Alibardi Lorenzo, Toni Mattia
Dipartimento di Biologia Evoluzionistica Sperimentale, University of Bologna, Italy.
Zoolog Sci. 2006 Sep;23(9):801-7. doi: 10.2108/zsj.23.801.
Reptilian scales are mainly composed of alpha-and beta-keratins. Epidermis and molts from adult individuals of an ancient reptilian species, the tuatara (Sphenodon punctatus), were analysed by immunocytochemistry, mono- and bi-dimensional electrophoresis, and western blotting for alpha- and beta-keratins. The epidermis of this reptilian species with primitive anatomical traits should represent one of the more ancient amniotic epidermises available. Soft keratins (AE1- and AE3-positive) of 40-63 kDa and with isoelectric points (pI) at 4.0-6.8 were found in molts. The AE3 antibody was diffusely localised over the tonofilaments of keratinocytes. The lack of basic cytokeratins may be due to keratin alteration in molts, following corneification or enzymatic degradation of keratins. Hard (beta-) keratins of 16-18 kDa and pI at 6.8, 8.0, and 9.2 were identified using a beta-1 antibody produced against chick scale beta-keratin. The antibody also labeled filaments of beta-cells and of the mature, compact beta-layer. We have shown that beta-keratins in the tuatara resemble those of lizards and snakes, and that they are mainly basic proteins. These proteins replace cytokeratins in the pre-corneoum beta-layers, from which a hard, mechanically resistant corneoum layer is formed over scales. Beta-keratins may have both a fibrous and a matrix role in forming the hard texture of corneoum scales in this ancient species, as well as in more recently evolved reptiles.
爬行动物的鳞片主要由α - 角蛋白和β - 角蛋白组成。通过免疫细胞化学、一维及二维电泳以及蛋白质免疫印迹法，对一种古老爬行动物——喙头蜥（Sphenodon punctatus）成年个体的表皮和蜕下的皮进行了α - 角蛋白和β - 角蛋白分析。这种具有原始解剖特征的爬行动物的表皮应该代表了现存较为古老的羊膜动物表皮之一。在蜕下的皮中发现了分子量为40 - 63 kDa、等电点（pI）为4.0 - 6.8的软角蛋白（AE1和AE3阳性）。AE3抗体弥散性地定位于角质形成细胞的张力丝上。缺乏碱性细胞角蛋白可能是由于蜕下的皮中角蛋白在角质化或角蛋白酶解后发生了改变。使用针对鸡鳞片β - 角蛋白产生的β - 1抗体，鉴定出了分子量为16 - 18 kDa、pI为6.8、8.0和9.2的硬（β - ）角蛋白。该抗体还标记了β - 细胞的细丝以及成熟、致密的β - 层。我们已经表明，喙头蜥中的β - 角蛋白与蜥蜴和蛇的β - 角蛋白相似，并且它们主要是碱性蛋白。这些蛋白质在角质前β - 层中替代细胞角蛋白，在鳞片上形成坚硬、机械抗性强的角质层。β - 角蛋白在这个古老物种以及较新进化的爬行动物中，可能在形成角质鳞片的坚硬质地方面同时具有纤维状和基质的作用。
