A new lincRNA network controlling USP18, the negative regulator of type I interferon signaling

Linc-DGCR6-1 as a new potential “bodyguard” of human germ cell survival Immune responses are essential to protect us from pathogens. However, there are distinct sites of our body, such as brain or testis, in which the action of systemic immune system is not well tolerated. For this reason, these sites evolved different strategies to suppress immune responses, creating what is known as “immune privilege”. We Identified a long non-coding RNA (RNA species longer than 200 nucleotides), uniquely expressed in germ cells, potentially contributing to the maintenance of immune-privileged environment of testis. The testicular immune privilege protects germ cells within the seminiferous tubules from immune attack, both physically through a blood-testis barrier and actively through the production of immune suppressive mediators. Impairment of these protective mechanisms can result in orchitis, an inflammatory condition that can lead to germ cells death and, therefore, male infertility. On the other hand, some viruses, such as Zika virus, can take advantage of this isolated environment, persist in germ cells for months after infection and, eventually, be sexually transmitted. Type I interferons (here IFN) are crucial mediators of antimicrobial immunity and represent a first line of defense against viruses. However, IFN can also induce cell death of germ cells. Mice germ cells lack one of the subunits of IFN receptor, therefore they do not respond to IFN. In humans, the mechanism by which germ cells counteract the deleterious action of IFN is not known. My master project focused on linc-DGCR6-1, a long non-coding RNA, which may contribute to dampen IFN response in human germ cells. Interestingly, this RNA contains a sequence identical to the 3´UTR (untranslated region) of USP18. This attracted our attention since USP18 is the key negative regulator of IFN signaling and is highly expressed in human germ cells. Moreover, it is known that lincRNAs sharing 3´ UTR of protein-coding genes can positively regulate the levels of their cognate gene. Given these, we propose that, through a mechanism based on this shared 3´ UTR sequence, linc-DGCR6-1 may sustain USP18 levels and favor a low responsiveness of germ cells to IFN. In this work, we have shown that the expression of linc-DGCR6-1 is restricted to testis, more precisely, germ cells. We have also characterized the sequence of this molecule, unveiling isoforms which have not been previously identified. These findings lay solid foundations for future functional studies and shed light on a highly complex RNA network that may sustain USP18 levels in germ cells. Further dissection of this mechanism may give insights on contribution of long non-coding RNAs to the regulation of immune responses and address questions of public health concerning inflammation-induced sterility and viral persistence in human testis. Master’s Degree Project Molecular Biology 45 credits 2020 Department of Biology, Lund University Advisor: Sandra Pellegrini Cytokine Signaling Unit, Immunology Department, Institut Pasteur (Less)