Localization of SUN1 and TRF1 in WT and Smc1β^−/− spermatocytes. Images represent projections of confocal z stacks. (A–C) In WT, TRF1 (A, red), and SUN1 (B, green), both localize to the ends of the SCs (A, green; B, red) and colocalize with each other (C). (D–D″) Fluorescent images of a Smc1β^−/− spermatocyte simultaneously labeled with SYCP2 (red) and TRF1 (green). The small arrow indicates TRF1 signals not associated with SC structures, and the large arrow denotes a subtelomeric unpaired and stretched AE. The arrowhead indicates an SC end without TRF1 signal. (E–E″) Simultaneous labeling with SYCP2 (red) and SUN1 (green). Ends that appear free of SUN1 are indicated by arrowheads. SC-less SUN1 spots are indicated by arrows. (D″ and E″) Asterisks indicate gaps in SCs. (F–F″) Double labeling for TRF1 (red) and SUN1 (green). Arrows indicate TRF1 signals lacking SUN1 signals. (G) Quantification of TRF1 and SUN1 signals. WT, ∼41 TRF1 (40.88 ± 0.45; n = 42) and SUN1 (40.61 ± 0.59; n = 41) spots; Smc1β^−/−, increased TRF1 (43.85 ± 2.12; P < 0.001; n = 53) and decreased SUN1 signals (35.89 ± 4.21; P < 0.001; n = 58). A mean of 7.63 (±3.97; n = 32) SUN1-less TRF1 signals are seen in Smc1β^−/− (WT, 0.38 ± 0.50; n = 21). The red line is drawn at 41, the number of telomere signals in cells with fully synapsed chromosomes. Error bars indicate SD. Bar, 10 µm.