Deconstructing evolution of adult phenotypes: genetic analyses ofkitreveal homology and evolutionary novelty during adult pigment pattern development ofDaniofishes

Citations Over TimeTop 19% of 2007 papers

Abstract

The cellular bases for evolutionary changes in adult form remain largely unknown. Pigment patterns of Danio fishes are a convenient system for studying these issues because of their diversity and accessibility and because one species, the zebrafish D. rerio, is a model organism for biomedical research. Previous studies have shown that in zebrafish, stripes form by migration and differentiation of distinct populations of melanophores: early metamorphic (EM) melanophores arise widely dispersed and then migrate into stripes, whereas late metamorphic (LM) melanophores arise already within stripes. EM melanophores require the kit receptor tyrosine kinase, as kit mutants lack these cells but retain LM melanophores, which form a residual stripe pattern. To see if similar cell populations and genetic requirements are present in other species, we examined D. albolineatus, which has relatively few, nearly uniform melanophores. We isolated a D. albolineatus kit mutant and asked whether residual, LM melanophores develop in this species, as in D. rerio. We found that kit mutant D. albolineatus lack EM melanophores, yet retain LM melanophores. Histological analyses further show that kit functions during a late step in metamorphic melanophore development in both species. Interestingly, kit mutant D. albolineatus develop a striped melanophore pattern similar to kit mutant D. rerio, revealing latent stripe-forming potential in this species, despite its normally uniform pattern. Comparisons of wild types and kit mutants of the two species further show that species differences in pigment pattern reflect: (1) changes in the behavior of kit-dependent EM melanophores that arise in a dispersed pattern and then migrate into stripes in D. rerio, but fail to migrate in D. albolineatus; and (2) a change in the number of kit-independent LM melanophores that arise already in stripes and are numerous in D. rerio, but few in D. albolineatus. Our results show how genetic analyses of a species closely related to a biomedical model organism can reveal both conservatism and innovation in developmental mechanisms underlying evolutionary changes in adult form.

Related Papers

• → Studies of pigment transfer between Xenopus laevis melanophores and fibroblasts in vitro and in vivo1(2005)40 cited
• → Ultrastructure of the integumental melanophores of the coelacanth, Latimeria chalumnae(1975)9 cited
• → The Response of Single Melanophores to Extracellular and Intracellular Iontophoretic Injection of Melanocyte-Stimulating Hormone*(1980)7 cited
• → The localisation of lead in the skin of light- and dark-adapted Xenopus laevis(1979)3 cited
• → Ultrastructural study of the cutaneous pigment cells of wild-type and albinistic bullfrogs, Rana catesbeiana(1978)2 cited