Alterations to neurexin-2 convey autistic-like behaviours in mice.

James Dachtler, Nicole Watt, Nigel Hooper, John Rodgers, Steven Clapcote. University of Leeds, Leeds, UK

Neurexins are presynaptic cell adhesion molecules that link to postsynaptic neuroligins or leucine-rich transmembrane repeats (LRRTMs) (1). Converging evidence suggests that neurexins support synaptic function as opposed to neural patterning (1). Recent findings from genome-wide association studies have highlighted deletions and mutations within neurexin-2 from autism spectrum disorder (ASD) sufferers (2). Little is understood about the role of neurexin-2 in vivo, especially in terms of aberrations of its function. Thus we examined neurexin-2 knockouts to determine to what extent these mice may be useful preclinical models of ASD.

Methods

The generation and confirmation of depletion of neurexin-2 has been previously described (3). Adult (>p56) neurexin-2 knockout (n=18) and wild-type littermates (n=31) on a C57BL/6J background were tested in a wide ranging battery of behavioural tests. These included, in the following order: open field, elevated plus maze, forced swim, tail suspension, three chamber sociability test, emergence test, prepulse inhibition and passive avoidance test. A minimum of three days rest was provided between less invasive tests, while two weeks rest was provided for tests involving aversive stimuli. Scoring was made automatically by computer (Stoelting Any-Maze) or by the experimenter. The average weight of wild-types was 27.6 g and 26.6 g for knockouts (p>0.05).

Results

Knockout mice had a replicable anxiety phenotype. In the open field, knockout mice spent the majority of their time against the outer wall (thigmotaxis) (WT:1445±40 vs KO:1596±15s, p=0.015). In the plus maze, they spent significantly less time in the central platform (WT:100±6 vs KO:40±4s, p<0.0001) and the open arms (WT:5±1 vs KO:1±0.4%, p<0.0001), while in the emergence test, they took longer to emerge (WT:30±5 vs KO:112±26s, p<0.0001) and spent more time in the enclosed shelter (WT:413±32 vs KO:592±42s, p=0.001). There were no significant differences in cognition (the passive avoidance test) or in tests of motivation (forced swim test and tail suspension; all p>0.05). Of particular relevance to ASDs, knockout mice showed strong deficits in sociability with a novel conspecific (WT:141±7 vs KO:90±9s, p=0.001) and in social recognition when discriminating between a previously explored mouse and a second novel conspecific (second novel conspecific: WT:86±6 vs KO:55±7s, p=0.039).

In conclusion, neurexin-2 knockout mice replicate core symptoms of ASDs, and present a useful tool for further research into the pathophysiology of this disorder.

(1) Reichelt AC, et al. Neuropharmacology 62(3):1519-1526, 2012.

(2) Gauthier J, et al. Human genetics 130(4):563-573, 2011.

(3) Missler M, et al. Nature 423(6943):939-48, 2003.