Figure 5. The 2M6 antigen has a graded expression pattern in the chick retina. Embryonic day 10 chick retina was fixed, embedded in paraffin, sectioned, and stained with antibodies specific for 2M6 (green) and human natural killer cell antigen (HNK; red). Three regions of the retina were examined, including the ciliary margin (A–C), optic nerve (D–F), and fundus (G–I), which represent the different stages of development within the retina at this age. Note that the orientation of panels A–C and G–I are dorso–ventrally flipped relative to that of D–F. At the ciliary margin, 2M6 expression changes from a diffuse pattern to one that is more specific (arrowhead, A). Boundary cells (arrows, D–F) are positively labeled with the 2M6-specific antibody, whereas optic nerve tracks (arrowhead, D–F) are labeled with the HNK cell-specific antibody. The magnification bars for A–C and G–I are 47.62 μm; the magnification bars for D–F are 150 μm.