Vincent Christine, Bontoux Martine, Le Douarin Nicole M, Pieau Claude, Monsoro-Burq Anne-Hélène
Institut d'Embryologie Cellulaire et Moléculaire, CNRS, UMR7128, 94736 Nogent-sur-Marne, France.
Dev Genes Evol. 2003 Sep;213(9):464-9. doi: 10.1007/s00427-003-0347-3. Epub 2003 Aug 7.
The turtle shell forms by extensive ossification of dermis ventrally and dorsally. The carapacial ridge (CR) controls early dorsal shell formation and is thought to play a similar role in shell growth as the apical ectodermal ridge during limb development. However, the molecular mechanisms underlying carapace development are still unknown. Msx genes are involved in the development of limb mesenchyme and of various skeletal structures. In particular, precocious Msx expression is recorded in skeletal precursors that develop close to the ectoderm, such as vertebral spinous processes or skull. Here, we have studied the embryonic expression of Msx genes in the European pond turtle, Emys orbicularis. The overall Msx expression in head, limb, and trunk is similar to what is observed in other vertebrates. We have focused on the CR area and pre-skeletal shell condensations. The CR expresses Msx genes transiently, in a pattern similar to that of fgf10. In the future carapace domain, the dermis located dorsal to the spinal cord expresses Msx genes, as in other vertebrates, but we did not see expansion of this expression in the dermis located more laterally, on top of the dermomyotomes. In the ventral plastron, although the dermal osseous condensations form in the embryonic Msx-positive somatopleura, we did not observe enhanced Msx expression around these elements. These observations may indicate that common mechanisms participate in limb bud and CR early development, but that pre-differentiation steps differ between shell and other skeletal structures and involve other gene activities than that of Msx genes.
龟壳通过腹侧和背侧真皮的广泛骨化形成。背甲嵴（CR）控制早期背甲形成，并且被认为在背甲生长中发挥与肢体发育过程中的顶端外胚层嵴类似的作用。然而，背甲发育的分子机制仍然未知。Msx基因参与肢体间充质和各种骨骼结构的发育。特别地，在靠近外胚层发育的骨骼前体中记录到早熟的Msx表达，例如椎骨棘突或头骨。在这里，我们研究了欧洲池龟（Emys orbicularis）中Msx基因的胚胎表达。头部、肢体和躯干中Msx的整体表达与在其他脊椎动物中观察到的相似。我们重点关注了CR区域和骨骼前体背甲凝聚物。CR短暂表达Msx基因，其模式与fgf10相似。在未来的背甲区域，脊髓背侧的真皮表达Msx基因，与其他脊椎动物一样，但我们没有看到在位于更外侧、在皮肌节上方的真皮中这种表达的扩展。在腹甲中，虽然真皮骨凝聚物在胚胎期Msx阳性的体壁中形成，但我们没有观察到这些结构周围Msx表达增强。这些观察结果可能表明，共同机制参与肢体芽和CR的早期发育，但背甲与其他骨骼结构之间的预分化步骤不同，并且涉及Msx基因以外的其他基因活动。
