Figure 4. The mon/tif1γ Gene Is Highly Expressed in Hematopoietic Mesoderm.

(A) In situ hybridization of zebrafish embryos demonstrating the embryonic expression of tif1γ. tif1γ is initially expressed as a maternal mRNA. Increased expression of tif1γ in ventral-lateral mesoderm begins between the one- to three-somite stages and increases through early development. By five somites, tif1γ is strongly expressed in lateral stripes of mesoderm that also express scl. At 22 hpf tif1γ is expressed broadly in the brain, spinal cord, trunk, and tail mesenchyme, but is at much higher levels in hematopoietic cells of the blood island. Zebrafish tif1α is also broadly expressed but relatively more uniform in most tissues, in comparison to tif1γ. Tif1α is weakly expressed at early somite stages in hematopoietic mesoderm and uniformly expressed at 22 hpf, including expression in the blood islands. Expression of scl at five somites and 22 hpf highlights the embryonic blood island in comparison to tif1γ expression.

(B) In situ hybridization of mouse embryos detects broad expression of Tif1γ at embryonic day 8.5 including the yolk sac blood islands (arrow). AT embryonic day 12.5, there is high level expression in the fetal liver (arrow) and broad expression in the embryonic brain, spinal chord, gut, and muscle.