The small GTPase Rem2 has established roles in synaptic formation, shaping dendritic complexity and spine structure, and in the regulation of CaMKII-dependent long-term potentiation (LTP). Despite these cellular and synaptic roles, how Rem2 influences behavioral measures of learning and memory had not been clarified prior to this study.
To test the behavioral impact of Rem2 on spatial learning, the authors performed a conditional deletion of Rem2 specifically in dorsal CA1 neurons. They assessed spatial learning using a spatial object recognition (SOR) task in both male and female mice. The experimental approach combined targeted genetic manipulation with a behavioral assay that probes spatial memory for object location.
In the control condition (without Rem2 deletion), male mice performed better than female mice in the SOR task, indicating a baseline sex difference in this measure of spatial learning.
Deleting Rem2 from dorsal CA1 neurons produced a sex-specific effect on spatial learning. In males, Rem2 deletion did not alter SOR performance. In contrast, females with CA1-targeted Rem2 deletion showed significantly improved SOR performance and reached levels comparable to those of males. Thus, Rem2 deletion rescued or enhanced female performance in this spatial learning assay while leaving male performance unchanged.
To probe molecular correlates of the behavioral effects, the investigators used an automated Western blot system to quantify expression of all known AMPA- and NMDA-type glutamate receptor subunits (AMPAR and NMDAR) in each mouse. This comprehensive, subunit-level profiling enabled comparisons of receptor composition across sex and genotype.
The authors report that the sex-dependent improvement in spatial learning was likely driven by a Rem2-dependent increase in GluN2D expression localized to interneurons in female mice only. This change in GluN2D expression was not observed in males. According to the study, this selective upregulation of a specific NMDAR subunit in interneurons provides a plausible molecular mechanism linking Rem2 deletion to altered circuit function and improved spatial performance in females.
Beyond single-subunit changes, the study assessed overall glutamate receptor composition using S-statistics to compare covariance structures across AMPAR and NMDAR subunits among groups. Under normal conditions, males and females displayed divergent covariance structures of receptor composition. When Rem2 was deleted from CA1 neurons, this divergence in covariance between sexes was eliminated. The authors interpret these results to mean that Rem2 contributes to maintaining sex-specific organizational patterns of glutamate receptor composition at the level of covariance among subunits.
The findings identify Rem2 as a signaling molecule that contributes to sexual dimorphism in excitatory synapses and in a spatial learning behavior. The authors state that, to their knowledge, this is the first demonstration of a signaling molecule that confers sexual dimorphism to excitatory synapses. Because many neurodevelopmental and neurodegenerative disorders show sex-dependent symptoms, the study suggests Rem2 may be important for understanding mechanisms that underlie sex differences in these conditions.
These results are reported in a bioRxiv preprint and have not undergone peer review. The authors declared no competing interests and reported funding from the Charles E. Kaufman Foundation (KA2023-136491). Detailed methodological parameters, sample sizes, statistical values, and additional experimental specifics beyond those summarized here were not reported in the abstract and should be consulted in the full preprint for complete evaluation.