Journal: The EMBO Journal

Article Title: Speedy A governs non-homologous XY chromosome desynapsis as a unique prerequisite for XY loop-axis organization

doi: 10.1038/s44318-025-00528-8

Figure Lengend Snippet: ( A ) X-Y axis length measurements in late pachytene (RA13) Sync-Spdya fl/fl (a) and Sync-Spdya cKO (b) spermatocytes. Green and blue dashed lines show X and Y chromosome axes, respectively. (c–e) Measured lengths of the X axis (c), Y axis (d), and the calculated Y/X axis length ratio (e) in late pachytene Sync-Spdya fl/fl cells and Sync-Spdya cKO cells with full Y-X NH synapsis . Each dot represents a single nucleus. ( B ) Immuno-FISH staining of late pachytene Sync-Spdya fl/fl (a–a″) and Sync-Spdya cKO (b–b″) spermatocytes for γH2AX (light blue), Chr Y (green) and SYCP3 (red). The white dashed line-enclosed area indicates Y chromatin signals located outside the γH2AX area. Scale bars, 2 µm. (c) Percentage of Y chromatin loop signals outside γH2AX area in Sync-Spdya cKO spermatocytes, based on the fluorescence intensity measurements of Y loops inside and outside the γH2AX domain. ( C ) Immuno-FISH staining of late pachytene Sync-Spdya fl/fl (a–a″) and Sync-Spdya cKO (b–b″) spermatocytes for SCML2 (light blue), Chr Y (green) and SYCP3 (red). The white dashed line-enclosed area indicates Y chromatin signals located outside the SCML2 area. Scale bars, 2 µm. (c) Percentage of Y chromatin loop signals outside SCML2 area in Sync-Spdya cKO spermatocytes. ( D ) Sync-Spdya fl/fl (a) and Sync-Spdya cKO (b) spermatocytes immunostained for FK2 (green), SYCP3 (red) and ACA (light blue) showing the absence of FK2 signals in the full Y-X NH synapsis region (dashed circle in (b)) of X-Y chromosomes in Sync-Spdya cKO spermatocytes. Scale bars, 2 µm. (c) Percentage of late pachytene Sync-Spdya cKO spermatocytes lacking FK2 signals at the full Y-X NH synapsis region. ( E ) Illustration of a proposed mechanism underlying SpdyA-mediated X-Y loop-axis organization at late pachynema. Data information: All values are presented as the mean ± SD. “ n ” represents the total number of pachytene spermatocytes scored per genotype: from two mice in ( A – C ), and from three mice in ( D ). Statistical analyses were performed using Mann–Whitney test, and both exact P values in ( A -d) and ( A- e) ˂ 0.000000000000001. .

Article Snippet: The germline-specific Polycomb protein SCML2 (Sex comb on midleg-like 2) is recruited to X-Y chromatin at the early-to-mid-pachytene transition, suppressing the ubiquitination of H2A Lysine 119 (K119) on the X-Y chromosomes (Hasegawa et al, ; Luo et al, ).

Techniques: Staining, Fluorescence, MANN-WHITNEY