Fig. 2

Fig. 2

Expression of TgBAC(pax7a:GFP)ⁱ¹³¹ and TgBAC(pax3a:GFP)ⁱ¹⁵⁰ recapitulates the patterns of the endogenous genes in the myotome. A–C: At 24 hours post fertilization (hpf), Pax7 protein (A) and TgBAC(pax7a:GFP)ⁱ¹³¹ expression (B) mostly coincide (C), arrowheads highlight cells detected with α-Pax7, but barely GFP^+ve. Green fluorescent protein (GFP) expression is also detected in processes extending from the xanthophores (B, arrows). D–F: At 48 hpf, labeling with α-DP312 (Pax3/Pax7) (D) and GFP expression driven by TgBAC(pax3a:GFP)ⁱ¹⁵⁰ (E) show significant overlap (F); some nuclei labeled strongly by DP312 show little or no GFP expression, consistent with some cells expressing only Pax7 (arrows, inserts). G–I: Increasingly medial planes through 5 days postfertilization (dpf) TgBAC(pax7a:GFP)ⁱ¹³¹ larvae: at a superficial level, expression is observed in xanthophores (arrowheads) and along the horizontal and vertical myosepta (arrows, G). H: More medially, Pax7a cells align closely to myofibers, stained with Phalloidin (actin, red; arrows). I: Intense GFP expression in dorsal spinal cord (long arrow), dorsal neural crest cells (arrowheads), and alongside myofibers (small arrows). J: Individual fibers (α-actinin, red) are labeled in 48 hpf TgBAC(pax7a:GFP)ⁱ¹⁵⁰ reflecting perdurance of the GFP protein. K,L: TgBAC(pax3a:GFP)ⁱ¹⁵⁰ at 6 dpf: expression persists in fibers (K) and remains in rounded cells alongside the fibers at 10 dpf (L). M: Quantification of Pax7^+ve nuclei at 24 hpf to 5 dpf detected in fixed specimens with αPax7 mAb and in vivo pax7a:GFP^+ve cells. Counts include only weakly stained or weakly expressing Pax7^+ve cells per somite and exclude intensely stained elongated Pax7^+ve xanthophores. N–P: Cross-sections of Tg(Pax7a:GFP)ⁱ¹³¹ show a Pax7a:GFP^+ve cell fully surrounded by β-catenin (arrows) and persistence of GFP in an individual fiber (arrowhead) at 6 dpf. N,O are magnifications of the boxed area in P. Scale bars = 50 μm in A–L, 25 μm in N–P.