Department of Developmental and Regenerative Biology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo 113-8510, Japan.
J Cell Biochem. 2010 Jul 1;110(4):1022-37. doi: 10.1002/jcb.22616.
Stress-induced Sapk/Jnk signaling is involved in cell survival and apoptosis. Recent studies have increased our understanding of the physiological roles of Jnk signaling in embryonic development. However, still unclear is the precise function of Jnk signaling during gastrulation, a critical step in the establishment of the vertebrate body plan. Here we use morpholino-mediated knockdown of the zebrafish orthologs of the Jnk activators Mkk4 and Mkk7 to examine the effect of Jnk signaling abrogation on early vertebrate embryogenesis. Depletion of zebrafish Mkk4b led to abnormal convergent extension (CE) during gastrulation, whereas Mkk7 morphants exhibited defective somitogenesis. Surprisingly, Mkk4b morphants displayed marked upregulation of wnt11, which is the triggering ligand of CE and stimulates Jnk activation via the non-canonical Wnt pathway. Conversely, ectopic activation of Jnk signaling by overexpression of an active form of Mkk4b led to wnt11 downregulation. Mosaic lineage tracing studies revealed that Mkk4b-Jnk signaling suppressed wnt11 expression in a non-cell-autonomous manner. These findings provide the first evidence that wnt11 itself is a downstream target of the Jnk cascade in the non-canonical Wnt pathway. Our work demonstrates that Jnk activation is indispensable for multiple steps during vertebrate body plan formation. Furthermore, non-canonical Wnt signaling may coordinate vertebrate CE movements by triggering Jnk activation that represses the expression of the CE-triggering ligand wnt11.
应激诱导的 Sapk/Jnk 信号通路参与细胞存活和凋亡。最近的研究增加了我们对 Jnk 信号通路在胚胎发育中的生理作用的理解。然而，Jnk 信号通路在原肠胚形成过程中的精确功能仍不清楚，原肠胚形成是脊椎动物体轴建立的关键步骤。在这里，我们使用 MKK4 和 MKK7 的斑马鱼同源物的 morpholino 介导敲低来研究 Jnk 信号通路阻断对早期脊椎动物胚胎发生的影响。MKK4b 的耗尽导致原肠胚形成期间的异常会聚延伸（CE），而 MKK7 缺陷体则表现出体节形成缺陷。令人惊讶的是，MKK4b 缺陷体表现出明显的 wnt11 上调，wnt11 是 CE 的触发配体，并通过非经典 Wnt 途径刺激 Jnk 激活。相反，通过过表达活性形式的 MKK4b 异位激活 Jnk 信号导致 wnt11 下调。嵌合体谱系追踪研究表明，MKK4b-Jnk 信号以非细胞自主的方式抑制 wnt11 的表达。这些发现首次证明 wnt11 本身是非经典 Wnt 途径中 Jnk 级联反应的下游靶标。我们的工作表明，Jnk 激活对于脊椎动物体轴形成的多个步骤是必不可少的。此外，非经典 Wnt 信号可能通过触发 Jnk 激活来协调脊椎动物的 CE 运动，从而抑制 CE 触发配体 wnt11 的表达。
