Initiate then elongate

Studies on yeast have provided significant insights into eukaryotic DNA replication, but it has been difficult to examine the process in more complex organisms. On page 225, Claycomb et al. have taken advantage of a peculiar aspect of insect biology to develop a new model for studying metazoan DNA replication, and have already made one surprising finding with the system.During a specific period of oocyte development in Drosophila, the ovarian follicle cells surrounding the oocyte begin to amplify several defined clusters of genes. Using real-time PCR and a combination of microscopy techniques, the authors discovered that this amplification occurs stepwise. First, initiation takes place at the loci that will be amplified, and then, in a separate developmental stage, the replication forks elongate. The natural separation of initiation and elongation provides...