Sagerström Charles G, Gammill Laura S, Veale Robin, Sive Hazel
Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA.
Dev Dyn. 2005 Jan;232(1):85-97. doi: 10.1002/dvdy.20198.
We have analyzed the roles of cell contact during determination of the outermost enveloping layer (EVL) and deeper neurectoderm in zebrafish embryos. Outer cells, but not deeper cells, are specified to express the EVL-specific marker, cyt1 by late blastula. EVL specification requires cell contact or close cell proximity, because cyt1 is not expressed after explant dissociation. The EVL may be homologous to the Xenopus epithelial layer, including the ventral larval epidermis. While Xenopus epidermal cytokeratin gene expression is activated by bone morphogenetic protein (BMP) signaling, zebrafish cyt1 is not responsive to BMPs. Zebrafish early gastrula ectodermal explants are specified to express the neural markers opl (zic1) and otx2, and this expression is prevented by BMP4. Dissociation of zebrafish explants prevents otx2 and opl expression, suggesting that neural specification in zebrafish requires cell contact or close cell proximity. This finding is in contrast to the case in Xenopus, where ectodermal dissociation leads to activation of neural gene expression, or autoneuralization. Our data suggest that distinct mechanisms direct development of homologous lineages in different vertebrates.
我们分析了细胞接触在斑马鱼胚胎最外层包被层（EVL）和更深层神经外胚层的决定过程中的作用。到囊胚晚期，外层细胞而非更深层细胞被指定表达EVL特异性标记物cyt1。EVL的指定需要细胞接触或细胞紧密相邻，因为外植体解离后cyt1不表达。EVL可能与非洲爪蟾的上皮层同源，包括腹侧幼虫表皮。虽然非洲爪蟾表皮细胞角蛋白基因表达由骨形态发生蛋白（BMP）信号激活，但斑马鱼的cyt1对BMP无反应。斑马鱼早期原肠胚外胚层外植体被指定表达神经标记物opl（zic1）和otx2，而BMP4可阻止这种表达。斑马鱼外植体的解离会阻止otx2和opl的表达，这表明斑马鱼的神经指定需要细胞接触或细胞紧密相邻。这一发现与非洲爪蟾的情况相反，在非洲爪蟾中，外胚层解离会导致神经基因表达的激活，即自动神经化。我们的数据表明，不同的机制指导不同脊椎动物中同源谱系的发育。
