Melanophores in the stripes of adult zebrafish do not have the nature to gather, but disperse when they have the space to move

Abstract

SummaryAnimal skin pattern is one of the good model systems used to study the mechanism of pattern formation.Molecular genetic studies with zebrafish have shown that pigment cells play a major role in the mechanism of stripe formation. Among the variety of cellular events that may be involved in the mechanism, aggregation of melanophores has been suggested as an important factor for pattern formation. However, only a few experimental studies detected the migration ability of melanophores in vivo. Here, we tried to determine whether melanophores really have the ability to aggregate in the skin of zebrafish. Melanophores in the adult stripes are packed densely and they rarely move. However, when the neighboring pigment cells are killed, they move and regenerate the stripe pattern, suggesting that melanophores retain the migration ability. To analyze the migration, we ablated a part of the melanophores by laser to give free space to the remaining cells; we then traced the migration. Contrary to our expectation, we found that melanophores repulsed one another and dispersed from the aggregated condition in the absence of xanthophores. Apparent aggregation may be forced by the stronger repulsive effect against the xanthophores, which excludes melanophores from the yellow stripe region.

In vitro analysis suggests that difference in cell movement during direct interaction can generate various pigment patterns in vivo

“…In this system, we found that the interaction was not a simple repulsive response but a more active and continuous run-and-chase movement. The run-and-chase movement was quite similar to the exclusive movement of melanophores in vivo (16). The similarity between these movements suggested that the cell movement observed in vitro was related to pattern formation in vivo.…”

“…Although pigment cell interaction has been suggested to play an important role in pigment patterning (16,19), the details of the interaction remained to be elucidated, because an appropriate system for observation did not exist. In this report, we established a unique protocol to harvest pigment cells and observe them in vitro.…”

“…The mean scalar speeds of the xanthophores and melanophores were 0.64 and 2.02 μm/h, respectively. In our previous study, we traced the track of melanophores during pattern formation (16). Melanophores moved 80-100 μm in 1 wk in vivo, which corresponds to 0.48-0.60 μm/h.…”

Modelling stripe formation in zebrafish: an agent-based approach

“…Numerous experimental studies have been conducted to elucidate the cellular interactions that drive pattern formation. These experiments range from using laser or transgenic ablation to remove pigment cells in vivo [5,7,12,16,17] to observing pairs of cells interacting in vitro [18,19] and exploring altered cell behaviour through mutational analysis, transplantation and other methods [14,20,21]. Researchers also study time-lapse images of wild-type development [10,15,16,20,22] and analyse mutations [4,8,10,11,[14][15][16][19][20][21][22][23][24][25].…”

Comment on “Local reorganization of xanthophores fine-tunes and colors the striped pattern of zebrafish”

“…Because we and others observed the migration of pigment cells and their precursors, we wonder if this conflict might be from a difference in some experimental conditions (8)(9)(10)(11). More fundamentally, however, migration is not a crucial requirement of our Turing-based model.…”