Animal cell cytokinesis: The role of dynamic changes in the plasma membrane proteome and lipidome

ARF6, a component of intercellular bridges, is essential for spermatogenesis in mice

Male germ cells are connected by intercellular bridges (ICBs) in a syncytium due to incomplete cytokinesis. Syncytium is thought to be important for synchronized germ cell development by interchange of cytoplasmic factors via ICBs. Mammalian ADP-ribosylation factor 6 (ARF6) is a small GTPase that is involved in many cellular mechanisms including but not limited to regulating cellular structure, motility, vesicle trafficking and cytokinesis. ARF6 localizes to ICBs in spermatogonia and spermatocytes in mice. Here we report that mice with global depletion of ARF6 in adulthood using Ubc-CreERT2 display no observable phenotypes but are male sterile. ARF6-deficient males display a progressive loss of germ cells, including LIN28A-expressing spermatogonia, and ultimately develop Sertoli-cell-only syndrome. Specifically, intercellular bridges are lost in ARF6-deficient testis. Furthermore, germ cell-specific inactivation using the Ddx4-CreERT2 results in the same testicular morphological phenotype, showing the germ cell-intrinsic requirement of ARF6. Therefore, ARF6 is essential for spermatogenesis in mice and this function is conserved from Drosophila to mammals.

Anillin governs mitotic rounding during early epidermal development

Background

The establishment of tissue architecture requires coordination between distinct processes including basement membrane assembly, cell adhesion, and polarity; however, the underlying mechanisms remain poorly understood. The actin cytoskeleton is ideally situated to orchestrate tissue morphogenesis due to its roles in mechanical, structural, and regulatory processes. However, the function of many pivotal actin-binding proteins in mammalian development is poorly understood.

Results

Here, we identify a crucial role for anillin (ANLN), an actin-binding protein, in orchestrating epidermal morphogenesis. In utero RNAi-mediated silencing of Anln in mouse embryos disrupted epidermal architecture marked by adhesion, polarity, and basement membrane defects. Unexpectedly, these defects cannot explain the profoundly perturbed epidermis of Anln-depleted embryos. Indeed, even before these defects emerge, Anln-depleted epidermis exhibits abnormalities in mitotic rounding and its associated processes: chromosome segregation, spindle orientation, and mitotic progression, though not in cytokinesis that was disrupted only in Anln-depleted cultured keratinocytes. We further show that ANLN localizes to the cell cortex during mitotic rounding, where it regulates the distribution of active RhoA and the levels, activity, and structural organization of the cortical actomyosin proteins.

Conclusions

Our results demonstrate that ANLN is a major regulator of epidermal morphogenesis and identify a novel role for ANLN in mitotic rounding, a near-universal process that governs cell shape, fate, and tissue morphogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01345-9.

Fission yeast paxillin contains two Cdc15 binding motifs for robust recruitment to the cytokinetic ring

The F-BAR protein Cdc15 mediates attachment of the cytokinetic ring (CR) to the plasma membrane and is essential for cytokinesis in Schizosaccharomyces pombe. While its N-terminal F-BAR domain is responsible for oligomerization and membrane binding, its C-terminal SH3 domain binds other partners at a distance from the membrane. We previously demonstrated that the essential cytokinetic formin Cdc12, through an N-terminal motif, directly binds the cytosolic face of the F-BAR domain. Here, we show that paxillin-like Pxl1, which is important for CR stability, contains a motif highly related to that in formin Cdc12, and also binds the Cdc15 F-BAR domain directly. Interestingly, Pxl1 has a second site for binding the Cdc15 SH3 domain. To understand the importance of these two Pxl1-Cdc15 interactions, we mapped and disrupted both. Disrupting the Pxl1-Cdc15 F-BAR domain interaction reduced Pxl1 levels in the CR, whereas disrupting Pxl1’s interaction with the Cdc15 SH3 domain, did not. Unexpectedly, abolishing Pxl1-Cdc15 interaction greatly reduced but did not eliminate CR Pxl1 and did not significantly affect cytokinesis. These data point to another mechanism of Pxl1 CR recruitment and show that very little CR Pxl1 is sufficient for its cytokinetic function.

Anillin is a prognostic factor and is correlated with genovariation in pancreatic cancer based on databases analysis

