Department of Biological Sciences, University of Cincinnati, 45221, Cincinnati, OH, USA.
Sci Rep. 2018 May 3;8(1):7015. doi: 10.1038/s41598-018-25107-2.
The precise mechanisms underlying cranial bone development, evolution and patterning remain incompletely characterised. This poses a challenge to understanding the etiologies of craniofacial malformations evolving in nature. Capitalising on natural variation, "evolutionary model systems" provide unique opportunities to identify underlying causes of aberrant phenotypes as a complement to studies in traditional systems. Mexican blind cavefish are a prime evolutionary model for cranial disorders since they frequently exhibit extreme alterations to the skull and lateral asymmetries. These aberrations occur in stark contrast to the normal cranial architectures of closely related surface-dwelling fish, providing a powerful comparative paradigm for understanding cranial bone formation. Using a longitudinal and in vivo analytical approach, we discovered two unusual ossification processes in cavefish that underlie the development of 'fragmented' and asymmetric cranial bones. The first mechanism involves the sporadic appearance of independent bony elements that fail to fuse together later in development. The second mechanism involves the "carving" of channels in the mature bone, a novel form of post-ossification remodeling. In the extreme cave environment, these novel mechanisms may have evolved to augment sensory input, and may indirectly result in a trade-off between sensory expansion and cranial bone development.
颅骨发育、进化和模式形成的精确机制仍不完全清楚。这给理解自然进化中的颅面畸形的病因带来了挑战。利用自然变异，“进化模型系统”为识别异常表型的潜在原因提供了独特的机会，这是对传统系统研究的补充。墨西哥盲眼洞穴鱼是颅部疾病的主要进化模型，因为它们的头骨经常发生极端变化和侧面不对称。这些异常与亲缘关系密切的地表鱼类的正常颅部结构形成鲜明对比，为理解颅骨形成提供了一个强大的比较范例。我们采用纵向和体内分析方法，发现了洞穴鱼中两种不寻常的骨化过程，这两种过程是“碎片化”和不对称颅骨发育的基础。第一种机制涉及到独立骨元素的偶然出现，这些骨元素在发育后期未能融合在一起。第二种机制涉及到成熟骨骼中的通道“雕刻”，这是一种新的骨化后重塑形式。在极端的洞穴环境中，这些新的机制可能是为了增加感官输入而进化的，并且可能间接地导致感官扩张和颅骨发育之间的权衡。
