Figure 1.

Ultrathin cryosections of PC12 cells showing immunogold labeling for endogenous rab4 (A and B) and overexpressed rab4 (C). (A) Endogenous rab4 is present on EE vacuoles (EE) and nearby located vesicles and tubules (arrowheads), whereas the plasma membrane (PM) is devoid of label. (B) Rab4-positive vesicles (arrowheads) are also present at the trans-side of the Golgi (G). (C) In rab4 overexpressing cells, a similar labeling pattern is seen as for endogenous rab4, but with significantly increased density. The small arrowheads point to a cluster of rab4-positive vesicles in the peripheral cytoplasm. The large arrowheads point to vesicles more closely located near an EE. M, mitochondrion; SG, secretory granule; L, lysosome. Bars, 100 nm.