The molecular basis of hard cornification in the keratinized jaw sheaths and keratodonts of anuran tadpoles
- 1Leibniz Institute for the Analysis of Biodiversity Change, Hamburg, Germany
Abstract
Hard cornification is the developmental process that produces the hardened epidermal structures that characterize tetrapod diversity, including scales, feathers, hair, and claws. This process relies on keratin proteins and additional reinforcing proteins that assemble, cross-link, and strengthen tissues to become mechanically resilient. Although the molecular composition of hard cornified tissues is known to vary among tetrapods, the program is least understood in amphibians. Within frogs, hard cornification occurs in the mouthparts of most tadpoles and in the nuptial pads, hindfoot claws, and foot tubercles of some adults. We characterized transcriptomic profiles of Bombina orientalis tadpoles at three developmental stages before, during, and after mouthpart cornification. We identified 25 keratin genes orthologous to amniote hard keratins in the B. bombina genome, 18 of which are upregulated in cornifying larval mouthparts. Furthermore, two of these hard keratin paralogs and an amphibian epidermal differentiation gene exhibit distinct spatial expression patterns within the jaw sheaths and keratodonts evidenced by in situ hybridization, suggesting they have discrete functional roles. The newly discovered diversity of the hard keratin repertoire in Bombina , and the concurrent expression of many of these paralogs in tadpole mouthparts, suggests that anuran hard cornification is much more complex than adult cornified traits thus far characterized in Xenopus frogs. Our results also challenge the notion that the diversification of keratins in Amphibia is primarily associated with the transition to more terrestrial habits, and may instead be shaped, in part, by the novel feeding apparatus of aquatic tadpoles.
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BibTeX
@misc{dias2026molecular,
title = {{The molecular basis of hard cornification in the keratinized jaw sheaths and keratodonts of anuran tadpoles}},
author = {P. H. d. S. Dias and K. Hsiung and N. Stallard and J. Jones and A. Capitosti and S. Harrington and P. Lukas and I. Chrysostomakis and F. Vera Candioti and O. Hawlitschek and A. Haas and A. Bohne and D. J. Paluh},
howpublished = {bioRxiv},
year = {2026},
month = sep,
doi = {10.64898/2026.09.30.755311},
url = {https://www.biorxiv.org/content/10.64898/2026.09.30.755311v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - The molecular basis of hard cornification in the keratinized jaw sheaths and keratodonts of anuran tadpoles
AU - P. H. d. S. Dias
AU - K. Hsiung
AU - N. Stallard
AU - J. Jones
AU - A. Capitosti
AU - S. Harrington
AU - P. Lukas
AU - I. Chrysostomakis
AU - F. Vera Candioti
AU - O. Hawlitschek
AU - A. Haas
AU - A. Bohne
AU - D. J. Paluh
PY - 2026
DA - 2026/09/30
PB - bioRxiv
DO - 10.64898/2026.09.30.755311
UR - https://www.biorxiv.org/content/10.64898/2026.09.30.755311v1
AB - Hard cornification is the developmental process that produces the hardened epidermal structures that characterize tetrapod diversity, including scales, feathers, hair, and claws. This process relies on keratin proteins and additional reinforcing proteins that assemble, cross-link, and strengthen tissues to become mechanically resilient. Although the molecular composition of hard cornified tissues is known to vary among tetrapods, the program is least understood in amphibians. Within frogs, hard cornification occurs in the mouthparts of most tadpoles and in the nuptial pads, hindfoot claws, and foot tubercles of some adults. We characterized transcriptomic profiles of Bombina orientalis tadpoles at three developmental stages before, during, and after mouthpart cornification. We identified 25 keratin genes orthologous to amniote hard keratins in the B. bombina genome, 18 of which are upregulated in cornifying larval mouthparts. Furthermore, two of these hard keratin paralogs and an amphibian epidermal differentiation gene exhibit distinct spatial expression patterns within the jaw sheaths and keratodonts evidenced by in situ hybridization, suggesting they have discrete functional roles. The newly discovered diversity of the hard keratin repertoire in Bombina , and the concurrent expression of many of these paralogs in tadpole mouthparts, suggests that anuran hard cornification is much more complex than adult cornified traits thus far characterized in Xenopus frogs. Our results also challenge the notion that the diversification of keratins in Amphibia is primarily associated with the transition to more terrestrial habits, and may instead be shaped, in part, by the novel feeding apparatus of aquatic tadpoles.
ER -