Pasqualetti M, Ori M, Nardi I, Rijli F M
Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, Collège de France, BP 163 - 67404 Illkirch Cedex, C.U. de Strasbourg, France.
Development. 2000 Dec;127(24):5367-78. doi: 10.1242/dev.127.24.5367.
Hox genes are required to pattern neural crest (NC) derived craniofacial and visceral skeletal structures. However, the temporal requirement of Hox patterning activity is not known. Here, we use an inducible system to establish Hoxa2 activity at distinct NC migratory stages in Xenopus embryos. We uncover stage-specific effects of Hoxa2 gain-of-function suggesting a multistep patterning process for hindbrain NC. Most interestingly, we show that Hoxa2 induction at postmigratory stages results in mirror image homeotic transformation of a subset of jaw elements, normally devoid of Hox expression, towards hyoid morphology. This is the reverse phenotype to that observed in the Hoxa2 knockout. These data demonstrate that the skeletal pattern of rhombomeric mandibular crest is not committed before migration and further implicate Hoxa2 as a true selector of hyoid fate. Moreover, the demonstration that the expression of Hoxa2 alone is sufficient to transform the upper jaw and its joint selectively may have implications for the evolution of jaws.
Hox基因对于构建源自神经嵴（NC）的颅面和内脏骨骼结构至关重要。然而，Hox模式形成活性的时间需求尚不清楚。在此，我们使用一种诱导系统在非洲爪蟾胚胎的不同NC迁移阶段建立Hoxa2活性。我们揭示了Hoxa2功能获得的阶段特异性效应，这表明后脑NC存在多步骤模式形成过程。最有趣的是，我们表明在迁移后阶段诱导Hoxa2会导致一部分通常不表达Hox的颌骨元素向舌骨形态发生镜像同源异型转化。这与在Hoxa2基因敲除中观察到的表型相反。这些数据表明，菱脑节下颌嵴的骨骼模式在迁移前并未确定，并且进一步表明Hoxa2是舌骨命运的真正决定因子。此外，仅Hoxa2的表达就足以选择性地转化上颌及其关节，这一发现可能对颌骨的进化具有重要意义。
