Phosphorylation of Bub1 by Mph1 promotes Bub1 signaling at the kinetochore to ensure accurate chromosome segregation.

Bub1 is a conserved mitotic kinase involved in signaling of the spindle assembly checkpoint. Multiple phosphorylation sites on Bub1 have been characterized, yet it is challenging to understand the interplay between the multiple phosphorylation sites due to the limited availability of phosphospecific antibodies. In addition, phosphoregulation of Bub1 in Schizosaccharomyces pombe is poorly understood. Here we report the identification of a new Mph1/Mps1-mediated phosphorylation site, i.e., Ser532, of Bub1 in Schizosaccharomyces pombe. A phosphospecific antibody against phosphorylated Bub1-Ser532 was developed. Using the phosphospecific antibody, we demonstrated that phosphorylation of Bub1-Ser352 was mediated specifically by Mph1/Mps1 and took place during early mitosis. Moreover, live-cell microscopy showed that inhibition of the phosphorylation of Bub1 at Ser532 impaired the localization of Bub1, Mad1, and Mad2 to the kinetochore. In addition, inhibition of the phosphorylation of Bub1 at Ser532 caused anaphase B lagging chromosomes. Hence, our study constitutes a model in which Mph1/Mps1-mediated phosphorylation of fission yeast Bub1 promotes proper kinetochore localization of Bub1 and faithful chromosome segregation.

The fission yeast kinetochore complex Mhf1-Mhf2 regulates the spindle assembly checkpoint and faithful chromosome segregation.

The outer kinetochore serves as a platform for the initiation of the spindle assembly checkpoint (SAC) and for mediating kinetochore-microtubule attachments. How the inner kinetochore subcomplex CENP-S-CENP-X is involved in regulating the SAC and kinetochore-microtubule attachments has not been well characterized. Using live-cell microscopy and yeast genetics, we found that Mhf1-Mhf2, the CENP-S-CENP-X counterpart in the fission yeast Schizosaccharomyces pombe, plays crucial roles in promoting the SAC and regulating chromosome segregation. The absence of Mhf2 attenuates the SAC, impairs the kinetochore localization of most of the components in the constitutive centromere-associated network (CCAN), and alters the localization of the kinase Ark1 (yeast homolog of Aurora B) to the kinetochore. Hence, our findings constitute a model in which Mhf1-Mhf2 ensures faithful chromosome segregation by regulating the accurate organization of the CCAN complex, which is required for promoting SAC signaling and for regulating kinetochore-microtubule attachments. This article has an associated First Person interview with the first author of the paper.

Mad2 promotes Cyclin B2 recruitment to the kinetochore for guiding accurate mitotic checkpoint.

Accurate mitotic progression relies on the dynamic phosphorylation of multiple substrates by key mitotic kinases. Cyclin-dependent kinase 1 is a master kinase that coordinates mitotic progression and requires its regulatory subunit Cyclin B to ensure full kinase activity and substrate specificity. The function of Cyclin B2, which is a closely related family member of Cyclin B1, remains largely elusive. Here, we show that Mad2 promotes the kinetochore localization of Cyclin B2 and that their interaction at the kinetochores guides accurate chromosome segregation. Our biochemical analyses have characterized the Mad2-Cyclin B2 interaction and delineated a novel Mad2-interacting motif (MIM) on Cyclin B2. The functional importance of the Cyclin B2-Mad2 interaction was demonstrated by real-time imaging in which MIM-deficient mutant Cyclin B2 failed to rescue the chromosomal segregation defects. Taken together, we have delineated a previously undefined function of Cyclin B2 at the kinetochore and have established, in human cells, a mechanism of action by which Mad2 contributes to the spindle checkpoint.

Group A Streptococcal meningitis in children: a short case series and systematic review.

