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Fig. 3 cyp26b1 is expressed in osteoblasts and their precursors. Stainings of wild-type zebrafish at the stages indicated in the upper right corners and with the in situ RNA probes indicated in the lower right corners. (A-F) Confocal sections of double fluorescent in situ hybridizations and Alizarin Red stainings (alR), counterstained with DAPI (blue). Cells with weak cyp26b1 and strong col10a1 expression are indicated with white arrows, cells with strong cyp26b1 but absent col10a1 expression with red arrows, and cells with strong col10a1 but absent cyp26b1 expression, which most likely represent fully mature/active osteoblasts, with green arrows. See text for details. For single-channel images of B,E, see Fig. S4 in the supplementary material. (G-I) cyp26b1 displays uniform expression in perichordal cells in anterior regions of the notochord (n) (G; left panel shows longitudinal section; right panel shows transverse section; counterstained with Eosin), and metameric expression in the trunk (H,I; lateral views). In H, cyp26b1-positive cells are (still) underneath the notochord (arrowhead) and others are (already) in perichordal positions (arrows), whereas in I all cells are perichordal (arrows). Positive cells dorsal of the notochord in H most likely represent ventral spinal cord neurons (scn). (J-O) col10a1 and opn show a similar expression pattern to cyp26b1 (L-N) and transient coexpression with cyp26b1 (J,K) at intersomitic borders, coincident with the anterior borders of the the Alizarin Red-positive vertebral bodies (O). Arrows in L-N point to positive cells, arrowheads to borders of somites 5-8. (P) Numbers of perichordal cyp26b1-, col10a1- and opn-positive cells at different developmental time points. Ten fish were evaluated per condition; standard errors are indicated.