N6-methyladenosine (m⁶A) is the most prevalent and reversible modification in mammalian mRNA. According to their function in the installation, removal, and recognition of the methyl group on the adenine, the enzymes and proteins related to m⁶A modification are classified as “writers”, “erasers”, and “readers”. This modification constitutes another layer of regulation in gene expression and regulates many biological processes. Specially, it has been demonstrated to regulate hippocampus-dependent spatial memory consolidation in mice. However, the mechanism by which the hippocampus functions are regulated by mRNA methylation has not yet been elucidated. Moreover, the function of which subregion of hippocampus is subject to regulation via m⁶A has also been limited investigated.

To address a...[ Read more ]

N6-methyladenosine (m⁶A) is the most prevalent and reversible modification in mammalian mRNA. According to their function in the installation, removal, and recognition of the methyl group on the adenine, the enzymes and proteins related to m⁶A modification are classified as “writers”, “erasers”, and “readers”. This modification constitutes another layer of regulation in gene expression and regulates many biological processes. Specially, it has been demonstrated to regulate hippocampus-dependent spatial memory consolidation in mice. However, the mechanism by which the hippocampus functions are regulated by mRNA methylation has not yet been elucidated. Moreover, the function of which subregion of hippocampus is subject to regulation via m⁶A has also been limited investigated.

To address above two questions, the mice with the m⁶A reader protein YTHDF1 or YTHDF2 specifically ablated in each of the three different subregions of the hippocampus were generated in this study. The hippocampus-dependent long-term spatial memory in the mutant mice was tested with the Morris Water Maze test. Only ablation of YTHDF2 in the dentate gyrus region was found to cause the malfunction of the hippocampus. With in vitro axon growth assay and in vivo labeling of mossy fiber, YTHDF2 was proved to inhibit the overgrowth of granule cell axons. In addition, the formation of mossy fiber boutons and excitatory synapses on them was impaired in DG-specific Ythdf2 conditional knockout mice. The potential targets of YTHDF2 were screened by integrating the transcriptome sequencing and anti-YTHDF2 RNA precipitation sequencing results and then verified by the mRNA half-life assay. The mediation of YTHDF2-regulated dentate gyrus granule cell axon growth by these targets was directly demonstrated by the axon growth assays.

This study proved that the role of m⁶A modification in regulating hippocampusdependent learning is mainly mediated by YTHDF2 in dentate gyrus.

Keywords: m⁶A, YTHDF2, hippocampus, dentate gyrus, spatial memory, mossy fiber