BACKGROUND: Group A streptococcal(GAS) meningitis is a severe disease with a high case fatality rate. In the era of increasing GAS meningitis, our understanding about this disease is limited. PURPOSE: To gain a better understanding about GAS meningitis. METHODS: Five new cases with GAS meningitis were reported. GAS meningitis related literatures were searched for systematic review in PUBMED and EMBASE. Case reports and case series on paediatric cases were included. Information on demographics, risk factors, symptoms, treatments, outcomes, and emm types of GAS was summarized. RESULTS: Totally 263 cases were included. Among 100 individuals, 9.9% (8/81) had prior varicella, 11.1% (9/81) had anatomical factors, and 53.2% (42/79) had extracranial infections. Soft tissue infections were common among infants (10/29, 34.5%), while ear/sinus infections were more prevalent in children ≥ 3 years (21/42, 50.0%). The overall case fatality rate (CFR) was 16.2% (12/74). High risk of death was found in patients with shock or systemic complications, young children(< 3 years) and cases related to hematogenic spread. The predominate cause of death was shock(6/8). Among the 163 patients included in case series studies, ear/sinus infections ranged from 21.4 to 62.5%, while STSS/shock ranged from 12.5 to 35.7%, and the CFR ranged from 5.9 to 42.9%. CONCLUSIONS: A history of varicella, soft tissue infections, parameningeal infections and CSF leaks are important clinical clues to GAS in children with meningitis. Young children and hematogenic spread related cases need to be closely monitored for shock due to the high risk of death.

A recyclable Eu3+-functionalized dual-emissive metal-organic framework for portable, rapid detection and efficient removal of malachite green.

A europium-functionalized, dual-emissive, metal-organic framework-based fluorescence sensor (EuUCNDA) was constructed via post-synthetic modification of an UiO-66-type precursor through coordination interactions. EuUCNDA exhibited extremely high selectivity and sensitivity for malachite green (MG) with a low detection limit of 13.01 nM, a wide linear concentration range (0.05-50 µM), excellent anti-interference properties, a rapid response (<1 min), and the possibility of recycling. The good sensing performance of EuUCNDA enables the practical detection of MG in fish pond water and grass carp with good recoveries. Moreover, EuUCNDA can be reused for sensing MG and over 90% of fluorescence intensity can be restored after 7 cycles. Furthermore, EuUCNDA-embedded paper-based sensors combined with smartphone imaging afford portable and visual monitoring of MG in real samples. Notably, besides good sensing performance, EuUCNDA could efficiently remove MG from water. Hence, this work provides a recyclable and sensitive fluorescence sensor for portable, visual, rapid detection and efficient removal of MG.

Dynamic crotonylation of EB1 by TIP60 ensures accurate spindle positioning in mitosis.

Spindle position control is essential for cell fate determination and organogenesis. Early studies indicate the essential role of the evolutionarily conserved Gαi/LGN/NuMA network in spindle positioning. However, the regulatory mechanisms that couple astral microtubules dynamics to the spindle orientation remain elusive. Here we delineated a new mitosis-specific crotonylation-regulated astral microtubule-EB1-NuMA interaction in mitosis. EB1 is a substrate of TIP60, and TIP60-dependent crotonylation of EB1 tunes accurate spindle positioning in mitosis. Mechanistically, TIP60 crotonylation of EB1 at Lys66 forms a dynamic link between accurate attachment of astral microtubules to the lateral cell cortex defined by NuMA-LGN and fine tune of spindle positioning. Real-time imaging of chromosome movements in HeLa cells expressing genetically encoded crotonylated EB1 revealed the importance of crotonylation dynamics for accurate control of spindle orientation during metaphase-anaphase transition. These findings delineate a general signaling cascade that integrates protein crotonylation with accurate spindle positioning for chromosome stability in mitosis.

Phase separation drives decision making in cell division.

Liquid-liquid phase separation (LLPS) of biomolecules drives the formation of subcellular compartments with distinct physicochemical properties. These compartments, free of lipid bilayers and therefore called membraneless organelles, include nucleoli, centrosomes, heterochromatin, and centromeres. These have emerged as a new paradigm to account for subcellular organization and cell fate decisions. Here we summarize recent studies linking LLPS to mitotic spindle, heterochromatin, and centromere assembly and their plasticity controls in the context of the cell division cycle, highlighting a functional role for phase behavior and material properties of proteins assembled onto heterochromatin, centromeres, and central spindles via LLPS. The techniques and tools for visualizing and harnessing membraneless organelle dynamics and plasticity in mitosis are also discussed, as is the potential for these discoveries to promote new research directions for investigating chromosome dynamics, plasticity, and interchromosome interactions in the decision-making process during mitosis.

Structural analysis of fungal CENP-H/I/K homologs reveals a conserved assembly mechanism underlying proper chromosome alignment.

