Fig. 1

Fig. 1 Expression of Blimp1 protein precedes the onset of slow muscle differentiation. (A–C) Blimp1 (red) is expressed and localized in the nuclei of adaxial cells (arrows) of 14 hpf zebrafish embryos labeled with GFP from the actin::gfp transgene. Blimp1 is expressed in the adaxial cell of the somites (B) as well as the presomitic mesoderm (C). (D–F) Blimp1 protein expression recedes in the more anterior somites (D, E) and is stronger in the newly formed posterior somites (F) in 18 hpf wild-type embryos. (G–I) Double staining of Blimp1 (red) and Prox1 (green) reveals reduced levels of Blimp1 in anterior somites (G, H) where Prox1 is highly expressed, while Prox1 is barely detectable in slow muscle cells of posterior somites (I), where Blimp1 is strongest. (J) Adaxial expression of Blimp1 (red) in a wild-type 14 hpf embryo immediately adjacent to the notochord (green, highlighted by GFP expression from the shh::gfp transgene). (K) Ectopic expression of Blimp1 is induced throughout the somites by constitutive activation of the Hh signaling pathway in response to dominant negative Protein Kinase A mis-expression in a 14 hpf wild-type embryo. (L) Blimp1 expression is absent in a 14 hpf smo mutant embryo deficient in Hh signaling. Nuclei in panels A, J–L were stained with DAPI (blue). In panels A–C and J–L, “N” marks the position of the notochord. Panel A depicts transverse section; panels B, C and J–L depict flat mounted embryos; panels D–I show laterally mounted embryos. In this and subsequent figures, all laterally and flat mounted embryos are oriented anterior to the left; dorsal is on top for embryos depicted in transverse sections. Scale bars = 25 μm. The scale bar in B applies to C; the scale bar in G applies to D–I and the scale bar in J applies to K and L.