Fig. 6

Stereotypic generation of axial tenocytes from different sclerotome domains.

(A) Snapshots of time-lapse imaging of an nkx3.1^NTR-mCherry embryo between 25 hpf and 50 hpf. Tenocytes were retrospectively traced to determine their cells of origin. Four representative cells (at 0h) from the dorsal sclerotome (2 cells, white arrow and yellow arrowhead), sclerotome derived notochord associated cells (1 cell, green arrow), and the ventral sclerotome (1 cell, cyan arrow) were traced over 25 hours with their daughter cells indicated by the same colored arrows/arrowheads. Based on its initial position, the traced sclerotome derived notochord associated cell was likely derived from the same somite (S1) as the traced dorsal sclerotome cells, whereas the ventral sclerotome cell was from the adjacent posterior somite (S2). Three of the traced cells generated tenocytes along the MTJ (solid arrows) along with several other interstitial cells (open arrows) at the 24.5 hour time frame, whereas one traced dorsal sclerotome cell gave rise to 2 fin mesenchymal cells. The corresponding time-lapse movie is shown in S5 Video. n = 7 embryos. (B) Schematic representation of how tenocytes were quantified based on their origin and positioning along the MTJ. Starting locations of each sclerotome cell at 24 hpf were divided into three compartments: the dorsal sclerotome, the ventral sclerotome, or sclerotome derived notochord associated cells. At 48 hpf, tenocytes were quantified based on their final locations along the “V” of each MTJ: dorsal MTJ (grey, above the notochord), ventral MTJ (cyan, below the notochord), or MTJ tip (green, near the notochord). (C) Quantification of contribution of different sclerotome compartments to axial tenocytes. Tenocytes originated from the ventral sclerotome, sclerotome derived notochord associated cells, or the dorsal sclerotome were graphed based on their final locations along the MTJ. Since sclerotome derived notochord associated cells are derived from the ventral sclerotome, the graph on the right depicts the combined contribution of all cells from the ventral domain. Overall, the dorsal sclerotome mainly gives rise to tenocytes found in the dorsal MTJ, while the ventral sclerotome generates tenocytes along the entire MTJ axis. n = 233 tenocytes from 7 movies. Scale bars: 50 μm.