In our first-ever Snippet, I urged you to join me in reverent admiration for bats, those extraordinary mammals that harbor viruses by the truckload but don’t get sick. That’s quite the superpower, but let’s not forget that these mammals can FLY, because their ancestors took mammalian arms and hands and turned them into wings. But how? (And can I do that to my hands?) Here’s one part of the transformation: three of the mammalian fingers (digits II-IV) became spectacularly long, and all of a bat’s “fingers” are spanned by a membrane of skin called the chiropatagium.
All of us mammals once had webbed hands and feet (as fetuses), sculpted into fingers by cell death. This led to the reasonable hypothesis that bats have inactivated this process, but the evidence is inconclusive. In addition, we don’t know what cell types make the chiropatagium, how they do it, or where they come from. This seems a perfect question to tackle with single-cell transcriptomics, and that’s what a group of scientists report in a new paper in Nature Ecology & Evolution.
The authors collected single-cell data from mice and from bats during the key points in development when fingers and wings are forming. They find cell death and the genes that control it but no notable differences between mice and bats, and conclude that cell death programs are not the major player in wing-making. Instead, their single-cell data enabled them to identify the cell type that makes up most of the chiropatagium, a fibroblast type that is known elsewhere but seems to have been repurposed to build the chiropatagium. The authors identify the two transcription factors (MEIS2 and TBX3) that control these cells, and then they do a super-cool experiment: they express those proteins in the mouse “hand” and see that “the ectopic expression of MEIS2 or TBX3 in interdigital distal cells induces a gene programme that partially resembles that observed in bats and leads to tissue retention.”
The authors didn’t find a “bat wing gene” which would be an admittedly cool sci-fi premise but an unexpected event in evolution. What they did find is, to me, a lot more interesting, emphasized in their clear final sentence in the Abstract:
Our results elucidate fundamental molecular mechanisms of bat wing development and illustrate how drastic morphological changes can be achieved through repurposing of existing developmental programmes during evolution.
Not just changes. Drastic morphological changes. Nicely done.
Comparative single-cell analyses reveal evolutionary repurposing of a conserved gene programme in bat wing development
In Nature Ecology & Evolution, 16 July 2025
From the groups of Darío G. Lupiáñez (CABD, Seville, Spain), Stefan Mundlos (MPIMG, Berlin, Germany, and Francisca Martínez Real (CABD, Seville, Spain).
Snippet by Stephen Matheson
Image credit: Figure 1a from Schindler et al. cited above (CC BY). Full figure with legend here.