Fig. 4. (A) Phase-contrast microscopy and immunofluorescence staining of primary human breast fibroblast (HMF48) and epithelial (HMEC48) cells derived from reduction mammoplasty specimens with anti-Mcm2 MAb. Nuclei are counterstained with DNA stain 4,6-diamidino-2-phenylindole (DAPI). (B) Immunoblots of Mcm2 and ß-actin in total cell extracts from isogenic sets of human breast fibroblasts (HMF48) and epithelial cells (HMEC48). HMF and HMEC growth curves and BrdU labelling indices indicate the proliferative state. (C) Immunoblot analysis of ORC, Cdc6, MCM and p21 proteins in total cell extracts of asynchronously proliferating (AS) and replicative senescent (SEN) WI38 HDF. (D) Giant cell tumour of bone (B) stained with Haematoxylin and Eosin (left panel) and with rabbit anti-Mcm5 polyclonal antibody (indirect immunoperoxidase staining, right panel) (x130). The tumour is composed of multinucleate giant cells (G) regularly dispersed in a background of small mononuclear (M) neoplastic cells. Mcm5 expression is restricted to the mononuclear neoplastic cell population.