Eukaryotic mRNA is 5-end capped with m7 guanosine, forming the cap0 (m7GpppNpNp, N: any nucleotide). Cap methyltransferase (CMTR1) further catalyzes 2-O-ribose methylation of the first transcribed nucleotide (N1 2-O-Me) to produce the cap1 (m7GpppNmNp) structure in all eukaryotes except yeasts. To elucidate the molecular changes in the hippocampus caused by the deletion of CMTR1 in Emx1-lineage cells, hippocampal tissues from CMTR1-cWT and cKOEmx1 mice were processed for proteomic analysis.