Although many organisms can regenerate lost tissue, the ability to correct abnormalities in existing structures has been less well studied. Pre-metamorphic Xenopus laevis tadpoles are able to resolve some craniofacial malformations as they grow; however, little is known about this process of corrective remodelling. Now, Kelly McLaughlin and colleagues interrogate the ability of X. laevis tadpoles to self-correct malformed structures. The authors use small molecules and morpholino knockdown to reproducibly cause different types of craniofacial abnormalities. The type and severity of the malformations are then assessed over time by scoring craniofacial cartilage distribution. Using this approach, the researchers show that adaptive and corrective cartilage remodelling occurs in most cases. The authors use transcriptome analyses to identify candidate genes that regulate the remodelling process, and reveal that the matrix metalloproteinases mmp1 and mmp13 are upregulated in tissues undergoing adaptive correction. The transcriptome profiles also show that thyroid hormone, which is known to be important for metamorphosis, is not responsible for the remodelling, but prolactin signalling appears to be involved. Although the molecular mechanisms are not yet fully understood, these data indicate that a thyroid-hormone independent system triggers a corrective response to remodel craniofacial defects in X. laevis tadpoles before metamorphosis.
