FIGURE 5

Failed synapsis and anomalous pairing in smc1b^Q198X mutant spermatocytes. (A–F) Labeling of Sycp3 and Sycp1 proteins and telomeres (telo) on meiotic chromosome spreads from adult testes. (A–D) In wild-type spermatocytes, leptotene stage cells had Sycp3 protein localized near chromosome ends and exhibited either no Sycp1 signal or Sycp1 puncta. The synaptonemal complex proteins continued to assemble between homologous pairs through pachytene stages as homolog pairing and synapsis occurred. (D′) Sycp3 exhibited enrichment at or near telomeres. Images show enlarged views of the red boxed areas in D. (E,F)Smc1b mutant spermatocytes leptotene stage cells expressed Sycp3 in with a pattern similar to that of wild-type leptotene stage cells and Sycp1 was either absent or present in puncta. However, Sycp3 only labeled chromosomes near the ends and Sycp1 did not extend along chromosomes. A small percentage of mutant cells exhibited some telomere clustering one side of the nucleus (F), which we called bouquet-like and classified as leptotene stage as there was either no Sycp1 or only Sycp1 puncta visible. (G) Quantification of spermatocytes showed that all mutant cells are in leptotene stage compared to about 40% in wild type. Later stages were not observed in the mutants (N = 52 wild-type and 130 mutant cells). (H) Quantification of Sycp3 foci in wild-type bouquet (N = 13) and mutant “bouquet-like” (N = 23) nuclei shows abnormal pairing in smc1b mutant spermatocytes. Mutants have significantly fewer Sycp3 puncta than wild types (T-test, p = 0.000007). Horizontal bars in (H) show the averages. Scale bar is 10 μm.