The n-MTB is similar to a mitotic spindle, in that it can elongate within the nucleus (Fig. 1, j l), but it lacks SPBs at its ends [6] (compare Fig 1, c g to i l).
If Mps1 is indeed involved in the tension-dependent error correction, we may see the role of Mps1 in detaching a centromere from one SPB and attaching it to another SPB when tension is not applied on this centromere-SPB connection by microtubules.
This indicates that Cut12, albeit physically interacting with Plo1 (MacIver et al, 2003), is not a receptor that is directly responsible for recruitment of this kinase to the mitotic SPB, but instead it is Pcp1 that performs this task.
To examine whether anucleate compartments in cdc16-116 mutant cells contain SPBs, we visualized SPBs using the SPB marker Pcp1p-GFP, a calmodulin-binding protein, which is an essential component of SPB [19], [20].
This complex is conserved in fungi, in which it localises to the mitotic SPB and ensures proper spindle assembly; in particular it is required for the anchoring of the minus end of spindle microtubules to the SPB [11], [20].
Pheromone signaling also induces chromosome rearrangements that result in the bouquet conformation [ 15], in which centromeres move away from the SPB and telomeres cluster toward it [ 16].
Our finding that Bbp1 and Mps2 localize to the satellite region early in SPB duplication was unexpected; however it could explain, in part, how satellite components are anchored to the bridge and NE.
It is postulated that SPB movement from mother cell to daughter during anaphase sends a signal to Cdc5 at mitotic exit[22].
Unfortunately, degrons and many mutant alleles in SPB components destroy SPB structure, and it is challenging or impossible to sort out primary versus secondary effects based solely on localization data.
Our observation that Cnm67 is present at variable levels at the satellite is consistent with the idea that it is not required for SPB duplication.
