Driving cell type specific transgene expression using microRNA mediated gene regulation

Transgene delivery and expression have been widely exploited for both research and therapeutic purposes. The power of transgene delivery is enhanced by being able to express a transgene in a specific cell population. Many methods have been attempted for achieving expression specificity, including the commonly attempted use of cell type specific promoters in bacterial artificial chromosomes and plasmids. Unfortunately, the design of successful promoters in not straight forward and the approach often fails. We propose a system that bypasses the use of promoters and takes advantage of endogenous expression of cell type specific microRNA (miRNA) to positively regulate a transgene expression reporter. Our system takes the approach of a dual negative system, whereby a negatively regulated miRNA-mediated intermediary protein down-regulates a reporter transgene. Only in the presence of the miRNA would the reporter be expressed. The studies described here focus on demonstrating the concept of the system, and pursing initial steps in optimization. We have shown that the intermediary miRNA recognition regulator is down-regulated by high levels of endogenous miRNA; the reporter transgene is regulated by the intermediary regulator; and introduction of specific miRNA with the two system components results in positive reporter expression. Thus we demonstrated the concept whereby a reporter transgene can be positively regulated by miRNA expression. Our results provide support for the possibility of using miRNA expression to selectively manipulate different cell types for research and therapeutic use