TUNAR (TCL1 upstream neural differentiation-associated RNA) is a long noncoding RNA that encodes a conserved 48-amino-acid micropeptide called BNLN (beta cell- and neural cell-regulin) 1. BNLN functions as a single-pass transmembrane protein localized to the endoplasmic reticulum (ER) in pancreatic β cells, where it regulates intracellular calcium homeostasis by lowering ER calcium levels and enhancing glucose-stimulated insulin secretion 1. In β cells, TUNAR fine-tunes the Wnt signaling pathway by interacting with the histone modifier EZH2 to suppress the Wnt antagonist DKK3, thereby promoting β-cell proliferation 2. TUNAR expression is upregulated in β cells from type 2 diabetes patients and suppressed by diet-induced obesity 2, 1. Beyond pancreatic function, TUNAR plays critical roles in reproduction and embryonic development: it is highly expressed in metaphase II oocytes 3 and is downregulated in the endometrium during the implantation window, with aberrantly elevated expression associated with recurrent implantation failure 4, 5. TUNAR's dysregulation has prognostic significance in pediatric rhabdoid tumor of the kidney 6. These findings establish TUNAR as a multifunctional lncRNA-encoded micropeptide with critical roles in metabolic homeostasis, reproductive physiology, and disease pathogenesis.