Intellectual disability, previously termed mental retardation, is a disorder characterized by a significant delay in cognitive function and limitatios in adaptive behaviors. Although the causes of intellectual disability are highly heterogeneous, genetic defects that underlie some occurrences of inherited intellectual disability have begun to be identified. Among the genes linked to intellectual disability, genes encoding RNA- binding proteins have been implicated in a number of cases, including the most common form of inherited intellectual disability, Fragile X Syndrome. Recently, our group reported inactivating mutations in the ZC3H14 gene, which encodes an evolutionarily conserved, ubiquitously expressed polyadenosine RNA-binding protein, ZC3H14. Despite ubiquitous expression of the ZC3H14 protein, the patients with mutant ZC3H14 display non- syndromic, intellectual disability where only brain function is impaired. This finding suggests that ZC3H14 has a critical, specialized role in the brain. Studies in Drosophila reveal a key role specifically in neurons. A major difference between neurons and many other cell types is the need for highly regulated and localized translational control particularly in the neurite extensions. While the steady-state localization of ZC3H14 is nuclear, our recent studies reveal that a population of ZC3H14 is present in axons of primary hippocampal neurons. In addition, we also find that ZC3H14 associates with 80S ribosomes. These results suggest a cytoplasmic role for ZC3H14 that is similar to that of other RNA-binding proteins that regulate translation. Indeed, preliminary studies in Drosophila have identified functional interactions between the Drosophila orthologue of ZC3H14 and Drosophila orthologues of two other RNA-binding proteins that regulate translation Fragile X Mental Retardation Protein (FMRP) and Ataxin-2. As both FMRP and Ataxin-2 regulate translation, these functional interactions suggest that ZC3H14 could also modulate translation. Given our preliminary findings, we hypothesize that ZC3H14 works cooperatively with specific RNA regulatory factors to ensure local translation in neurons. In this proposal, we test our hypothesis by investigating the molecular functions of ZC3H14 through the following complementary aims.
In Aim 1, we assess the requirement for ZC3H14 in regulating translation by manipulating levels of ZC3H14 and examining protein synthesis, moving from global approaches to more targeted approaches.
In Aim 2, we will test for physical interactions between ZC3H14 and candidate translation regulators. These studies will exploit a ZC3H14 knockout mouse we have recently developed, providing an optimal system to assess the functional and molecular consequences of loss of ZC3H14. The broad long-term goal is to provide insight into how ZC3H14, along with other interacting proteins, influences post-transcriptional events and ensures proper higher order brain function. Understanding the function of ZC3H14 is a critical step in elucidating the complex roles of RNA-binding proteins in controlling spatial and temporal regulation of gene expression.
Intellectual disability or mental retardation is the most frequent cause of handicaps in children and young adults. This proposal examines the function of a protein recently found to be altered in some patients with intellectual disability. These studies will enhance our understanding of the underlying molecular mechanisms that cause the disease and provide insight into the impairments found in other forms of intellectual disability.