Marie Curie Seminar – How fish colour their skin: A paradigm for development and evolution of adult patternsDecember 10th 2018, 11am / Centre de Recherche - Paris - Amphithéâtre Constant-Burg - 12 rue Lhomond, Paris 5e Christiane Nüsslein-Volhard
Colour patterns are prominent features of most animals; they are highly variable and evolve rapidly leading to large diversities between species even within a single genus. As targets for natural as well as sexual selection, they are of high evolutionary significance. The zebrafish (Danio rerio) displays a conspicuous pattern of alternating blue and golden stripes on the body and on the anal- and tailfins. Pigment cells in zebrafish – melanophores, iridophores and xanthophores – originate from neural crest-derived stem cells associated with the dorsal root ganglia of the peripheral nervous system. Clonal analysis indicates that these progenitors remain multipotent and plastic beyond embryogenesis well into metamorphosis, when the adult colour pattern develops. Pigment cells share a lineage with neuronal cells of the peripheral nervous system; progenitors spread along the spinal nerves. The proliferation of pigment cells is regulated by competitive interactions among cells of the same type. An even spacing involves collective migration and contact inhibition of locomotion of the three cell types distributed in superimposed monolayers in the skin. This mode of colouring the skin is probably common to fish, whereas different patterns emerge by species specific cell interactions among the different pigment cell types. These interactions are mediated by channels involved in direct cell contact between the pigment cells, as well as unknown cues provided by the tissue environment.
The colour patterns in closely related Danio species are amazingly different; their variation offers a great opportunity to investigate the genetic and developmental basis of colour pattern evolution in vertebrates. Exciting technical developments of the recent years, especially next-generation sequencing technologies and the novel possibilities of genome editing with the CRISPR/Cas9 system, allow to easily expand from model organisms into other species and directly test the function of genes by targeted knock outs and allele replacements. Thus, models and hypotheses about pigment pattern formation derived from zebrafish can now be tested in other Danio species. These studies will lay the foundation to understand not only the genetic basis of colour pattern variation between Danio species, but also the evolution of colour patterns in other vertebrates.