPE, *= P < 0.05, **= P < 0.01; main effect of within subject factors (BIN, SESSION, DOSE, SPEED) #= P < 0.05, ###= P < 0.001.

Figure 2.

Emotional reactivity was intact in Cdkn1c^BACx1 animals. There were no differences between Cdkn1c^BACx1 animals and their WT littermates in measures on the EPM test, including (A) time spent on open arm, (B) entries into open arm and (C) latency to first enter open arm. Similarly, there were no differences between Cdkn1c^BACx1 animals and their WT littermates in measures on the OF test, including (D) time spent in centre zone, (E) entries into centre zone, and (F) latency to first enter centre zone. Data shown is ± SEM.

Figure 3.

Elevated Cdkn1c expression results in sensorimotor gating deficits. (A) Average ASR to a 105 dB pulse was not affected by genotype (B). However, PPI of the startle response was significantly blunted in Cdkn1c^BACx1 animals. Data shown is ± SEM. Main effect of GENOTYPE, *= P < 0.05; main effect of PPI, ##= P < 0.01.

Figure 4.

Cdkn1c^BACx1 animals show a reduced perceived palatability of a sucrose solution. (A) All animals preferred sucrose to water and this was not affected by genotype. (B) Cdkn1c^BACx1 animals had consistently smaller average lick cluster size compared to WT indicating altered hedonic processing. (C) Despite potentially reduced perceived palatability, consumption of a palatable solution was not different between Cdkn1c^BACx1 animals and WT. (D) Cdkn1c^BACx1 had significantly more Th-positive cells that wt in the periventricular hypothalamus (PVH), but not the A13 dopaminergic cell group. (E) Representative images showing Th staining. Scale bar is 100 μm. Data shown is ± SEM. Main effect of GENOTYPE, *=P ≤ 0.05; main effect of concentration ##= P < 0.01.

Figure 5.

Behavioural alterations in Cdkn1c^BACx1 animals were absent when Cdkn1c expression was not elevated. (A) There was no difference between Cdkn1c^BACLacZ animals and their WT littermates in LMA. (B–E) Duration of time spent in and number of entries into an anxiogenic zone was not affected by genotype in an (B,C) EPM or (D,E) OF. (F,G) ASR and PPI was not different between Cdkn1c^BACLacZ animals and WT littermates. Average lick cluster size (H) was equivalent between groups, as was consumption (I) of a palatable sucrose solution. Data shown is ± SEM. Main effects of within subject factors (PPI, Concentration) ###= P < 0.001.