Dhouailly Danielle
Department of Biology and Chemistry, Institute for Advanced Biosciences, University Grenoble-Alpes, 38700 La Tronche, France.
J Dev Biol. 2023 Jun 5;11(2):25. doi: 10.3390/jdb11020025.
All living jawed vertebrates possess teeth or did so ancestrally. Integumental surface also includes the cornea. Conversely, no other anatomical feature differentiates the clades so readily as skin appendages do, multicellular glands in amphibians, hair follicle/gland complexes in mammals, feathers in birds, and the different types of scales. Tooth-like scales are characteristic of chondrichthyans, while mineralized dermal scales are characteristic of bony fishes. Corneous epidermal scales might have appeared twice, in squamates, and on feet in avian lineages, but posteriorly to feathers. In contrast to the other skin appendages, the origin of multicellular glands of amphibians has never been addressed. In the seventies, pioneering dermal-epidermal recombination between chick, mouse and lizard embryos showed that: (1) the clade type of the appendage is determined by the epidermis; (2) their morphogenesis requires two groups of dermal messages, first for primordia formation, second for appendage final architecture; (3) the early messages were conserved during amniotes evolution. Molecular biology studies that have identified the involved pathways, extending those data to teeth and dermal scales, suggest that the different vertebrate skin appendages evolved in parallel from a shared placode/dermal cells unit, present in a common toothed ancestor, c.a. 420 mya.
所有现存的有颌脊椎动物都有牙齿，或者在其祖先中曾有牙齿。体表还包括角膜。相反，没有其他解剖特征能像皮肤附属器那样轻易地区分各个进化枝，两栖动物的多细胞腺体、哺乳动物的毛囊/腺体复合体、鸟类的羽毛以及不同类型的鳞片。齿状鳞片是软骨鱼类的特征，而矿化的真皮鳞片是硬骨鱼类的特征。角质表皮鳞片可能出现过两次，一次出现在有鳞目动物中，另一次出现在鸟类谱系的足部，但比羽毛出现得晚。与其他皮肤附属器不同，两栖动物多细胞腺体的起源从未得到探讨。在20世纪70年代，对鸡、小鼠和蜥蜴胚胎进行的开创性的真皮 - 表皮重组实验表明：（1）附属器的进化枝类型由表皮决定；（2）其形态发生需要两组真皮信号，第一组用于原基形成，第二组用于附属器的最终结构；（3）这些早期信号在羊膜动物进化过程中得以保留。分子生物学研究已经确定了相关途径，并将这些数据扩展到牙齿和真皮鳞片，这表明不同的脊椎动物皮肤附属器是从一个共同的基板/真皮细胞单元平行进化而来的，这个单元存在于大约4.2亿年前的一个有齿共同祖先中。
