A New Mechanistic Scenario for the Origin and Evolution of Vertebrate Cartilage
Figure 3
Expression of cartilage GRN components in pre-metamorphic ammocoete larvae and post-metamorphic juvenile lamprey.
A) Sections for the in situ hybridizations shown in B–E were cut from pre-metamorphic ammocoete larvae through the pharyngeal arches at approximately the level of the dotted line. B) Strong expression of Col2a1a is seen above background levels in the notochord (arrow) and in cells in and around the branchial bar cartilage (arrowhead). C) Specific expression of SoxE1 in the gills (arrowhead). Diffuse staining in the branchial cartilage (arrowhead) is likely due to background as can be seen with two negative control riboprobes corresponding to a lamprey SoxB1 gene (I, arrowhead) and Xenopus laevis FGF3 (J, arrowhead). No specific expression of Alx (D) or Barx (E) was seen in branchial bar cartilages. F) Sections for the in situ hybridizations shown in G–J were cut from post-metamorphic juvenile lampreys through the pharyngeal arches at approximately the level of the dotted line. No expression of RunxB (G) or SoxE1 (H) was seen in the branchial basket cartilage (arrowheads) after metamorphosis. In contrast, strong, specific reactivity with the SoxE1 and SoxB1a probes is seen in different subsets of spinal cord neurons (H, I, insets). SoxE1 mRNA is also detected in the notochord (H, arrow), and gills (H, double arrowhead). I) Control in situ hybridization with lamprey SoxB1a showing neural expression, and expression in the gills.