This research grant aims at dissecting Polycomb-group (PcG) and trithorax-group (trxG) gene function as a paradigm of epigenetic regulation of gene expression in mice. A combination of in vitro and in vivo approaches is proposed to dissect the function of this complex regulatory network in mouse embryonic development using the PcG gene eed as a molecular entry point. eed plays a pivotal role in this pathway by virtue of its direct physical interaction with histone deacetylases and histone methyltransferases.
Recent results indicate an antagonistic role of the PcG genes eed and Bmi1 in cerebellum development. Therein, eed and Bmi1 function as suppressor and enhancers of cerebellar cell proliferation, respectively. Furthermore, our eedxBmi1 double mutant analysis revealed that the eed mutation partially rescued the cerebellar defects from loss of function of Bmi1. Furthermore, mice heterozygous for eed and the trxG gene Mll exhibit defects in the hippocampus, such as disorganization of the pyramidal cell layer Double mutants of eed and Mll show an enhanced disruption and scattering of the CA3 hippocampal pyramidal cells. In collaboration with Dr. Richard Paylor in our Department, we detected numerous behavioral deviations in these mice, some of which may result from hippocampal defects. For example, motor learning measured by the rotarod test was reduced in both Mll single mutants and eedxMll double mutants. In the open-field test, Mll mutants show significant decreases in rearing and movement compared with wild-type littermates, which is considered indicative of high anxiety. In contrast, the eed mutants displayed hyperactivity and low anxiety. In collaboration with Dr. Arthur Beaudet in our Department, we are also testing a specific role for eed in the trans-regulation of genomic imprinting in the Prader-Willi/Angelman domain in mice. Given the role of MecP2 in Rett syndrome, we anticipate to extend the analysis to double mutant crosses with Dr. Huda Zoghbi's MecP2 mutant mouse strains.

Relevance of the project to MRDDRC Mission:
Our findings are significant with regard to the pervasiveness of hyperactivity in neurodevelopmental disorders such as autism. We will extend our preliminary studies by including additional tests to ascertain brain functions more specifically related to the hippocampus, such as learning and memory tests as well as electrophysiological recordings. Ultimately, we hope that these studies will provide insight into the mechanistic relationship between genomic imprinting patterns, CpG methylation, and chromatin structure in the context of certain neurodevelopmental abnormalities found in autism.