Figure 7.

Chromocenters replicate after the Xi in wild-type cells but coincident with the Xi in Suv39dn. (a) A large synchronously replicating body (indicated with arrowheads) is highly enriched for Me₃K27H3, a defining characteristic of the Xi. The Xi does not colocalize with DAPI-dense bodies that define chromocenters. (b) In wild-type (WT) cells, the Xi replicates during a distinctly different spatial replication pattern (pattern III) than do the chromocenters (pattern IV). In pulse-chase-pulse experiments like those shown in Fig. 6, 2 h of chase time are necessary to traverse from CldU-labeled Xi to IdU-labeled chromocenters. (c) In contrast to wild-type cells, in D15 cells, the Xi (arrowheads) can be seen to replicate synchronously with the replication of chromocenters in a single BrdU pulse (i.e., with no chase). (d) The percentage of cells displaying simultaneous colocalization of the Xi and chromocenters with BrdU label (after a 10-min pulse of BrdU) was scored for wild type, D15, and the D15 derivative rescued by the expression of a Suv39h1 cDNA. More than 100 cells showing Xi replication were scored for each cell line. The means and SD (error bars) for two independent experiments are shown.