Proliferation, dispersal and patterned aggregation of iridophores in the skin prefigure striped colouration of zebrafish

The few of these cells that transitioned from a nascent dense morphology to a loose morphology occurred already within prospective stripe regions.

“Contrary to the expectations of the morphogenetic respecification model12,20, the few of these cells that transitioned from a nascent dense morphology to a loose morphology occurred already within prospective stripe regions.”

In dark stripes, iridophores are sparse in number and stellate in shape, sometimes referred to as having a loose morphology.

“In the dark stripes, by contrast, iridophores are sparse in number and stellate in shape, and are sometimes referred to as having a “loose” morphology12 (Fig. 1b).”

This suggests differentiation with subsequent proliferation rather than active aggregation of widely dispersed cells.

“In addition, we found that the formation of secondary interstripes was characterized by the development of cells newly expressing pnp4a within this region, suggesting differentiation with subsequent proliferation rather than active aggregation of widely dispersed cells12 (Supplementary Fig. 3).”

Previous analyses used a sox10:CreERt2 transgene that can mark most or all postembryonic neural crest derivatives, including multipotent progenitors in the peripheral nervous system, and cells transiting from the peripheral nervous system to the hypodermis of the skin.

“Previous analyses used a sox10:CreERt2 transgene that can mark most or all postembryonic neural crest derivatives, including multipotent progenitors in the peripheral nervous system, and cells transiting from the peripheral nervous system to the hypodermis of the skin12,46”

Such behaviors occurred within prospective stripes, rather than at boundaries between interstripes and stripes, and involved cells that had not yet fully differentiated.

“Such behaviors occurred within prospective stripes, rather than at boundaries between interstripes and stripes, as previously postulated5,12, and involved cells that had not yet fully differentiated”

The apparent conflict between the authors' observations and those of prior studies may reflect differences in how iridophores and their progenitors have been visualized.

“The apparent conflict between our observations and those of prior studies5,12,19 may reflect differences in how iridophores and their progenitors have been visualized”