Fig. 8. PC12 cells also show cell-cycle-dependent expression of receptors for CTX. (a-c) represent identical cells. No binding of Cy2-ST is observed. Cy3-CTX binds almost exclusively to the large peripheral cells; (c) differential interference contrast picture. (d-g) NGF-differentiated cells show increased binding and uptake of Cy3-CTX (d) and (f), whereas undifferentiated cells characterized by their round shape and lack of axonal protrusions (small arrows in (d) and (e)) show little CTX-binding. (h) and (i) PC12 cells in S-phase as characterized by BrdU incorporation (i) do not bind CTX (h).