Fig. 3. MCM protein expression in differentiating and terminally differentiated tissues. (A,B) Indirect immunoperoxidase staining of colon with an anti-Mcm2 MAb. (A) The majority of Mcm2-expressing cells are located in the lower third of the crypt, which corresponds to the proliferative zone of the mucosa (x87). B, Notably, it appears to be the anatomical location corresponding to the transit amplifying population of cells that shows the highest levels of Mcm2 expression. The proportion of Mcm2-positive cells and the levels of Mcm2 expression decline in the middle third of the crypt, becoming undetectable in surface terminally differentiated cells (x156). (C) Indirect immunoperoxidase staining of adult brain with an anti-Mcm5 rabbit PAb. Neurones and glial cells lack Mcm5 expression (x170). (D) Hematoxylin and Eosin stained medulloblastoma showing sheets of undifferentiated mononuclear tumour cells containing well demarcated islands of glial differentiation (x68). (E,F) Indirect immunoperoxidase staining of medulloblastoma with an anti-neurofilament (NF) PAb (E) and anti-Mcm5 rabbit PAb (F) (x68). Mcm5 expression is strictly confined to the undifferentiated tumour cells with downregulation occurring in areas of differentiation.