The caudal fin is the zebrafish tail fin, which is comprised of bony rays that are separated by softer tissues called interray tissues (Blum and Begemann, 2012). The bony rays, or lepidotrichia, are dermal bone; they are segmented and have two hemirays that face each other and are concave, forming a sheath in which fibroblasts and osteoblasts along with blood vessels, nerves, and pigment cells reside (Gemberling et al., 2013). Figure 1 shows a cross-section of a fin ray and its constituent parts from Tu and Johnson (2011).

The process of regeneration involves coordinated steps beginning with wound healing. During the wound healing stage of regeneration, which occurs over twelve hours, epithelial cells migrate to the point of amputation to cover the wound (Gemberling et al. 2013). Once epithelial cells cover the entirety of the wound, a blastema begins to form. Blastemas are the region of undifferentiated cells used for regeneration which include mesenchymal cells and osteoblasts as well as fibroblast-like cells (Gemberling et al. 2013). It has been noted that migration of the cells forming the blastema is distal to the fin ray (Wehner and Weidinger, 2015). Blastema formation occurs over the course of two days, at which point mesenchymal cells …show more content…
Retinoic acid has been shown to have an effect on patterning and positional information, and through experiments involving RNA antisense probes, it has been determined that RA signaling ensures proliferation of blastemal cells by affecting Fgf and Wnt/β-catenin through stimulation. This pathway is similar to the pathway described by Stoick-Cooper et al. (2007) and adds the retinoic acid component of the pathway. Retinoic acid is positively regulated by Wnt/β-catenin and Fgf, which are reciprocally positively regulated by retinoic acid, as is indicated in Figure 3 (Blum and Begemann,