Wild-type mice are social animals and choose to spend more time in the chamber with another mouse (Figure 5A). This social interaction behavior was unaffected in MeCP2 S421A mice, demonstrating their ability to recognize other mice and their appropriate interest in their physical and social environment. Subsequently,
a second mouse that the test subject had never before encountered was placed within a small wire cage in the side-chamber opposite to the first, now familiar mouse. The wild-type test subjects spent the largest proportion of their time in the chamber containing the second, novel mouse and less time with the familiar choice (Figure 5B). By contrast, the MeCP2 S421A mice spent as much time with the familiar mouse as with the novel mouse. Because the MeCP2 S421A mice show appropriate interest in novel mice, it is unlikely that the increased time spent CHIR-99021 datasheet with familiar mice is due to a general deficit in social recognition upon VX 770 loss of MeCP2 S421 phosphorylation. Likewise, the MeCP2 S421A mice show no aversion to spending time alone and appear normal in tests of anxious behavior (Figure S2). Instead the increased interest in the familiar mouse suggests that the MeCP2 S421A mutants cannot distinguish between familiar and novel mice. This lack of discrimination between novel and familiar stimuli exhibited by the MeCP2 S421A mice was not limited to social behavior; when presented with both novel and
familiar inanimate objects, wild-type mice showed a behavioral preference for a novel object, whereas the MeCP2 S421A mice spent equal amounts of time investigating both familiar and novel objects (Figure 5C). This difference was evident at 30 min after the initial exposure to the familiar object, and persisted even after 24 hr had Dipeptidyl peptidase passed. Taken together, these findings support the conclusion that neuronal activity-dependent phosphorylation of MeCP2 at S421 is necessary to allow an animal to process novel experience and respond appropriately
to previously encountered objects or animals. This defect cannot be attributed to an absence of all learning and memory in these mice, as the performance of the MeCP2 S421A mice in spatial learning and memory tests is indistinguishable from wild-type (Figure S3). Instead the specific defect observed in the MeCP2 S421A mice suggests that the activity-dependent phosphorylation of MeCP2 S421 contributes to aspects of cognitive function underlying behavioral flexibility, and that the disruption of this aspect of MeCP2 regulation in RTT may be a factor in cognitive impairments observed in affected individuals. The abnormalities we observe in the MeCP2 S421A knockin animals demonstrate that this activity-dependent phosphorylation event is required for proper formation of the nervous system. We considered how the phosphorylation of S421 might modulate the molecular function of MeCP2 during neuronal development. Two distinct mechanisms have been proposed to explain how MeCP2 functions when bound to DNA.