Chang Cheng, Wu Ping, Baker Ruth E, Maini Philip K, Alibardi Lorenzo, Chuong Cheng-Ming
Department of Pathology, University of Southern California, Los Angeles, 90033, USA.
Int J Dev Biol. 2009;53(5-6):813-26. doi: 10.1387/ijdb.072556cc.
The purpose of this perspective is to highlight the merit of the reptile integument as an experimental model. Reptiles represent the first amniotes. From stem reptiles, extant reptiles, birds and mammals have evolved. Mammal hairs and feathers evolved from Therapsid and Sauropsid reptiles, respectively. The early reptilian integument had to adapt to the challenges of terrestrial life, developing a multi-layered stratum corneum capable of barrier function and ultraviolet protection. For better mechanical protection, diverse reptilian scale types have evolved. The evolution of endothermy has driven the convergent evolution of hair and feather follicles: both form multiple localized growth units with stem cells and transient amplifying cells protected in the proximal follicle. This topological arrangement allows them to elongate, molt and regenerate without structural constraints. Another unique feature of reptile skin is the exquisite arrangement of scales and pigment patterns, making them testable models for mechanisms of pattern formation. Since they face the constant threat of damage on land, different strategies were developed to accommodate skin homeostasis and regeneration. Temporally, they can be under continuous renewal or sloughing cycles. Spatially, they can be diffuse or form discrete localized growth units (follicles). To understand how gene regulatory networks evolved to produce increasingly complex ectodermal organs, we have to study how prototypic scale-forming pathways in reptiles are modulated to produce appendage novelties. Despite the fact that there are numerous studies of reptile scales, molecular analyses have lagged behind. Here, we underscore how further development of this novel experimental model will be valuable in filling the gaps of our understanding of the Evo-Devo of amniote integuments.
本文的目的是强调爬行动物皮肤作为实验模型的价值。爬行动物是最早的羊膜动物。从原始爬行动物开始,现存的爬行动物、鸟类和哺乳动物逐渐进化而来。哺乳动物的毛发和鸟类的羽毛分别从兽孔目和蜥形纲爬行动物进化而来。早期爬行动物的皮肤必须适应陆地生活的挑战,发展出具有屏障功能和紫外线防护能力的多层角质层。为了获得更好的机械保护,各种不同类型的爬行动物鳞片逐渐进化出来。恒温性的进化推动了毛囊和羽毛毛囊的趋同进化:二者都形成了多个局部生长单位,其干细胞和短暂增殖细胞在毛囊近端受到保护。这种拓扑结构使得它们能够在没有结构限制的情况下伸长、蜕皮和再生。爬行动物皮肤的另一个独特特征是鳞片和色素图案的精妙排列,这使得它们成为研究图案形成机制的可测试模型。由于它们在陆地上面临持续的损伤威胁,因此发展出了不同的策略来维持皮肤的稳态和再生。从时间上看,它们可以处于持续更新或蜕皮周期。从空间上看,它们可以是分散的,也可以形成离散的局部生长单位(毛囊)。为了理解基因调控网络是如何进化以产生日益复杂的外胚层器官的,我们必须研究爬行动物中形成鳞片的原型途径是如何被调节以产生新的附属结构的。尽管对爬行动物鳞片有大量研究,但分子分析却滞后了。在这里,我们强调进一步发展这个新的实验模型对于填补我们在羊膜动物皮肤进化发育生物学理解上的空白将具有重要价值。