Figure 4.

Change in the nuclear architecture upon transfer to sporulation medium. (a) Early in meiosis, centromere (red) clustering is striking and telomeric regions on the long arms of homologous chromosomes IV (green) tend to be located near the nuclear periphery opposite to the centromere cluster. As can be seen from the two examples depicted in a, this polarization may bring about a closer than random association between homologous telomeres, since their distribution is restricted to a relatively small domain of the nucleus. At later time points nuclei with scattered centromeres become predominant. In early nuclei of this type, homologous telomeres IV produce separate signals (b), whereas later the telomeric signals fuse (c) in the course of meiotic pairing. For the frequencies of the various structural aspects at different time points in the meiotic culture see Fig. 5. (d) At pachytene bivalents are condensed. The red FISH signals indicate centromeres of individual bivalents. The green spot marks the end of the synapsed long arms of chromosome IV. The region to the right, which is devoid of centromere signals, is the nucleolus (arrow). Chromatin is stained blue with DAPI. Bar, 2 μm.