Reedy M V, Faraco C D, Erickson C A
Section of Molecular and Cellular Biology, University of California at Davis, Davis, California, 95616, USA.
Dev Biol. 1998 Aug 15;200(2):234-46. doi: 10.1006/dbio.1998.8963.
Neural crest cells migrate along two pathways in the trunk: the ventral path, between the neural tube and somite, and the dorsolateral path, between the somite and overlying ectoderm. In avian embryos, ventral migration precedes dorsolateral migration by nearly 24 h, and the onset of dorsolateral migration coincides with the cessation of ventral migration. Neural crest cells in the ventral path differentiate predominantly as neurons and glial cells of the peripheral nervous system, whereas those in the dorsolateral path give rise to the melanocytes of the skin. Thus, early- and late-migrating neural crest cells exhibit unique morphogenetic behaviors and give rise to different subsets of neural crest derivatives. Here we present evidence that these differences reflect the appearance of specified melanocyte precursors, or melanoblasts, from late- but not early-migrating neural crest cells. We demonstrate that serum from Smyth line (SL) chickens specifically immunolabels melanocyte precursors, or melanoblasts. Using SL serum as a marker, we first detect melanoblasts immediately dorsal and lateral to the neural tube beginning at stage 18, which is prior to the onset of dorsolateral migration. At later stages every neural crest cell in the dorsolateral path is SL-positive, demonstrating that only melanoblasts migrate dorsolaterally. Thus, melanoblast specification precedes dorsolateral migration, and only melanoblasts migrate dorsolaterally at the thoracic level. Together with previous work (Erickson, C. A., and Goins, T. L., Development 121, 915-924, 1995), these data argue that specification as a melanoblast is a prerequisite for dorsolateral migration. This conclusion suggested that the delay in dorsolateral migration (relative to ventral migration) may reflect a delay in the emigration of melanogenic neural crest cells from the neural tube. Several experiments support this hypothesis. There are no melanoblasts in the ventral path, as revealed by the absence of SL-positive cells in the ventral path, and neural crest cells isolated from the ventral path do not give rise to melanocytes when explanted in culture, suggesting that early, ventrally migrating neural crest cells are limited in their ability to differentiate as melanocytes. Similarly, neural crest cells that emigrate from the neural tube in vitro during the first 6 h fail to give rise to any melanocytes or SL-positive melanoblasts, whereas neural crest cells that emigrate at progressively later times show a dramatic increase in melanogenesis under identical culture conditions. Thus, the timing of dorsolateral migration at the thoracic level is ultimately controlled by the late emigration of melanogenic neural crest cells from the neural tube.
腹侧路径，位于神经管和体节之间；背外侧路径，位于体节和上方的外胚层之间。在鸟类胚胎中，腹侧迁移比背外侧迁移早近24小时开始，背外侧迁移的起始与腹侧迁移的停止同时发生。腹侧路径中的神经嵴细胞主要分化为外周神经系统的神经元和神经胶质细胞，而背外侧路径中的神经嵴细胞则产生皮肤的黑素细胞。因此，早期和晚期迁移的神经嵴细胞表现出独特的形态发生行为，并产生不同的神经嵴衍生物亚群。在这里，我们提供证据表明，这些差异反映了特定黑素细胞前体，即黑素母细胞，在晚期而非早期迁移的神经嵴细胞中的出现。我们证明，来自史密斯品系（SL）鸡的血清特异性免疫标记黑素细胞前体，即黑素母细胞。使用SL血清作为标记物，我们首先在第18阶段开始时检测到神经管背侧和外侧紧邻的黑素母细胞，这早于背外侧迁移的起始。在后期阶段，背外侧路径中的每个神经嵴细胞都是SL阳性的，表明只有黑素母细胞向背外侧迁移。因此，黑素母细胞的特化先于背外侧迁移，并且只有黑素母细胞在胸段向背外侧迁移。与之前的研究（埃里克森，C.A.，和戈因斯，T.L.，《发育》121卷，915 - 924页，1995年）一起，这些数据表明，作为黑素母细胞的特化是背外侧迁移的先决条件。这一结论表明，背外侧迁移（相对于腹侧迁移）的延迟可能反映了黑素生成性神经嵴细胞从神经管迁出的延迟。几个实验支持了这一假设。腹侧路径中没有黑素母细胞，这通过腹侧路径中缺乏SL阳性细胞得以揭示，并且从腹侧路径分离的神经嵴细胞在培养时不会产生黑素细胞，这表明早期向腹侧迁移的神经嵴细胞分化为黑素细胞的能力有限。同样，在体外最初6小时内从神经管迁出的神经嵴细胞不会产生任何黑素细胞或SL阳性黑素母细胞，而在逐渐较晚时间迁出的神经嵴细胞在相同培养条件下黑素生成显著增加。因此，胸段背外侧迁移的时间最终由黑素生成性神经嵴细胞从神经管的晚期迁出所控制。
