SMC1β and SMC3 localization on spermatocyte telomeres. (A) Anti-SMC3 ChIP from GFP⁺ spermatocytes purified by FACS from SMC1βprom-GFP juvenile mice. ChIP slot-blot analysis of telomeric DNA. Antibodies used for IP and controls (anti–H4 3-meK₂₀ and rabbit [Rab] IgG) are indicated. The amount of input loaded on the blot, shown as a percentage of the total, is indicated on the left. Quantification of the signals, shown as a percentage of input DNA, is shown at the bottom. (B) Anti-SMC1β or anti-SMC3 ChIP from adult WT or Smc1β^−/− testis cells followed by slot-blot analysis as in A. No ab, no antibody. (C) Early pachytene spermatocyte spreads were stained with telo-FISH (red), anti-SMC3 (green), and DAPI. (left) An example of telo-FISH signals close to the SMC3-stained axis (boxed areas) are magnified in insets. (right) Quantification of SMC1β or SMC3 and telomere signals along individual chromosome axes. In WT cells, the anti-SMC1β and telo-FISH signals of the indicated chromosome (red lines) partially overlap. The marked WT chromosome stained with anti-SMC3 shows one full and one partial overlap with telomere signals. The indicated Smc1β^−/− chromosome shows one telomere signal not overlapping with the SMC3 signal and one partially overlapping. The digram shows the percentage of telomere signal overlap with SMC1β or SMC3 on WT or Smc1β^−/− chromosomes. n = 195 (WT SMC1β), 220 (WT SMC3), and 382 telomeres (KO SMC3). **, P < 0.001 by χ² test. Bars, 10 µM.