Seritrakul, P., Samarut, E., Lama, T.T., Gibert, Y., Laudet, V., and Jackman, W.R. (2012) Retinoic acid expands the evolutionarily reduced dentition of zebrafish. FASEB journal : official publication of the Federation of American Societies for Experimental Biology. 26(12):5014-5024.
Zebrafish lost anterior teeth during evolution but retain a posterior pharyngeal dentition that requires retinoic acid (RA)
cell-cell signaling for its development. The purposes of this study were to test the sufficiency of RA to induce tooth development
and to assess its role in evolution. We found that exposure of embryos to exogenous RA induces a dramatic anterior expansion
of the number of pharyngeal teeth that later form and shifts anteriorly the expression patterns of genes normally expressed
in the posterior tooth-forming region, such as pitx2 and dlx2b. After RA exposure, we also observed a correlation between cartilage malformations and ectopic tooth induction, as well as
abnormal cranial neural crest marker gene expression. Additionally, we observed that the RA-induced zebrafish anterior teeth
resemble in pattern and number the dentition of fish species that retain anterior pharyngeal teeth such as medaka but that
medaka do not express the aldh1a2 RA-synthesizing enzyme in tooth-forming regions. We conclude that RA is sufficient to induce anterior ectopic tooth development
in zebrafish where teeth were lost in evolution, potentially by altering neural crest cell development, and that changes in
the location of RA synthesis correlate with evolutionary changes in vertebrate dentitions.