Rnmt, short for RNA guanine-7 methyltransferase, is a crucial enzyme in RNA cap formation. It catalyzes the N7 methylation of the cap guanosine, a step essential for creating translation-competent mRNA. This process is central to eukaryotic gene expression, as the RNA cap recruits factors involved in splicing, nuclear export, and translation initiation [1,2,3,4,5,6,7].

During neural differentiation, repression of the RNMT complex (RNMT-RAM) is required for the repression of pluripotency-associated gene products [1]. In T cell activation, RNMT is induced by TCR stimulation and coordinates the mRNA, snoRNA, and rRNA production needed for ribosome biogenesis. Rnmt cKO CD4 T cells show decreased ribosome synthesis, reduced translation rates, and proliferation failure [2]. In breast cancer cells, a subset with oncogenic mutations in PIK3CA is highly dependent on RNMT for proliferation. Reducing RNMT activity by 50% leads to decreased proliferation and increased apoptosis in these cells [6].

In summary, Rnmt plays a vital role in multiple biological processes such as cell differentiation, T cell activation, and cell proliferation. Its function has been clearly demonstrated through conditional knockout (cKO) mouse models in the context of neural differentiation, T cell activation, and breast cancer. Understanding Rnmt's function provides insights into normal biological processes and potential therapeutic targets for related diseases.