The acquisition of a movable jaw and a jaw joint are key events in gnathostome evolution. Jaws are derived from the neural crest derived pharyngeal skeleton and the transition from jawless to jawed vertebrates consists of major morphological changes, which must have a genetic foundation. Recent studies on the effects of bapx1 knockdown in fish and chicken indicate that bapx1 has acquired such a role in primary jaw joint development during vertebrate evolution, but evidence from amphibians is missing so far. In the present study, we use Ambystoma mexicanum, Bombina orientalis, and Xenopus laevis to investigate the effects of bapx1 knockdown on the development of these three different amphibians. Using morpholinos we downregulated the expression of bapx1 and obtain morphants with altered mandibular arch morphology. In the absence of bapx1 Meckeĺs cartilage and the palatoquadrate jaw joint initially develop separately but during further development the joint cavity between both fills with chondrocytes. This results in the fusion of both cartilages and the loss of the jaw joint. Despite this the jaw itself remains usable for feeding and breathing. We show that bapx1 plays a role in jaw joint maintenance during development and that the morphants morphology possibly mirrors the morphology of the jawless ancestors of the gnathostomes.

中文翻译：

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两栖动物的颌关节发育需要Bapx1。

活动颚和颚关节的获取是gnathostome进化中的关键事件。颌骨来自神经c衍生的咽部骨骼，从无颌脊椎动物到颌骨脊椎动物的过渡包括主要的形态变化，必须具有遗传基础。最近对鱼和鸡中bapx1敲低的影响的研究表明bapx1在脊椎动物进化过程中的初级颌骨关节发育中已经获得了这种作用，但是到目前为止，尚缺乏两栖动物的证据。在当前的研究中，我们使用墨西哥Ambystoma，Bombina Orientalis和Xenopus laevis来研究bapx1的作用。击倒这三种不同两栖动物的发育。使用吗啉代，我们下调了bapx1的表达，并获得了具有改变下颌弓形态的吗啡。在没有bapx1的情况下，Mecke的软骨和the四下颌的颚关节最初分别发展，但在进一步发展期间，两者之间的关节腔充满了软骨细胞。这导致软骨融合和颚关节的丧失。尽管如此，颌骨本身仍可用于喂养和呼吸。我们显示bapx1在发育过程中在颌骨关节维护中起作用，并且吗啡酮的形态可能反映了食蚁兽的无颌祖先的形态。