Imprinted genes are highly expressed in monoaminergic regions of the midbrain and their functions in this area are thought to have an impact on mammalian social behaviors. One such imprinted gene is Grb10, of which the paternal allele is generally recognized as mediating social dominance behavior. However, there has been no detailed study of social dominance in Grb10 +/p mice. Moreover, the original study

Imprinted genes are highly expressed in monoaminergic regions of the midbrain and their functions in this area are thought to have an impact on mammalian social behaviors. One such imprinted gene is Grb10, of which the paternal allele is currently recognized as mediating social dominance behavior. However, there has been no detailed study of social dominance in Grb10 +/p mice. Moreover, the original study examined tube-test behavior in isolated mice 10 months of age. Isolation testing favors more territorial and aggressive behaviors, and does not address social dominance strategies employed in group housing contexts. Furthermore, isolation stress impacts midbrain function and dominance related behavior, often through alterations in monoaminergic signaling. Thus, we undertook a systematic study of Grb10 +/p social rank and dominance behavior within the cage group, using a number of convergent behavioral tests. We examined both male and female mice to account for sex differences, and tested cohorts aged 2, 6, and 10 months to examine any developments related to age. We found group-housed Grb10 +/p mice do not show evidence of enhanced social dominance, but cages containing Grb10 +/p and wildtype mice lacked the normal correlation between three different measures of social rank. Moreover, a separate study indicated isolation stress induced inconsistent changes in tube test behavior. Taken together, these data suggest future research on Grb10 +/p mice should focus on on the stability of social behaviors, rather than dominance per se.

Mice lacking paternal expression of imprinted Grb10 show a number of social behaviour deficits, including an enhanced allogrooming phenotype. However, this could also index compulsive behaviour, and the increased whisker barbering seen in Grb10 +/p mice has been suggested to be indicative of a trichotillomania-type behaviour. Here we test whether compulsive behaviour is a more general phenotype in Grb10 +/p mice by examining marble burying at three different adult ages (2, 6 and 10 months). We also examined the mice for potentially confounding anxiety phenotypes using the elevated plus maze (EPM). Grb10 +/p mice showed no difference from wild-type littermate controls on any measure in the marble burying test at any age. There was no difference in standard anxiety measures either, although Grb10 +/p mice displayed more risk-taking behaviours on the EPM than wild-type mice. These data suggest that Grb10 +/p mice are not generally more compulsive, and that the enhanced allogrooming is probably indicative of altered social behaviour. Furthermore, the altered behaviours seen on the EPM adds to other published findings suggesting that Grb10, and imprinted genes more generally, have a role in mediating risk-taking behaviour.