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Abstract
The extent of adult stem cell involvement in embryonic growth is often unclear, as
reliable markers or assays for whether a cell is derived from an adult stem cell,
such as the melanocyte stem cell (MSC), are typically not available. We have previously
shown that two lineages of melanocytes can contribute to the larval zebrafish pigment
pattern. The embryo first develops an ontogenetic pattern that is largely composed
of ErbB-independent, direct-developing melanocytes. This population can be replaced
during regeneration by an ErbB-dependent MSC-derived population following melanocyte
ablation. In this study, we developed a melanocyte differentiation assay used together
with drugs that ablate the MSC to investigate whether MSC-derived melanocytes contribute
to the ontogenetic pattern. We found that essentially all melanocytes that develop
before 3 dpf arise from the ErbB-independent, direct-developing population. Similarly,
late-developing (after 3 dpf) melanocytes of the head are also ErbB independent. In
contrast, the melanocytes that develop after 3 days postfertilization in the lateral
and dorsal stripe are sensitive to ErbB inhibitor, indicating that they are derived
from the MSC. We show that melanocyte regeneration mutants kit(j1e99) and skiv2l2(j24e1)
that are grossly normal for the overall ontogenetic pattern also lack the MSC-derived
contribution to the lateral stripe. This result suggests that the underlying regeneration
defect of these mutations is a defect in MSC regulation. We suggest that the regulative
functions of the MSC may serve quality control roles during larval development, in
addition to its established roles in larval regeneration and growth and homeostasis
in the adult.
Copyright 2009 Elsevier Inc. All rights reserved.