The kinetochore is a proteinaceous complex that is essential for proper chromosome segregation. As a core member of the inner kinetochore, defects of each subunit in the CENP-H/I/K complex cause dysfunction of kinetochore that leads to chromosome mis-segregation and cell death. However, how the CENP-H/I/K complex assembles and promotes kinetochore function are poorly understood. We here determined the crystal structures of CENP-I N-terminus alone from Chaetomium thermophilum and its complex with CENP-H/K from Thielavia terrestris, and verified the identified interactions. The structures and biochemical analyses show that CENP-H and CENP-K form a heterodimer through both N- and C-terminal interactions. CENP-I integrates into the CENP-H/K complex by binding to the C-terminus of CENP-H, leading to formation of the ternary complex in which CENP-H is sandwiched between CENP-K and CENP-I. Our sequence comparisons and mutational analyses showed that this architecture of the CENP-H/I/K complex is conserved in human. Mutating the binding interfaces of CENP-H for either CENP-K or CENP-I significantly reduced their localizations at centromeres and induced massive chromosome alignment defects during mitosis, suggesting that the identified interactions are critical for CENP-H/I/K complex assembly at the centromere and kinetochore function. Altogether, our findings unveil the evolutionarily conserved assembly mechanism of the CENP-H/I/K complex that is critical for proper chromosome alignment.

Dynamic acetylation of the kinetochore-associated protein HEC1 ensures accurate microtubule-kinetochore attachment.

Faithful chromosome segregation during mitosis is critical for maintaining genome integrity in cell progeny and relies on accurate and robust kinetochore-microtubule attachments. The NDC80 complex, a tetramer comprising kinetochore protein HEC1 (HEC1), NDC80 kinetochore complex component NUF2 (NUF2), NDC80 kinetochore complex component SPC24 (SPC24), and SPC25, plays a critical role in kinetochore-microtubule attachment. Mounting evidence indicates that phosphorylation of HEC1 is important for regulating the binding of the NDC80 complex to microtubules. However, it remains unclear whether other post-translational modifications, such as acetylation, regulate NDC80-microtubule attachment during mitosis. Here, using pulldown assays with HeLa cell lysates and site-directed mutagenesis, we show that HEC1 is a bona fide substrate of the lysine acetyltransferase Tat-interacting protein, 60 kDa (TIP60) and that TIP60-mediated acetylation of HEC1 is essential for accurate chromosome segregation in mitosis. We demonstrate that TIP60 regulates the dynamic interactions between NDC80 and spindle microtubules during mitosis and observed that TIP60 acetylates HEC1 at two evolutionarily conserved residues, Lys-53 and Lys-59. Importantly, this acetylation weakened the phosphorylation of the N-terminal HEC1(1-80) region at Ser-55 and Ser-62, which is governed by Aurora B and regulates NDC80-microtubule dynamics, indicating functional cross-talk between these two post-translation modifications of HEC1. Moreover, the TIP60-mediated acetylation was specifically reversed by sirtuin 1 (SIRT1). Taken together, our results define a conserved signaling hierarchy, involving HEC1, TIP60, Aurora B, and SIRT1, that integrates dynamic HEC1 acetylation and phosphorylation for accurate kinetochore-microtubule attachment in the maintenance of genomic stability during mitosis.

Acetylation of Aurora B by TIP60 ensures accurate chromosomal segregation.

Faithful segregation of chromosomes in mammalian cells requires bi-orientation of sister chromatids, which relies on the sensing of correct attachments between spindle microtubules and kinetochores. Although the mechanisms underlying cyclin-dependent kinase 1 (CDK1) activation, which triggers mitotic entry, have been extensively studied, the regulatory mechanisms that couple CDK1-cyclin B activity to chromosome stability are not well understood. Here, we identified a signaling axis in which Aurora B activity is modulated by CDK1-cyclin B via the acetyltransferase TIP60 in human cell division. CDK1-cyclin B phosphorylates Ser90 of TIP60, which elicits TIP60-dependent acetylation of Aurora B and promotes accurate chromosome segregation in mitosis. Mechanistically, TIP60 acetylation of Aurora B at Lys215 protects Aurora B's activation loop from dephosphorylation by the phosphatase PP2A to ensure a robust, error-free metaphase-anaphase transition. These findings delineate a conserved signaling cascade that integrates protein phosphorylation and acetylation with cell cycle progression for maintenance of genomic stability.

Dynamic localization of Mps1 kinase to kinetochores is essential for accurate spindle microtubule attachment.

