Investigating the role of O-GlcNAc in silencing retrotransposons in the skin - Retrotransposons are interspersed genomic repeats that constitute almost half of the mammalian genome. Largely residing in the heterochromatin, retrotransposons are transiently induced during early development to regulate lineage differentiation, and kept silenced in adult terminally differentiated tissues. However, in human diseases such as cancer and aging, retrotransposons often exhibit aberrantly elevated activities, whose underlying molecular trigger and functional consequences are less understood. Murine skin represents an excellent model to study retrotransposon silencing mechanisms. As our largest organ, skin harbors highly abundant, well characterized, and genetically accessible adult stem cells. Hair follicle stem cells reside in an anatomically distinct niche known as the bulge, alternating between quiescence and activation in a synchronized fashion to fuel cyclic bouts of hair growth. Over repeated insults, hair follicle stem undergo functional exhaustion, the molecular driving events of which were often unclear. In the current proposal, I plan to examine chromatin regulators that couple adult stem cell activation with retrotransposon suppression during adult skin and hair follicle regenerations. Two central heterochromatin pathways are known to silence retrotransposons: tri-methylation on histone 3 lysine 9 (H3K9), catalyzed by histone lysine methyltransferases (KMTs), and DNA cytosine methylation, catalyzed by DNA methyltransferases (DNMTs). Moreover, lineage gene expression during stem cell differentiation depends on DNA demethylation, catalyzed by the DNA demethylase ten-eleven translocation (TET). While TETs are crucial for DNA methylome remodeling in early development, their regulations of retrotransposons in adult tissues remain underexplored. My preliminary analysis of genetic models in which the endogenous retroviruses (ERVs, a type of retrotransposons), are reactivated to drive skin stem cell exhaustion and hair loss, afforded me a unique tool to tackle these questions. Specifically, my prelim data indicated that a critical signal connecting TET to H3K9 KMT and DNMT function is the post-translational modification known as O-linked-β-N-acetylglucosamine (O-GlcNAc). I hypothesize that OGlcNAc catalyzed by the OGlcNAc transferase (OGT) is essential to suppress ERVs by interacting with H3K9 KMT and DNMT in the skin. I will examine OGT-deficient skin phenotypes and O-GlcNAc changes upon ERV reactivation, and dissect the mechanisms of OGlcNAc-orchestrated ERV suppressions. Study proposed here leverage my previous training in mouse genetics, development, epigenetics, and skin biology, and are designed to further train me with the state-of-art technologies such as CRISPR and classic methodologies in biochemistry and molecular biology. My training plan and my sponsor/co-sponsor support have been tailored to further foster my critical thinking, scientific communication, leadership and career development goals within MDACC and GSBS training environment. The proposed study, if successful, will provide important mechanistic insights into retrotransposon biology in adult skin, and mature me into an independent researcher.
