Cellular plasticity among axolotl neural crest-derived pigment cell lineages

Coloration of Anuran Tadpoles (Amphibia): Development, Dynamics, Function, and Hypotheses

Colorations of anuran tadpoles surely function in many of the same ways that have been ascribed to color and pattern in other animals, but the paucity of data forces one to look to other groups to generate hypotheses. Such an action often occurs because of the difficulty of defining specific fitness parameters to larval forms. The commonly muted colorations of tadpoles are typically considered to function only in some form of crypsis, but we discuss other functions in the particular context of behavioral ecology and changes induced by various kinds of coinhabitants. We review the development, terminology, diversity, and functions of coloration in tadpoles and then pose various questions for future research. We strongly support a broad-based perspective that calls for an integration of several fields of research.

Glial versus melanocyte cell fate choice: Schwann cell precursors as a cellular origin of melanocytes

Melanocytes and Schwann cells are derived from the multipotent population of neural crest cells. Although both cell types were thought to be generated through completely distinct pathways and molecular processes, a recent study has revealed that these different cell types are intimately interconnected far beyond previously postulated limits in that they share a common post-neural crest progenitor, i.e. the Schwann cell precursor. This finding raises interesting questions about the lineage relationships of hitherto unrelated cell types such as melanocytes and Schwann cells, and may provide clinical insights into mechanisms of pigmentation disorders and for cancer involving Schwann cells and melanocytes.

Small molecule-induced ablation and subsequent regeneration of larval zebrafish melanocytes

We developed a method to efficiently ablate a single cell type, the zebrafish melanocyte, and study the mechanisms of its regeneration. We found that a small molecule, (2-morpholinobutyl)-4-thiophenol (MoTP), specifically ablates zebrafish larval melanocytes or melanoblasts, and that this melanocytotoxicity is dependent on tyrosinase activity, which presumably converts MoTP to cytotoxic quinone species. Following melanocyte ablation by MoTP treatment, we demonstrate by BrdU incorporation experiments that regenerated melanocytes are derived from the division of otherwise quiescent melanocyte precursors or stem cells. We further show that larval melanocyte regeneration requires the kit receptor tyrosine kinase. Our results suggest that a small number of melanocyte precursors or stem cells unevenly distributed in larvae are drawn upon to reconstitute the larval melanocyte population following melanocyte ablation by MoTP.

Pigment pattern formation in zebrafish: a model for developmental genetics and the evolution of form

The zebrafish Danio rerio is an emerging model organism for understanding vertebrate development and genetics. One trait of both historical and recent interest is the pattern formed by neural crest-derived pigment cells, or chromatophores, which include black melanophores, yellow xanthophores, and iridescent iridophores. In zebrafish, an embryonic and early larval pigment pattern consists of several stripes of melanophores and iridophores, whereas xanthophores are scattered widely over the flank. During metamorphosis, however, this pattern is transformed into that of the adult, which comprises several dark stripes of melanophores and iridophores that alternate with light stripes of xanthophores and iridophores. In this review, we place zebrafish relative to other model and non-model species; we review what is known about the processes of chromatophore specification, differentiation, and morphogenesis during the development of embryonic and adult pigment patterns, and we address how future studies of zebrafish will likely aid our understanding of human disease and the evolution of form.

Anterior/posterior influences on neural crest-derived pigment cell differentiation

The neural crest of vertebrate embryos has been used to elucidate steps involved in early embryonic cellular processes such as differentiation and migration. Neural crest cells form a ridge along the dorsal midline and subsequently they migrate throughout the embryo and differentiate into a wide variety of cell types. Intrinsic factors and environmental cues distributed along the neural tube, along the migratory pathways, and/or at the location of arrest influence the fate of neural crest cells. Although premigratory cells of the cranial and trunk neural crest exhibit differences in their differentiation potentials, premigratory trunk neural crest cells are generally assumed to have equivalent developmental potentials. Axolotl neural crest cells from different regions of origin, different stages of development, and challenged with different culture media have been analyzed for differentiation preferences pertaining to the pigment cell lineages. We report region-dependent differentiation of chromatophores from trunk neural crest at two developmental stages. Also, dosage with guanosine produces region-specific influences on the production of xanthophores from wild-type embryos. Our results support the hypothesis that spatial and temporal differences among premigratory trunk neural crest cells found along the anteroposterior axis influence developmental potentials and diminish the equivalency of axolotl neural crest cells.