LeBlanc Aaron R H, Meredith Smith Moya, Debiais-Thibaud Melanie, Manzanares Esther, Dean Mason, Underwood Charlie, Johanson Zerina
Faculty of Dentistry, Oral & Craniofacial Sciences, King's College London, London, UK.
Natural History Museum, London, UK.
Proc Biol Sci. 2025 Sep;292(2054):20250489. doi: 10.1098/rspb.2025.0489. Epub 2025 Sep 3.
Chondrichthyans (cartilaginous fishes) have lost the cellular bone characteristic of other jawed vertebrate skeletons. However, we identify cellular bone-like tissue in modified scales with enlarged bases, called 'bucklers' and 'thorns', which are distinctive for one group of extant batoids (rays). As placoid scales, they possess spines of orthodentine and osteodentine, but a unique basal structure. This consists of a cell-rich material, previously misidentified as an acellular tissue. Newly formed basal tissue grows appositionally and episodically from a cell-rich periosteum-like layer and closely resembles cellular bone, with entombed cells situated between bundles of attachment fibres anchoring the scale to the underlying dermal tissue and the 'periosteum' to the scale surface. In histologically more mature tissue, the cell spaces and attachment fibres are remodelled, forming enlarged, elongated spaces. The result is a unique mineralized tissue in these rays, initially sharing similarities with cellular bone, but with a mature state where cell spaces are modified throughout the base, by proposed remodelling of the matrix. Our findings of cellular bone forming the attachment tissues in ray scales demonstrate the chondrichthyan capacity to deposit bone-like tissues within the odontode module, contrary to previous understandings of hard tissue evolution in vertebrates.
软骨鱼类已经失去了其他有颌脊椎动物骨骼所具有的细胞性骨的特征。然而，我们在具有扩大基部的改良鳞片中发现了类似细胞性骨的组织，这些鳞片被称为“盾鳞”和“棘”，是现存的一类鲼形目（鲼类）所特有的。作为盾鳞，它们具有正牙本质和骨牙本质的棘，但有独特的基部结构。这一结构由富含细胞的物质组成，以前被错误地鉴定为无细胞组织。新形成的基部组织从富含细胞的类骨膜层以贴壁生长的方式间歇性生长，与细胞性骨非常相似，包埋的细胞位于将鳞片固定到下面的真皮组织以及将“骨膜”固定到鳞片表面的附着纤维束之间。在组织学上更成熟的组织中，细胞间隙和附着纤维会发生重塑，形成扩大的、拉长的间隙。结果是在这些鲼类中形成了一种独特的矿化组织，最初与细胞性骨有相似之处，但在成熟状态下，通过推测的基质重塑，整个基部的细胞间隙都会发生改变。我们关于细胞性骨形成鲼类鳞片附着组织的发现表明，软骨鱼类有能力在牙质小体模块内沉积类骨组织，这与之前对脊椎动物硬组织进化的理解相反。
