Panels a–m’ and n–o are of the same magnification. The black arrowheads indicate the caudal fin fold primordia. DDBJ/EMBL/GemBank accession numbers of chdA, chdB, and bmp4 are AB874473, AB874475, and AB874475, respectively. White arrowheads indicate the ranges of gene expression in the early‐stage embryos (a–m’). All these panels show ventral views of caudal region. Panels n, o, and p were photographed from lateral, ventral, and oblique lateral side, respectively. The italicized letters at the left bottom corner of panels from a to m’ represent the orientation of embryos “ l,” “ d,” and “ v” indicate lateral, dorsal, and ventral views. Panels i, i’, l, l’, and o show gf‐chdA‐MO‐injected embryos. Panels e, e’, g, g’, j, j’, and p show gf‐szlA‐MO‐injected embryos. Bud (a, a’, c, c’, e, e’, f–m’), early segmentation (b, b’, d, d’), and late segmentation stage (n–p) embryos were analyzed for gene expression. © 2018 The Authors Journal of Experimental Zoology Part B: Molecular and Developmental Evolution Published by Wiley Periodicals, Inc.Īnalyses of gene expression patterns Note: Expression patterns of szlA, szlB, chdA, chdB, and bmp4 are shown in the indicated rows. These results highlight the uniqueness and rarity of mutations that are able to cause large-scale morphological changes, such as a bifurcated axial skeleton, with high viability and expressivity in natural and domesticated populations.Īrtificial selection axial skeleton dorsal-ventral patterning szl. Thus, even though szl gene mutations may produce twin-tail goldfish, these szl gene mutations might not be favorable for selection in domestic breeding. Interestingly, several phenotypes were observed in szlA-depleted fish, while low expressivity of the twin-tail phenotype was observed in szlB-depleted goldfish. Here we show that goldfish have at least two subfunctionalized szl genes, designated szlA and szlB, and depletion of these genes in single-fin goldfish was able to reproduce the bifurcated caudal fin found in twin-tail ornamental goldfish. This observation raises the question of whether the szl gene mutation could also reproduce the twin-tail morphology in goldfish. However, zebrafish with mutated szl gene (another DV patterning-related gene) also exhibit twin-tail morphology and higher viability than dino/chordin-mutant zebrafish. Since all of the multiple twin-tail ornamental goldfish strains share the same mutation, it is reasonable to presume that this mutation occurred only once in domesticated goldfish. This morphological change is known to be caused by a nonsense mutation in one of the recently duplicated chordin genes, which are key players in dorsal-ventral (DV) patterning. The twin-tail of ornamental goldfish provides unique evolutionary evidence that the highly conserved midline localization of axial skeleton components can be changed by artificial selection.
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