Epidermal regulation of bone morphogenesis through the development and regeneration of osteoblasts in the zebrafish scale.
Iwasaki M., Kuroda J., Kawakami K., Wada H.
Developmental Biology 437, 105-119, 2018. DOI:10.1016/j.ydbio.2018.03.005
The scale of the teleost fish is a dermal bone embedded in the skin. We investigated the mechanisms of bone patterning in the zebrafish scale by using transgenic lines that visualize osteoblasts. We showed that the zebrafish scale contains two distinct types of osteoblasts: a monolayer sheet of central osteoblasts along the surface of scales; and marginal osteoblasts elongated along the scale edge (Fig. A). During scale growth, central osteoblasts progressively increase in size without cell proliferation. Sonic hedgehog (shh) is expressed in the epidermal cells overlying marginal osteoblasts. Inhibition of Hh signaling reduces the number of marginal osteoblasts and interferes with scale growth. Moreover, inhibition of Wnt/planar cell polarity (PCP) signaling in the epidermis caused a misorientation of scales (Fig. B), correlated to the altered expression pattern of shh. This study reveals a novel role of the epidermis in the regulation of bone patterning.
Figure: (A) Gal4 enhancer trap line (hspGFFDMC13F;UAS:GFP) expressing GFP in a specific population of osteoblasts along the scale edge. (B) Disrupted Wnt/PCP signaling in the epidermis causes a misorientation of scales, indicating a role of the epidermis in bone patterning.