Teeth outside the mouth: The evolution and development of shark denticles
Teeth outside the mouth: The evolution and development of shark denticles
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DOI：
10.1111/ede.12427
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发表时间：
2023-01-03
影响因子：
2.9
通讯作者：
Fraser，Gareth J.
中科院分区：
文献类型：
--
作者：
Cooper，Rory L.;Nicklin，Ella F.;Fraser，Gareth J.
脊椎动物的皮肤附属物非常多样。这种多样性，包括鳞片、羽毛和毛发等结构，很可能是从一个共同的解剖平台进化而来的，这表明这些器官的早期发育得到了广泛的保护。已知的一些最早的皮肤附属物是牙本质和富含牙釉质的牙齿状结构，统称为齿状结构。这些附属物是在4.5亿年前进化而来的。鳍鲨(鲨鱼、溜冰鞋和放射鱼)保留了这些古老的皮肤附属物，既有真皮上的牙鳞，也有口腔牙齿。尽管我们知道成年鲨鱼的牙齿功能，但我们对它们的发育和形态发生的了解还不够深入。尽管鲨鱼的牙齿在结构上看起来与口腔牙齿相似，但直接比较这些不同元素的分子发育的数据有限。在这里，我们绘制了胚胎小斑猫鲨(Scyliorhinus Canula)牙齿发育的图表，并表征了已知的调节牙齿发育的保守基因的表达。我们发现鲨鱼牙齿的发育与发育中的牙齿有着巨大的基因表达特征。然而，牙齿的再生潜力有限，因为它们缺乏与维持牙板相关的asox2+干细胞生态位，而牙板是持续牙齿替换的基本要求。我们将发育中的牙齿与其他皮肤附属物进行比较，包括感官皮肤附属物和鸟类羽毛。这表明牙齿不仅在结构上类似牙齿，而且它们还共享一个古老的发育基因组，这可能是所有表皮附属物共同的。
Vertebrate skin appendages are incredibly diverse. This diversity, which includes structures such as scales, feathers, and hair, likely evolved from a shared anatomical placode, suggesting broad conservation of the early development of these organs. Some of the earliest known skin appendages are dentine and enamel‐rich tooth‐like structures, collectively known as odontodes. These appendages evolved over 450 million years ago. Elasmobranchs (sharks, skates, and rays) have retained these ancient skin appendages in the form of both dermal denticles (scales) and oral teeth. Despite our knowledge of denticle function in adult sharks, our understanding of their development and morphogenesis is less advanced. Even though denticles in sharks appear structurally similar to oral teeth, there has been limited data directly comparing the molecular development of these distinct elements. Here, we chart the development of denticles in the embryonic small‐spotted catshark (Scyliorhinus canicula) and characterize the expression of conserved genes known to mediate dental development. We find that shark denticle development shares a vast gene expression signature with developing teeth. However, denticles have restricted regenerative potential, as they lack asox2+ stem cell niche associated with the maintenance of a dental lamina, an essential requirement for continuous tooth replacement. We compare developing denticles to other skin appendages, including both sensory skin appendages and avian feathers. This reveals that denticles are not only tooth‐like in structure, but that they also share an ancient developmental gene set that is likely common to all epidermal appendages.