Buchtová Marcela, Boughner Julia C, Fu Katherine, Diewert Virginia M, 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):231-51. doi: 10.1016/j.zool.2007.01.006. Epub 2007 May 17.
This study explores the microscopic craniofacial morphogenesis of the oviparous African rock python (Python sebae) spanning the first two-thirds of the post-oviposition period. At the time of laying, the python embryo consists of largely undifferentiated mesenchyme and epithelium with the exception of the cranial base and trabeculae cranii, which are undergoing chondrogenesis. The facial prominences are well defined and are at a late stage, close to the time when lip fusion begins. Later (11-12d), specializations in the epithelia begin to differentiate (vomeronasal and olfactory epithelia, teeth). Dental development in snakes is different from that of mammals in several aspects including an extended dental lamina with the capacity to form 4 sets of generational teeth. In addition, the ophidian olfactory system is very different from the mammalian. There is a large vomeronasal organ, a nasal cavity proper and an extraconchal space. All of these areas are lined with a greatly expanded olfactory epithelium. Intramembranous bone differentiation is taking place at stage 3 with some bones already ossifying whereas most are only represented as mesenchymal condensations. In addition to routine histological staining, PCNA immunohistochemistry reveals relatively higher levels of proliferation in the extending dental laminae, in osseous mesenchymal condensations and in the olfactory epithelia. Areas undergoing apoptosis were noted in the enamel organs of the teeth and osseous mesenchymal condensations. We propose that localized apoptosis helps to divide a single condensation into multiple ossification centres and this is a mechanism whereby novel morphology can be selected in response to evolutionary pressures. Several additional differences in head morphology between snakes and other amniotes were noted including a palatal groove separating the inner and outer row of teeth in the upper jaw, a tracheal opening within the tongue and a pharyngeal adhesion that closes off the pharynx from the oral cavity between stages 1 and 4. Our studies on these and other differences in the python will provide valuable insights into in developmental, molecular and evolutionary mechanisms of patterning.
本研究探讨了产卵后三分之二时期内卵生非洲岩蟒（Python sebae）的微观颅面形态发生过程。在产卵时，蟒蛇胚胎主要由未分化的间充质和上皮组成，颅底和颅小梁除外，它们正在进行软骨形成。面部隆起清晰可辨，处于后期阶段，接近唇融合开始的时间。之后（11 - 12天），上皮开始分化出特化结构（犁鼻器和嗅觉上皮、牙齿）。蛇的牙齿发育在几个方面与哺乳动物不同，包括具有形成4代牙齿能力的延长牙板。此外，蛇类嗅觉系统与哺乳动物的差异很大。有一个大的犁鼻器、一个真正的鼻腔和一个鼻甲外间隙。所有这些区域都衬有大幅扩展的嗅觉上皮。膜内骨分化在第3阶段发生，一些骨骼已经骨化，而大多数仅表现为间充质凝聚。除了常规组织学染色外，PCNA免疫组织化学显示在延长的牙板、骨间充质凝聚和嗅觉上皮中增殖水平相对较高。在牙齿釉器和骨间充质凝聚中发现了正在发生凋亡的区域。我们认为局部凋亡有助于将单个凝聚物分成多个骨化中心，这是一种机制，通过该机制可以根据进化压力选择新的形态。还注意到蛇与其他羊膜动物在头部形态上的几个其他差异，包括上颌中分隔内排和外排牙齿的腭沟、舌内的气管开口以及在第1阶段和第4阶段之间封闭咽部与口腔的咽粘连。我们对蟒蛇这些及其他差异的研究将为发育、分子和进化模式机制提供有价值的见解。
