Alibardi L, Thompson M B
Dipartimento di Biologia evoluzionistica e sperimentale, University of Bologna, Italy.
J Anat. 1999 May;194 ( Pt 4)(Pt 4):531-45. doi: 10.1046/j.1469-7580.1999.19440531.x.
As part of a large comparative study on the development of reptilian skin, we provide the first ultrastructural description of differentiation of the epidermis of the carapace and plastron in the Chelonia, using the Australian pleurodiran turtle Emydura macquarii as a model. The epidermis is initially composed of an external flat peridermis and a basal layer of cuboidal cells. During differentiation, the peridermis darkens, flakes off and is partially lost before hatching. Four to 6 layers of flat cells containing lipids and mucus form from the basal layer beneath the external peridermis. Because such cells are found only during embryogenesis, we have referred to these layers as embryonic epidermis. They contain reticulate bodies made of a meshwork of coarse filaments similar to those described in the inner peridermis of lizard and bird embryos. In advanced embryos, cells of the embryonic epidermis condense into a thin dark stratum which is subsequently lost after hatching. The lowermost 2 layers of the embryonic epidermis keratinise, as for a typical lepidosaurian alpha-layer. A splitting zone is progressively formed beneath the alpha-layer to separate the embryonic epidermis from the underlying beta-layer. Patterns of cytodifferentiation of the beta-synthesising cells over the carapace and plastron essentially resemble those of the lepidosaurian epidermis. The beta-keratin matrix initially accumulates among ribosomes as round bodies not clearly surrounded by a membrane. These bodies appear not to be derived from the Golgi apparatus. Melanosomes and other dark granules of uncertain nature are present among early differentiating beta-cells. The round beta-keratin bodies merge with the dense bodies to produce the definitive variegated pattern of the mature beta-keratin layer. The histochemistry suggests that calcium combines with organic molecules within beta-keratinising cells to harden the tissue. In contrast to the beta-keratin cells of lizards and snakes, cells of the mature beta-keratin layer of E. macquarii maintain their cell boundaries in part or completely, a characteristics shared with the beta-keratin layer of Sphenodon and crocodilians.
作为一项关于爬行动物皮肤发育的大型比较研究的一部分，我们以澳大利亚侧颈龟黄斑澳龟为模型，首次对龟鳖目动物背甲和腹甲表皮分化进行了超微结构描述。表皮最初由外部扁平的周皮和一层立方体细胞组成。在分化过程中，周皮变黑、脱落并在孵化前部分消失。在外部周皮下方的基底层形成了4至6层含有脂质和黏液的扁平细胞。由于这些细胞仅在胚胎发育期间出现，我们将这些层称为胚胎表皮。它们含有由粗丝网络构成的网状体，类似于蜥蜴和鸟类胚胎内周皮中所描述的那样。在发育晚期的胚胎中，胚胎表皮细胞浓缩成一层薄的深色层，随后在孵化后消失。胚胎表皮的最下面两层角质化，如同典型的鳞龙类α层。在α层下方逐渐形成一个分裂区，将胚胎表皮与下面的β层分开。背甲和腹甲上β合成细胞的细胞分化模式基本上与鳞龙类表皮相似。β角蛋白基质最初在核糖体之间积累，形成未被膜清晰包围的圆形小体。这些小体似乎不是来自高尔基体。在早期分化的β细胞中存在黑素体和其他性质不确定的深色颗粒。圆形的β角蛋白小体与致密小体融合，形成成熟β角蛋白层最终的斑驳图案。组织化学表明，钙与β角质化细胞内的有机分子结合，使组织变硬。与蜥蜴和蛇的β角蛋白细胞不同，黄斑澳龟成熟β角蛋白层的细胞部分或完全保持其细胞边界，这一特征与楔齿蜥和鳄鱼的β角蛋白层相同。
