Boughner Julia C, Buchtová Marcela, Fu Katherine, Diewert Virginia, Hallgrímsson Benedikt, Richman Joy M
Department of Oral Health Sciences, Life Sciences Institute, University of British Columbia, Life Sciences Centre, 2350 Health Sciences Mall, Vancouver, BC, Canada V6T 1Z3.
Zoology (Jena). 2007;110(3):212-30. doi: 10.1016/j.zool.2007.01.005. Epub 2007 May 17.
This study explores the post-ovipositional craniofacial development of the African Rock Python (Python sebae). We first describe a staging system based on external characteristics and next use whole-mount skeletal staining supplemented with Computed tomography (CT) scanning to examine skeletal development. Our results show that python embryos are in early stages of organogenesis at the time of laying, with separate facial prominences and pharyngeal clefts still visible. Limb buds are also visible. By 11 days (stage 3), the chondrocranium is nearly fully formed; however, few intramembranous bones can be detected. One week later (stage 4), many of the intramembranous upper and lower jaw bones are visible but the calvaria are not present. Skeletal elements in the limbs also begin to form. Between stages 4 (day 18) and 7 (day 44), the complete set of intramembranous bones in the jaws and calvaria develops. Hindlimb development does not progress beyond stage 6 (33 days) and remains rudimentary throughout adult life. In contrast to other reptiles, there are two rows of teeth in the upper jaw. The outer tooth row is attached to the maxillary and premaxillary bones, whereas the inner row is attached to the pterygoid and palatine bones. Erupted teeth can be seen in whole-mount stage 10 specimens and are present in an unerupted, mineralized state at stage 7. Micro-CT analysis reveals that all the young membranous bones can be recognized even out of the context of the skull. These data demonstrate intrinsic patterning of the intramembranous bones, even though they form without a cartilaginous template. In addition, intramembranous bone morphology is established prior to muscle function, which can influence bone shape through differential force application. After careful staging, we conclude that python skeletal development occurs slowly enough to observe in good detail the early stages of craniofacial skeletogenesis. Thus, reptilian animal models will offer unique opportunities for understanding the early influences that contribute to perinatal bone shape.
本研究探讨了非洲岩蟒（Python sebae）产卵后的颅面发育情况。我们首先基于外部特征描述了一个分期系统，接着使用全胚骨骼染色并辅以计算机断层扫描（CT）来检查骨骼发育。我们的研究结果表明，蟒蛇胚胎在产卵时处于器官发生的早期阶段，面部突起和咽裂仍清晰可见，肢芽也可见。到第11天（第3阶段），软骨颅几乎完全形成，但几乎检测不到膜内骨。一周后（第4阶段），许多膜内的上颌骨和下颌骨可见，但颅盖骨不存在。四肢的骨骼元素也开始形成。在第4阶段（第18天）到第7阶段（第44天）之间，颌骨和颅盖骨的全套膜内骨发育完成。后肢发育在第6阶段（第33天）之后不再进展，在整个成年期都保持未发育完全的状态。与其他爬行动物不同，蟒蛇上颌有两排牙齿。外排牙齿附着在上颌骨和前颌骨上，而内排牙齿附着在翼骨和腭骨上。在全胚第10阶段的标本中可以看到萌出的牙齿，在第7阶段则以未萌出的矿化状态存在。显微CT分析表明，即使脱离头骨背景，所有年轻的膜性骨也能被识别。这些数据表明，尽管膜内骨在没有软骨模板的情况下形成，但它们具有内在的模式形成机制。此外，膜内骨形态在肌肉功能之前就已确立，而肌肉功能可通过不同的力施加来影响骨骼形状。经过仔细分期后，我们得出结论，蟒蛇的骨骼发育足够缓慢，足以详细观察颅面骨骼发生的早期阶段。因此，爬行动物模型将为理解影响围产期骨骼形状的早期因素提供独特的机会。
