| Parichy Lab |
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| Overview | |
Our studies suggest that latent precursors or stem cells play a critical role in pigment pattern development and evolution. In the spotted danio, D. nigrofasciatus, this lineage is dramatically reduced compared to the sister species, D. rerio.
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| 1. Superficially similar stripes with different cellular origins | |
| The stripes of D. rerio and D. nigrofasciatus are superficially similar. Yet, closer inspection reveals major differences. In D. rerio, there are many cells, and most have differentiated from latent precursors during metamorphosis. In D. nigrofasciatus, however, there are far fewer melanophores overall, and many of these are early larval melanophores that differentiated in embryos to make the early larval pattern, only to be redeployed later into the adult stripes (movies). So these similar stripes depend on very different populations of melanophores! |
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D. rerio
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D. nigrofasciatus
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| 2. Adult pigment patterns develop ancestrally from stem cell-derived melanophores | |
To see if either the D. rerio or D. nigrofasciatus mode is ancestral, we followed individual cells in additional species. For each species, the adult pigment pattern developed from stem cell-derived melanophores, not from early larval melanophores. This implies that: (i) pigment pattern evolution occurs by changes in the stem cell-derived melanophore lineage; and (ii) D. nigrofasciatus has a unique, derived mode of pigment pattern metamorphosis with a significant reduction in this lineage.
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| 3. Reduced metamorphic melanophore lineage in D. nigrofasciatus | |
Molecular markers for melanophore precursors reveal far fewer of these cell in D. nigrofasciatus, implying the evolution of an early block in this lineage. Additional studies suggest a genetic pathway that may be responsible.
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| 4. Interspecific cell transplants indicate that evolutionary changes are extrinsic to the melanophores | ||||
| To see if differences between species are intrinsic (autonomous) or extrinsic (non-autonomous) to pigment cell lineages, we transplanted cells from D. nigrofasciatus to albino mutant D. rerio. | Danio nigrofasciatus melanophores behaved like D. rerio melanophores in D. rerio hosts! So the evolutionary changes are extrinsic to the melanophores themselves. | |||
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| 5. Current studies | |
Our results suggest a model for evolutionary changes in pigment pattern across danios, and alterations specifically in the development of stem cell-derived melanophores in D. nigrofasciatus. We are now working to identify the molecular bases for these differences between species.
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