Collagen duplicate genes of bone and cartilage participate during regeneration of zebrafish fin skeleton

• Zebrafish genome presents duplicated collagen genes.
• Collagens 1a1, 2a1, 5a2, 5a3, 11a1 and 27a1 are duplicated while 3a1 is not present.
• Fin skeleton present hybrid composition between bone and cartilage.
• Fibrillar collagens participate in zebrafish fin skeleton regeneration.

The zebrafish fin is widely used as a model for skeleton regeneration. For years, the nature of the fin skeleton has been controversial as its extracellular matrix shows hybrid characteristics of both bone and cartilage. The presence of co-orthologs genes also increases the complexity of these tissues. In this article, we have identified and described the expression of fibrillar collagens in zebrafish fin skeleton. We found that genes coding for types I, II, V, XI and XXVII collagens are duplicated, showing in several cases, different expression domains. We also identified specific genomic features, such as the presence of type XXIV collagen and the absence of type III collagen in the zebrafish genome. Our study showed that actinotrichia-forming cells and osteoblasts synthesize a wide variety of these fibrillar collagens during fin regeneration. An intertrichial domain expressing most of the collagens was located in the transition between the mesenchyme condensations of actinotrichia and lepidotrichia and may determine an important niche associated with fin skeleton morphogenesis. We also confirmed the hybrid nature of the fin exoskeleton and provided a complete description of those fibrillar collagens expressed during the formation of the fin skeleton.