Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität, Jena, Germany.
J Anat. 2011 Feb;218(2):226-42. doi: 10.1111/j.1469-7580.2010.01315.x. Epub 2010 Nov 3.
The origin of morphological novelties is a controversial topic in evolutionary developmental biology. The heads of anuran larvae have several unique structures, including the supra- and infrarostral cartilages, the specialised structure of the gill basket (used for filtration), and novel cranial muscle arrangements. FoxN3, a member of the forkhead/winged helix family of transcription factors, has been implicated as important for normal craniofacial development in the pipid anuran Xenopus laevis. We have investigated the effects of functional knockdown of FoxN3 (using antisense oligonucleotide morpholino) on the development of the larval head skeleton and the associated cranial muscles in X. laevis. Our data complement earlier studies and provide a more complete account of the requirement of FoxN3 in chondrocranium development. In addition, we analyse the effects of FoxN3 knockdown on cranial muscle development. We show that FoxN3 knockdown primarily affects the novel skeletal structures unique to anuran larvae, i.e. the rostralia or the fine structure of the gill apparatus. The articulation between the infrarostral and Meckel's cartilage is malformed and the filigreed processes of the gill basket do not develop. Because these features do not develop after FoxN3 knockdown, the head morphology resembles that in the less specialised larvae of salamanders. Furthermore, the development of all cartilages derived from the neural crest is delayed and cranial muscle fibre development incomplete. The cartilage precursors initially condense in their proper position but later differentiate incompletely; several visceral arch muscles start to differentiate at their origin but fail to extend toward their insertion. Our findings indicate that FoxN3 is essential for the development of novel cartilages such as the infrarostral and other cranial tissues derived from the neural crest and, indirectly, also for muscle morphogenesis.
形态新颖的起源是进化发育生物学中一个有争议的话题。蛙类幼虫的头部有几个独特的结构，包括上、下额骨软骨、专门的鳃篮结构（用于过滤）和新的颅部肌肉排列。叉头/翼状螺旋家族的转录因子 FoxN3 已被认为对 pipid 蛙 Xenopus laevis 的正常颅面发育很重要。我们研究了 FoxN3（使用反义寡核苷酸 morpholino）功能敲低对 X. laevis 幼虫头部骨骼发育和相关颅部肌肉的影响。我们的数据补充了早期的研究，并提供了 FoxN3 在软骨颅发育中的需求的更完整描述。此外，我们分析了 FoxN3 敲低对颅部肌肉发育的影响。我们表明，FoxN3 敲低主要影响蛙类幼虫特有的新型骨骼结构，即额骨或鳃器官的精细结构。下额骨和 Meckel 软骨之间的关节畸形，鳃篮的细丝状结构不发育。由于这些特征在 FoxN3 敲低后不会发育，头部形态类似于神经嵴衍生的不太特化的蝾螈幼虫。此外，所有来自神经嵴的软骨发育都被延迟，颅部肌肉纤维发育不完全。软骨前体最初在适当的位置凝聚，但后来分化不完全；几个内脏弓肌肉在起源处开始分化，但未能向插入部位延伸。我们的发现表明，FoxN3 对于新颖软骨的发育是必不可少的，如下额骨和其他来自神经嵴的颅组织，间接地也对于肌肉形态发生是必不可少的。
