We would also like to thank Ms. Rowan Tweedale for helpful editing of the manuscript.Significance statement: How does the pattern of immediate early gene (IEG) transcription in the brain relate to the storage and accession of information, and what controls these patterns? This paper explores how GADD45g , a gene that is known to be involved with DNA modification and repair, regulates the temporal coding of IEGs underlying associative learning and memory. We reveal that, during fear learning, GADD45g serves to act as a coordinator of IEG expression and subsequent memory consolidation by directing temporally specific changes in active DNA demethylation at the promoter of plasticity-related IEGs.not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/265355 doi: bioRxiv preprint first posted online Feb. 14, 2018; PNAS Gadd45 g and memory Visual abstract AbstractWe have identified a member of the Growth arrest and DNA damage (Gadd45) family, Gadd45g , which is known to be involved in the regulation of DNA repair, as a key player in the formation of associative fear memory. Gadd45g regulates the temporal dynamics of learning-induced immediate early gene (IEG) expression in the prelimbic prefrontal cortex through its interaction with DNA double-strand break (DSB)-mediated changes in DNA methylation. Our findings suggest a two-hit model of experience-dependent IEG activity and learning that comprises 1) a first wave of IEG expression governed by DSBs followed by an increase in DNA methylation, and 2) a second wave of IEG expression associated with Gadd45g and active DNA demethylation at the same site, which is necessary for memory consolidation.

RNA modification has recently emerged as an important mechanism underlying gene diversity linked to behavioral regulation. The conversion of adenosine to inosine by the ADAR family of enzymes is a particularly important RNA modification as it impacts the physiological readout of protein-coding genes. However, not all variants of ADAR appear to act solely on RNA. ADAR1 binds directly to DNA when it is in a non-canonical, left handed, "Z" conformation, but little is known about the functional relevance of this interaction. Here we report that ADAR1 binds to Z-DNA in an activity-dependent manner and that fear extinction learning leads to increased ADAR1 occupancy at DNA repetitive elements, with targets adopting a Z-DNA structure at sites of ADAR1 recruitment.Knockdown of ADAR1 leads to an inability to modify a previously acquired memory trace and this is associated with a concomitant change in DNA structure and a decrease in RNA editing. These findings suggest a novel mechanism of learning-induced gene regulation whereby ADAR1 physically interacts with Z-DNA in order to mediate its effect on RNA, and both are required for memory flexibility following fear extinction learning.

from the University of Queensland and the ANZ trustees Queensland for medical research. The authors 41 would also like to thank Ms. Rowan Tweedale for helpful editing of the manuscript, and especially Sunil 42Gandhi for comments and discussion.