Kapadia, E. | Search bioRxiv

bioRxiv2025

Graded BMP signals modulate yellow and red color in fishes impacting adult pigment pattern and behavior

Among the most interesting adult traits are those with roles in animal communication. Yet developmental mechanisms by which genes drive cell behaviors in building the final forms of such traits are rarely known. In this context, pigmentation is useful because colors and patterns often provide signals in mate choice, predation avoidance and other behaviors and pigmentation is unusually accessible to observation and manipulation. Here we focus on some of the most prominent signaling colors--red, orange and yellow--and show how BMP signaling at the cellular level allows for a very different kind of signal at the organismal level. Using pearl danio, Danio albolineatus, we find that spatially and temporally graded BMP signals promote development of yellow/orange xanthophores over red erythrophores in the fin of this species and a distantly related minnow, Tanichthys albonubes, and that conserved mechanisms, involving BMP co-receptor Rgmb, regulate differentiation of other pigment cell types in corresponding locations of zebrafish, D. rerio. We further use mutants of D. albolineatus with more red or more yellow cells than wild-type to demonstrate female responsiveness to carotenoid-based color differences between males in shoaling preference assays, and we show the existence of polygenic standing variation for this pigmentary trait. Our findings illustrate a chain of function spanning hierarchical levels and provide a deeper understanding of pigmentary form and function and its evolution. HIGHLIGHTSO_LIFate specification of alternative red or yellow pigment cell types in the fin of a minnow, pearl danio, depends on thresholds and gradients in BMP signaling during fin outgrowth. C_LIO_LIGenetic loss of BMP signaling leads to production of red over yellow carotenoids with resulting "super-red" fish preferred by females in shoaling assays. C_LIO_LIBMP-dependence of pigmentary traits is conserved across species with standing, polygenic variation for fin pattern and color in pearl danio. C_LI

developmental biology↗

bioRxiv2024

Agouti and BMP signaling drive a naturally occurring fate conversion of melanophores to leucophores in zebrafish

The often-prominent pigment patterns of vertebrates are varied in form and function and depend on several types of pigment cells derived from embryonic neural crest or latent stem cells of neural crest origin. These cells and the patterns they produce have been useful for uncovering features of differentiation and morphogenesis that underlie adult phenotypes, and they offer opportunities to discover how patterns and the cell types themselves have diversified. In zebrafish, a body pattern of stripes arises by self organizing interactions among three types of pigment cells. Yet these fish also exhibit white ornamentation on their fins that depends on the transdifferentiation of black melanophores to white cells, "melanoleucophores." To identify mechanisms underlying this conversion we used ultrastructural, transcriptomic, mutational and other approaches. We show that melanophore- melanoleucophore transition depends on regional BMP signals transduced through non-canonical receptors (Rgmb-Neo1a-Lrig2) as well as BMP-dependent signaling by Agouti genes, asip1 and asip2b. These signals lead to expression of transcription factor genes including foxd3 and runx3 that are necessary to induce loss of melanin by an autophagy-like process, curtail new melanin production, and deploy a pathway for accumulating guanine crystals that, together, confer a white phenotype. These analyses uncover an important role for positional information in specifying ornamentation in zebrafish and show how tissue environmental cues and a novel gene regulatory program have allowed terminal addition of a distinct phenotype to a pre-existing cell type. SignificanceFish often have striking color patterns with important functions in behavior. In zebrafish, the familiar striped pattern forms through self-organizing interactions between pigment cells, yet the white highlights on their fins arise differently--through the transformation of black pigment cells into white ones. This study reveals how this dramatic cell transformation happens: signals from the surrounding tissue, specifically BMP and Agouti proteins, instruct black cells to change their fate. These signals trigger expression of specific genes that cause the cells to break down their black pigment while acquiring white, crystal-like structures. This work shows how local signals in tissues can drive the development of ornamental features and provides insights into how new cell types evolve.

developmental biology↗