Unique and shared gene expression patterns in Atlantic salmon (Salmo salar) tooth development
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To validate the use of Atlantic salmon (Salmo salar L.) as a model species in research on the mechanism of continuous tooth replacement, we have started to collect data on the molecular control underlying tooth formation in this species. This study reports expression patterns in the lower jaw dentition of a number of key regulatory genes such as bmp2, bmp4, and sox9 and structural genes such as col1α 1 and osteocalcin (= bgp, Bone Gla Protein) by means of in situ hybridization using salmon-specific, digoxygenin-labeled antisense riboprobes. We compare expression of these genes to that in other skeletogenic cells in the lower jaw (osteoblasts, chondroblasts, and chondrocytes). Our studies reveal both expression patterns that are in accordance to studies on mammalian tooth development and patterns that are specific to salmon, or teleosts. The epithelial expression of sox9 and a shift of the expression of bmp2 from epithelium to mesenchyme have also been observed during mammalian tooth development. Different from previous reports are the expressions of col1α 1 and osteocalcin. In contrast to what has been reported for zebrafish, osteocalcin is not expressed in odontoblasts, nor in the osteoblasts involved in the attachment of the teeth. At the lower jaw, osteocalcin is expressed in mature and/or resting osteoblasts only. As expected, col1α 1 is expressed in odontoblasts. Surprisingly, it is also strongly expressed in the inner dental epithelium, representing the first report of ameloblast involvement in collagen type I transcription. Whether the collagen is translated and secreted into the enameloid remains to be demonstrated.
KeywordsTooth development Atlantic salmon Bmp Collagen type I Osteocalcin
This work was carried out within the frame of the European COST Action B23 “Oral facial development and regeneration”. AH and MS acknowledge a grant from the FWO 3G0159.05. AH, HT, and PEW acknowledge the support from the Research Council of Norway project “Skeletal malformations in farmed salmon and cod: a functional approach to determine causalities and mechanisms” (Contract no. 172483/s40). The authors thank two anonymous reviewers for helpful comments and suggestions.
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