Fig 1. Meiotic pairing is perturbed in Mcm5A7 mutants.
a. Schematic depiction of the Drosophila germarium. At the anterior portion (the pre-meiotic region, Region 1), the germline stem cell (brown cell) divides to yield a cytoblast, which undergoes four subsequent rounds of division to yield a 16-cell cyst. In the pre-meiotic region, proteins, such as SMC1 and C(3)G, are enriched at the centromeres, and within the 8-cell cyst, chromosomes exhibit centromere-direct rapid movements. Within the first 16-cell cyst (zygotene; Region 2A), homologous chromosomes pair, centromeres cluster into 1 or 2 groups, and up to four cells initiate meiosis, expressing patches of SC (red dots). As the 16-cell cyst enters early pachytene (EP) (Region 2A), only two continue as pro-oocytes to form full length synaptonemal complex (red). Meiotic double-strand breaks (DSBs) are formed and repaired via homologous recombination (HR) throughout the germarium’s posterior (Regions 2A, 2B) to yield noncrossover and crossover products. At the most posterior tip, signifying mid-pachytene (MP), only one cell within the cyst has been selected to become the oocyte, and all DSBs are repaired. Cytological regions of the germarium (Region 1, 2A, 2B, and 3) are depicted. b. Top: schematic of X chromosome and relative location of X-probe, not drawn to scale. Left: Representative images paired (WT) and unpaired (Mcm5A7) X-probes (green) in meiotic cells, indicated by C(3)G expression (magenta). Images are of meiotic nuclei in Region 2A. Scale bar = 1 μm. Right: Quantification of percent paired and unpaired nuclei in WT and Mcm5A7 in Z (WT n = 33, Mcm5A7 = 32), EP (WT n = 130, Mcm5A7 = 118; ***p < 0.0001, chi-square), and MP (WT n = 10, Mcm5A7 = 11; *p = 0.01, chi-square). c. Top: schematic of the right arm of chromosome 3 (3R) and relative location of 3R-probe, not drawn to scale. Left: Representative images paired (WT) and unpaired (Mcm5A7) 3R-probes (green) in meiotic cells, represented by C(3)G expression (magenta). WT image is of 2A nucleus, Mcm5A7 is of Region 3 nucleus. Right: Quantification of percent paired and unpaired nuclei in WT and Mcm5A7 in Z (WT n = 37, Mcm5A7 = 33), EP (WT n = 104, Mcm5A7 = 97; ***p < 0.0001, chi-square), and MP (WT n = 10, Mcm5A7 = 9; **p = 0.0066, chi-square). Brightness, contrast, and texture (smoothed) of images have been adjusted for clarity.