DEOXYRIBONUCLEIC-ACID REPLICATION IN FETAL CELLS

OBJECTIVES: Our purpose was to develop a sensitive method for assessin g the replication time of specific human genes in cultured fetal cells and for detecting potential replication defects. STUDY DESIGN: Synchr onous progression of diploid human fetal lung cells through S phase wa s achieved by releasing from serum restriction with minimum essential medium alpha modification plus 10% fetal bovine serum, followed by hyd roxyurea blockage at the G(1)/S boundary. Deoxyribonucleic acid replic ation was studied in permeabilized cells using mercurated nucleotides to label nascent deoxyribonucleic acid. RESULTS: A high degree of sync hrony in traversal of S phase was indicated by flow cytometry and a we ll-defined 7-hour period of deoxyribonucleic acid synthesis. The repli cation of the topoisomerase II gene occurred in a narrow time span 3 h ours after entry into S phase. CONCLUSIONS: Fetal cells have been high ly synchronized at the beginning of S phase, and the replication time of a specific gene can be defined within a narrow time window.