Fish of Many Colors

Researchers seek insight into the pigmentation patterns of guppies and zebrafish.

By | January 23, 2014

Male guppyEUREKALERT, ANNA PRICEMale guppies’ vibrant colors and the yellow and black stripes that give the zebrafish its name are both products of pigment cells. Two research groups have now learned more about how these cells are organized to form these characteristic patterns.

In work published in PLOS One this week (January 22), a team from the Max Planck Institute for Developmental Biology in Tübingen, Germany, showed that at least two of three types of pigment cells—melanophores, xanthophores, and iridophores—contribute to male guppies’ colors. Using electron microscopy, the researchers found that pigment layers in both the dermis and hypodermis played a role in generating the fishes’ spots. Iridophores were present in each color trait the researchers studied, which they wrote suggested “that complex interactions between different chromatophore types both may be involved in establishing color patterns and [enhancing] color signals.”

Meanwhile, Hiroaki Yamanaka and Shigeru Kondo of Osaka University in Japan investigated the formation of the zebrafish’s stripes, which the literature suggests are generated by the interactions of two types of pigment cells—melanophores and xanthophores. Their findings, which were published this week (January 21) in PNAS, revealed that in vitro normal xanthophores—harvested from the tail fin of an adult fish—contacted melanophores by extending pseudopodia. The melanophores then moved away from the contact. When the researchers studied pigment cells from a mutant fish called leopard, which has spots instead of stripes, they found that even though the xanthophores extended processes toward the melanophores, the melanophores did not move away. The authors suggested a model of stripe formation where “cells themselves move actively to form patterns through mutual interactions.”

While the in vitro system may be useful for studying pigment cell communication, it is still unclear how biologically relevant the findings are. Current Biology Editor Florian Maderspacher, who studied pigment patterns in zebrafish during his graduate training, told National Geographic’s Not Exactly Rocket Science that “the fact that it’s in a culture dish [means] we have no real way of knowing that the cell behaviors they document are really what underlies stripe formation.”

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