New @Nature Genetics paper mapped human skin at single-cell spatial resolution across 15 anatomic sites and 1.2 million cells — and the headline finding deserves attention: Anatomy is encoded in cell states, not just cell types. A fibroblast in your scalp and a fibroblast in your palm are both fibroblasts. Same cell type, same surface markers. But their gene expression programs are tuned to their location. The body doesn't just sort cells into the right places — it writes positional information directly into molecular state. This has been hinted at in vitro for years (fibroblasts cultured from different body sites retain "positional memory"). What Ji lab did is put spatial context back in. Using MERFISH across 22 donors with matched sites, they could distinguish whether anatomic differences reflect cell abundance, cell state, or neighborhood architecture — and the answer is all three, operating together. The cell-cell communication finding is equally striking. TNF emerges as a key regulator of immune-fibroblast crosstalk in a perivascular niche that resembles organized lymphoid tissue — right in the skin. When those neighborhoods break down, you get disease. This points directly at one of the hardest unsolved problems in building single cells foundation models. Most single-cell models treat cells as isolated units — a transcriptomic snapshot divorced from where the cell lives and who its neighbors are. But biology doesn't work that way. A cell's state is partly a function of the signals it receives from adjacent cells, the extracellular matrix it sits in, and the tissue niche it belongs to. Spatial context and cell-cell interaction aren't annotations on top of the biology — they are the biology. Any virtual cell worth the name will need to internalize that. Atlases like this one are what that training data looks like. Press release : mountsinai.org/about/newsroo… Paper: nature.com/articles/s41588-0…