Alx1 is a pivotal transcription factor in a gene regulatory network that controls skeletogenesis throughout the echinoderm phylum. We performed a structure-function analysis of sea urchin Alx1 using a rescue assay and identified a novel, conserved motif (Domain 2) essential for skeletogenic function. The paralogue of Alx1, Alx4, was not functionally interchangeable with Alx1, but insertion of Domain 2 conferred robust skeletogenic function on Alx4. We used cross-species expression experiments to show that Alx1 proteins from distantly related echinoderms are not interchangeable, although the sequence and function of Domain 2 are highly conserved. We also found that Domain 2 is subject to alternative splicing and provide evidence that this domain was originally gained through exon extension. Our findings show that a gene duplication event permitted the functional specialization of a transcription factor through changes in exon-intron organization and thereby supported the evolution of a major morphological novelty.
- Charles A Ettensohn
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Diethard Tautz, Max-Planck Institute for Evolutionary Biology, Germany
© 2017, Khor & Ettensohn
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