Differential contribution of direct-developing and stem cell-derived melanocytes to the XXXX larval pigment pattern.

@entity71109 @entity3392 @entity71110
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 @entity3392 pigment pattern. The embryo first develops an ontogenetic pattern that is largely composed of @entity71109 -independent, direct-developing melanocytes. This population can be replaced during regeneration by an @entity71109 -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 @entity71109 -independent, direct-developing population. Similarly, late-developing (after 3 dpf) melanocytes of the head are also @entity71109 independent. In contrast, the melanocytes that develop after 3 days postfertilization in the lateral and dorsal stripe are sensitive to @entity71109 inhibitor, indicating that they are derived from the MSC. We show that melanocyte regeneration mutants kit(j1e99) and @entity71110 (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.