The spindle assembly checkpoint (SAC) is a conserved signaling pathway that monitors faithful chromosome segregation during mitosis. As a core component of SAC, the evolutionarily conserved kinase monopolar spindle 1 (Mps1) has been implicated in regulating chromosome alignment, but the underlying molecular mechanism remains unclear. Our molecular delineation of Mps1 activity in SAC led to discovery of a previously unidentified structural determinant underlying Mps1 function at the kinetochores. Here, we show that Mps1 contains an internal region for kinetochore localization (IRK) adjacent to the tetratricopeptide repeat domain. Importantly, the IRK region determines the kinetochore localization of inactive Mps1, and an accumulation of inactive Mps1 perturbs accurate chromosome alignment and mitotic progression. Mechanistically, the IRK region binds to the nuclear division cycle 80 complex (Ndc80C), and accumulation of inactive Mps1 at the kinetochores prevents a dynamic interaction between Ndc80C and spindle microtubules (MTs), resulting in an aberrant kinetochore attachment. Thus, our results present a previously undefined mechanism by which Mps1 functions in chromosome alignment by orchestrating Ndc80C-MT interactions and highlight the importance of the precise spatiotemporal regulation of Mps1 kinase activity and kinetochore localization in accurate mitotic progression.

Phosphorylation of PP1 Regulator Sds22 by PLK1 Ensures Accurate Chromosome Segregation.

During cell division, accurate chromosome segregation is tightly regulated by Polo-like kinase 1 (PLK1) and opposing activities of Aurora B kinase and protein phosphatase 1 (PP1). However, the regulatory mechanisms underlying the aforementioned hierarchical signaling cascade during mitotic chromosome segregation have remained elusive. Sds22 is a conserved regulator of PP1 activity, but how it regulates PP1 activity in space and time during mitosis remains elusive. Here we show that Sds22 is a novel and cognate substrate of PLK1 in mitosis, and the phosphorylation of Sds22 by PLK1 elicited an inhibition of PP1-mediated dephosphorylation of Aurora B at threonine 232 (Thr232) in a dose-dependent manner. Overexpression of a phosphomimetic mutant of Sds22 causes a dramatic increase in mitotic delay, whereas overexpression of a non-phosphorylatable mutant of Sds22 results in mitotic arrest. Mechanistically, the phosphorylation of Sds22 by PLK1 strengthens the binding of Sds22 to PP1 and inhibits the dephosphorylation of Thr232 of Aurora B to ensure a robust, error-free metaphase-anaphase transition. These findings delineate a conserved signaling hierarchy that orchestrates dynamic protein phosphorylation and dephosphorylation of critical mitotic regulators during chromosome segregation to guard chromosome stability.

The 68-kDa telomeric repeat binding factor 1 (TRF1)-associated protein (TAP68) interacts with and recruits TRF1 to the spindle pole during mitosis.

The telomere capping protein TRF1 is a component of the multiprotein complex "shelterin," which organizes the telomere into a high order structure. Besides telomere maintenance, telomere-associated proteins also have nontelomeric functions. For example, tankyrase 1 and TRF1 are required for the maintenance of faithful mitotic progression. However, the functional relevance of their centrosomal localization has not been established. Here, we report the identification of a TRF1-binding protein, TAP68, that interacts with TRF1 in mitotic cells. TAP68 contains two coiled-coil domains and a structural maintenance of chromosome motifs and co-localizes with TRF1 to telomeres during interphase. Immediately after nuclear envelope breakdown, TAP68 translocates toward the spindle poles followed by TRF1. Dissociation of TAP68 from the telomere is concurrent with the Nek2A-dependent phosphorylation at Thr-221. Biochemical characterization demonstrated that the first coiled-coil domain of TAP68 binds and recruits TRF1 to the centrosome. Inhibition of TAP68 expression by siRNA blocked the localization of TRF1 and tankyrase 1 to the centrosome. Furthermore, siRNA-mediated depletion of TAP68 perturbed faithful chromosome segregation and genomic stability. These findings suggest that TAP68 functions in mediating TRF1-tankyrase 1 localization to the centrosome and in mitotic regulation.

Mitotic regulator Mis18ß interacts with and specifies the centromeric assembly of molecular chaperone holliday junction recognition protein (HJURP).

