Summary The spindle assembly checkpoint (SAC) delays anaphase until all chromosomes are bi-oriented on the mitotic spindle. Under current models, unattached kinetochores transduce the SAC by catalyzing the intramitotic production of a diffusible APC/CCdc20 inhibitor. Here we show that nuclear pore complexes (NPCs) in interphase cells also function as scaffolds for anaphase-inhibitory signaling. This role is mediated by Mad1-Mad2 complexes tethered to the nuclear basket, which activate soluble Mad2 as a binding partner and inhibitor of Cdc20 in the cytoplasm. Displacing Mad1-Mad2 from nuclear pores accelerated anaphase onset, prevented effective correction of merotelic errors, and increased the threshold of kinetochore-dependent signaling needed to halt mitosis in response to spindle poisons. A heterologous Mad1-NPC tether restored Cdc20 inhibitor production and normal M phase control. We conclude that nuclear pores and kinetochores both emit “wait anaphase” signals that preserve genome integrity.

Summary The Mad1-Mad2 heterodimer is the catalytic hub of the spindle assembly checkpoint (SAC), which controls M phase progression through a multi-subunit anaphase inhibitor, the mitotic checkpoint complex (MCC) [1, 2]. During interphase, Mad1-Mad2 generates MCC at nuclear pores [3]. After nuclear envelope breakdown (NEBD), kinetochore-associated Mad1-Mad2 catalyzes MCC assembly until all chromosomes achieve bipolar attachment [1, 2]. Mad1-Mad2 and other factors are also incorporated into the fibrous corona, a phospho-dependent expansion of the outer kinetochore that precedes microtubule attachment [4–6]. The factor(s) involved in targeting Mad1-Mad2 to kinetochores in higher eukaryotes remain controversial [7–12], and the specific phosphorylation event(s) that trigger corona formation remain elusive [5, 13]. We used genome editing to eliminate Bub1, KNL1, and the Rod-Zw10-Zwilch (RZZ) complex in human cells. We show that RZZ’s sole role in SAC activation is to tether Mad1-Mad2 to kinetochores. Separately, Mps1 kinase triggers fibrous corona formation by phosphorylating two N-terminal sites on Rod. In contrast Bub1 and KNL1 activate kinetochore-bound Mad1-Mad2 to produce a “wait anaphase” signal, but are not required for corona formation. We also show that clonal lines isolated after BUB1 disruption recover Bub1 expression and SAC function through nonsense-associated alternative splicing (NAS). Our study reveals a fundamental division of labor in the mammalian SAC and highlights a transcriptional response to nonsense mutations that can reduce or eliminate penetrance in genome editing experiments.

The liver is an immunocompetent organ that plays a key role in the immune response to infections, and the development of hepatic immune function during early postnatal stages has not been thoroughly characterized. This study analyzed the constitutive expression of complement factors, namely C3 and C9, and pattern recognition receptors, namely CD14, toll-like receptor (TLR)-4, and lipopolysaccharide binding protein (LBP), in the liver of postnatal day (P)1, P21, and P70 rats, and compared the kinetics of induction of cytokines and chemokines in the liver of P 1 and P 21 animals. Our studies found that while the mRNA expression of C3, C9, CD14, and TLR-4 was lower in P1 animals, the mRNA level of LBP was higher in P1 animals as compared to older animals, and that the kinetics of induction of cytokines and chemokines was significantly delayed in P1 as compared to P21 liver following LPS stimulation. Our data suggest that hepatic innate immunity is deficient in the neonates and undergo significant development during early postnatal life.

SummaryThe Mad1-Mad2 heterodimer is the catalytic hub of the spindle assembly checkpoint (SAC), which controls mitosis through assembly of a multi-subunit anaphase inhibitor, the mitotic checkpoint complex (MCC) [1,2]. Mad1-Mad2 first catalyzes MCC assembly at interphase nuclear pores [3], then migrates to kinetochores at nuclear envelope breakdown (NEBD) and resumes MCC assembly until bipolar spindle attachment is complete [1,2]. There is significant debate about the factor(s) involved in targeting Mad1-Mad2 to kinetochores in higher eukaryotes [4][5][6][7][8][9]. Through gene editing and livecell imaging, we found that the human Rod-Zw10-Zwilch (RZZ) complex is dispensable for cell viability and initial recruitment of Mad1-Mad2 to kinetochores at NEBD, but then becomes necessary to tether Mad1-Mad2 at kinetochores and sustain SAC arrest in cells challenged with spindle poisons. We also show that RZZ forms the mesh-like fibrous corona, a structural expansion of the outer kinetochore important for timely chromosome congression [10][11][12][13] once Mps1 phosphorylates the N-terminus of Rod.Artificially tethering Mad1-Mad2 to kinetochores enabled long-term mitotic arrest in the absence of RZZ. Conversely, blocking early RZZ-independent recruitment of Mad1-Mad2 eliminated the transient SAC response in RZZ-null cells. We conclude that RZZ drives structural changes in the outer kinetochore that facilitate chromosome biorientation and chronic SAC transduction, a key determinant of cytotoxicity during antimitotic drug therapy [14][15][16].All rights reserved. No reuse allowed without permission.was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint (which . http://dx.doi.org/10.1101/297580 doi: bioRxiv preprint first posted online Apr. 9, 2018; 3 Results RZZ is required for long-term mitotic arrest in response to spindle poisonsRecent studies have reached different conclusions about the specific roles and relative importance of Bub1 and the RZZ complex in targeting Mad1-Mad2 to kinetochores and transducing SAC arrest [4][5][6][7][8]. To interrogate RZZ function with maximum penetrance, we used AAV (adeno-associated virus)-and CRISPR-mediated gene editing to target the KNTC1 (Rod) locus in HCT116 cells, a diploid colorectal cell line ( Fig. S1A-C). The resulting KNTC1 HF/-(hypomorph-flox) cells expressed Rod at ~20% of the wildtype level ( Fig. 1A-B and S1D) and exited mitosis prematurely when microtubule polymerization (nocodazole, 99 ± 6 min s.e.m.) or Eg5-dependent spindle bipolarity (S-trityl-L-cysteine (STLC), 193 ± 9 min s.e.m.) were inhibited, whereas wildtype cells never exited mitosis during the 16-hour timelapse (Fig. 1A-B). To determine if complete loss of the RZZ complex is compatible with clonogenic survival, KNTC1 HF/-cells were transduced with an adenovirus expressing Cre recombinase (AdCre) and subjected to limiting dilution.Unlike most SAC gene knockouts in mammals, KNTC1 -/-cells were viable (Fig. 1...