Sawyer Roger H, Rogers Loren, Washington Lynette, Glenn Travis C, Knapp Loren W
Department of Biological Sciences, University of South Carolina, Columbia, SC 29802, USA.
Dev Dyn. 2005 Feb;232(2):256-67. doi: 10.1002/dvdy.20291.
The formation of scales and feathers in reptiles and birds has fascinated biologists for decades. How might the developmental processes involved in the evolution of the amniote ectoderm be interpreted to shed light on the evolution of integumental appendages? An Evo-Devo approach to this question is proving essential to understand the observation that there is homology between the transient embryonic layers covering the scale epidermis of alligators and birds and the epidermal cell populations of embryonic feather filaments. Whereas the embryonic layers of scutate scales are sloughed off at hatching, that their homologues persist in feathers demonstrates that the predecessors of birds took advantage of the ability of their ectoderm to generate embryonic layers by recruiting them to make the epidermis of the embryonic feather filament. Furthermore, observations on mutant chickens with altered scale and feather development (Abbott and Asmundson [1957] J. Hered. 18:63-70; Abbott [1965] Poult. Sci. 44:1347; Abbott [1967] Methods in developmental biology. New York: Thomas Y. Crowell) suggest that the ectodermal placodes of feathers, which direct the formation of unique dermal condensations and subsequently appendage outgrowth, provided the mechanism by which the developmental processes generating the embryonic layers diverged during evolution to support the morphogenesis of the epidermis of the primitive feather filament with its barb ridges.
几十年来，爬行动物和鸟类鳞片与羽毛的形成一直吸引着生物学家。羊膜外胚层进化过程中涉及的发育过程如何解释才能有助于理解体表附属器的进化呢？事实证明，采用进化发育生物学方法来研究这个问题，对于理解短吻鳄和鸟类鳞片表皮上覆盖的短暂胚胎层与胚胎羽毛丝的表皮细胞群之间存在同源性这一观察结果至关重要。有盾鳞的鳞片胚胎层在孵化时会脱落，而其在羽毛中的同源物却会保留下来，这表明鸟类的祖先利用了外胚层通过招募它们来生成胚胎羽毛丝表皮从而产生胚胎层的能力。此外，对鳞片和羽毛发育发生改变的突变鸡的观察（Abbott和Asmundson [1957]《遗传学杂志》18:63 - 70；Abbott [1965]《家禽科学》44:1347；Abbott [1967]《发育生物学方法》。纽约：托马斯·Y·克劳威尔）表明，羽毛的外胚层基板指导独特的真皮凝聚物的形成以及随后附属器的生长，它为在进化过程中产生胚胎层的发育过程发生分歧提供了机制，以支持具有羽枝嵴的原始羽毛丝表皮的形态发生。
