Mir125b-2 is a microRNA that appears to have significant functions in the brain and in cancer-related processes. In the context of brain function, it may be involved in genomic imprinting-related pathways, which play a crucial role in parent-of-origin-specific gene expression. In cancer, it may be associated with tumor-suppressing pathways [1,2].

In mice, Mir125b-2m-/p-(knockout) mice showed impaired learning and memory, as well as anxiety, with these functions being hippocampus-dependent. Hippocampal granule cells from these mice had increased neuronal excitability, increased excitatory synaptic transmission, and decreased inhibitory synaptic transmission. The gene Glutamate ionotropic receptor NMDA type subunit 2A (Grin2a), a key regulator of synaptic plasticity, was physically bound by miR-125b-2 and upregulated in the hippocampus of Mir125b-2m-/p-mice. This indicates that Mir125b-2 plays a role in regulating hippocampal function and circuit in mice [1]. In luminal A breast cancer, the aryl hydrocarbon receptor (AhR) agonist aminoflavone (AF) upregulates miR125b-2-3p, which acts as a tumor suppressor. miR125b-2-3p mimic decreased the expression of stemness genes and inhibited proliferation, migration, and mammosphere formation in breast cancer cells, while the antagomiR125b-2-3p had the opposite effects [2].

In conclusion, Mir125b-2 has important functions in the brain, regulating hippocampal-dependent behaviors and synaptic transmission. In luminal A breast cancer, it may act as a tumor suppressor. The use of Mir125b-2 knockout mouse models has been instrumental in revealing its role in brain-related processes, and research in breast cancer cells has further expanded our understanding of its potential anti-cancer functions.