Comparative Histolab Padova and University of Bologna, L.A., Dipartimento di Biologia, via Selmi 3, Univ Bologna, 40126, Bologna, Italy.
Protoplasma. 2020 Jul;257(4):1123-1138. doi: 10.1007/s00709-020-01494-0. Epub 2020 Mar 11.
The presence of specific protein types in claws and beaks of turtles is poorly known. The present immunological study describes the localization of some of the main corneous beta proteins (CBPs) coded in the epidermal differentiation complex of turtles. Three antibodies here utilized revealed that glycine-, cysteine-, tyrosine-, and valine-rich CBPs are present in differentiating keratinocytes of the beak and of the dorsal (unguis) and ventral (sub-unguis) sides of the claw in different species, semi-aquatic and terrestrial. These proteins provide mechanical resilience to the horny material of claws and beaks through the formation of numerous -S-S- bonds and also hydrophobicity that contributes to preserve wearing of the horny material. The thicker corneous layer of the unguis is made of elongated and partially merged corneocytes, and no or few cells desquamate superficially. Unknown junctional proteins may contribute to maintain corneocytes connected one to another. In contrast, corneocytes of the sub-unguis show an elongated but lenticular shape and form a looser corneous layer whose cells remain separate and desquamate superficially. This suggests that other specific corneous proteins are present in the unguis in comparison with the sub-unguis to determine this different compaction. The wearing process present in the sub-unguis creates a loss of tissue that may favor the slow by continuous apical migration of corneocytes from the unguis into the initial part of the sub-unguis. Beak corneocytes form a compact corneous layer like the unguis but numerous superficial cells desquamate on both outer (epidermal) and inner (oral) sides.
龟鳖类爪和喙中特定蛋白类型的存在知之甚少。本免疫研究描述了龟表皮分化复合物中编码的一些主要角蛋白β蛋白（CBPs）的定位。本文中使用的三种抗体表明，甘氨酸、半胱氨酸、酪氨酸和缬氨酸丰富的 CBPs 存在于不同物种半水生和陆生的喙和爪的背（爪）和腹（副爪）侧分化的角蛋白细胞中。这些蛋白质通过形成大量的-S-S-键和增加疏水性为角质材料提供机械弹性，从而有助于保持角质材料的磨损。爪的较厚角质层由拉长的和部分融合的角质细胞组成，表面几乎没有或很少有细胞剥落。未知的连接蛋白可能有助于保持角蛋白细胞彼此连接。相比之下，副爪的角蛋白细胞呈拉长但透镜状，形成较松散的角质层，其细胞保持分离并在表面剥落。这表明与副爪相比，爪中存在其他特定的角蛋白蛋白以确定这种不同的紧密度。副爪中的磨损过程会导致组织损失，这可能有利于角蛋白细胞从爪不断通过顶端迁移到副爪的初始部分。喙角蛋白细胞形成类似于爪的紧密角质层，但在内外侧（表皮和口腔）都有许多表面细胞剥落。
