IgM expression during development. (A) qRT-PCR analysis was performed on individual whole fish. Average expression plus SEM of IgM or IgZ relative to ef1α (ΔCt) for 3 to 4 fish per time point is shown. (B) Confocal imaging of the area between the dorsal aorta and the posterior cardinal vein of fli1:DsRed;IgM1:eGFP fish at 20 to 21 dpf. (C) Confocal imaging of the kidney of rag2:DsRed;IgM1:eGFP fish at 21 dpf. DsRed⁺eGFP⁺ cells are indicated with arrows. (D) Confocal imaging of the area between the dorsal aorta and the posterior cardinal vein of kdrl:cerulean;rag2:DsRed;IgM1:eGFP fish at 22 dpf. All of the cells near the vein are DsRed⁺eGFP⁺. These results are representative of results obtained with at least 3 individual fish of each type. All embryos were imaged in water at room temperature with an ×25 objective using a Leica SP5 inverted confocal microscope with Leica Application Suite Advanced Fluorescence (LAS AF) acquisition and analysis software.