Modulation of human endogenous retroviruses (HERVs) by CRISPR in human pluripotent stem cells
Virology
Final Report Abstract
The human genome project revealed that an incredible portion of our genome consists of viral elements. Among these, approx. 10% of the human genome contains so-called “human endogenous retroviral elements” (HERVs). From an evolutionary point of view HERVs are relics of ancestral infectious retroviruses that have successfully invaded the germ-line of the host. Research of recent years has unraveled over 30 groups of distinct HERVs, which clearly emphasizes that they are an integral part of our genome. Beside complete and partially truncated/deleted HERV elements, there also exist up to 500.000 copies of solitary “long terminal repeats” (LTRs) scattered throughout all chromosomes. LTRs are the control elements for viral gene expression (i.e. promoters), thus dictating whether or not a gene is transcribed. Intriguingly, HERVs have been essential to the evolution of our genomes and have considerably contributed to genome plasticity and the creation of novel genes. So far, around 100 genes have been identified to be exclusively activated by HERV LTRs. Current knowledge implies that certain pathologies, including neurological diseases, are associated with the expression of HERVs. However, their functional role remains to be elucidated. By differentiating hPSCs into several cell types of the brain, we found that specific HERV groups were differentially regulated to various extents in the distinct neuronal cell types. To functionally analyze their influence on neuronal differentiation I successfully established the CRISPR activation (CRIPSRa) system, to activate HERV expression in hPSCs. With this tool in hands, I specifically activated the expression of one HERV group in hPSCs and subsequently differentiated them into neurons. Intriguingly, I could detect a significant decrease in markers of neuronal development after overexpression of this particular HERV group. In line with this, neuronal functionality was also diminished, providing a proof of concept that HERVs play an important role in neuronal development. Hence, in future studies I will continue investigating the underlying mechanisms of how distinct HERVs influence brain development and how they impact brain-related diseases.
