Department of Biology and Biochemistry, University of Bath, Claverton Down, United Kingdom.
PLoS One. 2013;8(1):e54833. doi: 10.1371/journal.pone.0054833. Epub 2013 Jan 22.
Wnt signaling is crucial for the regulation of numerous processes in development. Consistent with this, the gene families for both the ligands (Wnts) and receptors (Frizzleds) are very large. Surprisingly, while we have a reasonable understanding of the Wnt ligands likely to mediate specific Wnt-dependent processes, the corresponding receptors usually remain to be elucidated. Taking advantage of the zebrafish model's excellent genomic and genetic properties, we undertook a comprehensive analysis of the expression patterns of frizzled (fzd) genes in zebrafish. To explore their functions, we focused on testing their requirement in several developmental events known to be regulated by Wnt signaling, convergent extension movements of gastrulation, neural crest induction, and melanocyte specification. We found fourteen distinct fzd genes in the zebrafish genome. Systematic analysis of their expression patterns between 1-somite and 30 hours post-fertilization revealed complex, dynamic and overlapping expression patterns. This analysis demonstrated that only fzd3a, fzd9b, and fzd10 are expressed in the dorsal neural tube at stages corresponding to the timing of melanocyte specification. Surprisingly, however, morpholino knockdown of these, alone or in combination, gave no indication of reduction of melanocytes, suggesting the important involvement of untested fzds or another type of Wnt receptor in this process. Likewise, we found only fzd7b and fzd10 expressed at the border of the neural plate at stages appropriate for neural crest induction. However, neural crest markers were not reduced by knockdown of these receptors. Instead, these morpholino knockdown studies showed that fzd7a and fzd7b work co-operatively to regulate convergent extension movement during gastrulation. Furthermore, we show that the two fzd7 genes function together with fzd10 to regulate epiboly movements and mesoderm differentiation.
Wnt 信号通路对于许多发育过程的调节至关重要。相应地，配体（Wnts）和受体（Frizzleds）的基因家族都非常庞大。令人惊讶的是，尽管我们对可能介导特定 Wnt 依赖性过程的 Wnt 配体有了相当的了解，但相应的受体通常仍有待阐明。利用斑马鱼模型出色的基因组和遗传特性，我们对斑马鱼中 frizzled（fzd）基因的表达模式进行了全面分析。为了探索它们的功能，我们重点测试了它们在几个已知受 Wnt 信号调节的发育事件中的需求，包括原肠胚的汇聚延伸运动、神经嵴诱导和黑素细胞特化。我们在斑马鱼基因组中发现了 14 个不同的 fzd 基因。对 1 体节至 30 小时受精后它们的表达模式进行系统分析，揭示了复杂、动态和重叠的表达模式。这项分析表明，只有 fzd3a、fzd9b 和 fzd10 在对应于黑素细胞特化时间的背神经管中表达。然而，令人惊讶的是，这些基因的单独或组合的 morpholino 敲低并没有显示黑素细胞减少的迹象，这表明在这个过程中重要的是未测试的 fzds 或另一种 Wnt 受体的参与。同样，我们只发现 fzd7b 和 fzd10 在适当的神经板边界表达，适合神经嵴诱导。然而，神经嵴标记物并没有因这些受体的敲低而减少。相反，这些 morpholino 敲低研究表明，fzd7a 和 fzd7b 协同作用，调节原肠胚期间的汇聚延伸运动。此外，我们还表明，这两个 fzd7 基因与 fzd10 一起共同调节外包运动和中胚层分化。
