Centrosomes catalyze microtubule formation for mitotic spindle assembly 1 . Centrosomes duplicate once per cell cycle in a process controlled the kinase PLK4 2 , 3 . Following chemical PLK4 inhibition, cell division in the absence of centrosome duplication generates centrosome-less cells that exhibit delayed, acentrosomal spindle assembly 4 . Whether PLK4 inhibitors can be leveraged for cancer treatment is not yet clear. Here, we show that acentrosomal spindle assembly following PLK4 inhibition depends on levels of the centrosomal ubiquitin ligase TRIM37. Low TRIM37 accelerates acentrosomal spindle assembly and improves proliferation following PLK4 inhibition, whereas high TRIM37 inhibits acentrosomal spindle assembly, leading to mitotic failure and cessation of proliferation. The Chr17q region containing the TRIM37 gene is frequently amplified in neuroblastoma and in breast cancer 5 – 8 , which renders these cancer types highly sensitive to PLK4 inhibition. TRIM37 inactivation improves acentrosomal mitosis because TRIM37 prevents PLK4 self-assembly into centrosome-independent condensates that serve as ectopic microtubule-organizing centers. By contrast, elevated TRIM37 expression inhibits acentrosomal spindle assembly via a distinct mechanism that involves degradation of the centrosomal component CEP192. Thus, TRIM37 is a critical determinant of mitotic vulnerability to PLK4 inhibition. Linkage of TRIM37 to prevalent cancer-associated genomic changes, including 17q gain in neuroblastoma and 17q23 amplification in breast cancer, may offer an opportunity to use PLK4 inhibition to trigger selective mitotic failure and provide new avenues to treatments for these cancers.

Eisosomes generate spatial domains in the plasma membrane of yeast cells. The core eisosome protein Pil1 is shown to form filaments in vitro and in cells. Pil1 filaments are stable at the cell cortex, and cytoplasmic Pil1 filament rods appear upon overexpression. This shows a role for self-assembly in organizing cortical domains.

Cell surface area rapidly increases during mechanical and hypoosmotic stresses. Such expansion of the plasma membrane requires 'membrane reservoirs' that provide surface area and buffer membrane tension, but the sources of this membrane remain poorly understood. In principle, the flattening of invaginations and buds within the plasma membrane could provide this additional surface area, as recently shown for caveolae in animal cells. Here, we used microfluidics to study the rapid expansion of the yeast plasma membrane in protoplasts, which lack the rigid cell wall. To survive hypoosmotic stress, yeast cell protoplasts required eisosomes, protein-based structures that generate long invaginations at the plasma membrane. Both budding yeast and fission yeast protoplasts lacking eisosomes were unable to expand like wild-type protoplasts during hypoosmotic stress, and subsequently lysed. By performing quantitative fluorescence microscopy on single protoplasts, we also found that eisosomes disassembled as surface area increased. During this process, invaginations generated by eisosomes at the plasma membrane became flattened, as visualized by scanning electron microscopy. We propose that eisosomes serve as tensiondependent membrane reservoirs for expansion of yeast cells in an analogous manner to caveolae in animal cells.

Aneuploidy and polyploidy can be beneficial or deleterious, depending on the context. In multinucleate fungal cells, mixed polyploidies can coexist in a common cytoplasm, but stress favors a return to haploid nuclei. Very low levels of aneuploidy are present, suggesting that there is limited buffering of ploidy variation despite a common cytosol.

Stable compartments of the plasma membrane promote a wide range of cellular functions. In yeast cells, cytosolic structures called eisosomes generate prominent cortical invaginations of unknown function. Through a series of genetic screens in fission yeast, we found that the eisosome proteins Pil1 and Sle1 function with the synaptojanin-like lipid phosphatase Syj1 and its ligand Tax4. This genetic pathway connects eisosome function with the hydrolysis of phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P 2 ] in cells. Defects in PI(4,5)P 2 regulation led to eisosome defects, and we found that the core eisosome protein Pil1 can bind to and tubulate liposomes containing PI(4,5)P 2 . Mutations in components of the Pil1-Sle1-Syj1-Tax4 pathway suppress the growth and morphology defects of TORC2 mutants, indicating that eisosome-dependent regulation of PI(4,5)P 2 feeds into signal transduction pathways. We propose that the geometry of membrane invaginations generates spatial and temporal signals for lipid-mediated signaling events in cells.