Fig. 4. Double immunolabelling on squashed primary spermatocytes with anti-SCP3 serum (green) and MPM-2 antibody (red). (A-B) Projection of three focal planes through a middle pachytene spermatocyte to reconstruct the whole XY body. (A) Anti-SCP3 labelling appears on the autosomal SCs (arrow) and the sex AEs (arrowhead). (B) MPM-2 labelling mainly appears on the sex chromosomal AEs (arrowhead) and as diffuse nuclear foci that do not correlate with autosomal SCs. At higher magnification (C,D) the outline of sex chromosomal AEs is clear. The chromosomes are connected at their ends by a fine thread that is recognised by both antibodies (arrowheads in C). The labelling with anti-SCP3 matches perfectly with that of MPM-2. (E,F) Projection of three focal planes through a late pachytene spermatocyte to reconstruct the whole XY body. (E) Autosomal SCs (arrow) are faintly labelled with anti-SCP3. The plate connecting sex chromosomal AEs (arrowhead) has increased in size and includes the four chromosome ends. (F) MPM-2 labelling only appears on the sex body. Higher magnification (G-H) shows details of the XY association. The intensity of labelling is so high on the plate that joins sex chromosomal AEs that it outshines the outline of chromosome AEs. This plate is larger than the region of attachment of AEs to the nuclear envelope. The two labels almost completely overlap. Note that in mid and late pachytene, sex chromosomes are located at the nuclear periphery. Bars, 5 µm in A,B,E,F; 1 µm in C,D,G,H.