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Fig. 7. NC contribution to the thymus. A: Experimental design to analyze the NC contribution to the thymus. Two-cell-stage embryos were injected in the animal pole with mRNA encoding Red Fluorescent Protein (RFP). At stage 17, the RFP-labeled cardiac NC was transplanted onto the same region of an unlabeled host embryo (NC graft). B: RFP-labeled NC graft at stage 26. Lateral views of the same embryo. Dorsal towards the top, anterior to the right (B,C) and left (D,E). Cells derived from the RFP-labeled NC graft were confined to the three most posterior streams of cranial NC, as previously described (Lee and Saint-Jeannet, 2011). At stage 41 (F), cells derived from the RFP-labeled NC graft (JO) formed most of the head mesenchyme, surrounding the thymus primordial (arrows). A fraction of the RFP-labeled NC cells also express hoxa3; however, these cells remained confined to a region posterior to the thymus primordia (G, I, M, J, N). H, L are higher magnification of F. I, M are higher magnification of G. Longitudinal sections, anterior towards the top. K and O are overlay of H and L, respectively. Insets in K, O are higher magnification views of the thymus primordia (arrows). P: At stage 47, the thymus primordia can be identified by Foxn1 expression (Q, S, W). A small number of RFP-labeled NC cells have colonized the thymus (T, U, X, Y). R are higher magnification views of the thymus primordium (arrows) in P, Q. R and V show two representative tadpoles form two independent experiments. U and Y are overlay of R and V, respec- tively. The scale bars (B, P, and Q) 1⁄4 200 mm; (H and R) 1⁄4 50 mm. |