The centromere is essential for precise and equal segregation of the parental genome into two daughter cells during mitosis. CENP-A is a unique histone H3 variant conserved in eukaryotic centromeres. The assembly of CENP-A to the centromere is mediated by Holliday junction recognition protein (HJURP) in early G1 phase. However, it remains elusive how HJURP governs CENP-A incorporation into the centromere. Here we show that human HJURP directly binds to Mis18ß, a component of the Mis18 complex conserved in the eukaryotic kingdom. A minimal region of HJURP for Mis18ß binding was mapped to residues 437-460. Depletion of Mis18ß by RNA interference dramatically impaired HJURP recruitment to the centromere, indicating the importance of Mis18ß in HJURP loading. Interestingly, phosphorylation of HJURP by CDK1 weakens its interaction with Mis18ß, consistent with the notion that assembly of CENP-A to the centromere is achieved after mitosis. Taken together, these data define a novel molecular mechanism underlying the temporal regulation of CENP-A incorporation into the centromere by accurate Mis18ß-HJURP interaction.

The spatiotemporal dynamics of chromatin protein HP1α is essential for accurate chromosome segregation during cell division.

Heterochromatin protein 1α (HP1α) is involved in regulation of chromatin plasticity, DNA damage repair, and centromere dynamics. HP1α detects histone dimethylation and trimethylation of Lys-9 via its chromodomain. HP1α localizes to heterochromatin in interphase cells but is liberated from chromosomal arms at the onset of mitosis. However, the structural determinants required for HP1α localization in interphase and the regulation of HP1α dynamics have remained elusive. Here we show that centromeric localization of HP1α depends on histone H3 Lys-9 trimethyltransferase SUV39H1 activity in interphase but not in mitotic cells. Surprisingly, HP1α liberates from chromosome arms in early mitosis. To test the role of this dissociation, we engineered an HP1α construct that persistently localizes to chromosome arms. Interestingly, persistent localization of HP1α to chromosome arms perturbs accurate kinetochore-microtubule attachment due to an aberrant distribution of chromosome passenger complex and Sgo1 from centromeres to chromosome arms that prevents resolution of sister chromatids. Further analyses showed that Mis14 and perhaps other PXVXL-containing proteins are involved in directing localization of HP1α to the centromere in mitosis. Taken together, our data suggest a model in which spatiotemporal dynamics of HP1α localization to centromere is governed by two distinct structural determinants. These findings reveal a previously unrecognized but essential link between HP1α-interacting molecular dynamics and chromosome plasticity in promoting accurate cell division.

Chromatin protein HP1 interacts with the mitotic regulator borealin protein and specifies the centromere localization of the chromosomal passenger complex.

Accurate mitosis requires the chromosomal passenger protein complex (CPC) containing Aurora B kinase, borealin, INCENP, and survivin, which orchestrates chromosome dynamics. However, the chromatin factors that specify the CPC to the centromere remain elusive. Here we show that borealin interacts directly with heterochromatin protein 1 (HP1) and that this interaction is mediated by an evolutionarily conserved PXVXL motif in the C-terminal borealin with the chromo shadow domain of HP1. This borealin-HP1 interaction recruits the CPC to the centromere and governs an activation of Aurora B kinase judged by phosphorylation of Ser-7 in CENP-A, a substrate of Aurora B. Consistently, modulation of the motif PXVXL leads to defects in CPC centromere targeting and aberrant Aurora B activity. On the other hand, the localization of the CPC in the midzone is independent of the borealin-HP1 interaction, demonstrating the spatial requirement of HP1 in CPC localization to the centromere. These findings reveal a previously unrecognized but direct link between HP1 and CPC localization in the centromere and illustrate the critical role of borealin-HP1 interaction in orchestrating an accurate cell division.

Phosphorylation of microtubule-binding protein Hec1 by mitotic kinase Aurora B specifies spindle checkpoint kinase Mps1 signaling at the kinetochore.

The spindle assembly checkpoint (SAC) is a quality control device to ensure accurate chromosome attachment to spindle microtubule for equal segregation of sister chromatid. Aurora B is essential for SAC function by sensing chromosome bi-orientation via spatial regulation of kinetochore substrates. However, it has remained elusive as to how Aurora B couples kinetochore-microtubule attachment to SAC signaling. Here, we show that Hec1 interacts with Mps1 and specifies its kinetochore localization via its calponin homology (CH) domain and N-terminal 80 amino acids. Interestingly, phosphorylation of the Hec1 by Aurora B weakens its interaction with microtubules but promotes Hec1 binding to Mps1. Significantly, the temporal regulation of Hec1 phosphorylation orchestrates kinetochore-microtubule attachment and Mps1 loading to the kinetochore. Persistent expression of phosphomimetic Hec1 mutant induces a hyperactivation of SAC, suggesting that phosphorylation-elicited Hec1 conformational change is used as a switch to orchestrate SAC activation to concurrent destabilization of aberrant kinetochore attachment. Taken together, these results define a novel role for Aurora B-Hec1-Mps1 signaling axis in governing accurate chromosome segregation in mitosis.

