Post-transcriptional modification by SUMOylation is involved in numerous cellular processes including human spermatogenesis. For human male meiosis, we previously showed that the small ubiquitin-related modifier-1 (SUMO-1) protein localizes to chromatin axes in early pachytene spermatocytes, then to kinetochores as meiosis progresses. Here, we delineate possible functional roles based on subcellular localization for SUMO-1 and SUMO-2/3.
Western and immunoprecipitation analyses were conducted on proteins isolated from the testis of two normal adult fertile men. Combinatorial immunofluorescence and chromosome-specific fluorescence in situ hybridization analyses were performed on male meiocytes obtainedduring testicular biopsy from four patients undergoing testicular sperm extraction for assisted reproduction technologies.
The synaptonemal complex (SC) and SC proteins (SCP)-1 and SCP2, but not SCP3, are SUMOylated by SUMO-1 during the pachytene substage. Likewise, two distinct localization patterns for SUMO-1 are identified: a linear pattern co-localized with autosomal SCs and isolated SUMO-1 near the centromeric heterochromatin of chromosomes 9 and 1. In contrast to SUMO-1, which is not detectable prior to pachytene in normal tissue, SUMO-2/3 is identified as early as leptotene and zygotene and in some, but not all, pachytene cells; no linear patterns were detected. Similar to SUMO-1, SUMO-2/3 localizes in two predominant subnuclear patterns: a single, dense signal near the centromere of human chromosome 9 and small, individual foci co-localized with autosomal centromeres.
Our data suggest that SUMO-1 may be involved in maintenance and/or protection of the autosomal SC. SUMO-2/3, though expressed similarly, may function separately and independently during pachytene in men.