Comprehensive Behavioral Phenotyping of a 16p11.2 Del Mouse Model for Neurodevelopmental Disorders

Abstract

The microdeletion of copy number variant 16p11.2 is one of the most common genetic mutations associated with neurodevelopmental disorders, such as Autism Spectrum Disorders (ASDs). Here, we describe our comprehensive behavioral phenotyping of the 16p11.2 deletion line developed by Alea Mills on a C57BL/6J and 129S1/SvImJ F1 background (Del m). Male and female Del m mice were tested in developmental milestones as preweanlings (PND2-PND12), and were tested in open field activity, elevated zero maze, rotarod, novel object recognition, fear conditioning, social approach, and other measures during post-weaning (PND21), adolescence (PND42), and adulthood (>PND70). Developmentally, Del m mice show distinct weight reduction that persists into adulthood. Del m males also have reduced grasp reflexes and limb strength during development, but no other reflexive deficits whereas Del m females show limb strength deficits and decreased sensitivity to heat. In a modified version of a rotarod task that measures balance and coordinated motor activity, Del m males, but not females, show improved performance at high speeds. Del m males and females also show agespecific reductions in anxiety-like behavior compared with WTs, but neither sex show deficits in a social preference task. When assessing learning and memory, Del m males and females show age-specific impairments in a novel object or spatial object recognition, but no deficits in contextual fear memory. This work extends the understanding of the behavioral phenotypes seen with 16p11.2 deletion by emphasizing age and sex-specific deficits; important variables to consider when studying mouse models for neurodevelopmental disorders.

Sex-specific stress-related behavioral phenotypes and central amygdala dysfunction in a mouse model of 16p11.2 microdeletion

“…After fear conditioning and upon memory retrieval, both female and male 16p11.2 del/+ mice showed levels of freezing similar to those of their WT littermates in response to the CS+ ( Figure B, D), consistent with previous findings that 16p11.2 del/+ mice have intact fear conditioning (Lynch et al, 2020;. Surprisingly, however, female, but not male 16p11.2 del/+ mice showed increased freezing to the CS-compared with WT littermates ( Figure 1B, D), resulting in reduced levels of fear discrimination in female, but not male 16p11.2 del/+ animals ( Figure 1C, E).…”

“…We found that female, but not male 16p11.2 del/+ mice showed enhanced fear generalization, a hallmark of anxiety disorders (Dunsmoor & Paz, 2015), after auditory fear conditioning. Furthermore, although at baseline 16p11.2 del/+ mice were not different from their wildtype littermates in the EPM test, consistent with previous studies (Arbogast et al, 2016; Lynch et al, 2020; Yang, Lewis, et al, 2015), we found that female, but not male 16p11.2 del/+ mice showed enhanced anxiety in the EPM after acute restraint stress. Lastly, we found that these sex-specific behavioral changes were paralleled by an increase in activity in the central amygdala – a major limbic structure that regulates anxiety in rodents and primates (Ahrens et al, 2018; Fox et al, 2012; Shackman & Fox, 2016) – of female, but not male 16p11.2 del/+ mice.…”

“…A few studies examined the 16p11.2 del/+ mice for anxiety or fear-related behaviors, but with mixed results. When tested in the open field (OPF) test and elevated plus maze (EPM) test, assays conventionally used to assess ‘anxiety’ in rodents, these mice appear not different from wildtype (WT) mice (Arbogast et al, 2016; Lynch et al, 2020; Yang, Lewis, et al, 2015), (however, see (Pucilowska et al, 2015)). The 16p11.2 del/+ mice were also examined in fear conditioning paradigms.…”

“…The 16p11.2 del/+ mice were also examined in fear conditioning paradigms. One study shows that the 16p11.2 del/+ mice have impaired contextual fear conditioning (Tian et al, 2015), whereas other studies show that the 16p11.2 del/+ mice have normal contextual fear conditioning and normal visually cued fear conditioning (Lynch et al, 2020; Yang, Lewis, et al, 2015).…”

“…In light of these findings and studies showing males and females can exhibit very different behavioral responses to threats or stress (Dalla & Shors, 2009; Gruene et al, 2015), we reasoned that under a stressful situation 16p11.2 del/+ mice may exhibit sex-specific behavioral changes. However, a potential sex-specific effect of the 16p11.2 deletion on anxiety or fear-related behaviors in mice has not been considered until recently (Lynch et al, 2020). Furthermore, only simple assays, such as OPF and EPM tests, have been used to assess “baseline anxiety” in 16p11.2 del/+ mice, which may not be sufficient to reveal potential changes in anxiety or fear processing in response to stress in these mice.…”