Expression of the genes that regulate the development of cranial musculoskeletal tissues in snake embryos. (A) Lateral view of the head of a snake embryo at stage 26. (B-E) Frontal sections prepared around the plane indicated by the red line in (A). (F-I) Frontal sections around the blue line in (A). (J) The head of a snake embryo at stage 29. (K-N) Frontal sections around the red line in (J). (O-R) Frontal sections around the blue line in (J). (S) The head of a snake embryo at stage 31. (T-W) Frontal sections around the red line in (S). (B, F, K, O, and T) Expression of Runx2. (C, G, L, P, and U) Expression of MyoD. (D, H, M, Q, and V) Expression of Sox9. (E, I, N, R, and W) Expression of Msx2. In snake embryos, expression of Runx2 and Msx2 are detected in the precursor cells of dermatocranial elements (arrows), as in crocodile and turtle embryos. However, these mesenchymal cells are not seen in the temporal region lateral to the jaw adductor muscles. Instead, these cells are distributed in the vicinity of the brain, laterally covering it, and differentiate into the parietal bone in older embryos. Open arrowheads in (F, K, N, O, R, T, and W) indicate the mesenchyme around Sox9-positive jaw cartilages, where the expression of Runx2 and Msx2 is detected. The red outlined domains in (O, Q, R, T, V, and W) indicate the location of the external adductor muscle deduced from adjacent sections where muscular tissues are labeled by MyoD probe. Scale bars in (A), (J), and (S) are 1 mm. Scale bars in other pictures are 0.5 mm.
Tokita et al. SpringerPlus 2013 2:336 doi:10.1186/2193-1801-2-336