TENT5A is a cytoplasmic non-canonical poly(A) polymerase that catalyzes adenosine transfer to mRNA poly(A) tails, functioning as a critical regulator of bone formation and secretory protein expression 1. During osteoblast differentiation, TENT5A is induced and selectively polyadenylates mRNAs encoding extracellular matrix proteins, particularly type I collagen (Col1α1, Col1α2) and other ER-targeted secreted proteins, thereby increasing their expression and promoting bone mineralization 1. This specificity for ER-imported proteins is mediated by TENT5A localization at the endoplasmic reticulum membrane through interaction with transmembrane FNDC3 proteins 2. Homozygous mutations in TENT5A cause osteogenesis imperfecta type XVIII, a rare heritable skeletal dysplasia characterized by bone fragility and hypomineralization resulting from impaired collagen deposition by osteoblasts 3. TENT5A knockout mice display bone fragility and skeletal hypomineralization phenotypes due to quantitative and qualitative collagen defects, confirming its essential role in bone homeostasis 1. Beyond bone biology, TENT5A re-adenylates mRNA-1273 vaccine transcripts in immune cells, enhancing mRNA stability and vaccine efficacy 4, and regulates myogenic differentiation through myogenin stabilization 5. As a member of the TENT5 family of secretory tuners, TENT5A represents a novel class of posttranscriptional regulators with emerging roles in cancer, immunity, and other physiological processes 2.