Figure 1. Brief Pulse-Labeling of DNA Synthesis Highlights Megabase-Sized "Replication Domains".

Figure 1

Brief Pulse-Labeling of DNA Synthesis Highlights Megabase-Sized "Replication Domains". Chinese hamster cells were pulse labeled for 10 minutes with either tritiated thymidine (left) or BrdU (right) during late S-phase or labeled continuously with BrdU except for 1 hour in late S-phase during which cells were labeled with thymidine (middle) and then chased with unlabeled medium into mitosis. Metaphase spreads were analyzed by autoradiography (left), BrdU quenching of Hoechst dye (middle) or indirect immunofluorescence using anti-BrdU antibodies (right). These cytogenetic methods demonstrated that megabase-sized segments of the genome are labeled in very short periods of time, producing banding patterns that were characteristic for each chromosome and varied during S-phase, with euchromatic R bands replicating early and heterochromatic G bands replicating late. Note that the heterochromatic Y chromosome is almost entirely labeled in a 10-minute period late in S-phase. With known rates of replication fork movement, this could only be achieved by the nearly synchronous firing of clusters of replication origins. Figure was adapted from J.H. Taylor15 (left-© Taylor, 1960. Originally published in The Journal of Biophysical and Biochemical Cytology. 7: 455-463), E. Stubblefield18 (middle) and D.M. Gilbert102 (right) with permissions from Journal of Biophysical and Biochemical Cytology15 and Chromosoma.18

From: Autosomal Lyonization of Replication Domains During Early Mammalian Development

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