Mir503, an associate of the "canonical" miRNA-16 family, is a microRNA that functions as a tumor suppressor gene in numerous cancers such as breast, prostate, lung, and colorectal cancers. It moderates post-transcriptional silencing by combining with 3' untranslated regions of target mRNAs. Mir503 also plays roles in regulating cell proliferation, migration, and invasion in tumor cells [2]. Additionally, it is involved in processes like maintaining intestinal epithelial integrity, and is associated with diseases like large-artery atherosclerosis, cholestatic liver injury, diabetic neuropathy, and aging-associated pancreatitis [3,4,5,6,7].

In a KO mouse model study, deletion of miR-503 rescued the growth of Zswim8-null embryos, directly implicating miR-503 in the regulation of mammalian body size through the target-directed microRNA degradation (TDMD) pathway [1]. In the context of aging-associated pancreatitis, miR-503-322 secreted from senescent β-cells of the endocrine pancreas targets MKNK1 in exocrine acinar cells, driving the disease process [7].

In conclusion, Mir503 has diverse biological functions, acting as a tumor suppressor and being involved in various disease-related processes. Mouse models, such as the KO model in the study of embryonic growth regulation and the model highlighting its role in aging-associated pancreatitis, have significantly contributed to understanding its functions in the context of mammalian development and disease.