Researchers at the University of Basel published weMERFISH, an extension of MERFISH that enables three‑dimensional, whole‑embryo spatial transcriptomics over time. The platform detected transcripts of nearly 500 genes at subcellular resolution in zebrafish embryos and, using computational imputation, reconstructed spatial expression for over 25,000 genes and chromatin accessibility for ~300,000 regions. Method innovations include covalently anchored probes for sample stability, gene‑specific readout designs, and amplified probe architectures to boost signal—allowing repeat imaging and large gene panels in intact 3D samples. One‑sentence clarification: MERFISH is a multiplexed FISH technique that reads combinatorial barcodes to localize transcripts at single‑molecule resolution in situ. Why it matters: whole‑embryo spatial, temporal maps will help decode developmental boundary formation, cell‑cell signaling, and lineage dynamics—tools useful for developmental biology, disease modeling, and translational research.