KDM5 proteins are multi-domain transcriptional co-factors that function by recognizing and enzymatically altering specific histone modifications. There are four broadly expressed KDM5 orthologs in mammalian cells (KDM5A-D) and a single KDM5 in Drosophila. Emphasizing the importance of KDM5 proteins, KDM5A and KDM5B are over expressed in a number of metastatic cancer types, and KDM5A, B and C are mutated in patients with intellectual disability (ID). To-date, 30 mutations in KDM5C, 7 in KDM5B and 1 in KDM5A have been identified in patients with either syndromic or non-syndromic ID. How mutations in KDM5 family genes result in cognitive phenotypes remains elusive.
As a first step in establishing Drosophila as a model system to understand KDM5-induced ID, we defined direct KDM5 target genes in adults, as this is the stage used to model cognitive disorders. By combining RNA-seq from kdm5 hypomorphic adults with anti-KDM5 ChIP-seq, we identified numerous direct targets. Among these were several genes previously implicated in neurological disorders. Using Drosophila, which encodes a single KDM5 protein, our lab carried out RNA-sequencing experiments using kdm5 hypomorphic adult flies. This revealed that KDM5 is required for the activation of several genes previously implicated in intellectual disability disorders such as fragile-X syndrome, Down syndrome, Autism and Alzheimer’s disease. Anti-KDM5 ChIP-seq experiments from wildtype flies demonstrate that many of these genes are direct KDM5 targets. Because patients with mutations in KDM5 genes show cognitive impairment, we used a behavioral assay in flies and found that the kdm5hypomorph have impaired appetitive-olfactory associative learning. To complement our analyses of kdm5 hypmorphic mutant adults, we have generated seven fly strains harboring mutations in KDM5 that are analogous to disease-associated missense mutations in KDM5 proteins. 6/7 of the ID mutants generated thus far are expressed at wild type levels re-enforcing that these mutations affect function and not protein stability. To-date, we have examined one ID mutant fly strain in more detail and found it to have a severe learning and memory defect. We are currently testing other ID allele fly strains for similar cognitive impairment, and defining the transcriptional defects in these strains. These analyses will allow us to define for the first time whether similar or distinct target genes are affected by disease-associated alleles. These studies will allow us to define the mechanistic link between KDM5 dysfunction and intellectual disability.