a-f, Electron micrographs of MCF7.control (clone 38) (a, b) and MCF7.beclin1 (clone 17) cells (c- f) grown in nutrient-rich media (a, c) or subjected to 4 h of serum and amino-acid deprivation (b, d-f). Asterisks in e and f denote autophagic vacuoles that would be counted in the experiment shown in g. Autophagic vacuoles were defined as double-membrane vacuolar structures containing recognizable cytoplasmic contents. Scale bars, 1 µm. 