Vertebrate non-retinal pigment cells are derived from neural crest (NC) cells, and several mutations have been identified
in the Mexican axolotl
Ambystoma mexicanum (Ambystomatidae) that affect the development of these cell lineages. In ”white” (
d) mutant axolotls, premigratory NC cells differentiate as pigment cells, yet fail to disperse, survive, or both, and this
leads to a nearly complete absence of pigment cells in the skin. Previous studies revealed that
d affects pigment cell development non-autonomously, and have reported differences between white and wild-type axolotls in
the structure and composition of the extracellular matrix through which NC and pigment cells migrate. Here we test the correspondence
of
d and two candidate genes:
steel and
AxPG. In amniotes,
Steel encodes the cytokine Steel factor (mast cell growth factor; stem cell factor; kit ligand), which is expressed along the migratory
pathways of melanocyte precursors and is required by these cells for their migration and survival; mammalian
Steel mutants resemble white mutant axolotls in having a deficit or complete absence of pigment cells. In contrast,
AxPG encodes aPG-M/versican-like proteoglycan that may promote the migration of
A. mexicanum pigment cells, and AxPGexpression is reduced in white mutant axolotls. We cloned a salamander orthologue of
steel and used a partial genetic linkage map of
Ambystoma to determine the genomic locations of
steel,
AxPG, and
d. We show that the three genes map to different linkage groups, excluding
steel and
AxPG as candidates for
d.
Key words Pigment cell - Growth factor - Extracellular matrix - Neural crest - Proteoglycan
Received: 11 November 1998 / Accepted: 30 January 1999