Pancreatic cancer has a low survival rate globally. Anillin (ANLN) is involved in the pathogenesis of pancreatic cancer (PC). The present study used databases and reverse transcription-quantitative PCR to investigate the association between ANLN expression, clinical variables and the survival rate of patients with pancreatic cancer. Gene expression of ANLN in normal and cancer tissues was analyzed using data from The Cancer Genome Atlas, Oncomine and Gene Expression database of Normal and Tumor tissues 2 and ANOVA, and the association between ANLN mRNA expression and ANLN genovariation was analyzed using cBioPortal. The association between ANLN expression and the survival, clinical, pathological and prognostic characteristics of PC was analyzed using Kaplan-Meier (K-M) survival analysis, Kruskal Wallis and Mann Whitney-U tests, and logistic and Cox regression models. Gene Set Enrichment Analysis (GSEA) revealed the molecular pathways underpinning ANLN function in PC. Overexpression of ANLN was observed in PC cells (normal vs. tumor, P<0.01) and tissues (normal vs. tumor, P=0.008). Enhanced ANLN expression was associated with high tumor grade (grade 1 vs. grade 3, odds ratio: 5.662, P<0.001). However, ANLN expression was not associated with other clinical features (all P>0.05). K-M analysis suggested that increased ANLN expression was associated with poor survival (P=0.002). Univariate and multivariate analysis revealed the ANLN is an independent prognostic factor for PC (P<0.001). GSEA demonstrated the p53, cell cycle, DNA replication, mismatch repair, nucleotide excision repair and PC pathways were associated with low expression of ANLN. Overall, ANLN is more highly expressed in PC compared with in normal tissue, and is associated with poor differentiation. The expression of ANLN may be a novel prognostic marker of poor survival. Finally, ANLN exert its functions in PC through the p53, cell cycle, DNA replication, mismatch repair and nucleotide excision repair and pathways.

Anillin is an emerging regulator of tumorigenesis, acting as a cortical cytoskeletal scaffold and a nuclear modulator of cancer cell differentiation

Remodeling of the intracellular cytoskeleton plays a key role in accelerating tumor growth and metastasis. Targeting different cytoskeletal elements is important for existing and future anticancer therapies. Anillin is a unique scaffolding protein that interacts with major cytoskeletal structures, e.g., actin filaments, microtubules and septin polymers. A well-studied function of this scaffolding protein is the regulation of cytokinesis at the completion of cell division. Emerging evidence suggest that anillin has other important activities in non-dividing cells, including control of intercellular adhesions and cell motility. Anillin is markedly overexpressed in different solid cancers and its high expression is commonly associated with poor prognosis of patient survival. This review article summarizes rapidly accumulating evidence that implicates anillin in the regulation of tumor growth and metastasis. We focus on molecular and cellular mechanisms of anillin-dependent tumorigenesis that include both canonical control of cytokinesis and novel poorly understood functions as a nuclear regulator of the transcriptional reprogramming and phenotypic plasticity of cancer cells.

Opposite Surfaces of the Cdc15 F-BAR Domain Create a Membrane Platform That Coordinates Cytoskeletal and Signaling Components for Cytokinesis

Many eukaryotes assemble an actin- and myosin-based cytokinetic ring (CR) on the plasma membrane (PM) for cell division, but how it is anchored there remains unclear. In Schizosaccharomyces pombe, the F-BAR protein Cdc15 links the PM via its F-BAR domain to proteins in the CR’s interior via its SH3 domain. However, Cdc15’s F-BAR domain also directly binds formin Cdc12, suggesting that Cdc15 may polymerize a protein network directly adjacent to the membrane. Here, we determine that the F-BAR domain binds Cdc12 using residues on the face opposite its membrane-binding surface. These residues also bind paxillin-like Pxl1, promoting its recruitment with calcineurin to the CR. Mutation of these F-BAR domain residues results in a shallower CR, with components localizing ~35% closer to the PM than in wild type, and aberrant CR constriction. Thus, F-BAR domains serve as oligomeric membrane-bound platforms that can modulate the architecture of an entire actin structure.

Multiple F-BAR domains link actin structures to membrane. Snider et al. show that the flat Cdc15 F-BAR domain utilizes opposite surfaces to bind the plasma membrane and cytokinetic ring proteins simultaneously. Disrupting Cdc15 F-BAR domain’s interaction with proteins results in an overall compression of the entire cytokinetic ring architecture.

Who Needs a Contractile Actomyosin Ring? The Plethora of Alternative Ways to Divide a Protozoan Parasite

Cytokinesis, or the division of the cytoplasm, following the end of mitosis or meiosis, is accomplished in animal cells, fungi, and amoebae, by the constriction of an actomyosin contractile ring, comprising filamentous actin, myosin II, and associated proteins. However, despite this being the best-studied mode of cytokinesis, it is restricted to the Opisthokonta and Amoebozoa, since members of other evolutionary supergroups lack myosin II and must, therefore, employ different mechanisms. In particular, parasitic protozoa, many of which cause significant morbidity and mortality in humans and animals as well as considerable economic losses, employ a wide diversity of mechanisms to divide, few, if any, of which involve myosin II. In some cases, cell division is not only myosin II-independent, but actin-independent too. Mechanisms employed range from primitive mechanical cell rupture (cytofission), to motility- and/or microtubule remodeling-dependent mechanisms, to budding involving the constriction of divergent contractile rings, to hijacking host cell division machinery, with some species able to utilize multiple mechanisms. Here, I review current knowledge of cytokinesis mechanisms and their molecular control in mammalian-infective parasitic protozoa from the Excavata, Alveolata, and Amoebozoa supergroups, highlighting their often-underappreciated diversity and complexity. Billions of people and animals across the world are at risk from these pathogens, for which vaccines and/or optimal treatments are often not available. Exploiting the divergent cell division machinery in these parasites may provide new avenues for the treatment of protozoal disease.

