Fig 2

(A) Schematic representation of the bipartite organization of the zebrafish sclerotome and the generation of perivascular fibroblasts. At 24 hpf, the zebrafish sclerotome in each somite is divided into three compartments: the dorsal sclerotome, the ventral sclerotome, and sclerotome derived notochord associated cells. Note that notochord associated cells originate from the ventral sclerotome and are located about half-somite posterior to the corresponding somite. At 48 hpf, perivascular fibroblasts appear along the length of the intersegmental vessels (ISVs, green). The dotted line indicates the position of the horizontal myoseptum, which divides any given ISV into a dorsal half and a ventral half. Perivascular fibroblasts were quantified based on their final locations along each ISV: dorsal ISV (above the horizontal myoseptum) or ventral ISV (below the horizontal myoseptum). Sc: sclerotome. (B) Snapshots from time-lapse imaging of a nkx3.1^NTR-mCherry; kdrl:EGFP embryo from 25 hpf to 49.5 hpf. Perivascular fibroblasts along ISVs were retrospectively traced to determine their cell of origin. One cell from the ventral sclerotome domain (cyan arrows) and one cell from sclerotome derived notochord associated cells (yellow arrows) were traced over 24.5 hours with their daughter cells indicated by the same colored arrows/arrowheads. Both sclerotome progenitors divided at least once to give rise to one perivascular fibroblast (arrowheads) as well as several interstitial cells (arrows). A schematic representation of color-coded traced cells at the last time point is shown with perivascular fibroblasts indicated by asterisks. The corresponding time-lapse movie is shown in S1 Video. n = 6 embryos. (C) Quantification of the contribution of each sclerotome domain to perivascular fibroblasts. Sclerotome progenitors from each domain were quantified based on the final dorsoventral location of perivascular fibroblasts along each ISV. A given sclerotome progenitor can give rise to perivascular fibroblasts in only dorsal ISV, in only ventral ISV, or in both dorsal and ventral ISV as indicated in (A). The ventral sclerotome (combined) group includes progenitors from both the ventral sclerotome domain and sclerotome derived notochord associated cells. n = 122 sclerotome progenitors from 6 embryos. Scale bar: 50 μm.