passages.id: PMC-2721088-sec-10__text
passages.type: sec
passages.text: Chicken CCN3 expression in embryonic and extraembryonic tissues
  Expression of CCN3 in axial structure becomes visible in the presegmentation stage and reaches to the highest level at the beginning of somitogenesis (HH stage 7, Fig. 1a). Strong similarity between CCN3 and Sonic Hedgehog was observed for the expression pattern in axial structure (notochord and floor plate), in which the left-right asymmetrical pattern in the node area is also conserved (Fig. 1b). However, Sonic Hedgehog expression is slightly broader than that of CCN3. Since CCN3 stimulates Notch signaling (Sakamoto et al. 2002), we investigated the expression of Notch signal genes. Among them, Serrate1, a ligand of Notch is unique because its expression is apparently a right deviated pattern in the node area (Fig. 1c). Another Notch ligand, Delta1 shows a right deviated pattern, but is more caudal area of the node extending to the primitive streak (data not shown). The expression of CCN3 in axial structure was followed by the presomitic mesoderm although it is diminished (Sakamoto et al. 2002). 
  Fig. 1
  Expression of mRNA in early stage chicken embryo; CCN3 (a), Sonic Hedgehog (b) and Serrate1 (c) at the beginning stage of somitogenesis (Hamburger and Hamilton (HH) Stage 7). Arrowheads indicate Hensen's node. Demonstrates the schematic view of tissue organization at this stage (d). Expression of CCN3 mRNA in blood islands of chicken extraembryonic tissue (HH stage 10) (e). Ventral part of the endothelial precursor cells in blood islands is positive for CCN3 expression. Coloration was stopped before the background staining started in sense probes (negative control)
  There is accumulating evidence of CCN3 commitment to hematopoiesis and therefore we investigated the CCN3 expression in extraembryonic tissues. Blood islands are formed in the yolk sac mesodermal area just between the visceral endodermal and ectodermal layers, which supply the red blood cells at the primary stage. The cells in blood islands are called hemangioblasts since they also differentiate into the endothelial cells of extraembryonic blood vessel structure. In chicken embryo, differentiating endothelial cells in the ventral part of blood islands express CCN3 from the initial stage (Fig. 1e). Erythroblasts in the center of blood islands (spherical cells in Fig. 1e) weakly express CCN3 and their expression is mildly enhanced in later stage (data not shown).
  