(A) Spontaneous proliferation of HUVEC, HAEC, HMEC-1, HMVEC-d, and AMEC. Proliferation was measured by using [methyl-³H]thymidine incorporation in different sets of experiments. Each experiment was performed in quintuplicate with cells obtained from 2 different cell cultures. Results are expressed as means and bars denote standard deviation. The results of spontaneous proliferation of AMEC are expressed as means of AMEC-1 and AMEC-2 (passages 2 and 3). (B through E) Histological studies show the staining of immature spindle AMEC by hematoxylin-eosin (B), and demonstration of c-ets-1 transcripts (light grains) by in situ hybridization (C, darkfield illumination of the section after fluorescent counterstaining of the nuclei with Hoechst 33258). (D) Negative results are obtained with the c-ets-1 sense riboprobe. (E) C-ets-1 expression within the stromal capillaries of an invasive ductal breast carcinoma was used as a positive control for active angiogenesis.8