Genetic analyses in Lake Malawi cichlids identify new roles for Fgf signaling in scale shape variation

Abstract

Elasmoid scales are the most common epithelial appendage among vertebrates, however an understanding of the genetic mechanisms that underlie variation in scale shape is lacking. Using an F2 mapping cross between morphologically distinct cichlid species, we identified >40 QTL for scale shape at different body positions. We show that while certain regions of the genome regulate variation in multiple scales, most are specific to scales at distinct positions. This suggests a degree of regional modularity in scale development. We also identified a single QTL for variation in scale shape disparity across the body. Finally, we screened a QTL hotspot for candidate loci, and identified the Fgf receptor fgfr1b as a prime target. Quantitative rtPCR and small molecule manipulation support a role for Fgf signaling in shaping cichlid scales. While Fgfs have previously been implicated in scale loss, these data reveal new roles for the pathway in scale shape variation.

The Genetic Basis of Scale-Loss Phenotype in the Rapid Radiation of Takifugu Fishes

“…In addition, it has recently been shown that Fgf signaling controls scale shape variation in a Lake Malawi cichlid (Tropheops sp.) [14]. Moreover, a pharmacological inhibition of Fgf signaling in zebrafish led to an immediate and complete arrest of scale initiation and outgrowth [15].…”

“…To observe the developmental pattern of scales in Takifugu species, three closely-related species, one scale-covered (T. niphobles) and two scale-uncovered (T. pardalis and T. snyderi), were obtained by in vitro fertilization and sampled at 1,2,3,5,7,14,21,28,29,56,63, and 101 days post-hatch (dph). Live fish were stained up to 63 dph with 0.1% alizarin red S or 2% cochineal dye (Kiriya Chemical, Osaka, Japan) dissolved in half-strength seawater for 8 hours, washed in half-strength seawater for 10 min, and then euthanized in ice-cold seawater.…”

“…The scale is attractive for comparative studies of phenotypic evolution since it is widely distributed among vertebrates, and shows an impressive diversity in morphology [14][15][16]. For example, scale loss or reduction is a recurring feature in a number of teleost lineages, such as anguilliformes (eels), cypriniformes (carps), gasterosteiformes (sticklebacks), and siluriformes (catfish) [17][18][19][20][21][22][23].…”

Do the Fish Scales Shape of Mugil curema Reflect the Genetic Structure Using Microsatellites Markers and the Mexican Marine Ecoregions Classification?

“…As far as we know, only two studies have analyzed the influence of genetics on the shape of fish scales, those of Staszny et al (2013) and Albertson et al (2018). The two articles agree that both genetic and environmental factors can significantly influence the formation of scales, and thus the shape of a scale may be used as a tool to explain and detect the potential variability of the environmental influences that affect groups of genetically homogeneous fish.…”

Evolution and developmental diversity of skin spines in pufferfish

“…For instance, during scale development in zebrafish (Danio rerio) the ligand of the Hh pathway shh is expressed in the epidermal layer of cells adjacent to the scale primordium in the mesoderm 10 . More recently a set of studies documenting the association of the Wnt/β-catenin and the Fgf signaling pathway in teleost scale development and morphogenesis have emerged [16][17][18] . In addition, mutant phenotypes of the edar (Ectodyplastin-A receptor) coding locus in Medaka (Oryzias latipes; Beloniformes) show an almost complete loss of scale formation suggesting that the eda/edar signaling pathway is necessary for normal scale formation in teleosts 12 .…”