Origins and evolution of a novel mechanism of post-transcriptional gene regulation by the HERC family

点击翻译按钮获取中文摘要

The long-term goal of our NSERC-funded research program is to advance our understanding of the evolution and biological functions of the “HECT domain and RCC1-like domain-containing” (HERC) family of proteins. Over the last 5 years, we performed evolutionary, structural and functional analyses of the small HERC family. We showed that this family has an ancient marine origin of >476 million years ago, and is well-conserved throughout vertebrate evolution, pointing to a potentially fundamental role for HERCs in biology (Paparisto et al., 2017, submitted). In support of this notion, our group and others have shown that HERC proteins impact a variety of cellular functions including the immune response, spermatogenesis, neurodevelopment, DNA damage repair and cell growth. Recently, our group discovered that HERC proteins can differentially inhibit the RanGTP-dependent nuclear export pathway (Woods et al., 2014). Over the next 5 years, we propose to characterize the origin, evolution and biological function of this HERC-mediated inhibition of the RanGTP-dependent nuclear export pathway.In recent years, much attention has been focused on the gene regulatory activity of micro RNAs (miRNAs). MicroRNA and the genes that process them are highly conserved across species and are thought to be a vital and evolutionarily ancient component of gene regulation, influencing >60% of a host's transcriptome. Since miRNAs are mainly exported to the cytoplasm from the nucleus by the RanGTP-dependent export pathway, we tested and discovered that HERC proteins can potently block the nuclear export of miRNAs (unpublished). Our working hypothesis is that HERC proteins modulate gene expression by a novel and evolutionarily conserved mechanism involving the regulation of miRNA nuclear export. To address this hypothesis, we propose to identify the key proteins involved in RanGTP-dependent nuclear export whose functions are affected by HERC expression, map the key protein-protein interactions and residues required for this activity, and characterize the guanine nucleotide exchange factor activity of recombinant HERC proteins using established in vitro assays. We will also investigate the biological role of HERC proteins by determining their impact on miRNA and mRNA expression profiles using RNA sequencing. Lastly, we will use a similar approach to determine if evolutionarily diverse HERC proteins inhibit RanGTP-dependent nuclear export and whether the mechanism is conserved.Impact: Our research will provide insight into the biological function(s) of the HERC proteins and characterize a potentially novel mechanism of post-transcriptional gene regulation that targets nuclear export of miRNAs. Importantly, our research will help elucidate how complex gene regulatory networks evolve and how their evolution results in phenotypic change and speciation.