A Nonsynonymous Mutation in the Transcriptional Regulator lbh Is Associated with Cichlid Craniofacial Adaptation and Neural Crest Cell Development; Critique

Aims of the Paper

The researchers hypothesized that the limb bud and heart homolog (lbh), a nonsynonymous mutation in transcriptional coactivator that is linked to adaptive variation in the lower limb of the Cichlid fish, play a role in craniofacial development, thereby contributing to the diversity of these fish. To test this hypothesis, the researchers used a zebrafish and Xenopus collected from the rift valley water bodies and samples extracted for genetic analysis. Genotyping was done to determine the genetic variation in the samples. Powder et al. (2014) then conducted a phenotypic analysis of the craniofacial structures for the samples with special reference to the jaw length, part of the geometric morphometric that quantifies the craniofacial difference to enable comparison. Based on existing literature, the researchers knew that the divided coding allele is only be found in Labeotropheus fuelleborni (LF). Since LF influences one side of the continuous craniofacial variation among the species, they could hypothesize that lbh and R>Q coding mutation, in particular, contributed to the observed adaptive mandible morphology.

The researchers found that there was an amino acid change in Lbh that was significantly associated with continuous, adaptive morphological variation. Embryonic patterns correlated with adult phenotypes, and the differences in mandible length were traced back to even before chondrogenesis, in the early stages of craniofacial development. The data from functional analysis, head shape analysis, and jaw lengths showed that amino acid polymorphism affects patterns of NCC migration. From these observations, Powder et al. (2014) concluded that the single amino acid change that was alternatively fixed in Cichlids with different facial morphologies resulted in discrete shifts in the multipotent cell type migration patterns consistent with phenotypes in embryos and adults. Further, cellular events sic as apoptosis, proliferation, and differentiation lead to species-specific differences in facial shapes consistent with the development theory where the phenotype is determined by earlier events. Finally, since the coding mutation occurs in a disordered domain and the derived allele leads to a loss of the predicted short linear motif, Powder et al. (2014) conclude that this supports the theory that modules within coding regions, including those mediating interactions between proteins, show evolutionary plasticity by a high magnitude.

Reference

Powder, K. E., Cousin, H., McLinden, G. P., & Albertson, R. C. (2014). A Nonsynonymous Mutation in the Transcriptional Regulator lbh Is Associated with Cichlid Craniofacial Adaptation and Neural Crest Cell Development. Molecular Biology and Evolution, 31(12), 3113–3124. https://doi.org/10.1093/molbev/msu267