Alx4 keeps its limb-building role even as its expression shifts across amniotes

A gene that helps build limbs has kept its protein function remarkably stable across millions of years of amniote evolution, even as the places where it is switched on in the developing limb have changed, according to a new open-access study published in Developmental Biology Advances on 27 September 2026.

The research, led by Ziqiu Jia, Shibin Bai, Shanshan Li and colleagues with senior author Zhe Wang, focused on Alx4, an Aristaless-like homeobox gene that is required for vertebrate limb development. Morphological diversification among amniote limbs is widely thought to arise through evolutionary changes in developmental gene regulation, yet whether divergent gene expression is accompanied by divergence in developmental function has remained unclear. The team set out to test that question directly.

Comparative expression analysis showed that Alx4 exhibits divergent spatial expression patterns in chicken and mouse limb buds, meaning the gene is active in different regions of the early limb in the two species.

In contrast, when the researchers examined evolutionary sequence conservation across 51 amniote species, they found the coding sequence to be strongly conserved. Key functional domains were completely conserved, and the analysis revealed pervasive purifying selection, indicating that evolution has consistently removed mutations that would alter the protein.

To probe function, the team carried out cross-species gain-of-function assays in chicken embryos. Chicken, mouse and human Alx4 orthologs induced highly similar limb phenotypes, characterized mainly by skeletal shortening and, less frequently, by tibial widening, syndactyly and ectopic sesamoid-like cartilage.

Transcriptomic profiling further identified shared downstream responses involving extracellular matrix organization, focal adhesion, Wnt signaling and skeletal development, suggesting that the different orthologs act through overlapping molecular pathways.

The authors conclude that Alx4 retains a conserved developmental function despite divergence in limb bud expression. This suggests that differences in Alx4 regulation may contribute to variation in limb development, whereas changes in Alx4 protein function are less likely to explain the observed evolutionary differences.

The study is being shared early to provide faster access to peer-reviewed, accepted research; it is citable and carries a permanent DOI, and this version is subject to further edits before the final Version of Record replaces it.

For evolutionary developmental biology, the finding adds a concrete example of a pattern long suspected in the field: regulatory changes, rather than alterations in the protein itself, may underlie much of the diversity in how amniote limbs take shape.

Subject of Research: Evolutionary conservation and divergence of the Alx4 gene in amniote limb development

Article Title: Divergent expression and conserved function of Alx4 for limb development in amniotes

Article References: Jia, Z., Bai, S., Li, S., Tang, Y., Li, X., Zhang, J., Irwin, D. M., Zhang, S., & Wang, Z. (2026). Divergent expression and conserved function of Alx4 for limb development in amniotes. Developmental Biology Advances. https://doi.org/10.1186/s13227-026-00275-9

Image Credits: AI Generated

DOI: 10.1186/s13227-026-00275-9

Keywords: Alx4, limb development, amniotes, gene regulation, chicken embryos, mouse, purifying selection, transcriptomics, Wnt signaling, evolutionary developmental biology, homeobox gene, skeletal development