Figure 1. M18BP1 associates with centromeres in a cell-cycle dependent manner. (A) Localization of endogenously tagged M18BP1-EGFP in the K1B2 mES cell line. K1B2 cells were stained for CENP-A and confocal stacks were recorded. Maximum intensity projections are shown. M18BP1-EGFP showed different patterns: strong enrichment at centromeres (s), weak enrichment (w), no enrichment/diffuse nuclear (d). Scale bars are 20 µm. (B) M18BP1 distribution during S phase. K1B2 cells were transfected with a RFP-PCNA expression construct to detect cells in different S phase stages. M18BP1-EGFP showed intermediate to low centromeric enrichment throughout S phase. Cells which are not in S phase fall into two different staining patterns: M18BP1 is highly enriched at centromeres (presumably G1) and cells with low/no centromeric M18BP1 signals (presumably G2). (C) M18BP1 distribution in G2/M phase. K1B2 cells were stained with H3S10P antibodies to visualize different stages of G2 and M phase. Starting from early G2 phase (weak H3S10P signal) to M phase (strong H3S10P signal) M18BP1 appeared to be largely absent from centromeres. (D) M18BP1 localization in different mitotic stages. In metaphase cells, M18BP1 is absent from centromeres, however, starting from late anaphase, M18BP1 showed strong signals at centromeric regions. Scale bars in (B–D) are 5 µm.