Tucker R P, Erickson C A
J Embryol Exp Morphol. 1986 Sep;97:141-68.
Neural crest-derived pigment cells form species-specific patterns of pigmentation in amphibian embryos. We have characterized the appearance and changes in pigment cell distribution in the embryos of the California newt, Taricha torosa. Black melanophores first appear scattered over the surface of the somites intermingled with yellow xanthophores in stage 34/35 embryos. The melanophores then migrate either dorsally to form a dorsal stripe at the apex of the somites or ventrally along the intersomitic furrows to form a midbody stripe at the somite-lateral plate mesoderm border. Xanthophores remain between the two melanophore stripes and are also found in the dorsal fin and head. The formation of the dorsal stripe coincides with a change in melanophore tissue affinity from the surface of the somites to the subectodermal extracellular matrix (ECM). The latter substratum is the location of the cue used to organize the dorsal stripe. In addition, melanophores become elongate and highly arborized, which would allow them to extend to the region where the dorsal stripe forms. In contrast, xanthophores do not form long processes in vitro. This suggests that the ability of melanophores but not xanthophores to search for a cue at the apex of the somites may account in part for the segregation of these cells types. Melanophores and xanthophores are trapped to form the midbody stripe by the pronephric duct, which is located just beneath the ectoderm at the bases of the intersomitic furrows. Ablation of the duct prevents formation of the midbody stripe, although melanophores and xanthophores still fail to migrate ventrally over the lateral plate mesoderm. Melanophores grafted to the ventral midline fail to leave the confines of the donor tissue. This suggests that a factor in the lateral plate mesoderm in addition to the pronephric duct is inhibiting further ventral migration. There is no gross morphological difference in the organization of the subectodermal ECM dorsal and ventral to the pronephric duct as revealed by alcian blue, ruthenium red and staining with antibodies to fibronectin. We also conclude that the directed dispersal of the neural crest into the space between the somites and ectoderm is due to contact inhibition of cell movement, since T. torosa neural crest cells demonstrate contact inhibition in vitro and there are enough cells in the lateral migratory spaces to make contact events likely during dispersal.
神经嵴衍生的色素细胞在两栖动物胚胎中形成物种特异性的色素沉着模式。我们已经描述了加州蝾螈（Taricha torosa）胚胎中色素细胞分布的出现和变化。在34/35期胚胎中，黑色的黑素细胞首先分散出现在体节表面，与黄色的黄色素细胞混合在一起。然后，黑素细胞要么背向迁移，在体节顶端形成一条背侧条纹，要么沿着体节间沟腹向迁移，在体节-侧板中胚层边界处形成一条中体条纹。黄色素细胞保留在两条黑素细胞条纹之间，也存在于背鳍和头部。背侧条纹的形成与黑素细胞组织亲和力从体节表面到外胚层下细胞外基质（ECM）的变化相吻合。后一种基质是用于组织背侧条纹的信号所在位置。此外，黑素细胞变得细长且高度分支，这使它们能够延伸到背侧条纹形成的区域。相比之下，黄色素细胞在体外不会形成长突起。这表明黑素细胞而非黄色素细胞在体节顶端寻找信号的能力可能部分解释了这些细胞类型的分离。黑素细胞和黄色素细胞被位于体节间沟底部外胚层下方的前肾管捕获，形成中体条纹。切除该管道会阻止中体条纹的形成，尽管黑素细胞和黄色素细胞仍然无法在侧板中胚层上方向腹侧迁移。移植到腹侧中线的黑素细胞无法离开供体组织的范围。这表明除了前肾管外，侧板中胚层中的一个因素也在抑制进一步的腹侧迁移。通过阿尔新蓝、钌红以及用抗纤连蛋白抗体染色发现，前肾管背侧和腹侧的外胚层下ECM组织在大体形态上没有差异。我们还得出结论，神经嵴向体节和外胚层之间空间的定向扩散是由于细胞运动的接触抑制，因为加州蝾螈神经嵴细胞在体外表现出接触抑制，并且在侧向迁移空间中有足够的细胞，使得在扩散过程中接触事件很可能发生。
