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Figure 3 Photomicrographs of sections through Xenopus retinas that received transplantation of
presumptive retinal tissue from dextran-fluorescein (FITC) labeled embryos of the same age
[isochronic (A,B)], or from an earlier age [heterochronic (C,D)]. Embryos were allowed to survive
to the stages of initial expression of photoreceptor antigens XAP-1 (A,C) or XAP-2 (B,D). This is
apparent because all cases demonstrated a spatial gradient of XAP antigen expression: strong in the
central retina and gradually lost at the margins. Thus, at the age of sacrifice, XAP expression was
at an early stage, and it was important that transplants were made in central retina. Note that the
XAP-1 stained retinas are as yet undifferentiated with no obvious cytoarchitectural lamination. In
addition, XAP-1 is expressed in the skin as well as the photoreceptors. By the time XAP-2 begins
to be expressed the inner and outer plexiform layers of the retina are apparent. This antigen, specific
to cone photoreceptors, exhibits a lower density of punctate staining. In isochronic transplants,
XAP-1 and -2 staining extends across the grafted portion of retina. In contrast, the graft of a
heterochronic transplant fails to express XAP-1 or -2 at any level in any region until the graft itself
reaches the stage of normal antigen expression. Scale bar: 50 mm. |