PhD Proposal Exam – Klotilda Karkaj – Tuesday, May 22nd, 2018

PhD Proposal Exam

Tuesday, May 22^nd, 2018 at 1:10 pm – CCT-4034, University of Toronto at Mississauga

Klotilda Narkaj (Zovkic lab)

“Histone Variant MacroH2A in Memory Formation”

Abstract

Epigenetic modifications are widely recognized for their role in memory formation. Although existing research has focused almost exclusively on DNA methylation and histone post-translational modifications (PTMs), we recently discovered that histone variant exchange, in which canonical histones are replaced by distinct variants, is a novel branch of epigenetics for regulating memory. Our initial work showed that binding of the histone variant H2A.Z is modified by learning, suggesting that the composition of histones that make up nucleosomes is subject to learning- and memory-related modification. Though H2A variants can replace one another in chromatin, which histones replace one another and how distinct variants influence memory is largely unknown. H2A.Z is one of several functionally diverse H2A variants that functions as a memory suppressor. For my thesis I will investigate another potential candidate for memory regulation, histone variant macroH2A (mH2A), its relationship with H2A.Z, and their interaction in memory formation. MacroH2A has a widely reported role in regulating gene expression, it is encoded by 2 genes, H2afy (encodes mH2A1) and H2afy2 (encodes mH2A2), both of which are expressed throughout the mouse brain, including the hippocampus, a brain region that is vital for memory formation. To explore the role of mH2A in memory, we use adeno-associated virus (AAV) to knock down either H2afy or H2afy2 in area CA1 and tested mice on an array of hippocampus-dependent memory tasks at the 24-hour and 7-day time points. We found that mice with depleted levels of both mH2A1 and mH2A2 had impaired fear memory 24 hours and 7 days after training, suggesting that both mH2A-encoding genes promote hippocampus-dependent memory formation. To identify the mechanism by which mH2A regulates memory, area CA1 was extracted 30 min after fear conditioning, exposed to mH2A chromatin-immunoprecipitation combined with next-generation sequencing, and compared to genome-wide gene-expression 1h after training, based on time points at which our lab previously found an association between H2A.Z dynamics and gene expression. To elucidate the relationship between H2A.Z and mH2A in memory, I will investigate binding of mH2A in chromatin in response to H2A.Z depletion, after learning. These data will explore involvement of histone variant exchange as a novel epigenetic regulator of behaviour and they are the first to show mH2A as a regulator of memory.