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Thyroid hormone–dependent adult pigment cell lineage and pattern in zebrafish

Science  12 Sep 2014:
Vol. 345, Issue 6202, pp. 1358-1361
DOI: 10.1126/science.1256251

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Origin of fish pigment cell for pattern

Zebrafish stripes arise from the interactions of pigment cells: black melanophores, iridescent iridophores, and yellow-orange xanthophores. Melanophores and iridophores develop from nerve-associated stem cells, but the origin of xanthophores is unclear. Two studies now reveal that adult xanthophores originate from xanthophores in embryonic and larval fish, when they proliferate to cover the skin before the arrival of black and silver cells in a striped arrangement. Mahalwar et al. show that xanthophores change their final shape and color depending on their location. In black cells, xanthophores appear faint and stellate, but in silver cells, they are bright and compact. Precise superposition creates the blue and golden colors. McMenamin et al. observe the loss of pigment in embryonic xanthophores and the later reappearance in the adult. They show that redifferentiation depends on the thyroid hormone that also limits melanophore population expansion.

Science, this issue p. 1362 and p. 1358

Abstract

Pigment patterns are useful for elucidating fundamental mechanisms of pattern formation and how these mechanisms evolve. In zebrafish, several pigment cell classes interact to generate stripes, yet the developmental requirements and origins of these cells remain poorly understood. Using zebrafish and a related species, we identified roles for thyroid hormone (TH) in pigment cell development and patterning, and in postembryonic development more generally. We show that adult pigment cells arise from distinct lineages having distinct requirements for TH and that differential TH dependence can evolve within lineages. Our findings demonstrate critical functions for TH in determining pigment pattern phenotype and highlight the potential for evolutionary diversification at the intersection of developmental and endocrine mechanisms.

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