ANALYSIS OF FETAL EXPRESSION SITES OF HUMAN TYPE-II DNA TOPOISOMERASEALPHA-MESSENGER-RNA AND BETA-MESSENGER-RNA BY IN-SITU HYBRIDIZATION

We present the first analysis of the sites of expression of DNA topois omerase II alpha and II beta mRNAs in human foetal tissues by in situ hybridisation, using S-35-radiolabelled probes. This revealed differen tial localisation of topoisomerase II alpha and II beta mRNAs in a ran ge of foetal organs, including foetal kidney (developing structures wi thin the neogenic zone), brain (cortical layers), small intestine (cry pt epithelium and muscle), liver (hepatocytes), lung (smooth muscle, a nd epithelium in the lining of primitive lung buds) and placenta (trop hoblastic epithelium). The intensity of expression of topoisomerase II alpha mRNA appeared higher than that of topoisomerase II beta, althou gh topoisomerase II beta mRNA was expressed in a broader range of cell types. The distinct patterns of expression of topoisomerase II alpha and beta mRNAs indicate differential regulation of these genes, sugges ting that the two isoforms may play important but different roles in f oetal development, with topoisomerase II alpha being expressed most st rongly in zones of proliferation.