PUBLICATION

nkx3.2 mutant zebrafish accommodate jaw joint loss through a phenocopy of the head shapes of Paleozoic jawless fish

Authors
Miyashita, T., Baddam, P., Smeeton, J., Oel, A.P., Natarajan, N., Gordon, B., Palmer, A.R., Crump, J.G., Graf, D., Allison, W.T.
ID
ZDB-PUB-200613-5
Date
2020
Source
The Journal of experimental biology   223(Pt 15): (Journal)
Registered Authors
Allison, Ted, Crump, Gage DeKoeyer, Oel, Phil
Keywords
Agnatha, Bapx, Developmental plasticity, Jaw, Joint, Nkx3.2, Skeletal remodeling, Zebrafish
MeSH Terms
  • Animals
  • Biological Evolution
  • Head
  • Jaw*
  • Male
  • Phenotype
  • Sheep
  • Skull
  • Zebrafish*/genetics
PubMed
32527964 Full text @ J. Exp. Biol.
Abstract
The vertebrate jaw is a versatile feeding apparatus. To function, it requires a joint between the upper and lower jaws, so jaw joint defects are often highly disruptive and difficult to study. To describe the consequences of jaw-joint dysfunction, we engineered two independent null alleles of a single jaw-joint marker gene, nkx3.2, in zebrafish. These mutations caused zebrafish to become functionally jawless via fusion of the upper and lower jaw cartilages (ankylosis). Despite lacking jaw joints, nkx3.2 mutants survived to adulthood and accommodate this defect by: a) having a remodelled skull with a fixed open gape, reduced snout, and enlarged branchial region; and b) performing ram feeding in the absence of jaw-generated suction. The late onset and broad extent of phenotypic changes in the mutants suggest that modifications to the skull are induced by functional agnathia, secondarily to nkx3.2 loss-of-function. Interestingly, nkx3.2 mutants superficially resemble ancient jawless vertebrates (anaspids and furcacaudiid thelodonts) in overall head shapes. Because no homology exists in individual skull elements between these taxa, the adult nkx3.2 phenotype is not a reversal, but convergence due to similar functional requirements of feeding without moveable jaws. This remarkable analogy strongly suggests that jaw movements themselves dramatically influence the development of jawed vertebrate skulls. Thus, these mutants provide a unique model with which to: a) investigate adaptive responses to perturbation in skeletal development; b) re-evaluate evolutionarily inspired interpretations of phenocopies generated by gene knockdowns and knockouts; and c) gain insights into feeding mechanics of the extinct agnathans.
Genes / Markers
Figures
Show all Figures
Expression
Phenotype
Mutations / Transgenics
Human Disease / Model
Sequence Targeting Reagents
Fish
Antibodies
Orthology
Engineered Foreign Genes
Mapping