The UCE model used frog data to distinguish regeneration from scarring in a mouse digit

The UCE model used frog data to distinguish regeneration from scarring in a mouse digit

On July 29, 2026, Hu Zan and Sha Sun published a preprint describing the UCE model for single-cell data. The authors used frog data to construct a scale of tissue states, then applied it to digit repair in adult mice.

Cross-species cell comparisons usually begin by asking which cells resemble one another. Regeneration raises another important question: whether a cell contributes to restoring the lost structure or to forming scar tissue. The same tissue can pass through both states at different stages of development.

UCE converts the set of active genes in each cell into coordinates that allow cells from different organisms to be matched. For Xenopus laevis, the authors kept the L- and S-copies of genes produced by genome duplication separate. This allowed the model to preserve a distinction that is lost when genes are conventionally collapsed under shared names.

To define the scale, the authors selected a well-established contrast in the frog tail. Regeneration-organizing cells initiate tail growth: removing them prevents regeneration, while transplanting them produces an additional outgrowth. The researchers compared the profile of these cells with that of ordinary epidermal cells, defined a direction in the model's coordinate space, and tested it in other datasets.

The scale distinguished tadpole limbs at stages 52 and 58: an amputated limb regenerates at the earlier stage, whereas the later stage produces a spike-like outgrowth. The authors then used this distinction to construct a second scale and applied it to cells from adult mice. The regenerating third digit phalanx P3 fell on the regenerative side of the scale, while the second phalanx P2, which heals through fibrosis, fell on the opposite side. Macrophages showed the same ordering across five repair timepoints.

This type of scale can be used to assess interventions by asking whether they shift cells toward regeneration and whether that shift corresponds to the outcome of tissue repair. It turns cross-species comparison into a measurable question about cell state.