Spatial cues and not spindle pole maturation drive the asymmetry of astral microtubules between new and preexisting spindle poles

Abstract

The distinct behavior of the spindle pole bodies (SPBs) during spindle orientation in yeast metaphase does not result from them being differently mature, but astral microtubule organization correlates with the subcellular position rather than the age of the SPBs.

Asymmetric Segregation of Aged Spindle Pole Bodies During Cell Division: Mechanisms and Relevance Beyond Budding Yeast?

“…Budding yeast cells also segregate their MTOCs, called spindle pole bodies (SPBs), non‐randomly. Some parts of the SPB duplicate conservatively such that each mitotic cell contains a pre‐existing SPB inherited from the previous mitosis and a newly assembled SPB . During mitosis, the older SPB partitions into the bud and the new one remains in the mother cell.…”

Orderly assembly underpinning built-in asymmetry in the yeast centrosome duplication cycle requires cyclin-dependent kinase

“…However, that study could not determine how Spc72 67 temporal asymmetry arises or its direct impact on gTC distribution at distinct nucleation 68 sites. Moreover, the idea that intrinsic SPB asymmetry has such structural basis has been 69 brought into question in a recent study (Lengefeld et al, 2018). 70 71 Here we undertook detailed analysis of the mode of distribution of Spc72 and components 72 of the gTC throughout the spindle pathway by SIM.…”

“…The 42 kar1∆15 mutation abrogates Spc72 binding to Kar1 (Pereira et al, 1999), thus precluding 43 gTC localization to the bridge. Strains also contained Spc72-Venus so that images in which 44 inner and outer plaques overlapped vertically could be excluded (top view), an issue with 45 previous single color SIM analysis of gTC (Lengefeld et al, 2018). Judging from the 46 apparent overlap between single Tub4 foci and the core outer plaque component Nud1, 47…”

“…Therefore, we anticipated to observe a correlative 5-10 IP:OP ratio in gTC levels 19 rather than the ~2-fold difference we measured. Previous SIM was unable to estimate the 20 overall proportion of SPBs presenting or lacking gTC at the outer plaque, in part, because a 21 fraction of SPBs were presumably aligned perpendicularly to the imaging plane, requiring 22 resolution in the z axis greater than achievable (Lengefeld et al, 2018). Our use of a 23 second label and three-dimensional realignment allowed us to include virtually all SPBs in 24 our analysis, including unduplicated SPBs, side-by-side SPBs and SPBs in short and long 25 spindles.…”

“…In 127 conclusion, CDK may enforce orderly SPB assembly that ensures both correct SPB 128 morphogenesis and structural asymmetry. Retention of Spc72 by the old SPB has been previously proposed although the mechanistic 147 basis of how this might be achieved was not discussed (Lengefeld et al, 2018). Such a 148 mechanism might effectively establish SPB identity on the basis of Spc72 inherited by the 149 old SPB from the preceding cell cycle.…”