Homology and evolutionary novelty in the deployment of extracellular matrix molecules during pigment pattern formation in the salamanders Taricha torosa and T-rivularis (Salamandridae)

Salamander larvae exhibit a diverse array of pigment patterns shortly after hatching. Previous studies have identified roles for the extracellular mat rix and lateral line sensory system in promoting the development of a phylo genetically common pattern of horizontal melanophore stripes. In contrast, salamanders in the genus Taricha exhibit evolutionarily derived pigment pat terns and pattern-forming mechanisms. Taricha torosa larvae exhibit compact melanophore stripes that develop via redundant, lateral line-independent m echanisms, whereas T. rivularis larvae lack stripes and instead have melano phores uniformly distributed over the flank. In this study, I test roles fo r candidate patterning molecules of the extracellular matrix in promoting t he development of species-specific pigment patterns in Taricha. I show that tenascin deposition is negatively correlated with melanophore distribution s both intraspecifically and interspecifically: this matrix molecule is pre sent where melanophores do not localize in II torosa and is absent from the se same regions where melanophores are abundant in T rivularis. Embryologic al manipulations further indicate that transient expression of tenascin in a prospective interstripe region of T. torosa reflects a phylogenetically c onserved effect of lateral line development. Finally, anti-laminin immunore activity is negatively correlated with melanophore distributions in I toros a, and this species exhibits a general retardation of extracellular matrix development that may allow persistent, evolutionarily novel melanophore mot ility in this species. Together these findings identify tenascin and lamini n, or molecules co-regulated with these matrix components, as candidates fo r promoting early larval pigment pattern development in Taricha. (C) 2001 W iley-Liss,Inc.