The functions of RNA are tightly regulated via diverse intracellular mechanisms. However, probing the complex dynamics of endogenous RNA in live cells is a challenging task. In the present study, a DNA transformer is designed for visualizing the abundance, distribution, and mobility of endogenous mRNAs in live human cells. The transformable tetrahedral DNA (T-TED) probe has a flexible hinge structure and is programmed to conform into a 3D tetrahedron upon binding with the target mRNA. By incorporating Förster resonance energy transfer (FRET) imaging, super-resolution localization, and single particle tracking, the T-TED biosensor is applied for investigating the dynamics of Delta-like ligand 4 (Dll4) mRNA, which encodes a transmembrane protein, in human pulmonary microvascular endothelial cells. The data reveal unprecedented subpopulations of Dll4 mRNA with distinct mobility organized spatially in association with the endoplasmic reticulum and microtubule networks. The ability to monitor the dynamics of endogenous RNA in live human cells will provide a useful tool for studying the functions and regulation of RNA.