Fennell et al. reveal that centromeres can stand in for telomeres and promote assembly of the fission yeast meiotic spindle.
During meiotic prophase, the telomeres of fission yeast chromosomes cluster at the nuclear envelope. This “telomere bouquet” connects, via the inner nuclear membrane SUN protein Sad1, to the spindle pole body (SPB), the yeast equivalent of the centrosome. Mutant yeast unable to form a telomere bouquet have problems inserting their SPBs into the nuclear envelope so that they can form a bipolar meiotic spindle. Around half of these bouquet-deficient yeast still manage to form a spindle, however, so Fennell et al. examined how these cells cope in the absence of telomere–SPB contacts.
The researchers discovered that bouquet-deficient cells could successfully assemble bipolar spindles if their centromeres contacted the SPB during meiotic prophase. Boosting centromere–SPB contacts completely restored meiotic spindle assembly in all bouquet-deficient cells. In contrast, forcing noncentromeric chromatin regions to contact SPBs failed to rescue spindle formation.
Fennell et al. found that telomeres or, in the absence of bouquets, centromeres, promoted the accumulation of Sad1 at SPBs. Reducing Sad1 levels inhibited meiotic segregation, suggesting that the SUN protein plays a key role in SPB insertion and spindle assembly. Senior author Julia Cooper now wants to investigate this pathway in more detail. Because telomeres cluster near the centrosomes of other meiotic cell types and centromeres gather next to interphase SPBs, the pathway may represent a conserved way for chromatin to regulate the spindle apparatus.
Text by Ben Short