The correlation between menstrual characteristics and fertility in women of reproductive age: a systematic review and meta-analysis.

IMPORTANCE: Menstruation serves as an indicator of women's reproductive well-being and plays a pivotal role in their fertility; nevertheless, there remains an ongoing debate regarding the epidemiological evidence linking menstrual characteristics as well as fertility. OBJECTIVE: To explore the correlation between menstrual characteristics and fertility in women of reproductive age. DATA SOURCES: A comprehensive literature search was conducted using PubMed, Embase, Web of Science, and Cochrane libraries to identify research articles published up until February 9, 2024. STUDY SELECTION AND SYNTHESIS: We included all studies in which the relationship between menstrual characteristics and pregnancy rates among women of reproductive age was investigated. We excluded studies involving the administration of oral contraceptives, the application of assisted reproductive technologies, and individuals with a documented history of infertility or partners with a known history of infertility. MAIN OUTCOME MEASURE(S): Clinical pregnancy and miscarriage. RESULT(S): This meta-analysis was composed of nine studies involving a total of 399,966 women, and the evidential quality derived from these studies was deemed to be high with a low risk of bias. Compared with a normal menstrual cycle length (25-32 days), the impact of a short (<25 days) or long (>32 days) menstrual cycle on a woman's pregnancy was relatively insignificant ([odds ratio {OR}, 0.81; 95% confidence interval {CI}, 0.65-1.01; I2, 68%]; [OR, 0.89; 95% CI, 0.75-1.06; I2, 60%], respectively); however, a change in cycle length may increase the risk of miscarriage ([relative risk, 1.87; 95% CI, 1.11-3.15; I2, 0]; [relative risk, 1.66; 95% CI, 1.07, 2.57; I2, 43%], respectively). In comparison to women experiencing menarche at a typical age (12-14 years), those with a late age at menarche (>14 years) exhibited a decreased likelihood of pregnancy (OR, 0.92; 95% CI, 0.91-0.93; I2, 0%); and compared with women experiencing a normal duration of menstrual bleeding (4-7 days), those with a short duration of menstrual bleeding (<4 days) exhibited reduced fertility potential (OR, 0.86; 95% CI, 0.84-0.88; I2, 29%). CONCLUSION(S): Short and long menstrual cycle lengths may elevate women's susceptibility to spontaneous abortion, whereas late age at menarche as well as short duration of menstrual bleeding appear to be linked to diminished fertility among women of reproductive age. CLINICAL TRIAL REGISTRATION: PROSPERO CRD42023487458 (9 December 2023).

Fluorescence complementation-based FRET imaging reveals centromere assembly dynamics.

Visualization of specific molecules and their assembly in real time and space is essential to delineate how cellular dynamics and signaling circuit are orchestrated during cell division cycle. Our recent studies reveal structural insights into human centromere-kinetochore core CCAN complex. Here we introduce a method for optically imaging trimeric and tetrameric protein interactions at nanometer spatial resolution in live cells using fluorescence complementation-based Förster resonance energy transfer (FC-FRET). Complementary fluorescent protein molecules were first used to visualize dimerization followed by FRET measurements. Using FC-FRET, we visualized centromere CENP-SXTW tetramer assembly dynamics in live cells, and dimeric interactions between CENP-TW dimer and kinetochore protein Spc24/25 dimer in dividing cells. We further delineated the interactions of monomeric CENP-T with Spc24/25 dimer in dividing cells. Surprisingly, our analyses revealed critical role of CDK1 kinase activity in the initial recruitment of Spc24/25 by CENP-T. However, interactions between CENP-T and Spc24/25 during chromosome segregation is independent of CDK1. Thus, FC-FRET provides a unique approach to delineate spatiotemporal dynamics of trimerized and tetramerized proteins at nanometer scale and establishes a platform to report the precise regulation of multimeric protein interactions in space and time in live cells.