Deoxyribonucleic acid replication in fetal cells

OBJECTIVES: Our purpose was to develop a sensitive method for assessing the replication time of specific human genes in cultured fetal cells and for detecting potential replication defects. STUDY DESIGN: Synchronous progression of diploid human fetal lung cells through S phase was achieved by releasing from serum restriction with minimum essential medium alpha modification plus 10% fetal bovine serum, followed by hydroxyurea blockage at the G 1 /S boundary. Deoxyribonucleic acid replication was studied in permeabilized cells using mercurated nucleotides to label nascent deoxyribonucleic acid. RESULTS: A high degree of synchrony in traversal of S phase was indicated by flow cytometry and a well-defined 7-hour period of deoxyribonucleic acid synthesis. The replication of the topoisomerase II gene occurred in a narrow time span 3 hours after entry into S phase. CONCLUSIONS: Fetal cells have been highly synchronized at the beginning of S phase, and the replication time of a specific gene can be defined within a narrow time window. (A M J O BSTET G YNECOL 1994;170:468-73.)