| Parichy Lab |
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| Overview | |
Our studies indicate a key role for interactions among pigment cells during stripe formation, and suggest that changes in these interactions contribute to pigment pattern differences among species.
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| 1. fms mutants suggest role for pigment cell interactions | |
Wild-type zebrafish pigment patterns include both yellow xanthophores and black melanophores. In contrast, fms mutants lack xanthophores and have disrupted melanophore stripes, raising the possibility that interactions between xanthophores and melanophores contribute to stripe formation.
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| 2. fms is expressed by xanthophores and precursors, but not melanophores | |
fms encodes a receptor tyrosine kinase. In situ hybridization reveals that fms is not expressed by melanophores but is expressed by xanthophores. This suggested the stripes might form because of interactions between fms-dependent xanthophores and melanophores. We tested this possibility in two ways...
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| 3. Cell transplantations reveal xanthophore–melanophore interactions in stripe development | |
If xanthophore–melanophore interactions are necessary for stripe formation, then restoring xanthophores in fms mutants should also restore stripes. We transplanted cells from nacre mutants (that have xanthophores but not melanophores) to fms mutants (that have melanophores but not xanthophores).
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Hosts that developed donor xanthophores also developed stripes of melanophores. This shows that fms-dependent xanthophores can organize melanophores into stripes.
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| 4. Temperature-sensitive fms allele demonstrates a continuous requirement for interactions | |
To discover when fms-dependent xanthophores are required for organizing melanophore stripes we isolated a temperature sensitive mutant allele. At low temperature (fms on), these fish are wild-type. At high temperature (fms off), they have the fms mutant phenotype.
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To test if stripes ever become independent of fms and fms-dependent xanthophores, we raised fish initially at low temperature (fms on) then transferred them to high temperature (fms off). Xanthophores were lost and stripes degenerated. |
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To test if fms can recruit xanthophores and whether these cells can organize melanophore stripes at late stages, we raised fish at high temperature (fms off) then shifted them to low temperature (fms on). Xanthophores were recovered and melanophores organized into normal stripes.... |
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...but stripes on the fin were randomly oriented, presumably because cues for directionality are no longer present or recognized.
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| 5. Current studies | |
We hypothesize that interactions between fms-dependent xanthophores and melanophores are a generalized pattern-forming mechanism. We are now working to identify the nature of pigment cell interactions using transgenesis and analyses of zebrafish mutants, and how evolutionary changes in the nature and timing of these interactions contribute to species differences in pigment pattern.
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