Ins and Outs of Interpreting Lipidomic Results

Membrane lipids are essential for life; however, research on how cells regulate cell lipid composition has been falling behind for quite some time. One reason was the difficulty in establishing analytical methods able to cope with the cell lipid repertoire. Development of a diversity of mass spectrometry-based technologies, including imaging mass spectrometry, has helped to demonstrate beyond doubt that the cell lipidome is not only greatly cell type dependent but also highly sensitive to any pathophysiological alteration such as differentiation or tumorigenesis. Interestingly, the current popularization of metabolomic studies among numerous disciplines has led many researchers to rediscover lipids. Hence, it is important to underscore the peculiarities of these metabolites and their metabolism, which are both radically different from protein and nucleic acid metabolism. Once differences in lipid composition have been established, researchers face a rather complex scenario, to investigate the signaling pathways and molecular mechanisms accounting for their results. Thus, a detail often overlooked, but of crucial relevance, is the complex networks of enzymes involved in controlling the level of each one of the lipid species present in the cell. In most cases, these enzymes are redundant and promiscuous, complicating any study on lipid metabolism, since the modification of one particular lipid enzyme impacts simultaneously on many species. Altogether, this review aims to describe the difficulties in delving into the regulatory mechanisms tailoring the lipidome at the activity, genetic, and epigenetic level, while conveying the numerous, stimulating, and sometimes unexpected research opportunities afforded by this type of studies.

A cell separation checkpoint that enforces the proper order of late cytokinetic events

Eukaryotic cell division requires dependency relationships in which late processes commence only after early ones are appropriately completed. We have discovered a system that blocks late events of cytokinesis until early ones are successfully accomplished. In budding yeast, cytokinetic actomyosin ring contraction and membrane ingression are coupled with deposition of an extracellular septum that is selectively degraded in its primary septum immediately after its completion by secreted enzymes. We find this secretion event is linked to septum completion and forestalled when the process is slowed. Delay of septum degradation requires Fir1, an intrinsically disordered protein localized to the cytokinesis site that is degraded upon septum completion but stabilized when septation is aberrant. Fir1 protects cytokinesis in part by inhibiting a separation-specific exocytosis function of the NDR/LATS kinase Cbk1, a key component of "hippo" signaling that induces mother-daughter separation. We term this system enforcement of cytokinesis order, a checkpoint ensuring proper temporal sequence of mechanistically incompatible processes of cytokinesis.

Regulation and Assembly of Actomyosin Contractile Rings in Cytokinesis and Cell Repair

Cytokinesis and single-cell wound repair both involve contractile assemblies of filamentous actin (F-actin) and myosin II organized into characteristic ring-like arrays. The assembly of these actomyosin contractile rings (CRs) is specified spatially and temporally by small Rho GTPases, which trigger local actin polymerization and myosin II contractility via a variety of downstream effectors. We now have a much clearer view of the Rho GTPase signaling cascade that leads to the formation of CRs, but some factors involved in CR positioning, assembly, and function remain poorly understood. Recent studies show that this regulation is multifactorial and goes beyond the long-established Ca²⁺ -dependent processes. There is substantial evidence that the Ca²⁺ -independent changes in cell shape, tension, and plasma membrane composition that characterize cytokinesis and single-cell wound repair also regulate CR formation. Elucidating the regulation and mechanistic properties of CRs is important to our understanding of basic cell biology and holds potential for therapeutic applications in human disease. In this review, we present a primer on the factors influencing and regulating CR positioning, assembly, and contraction as they occur in a variety of cytokinetic and single-cell wound repair models. Anat Rec, 301:2051-2066, 2018. © 2018 Wiley Periodicals, Inc.

Lipid Cell Biology: A Focus on Lipids in Cell Division

Cells depend on hugely diverse lipidomes for many functions. The actions and structural integrity of the plasma membrane and most organelles also critically depend on membranes and their lipid components. Despite the biological importance of lipids, our understanding of lipid engagement, especially the roles of lipid hydrophobic alkyl side chains, in key cellular processes is still developing. Emerging research has begun to dissect the importance of lipids in intricate events such as cell division. This review discusses how these structurally diverse biomolecules are spatially and temporally regulated during cell division, with a focus on cytokinesis. We analyze how lipids facilitate changes in cellular morphology during division and how they participate in key signaling events. We identify which cytokinesis proteins are associated with membranes, suggesting lipid interactions. More broadly, we highlight key unaddressed questions in lipid cell biology and techniques, including mass spectrometry, advanced imaging, and chemical biology, which will help us gain insights into the functional roles of lipids.

Do lipids shape the eukaryotic cell cycle?

Successful passage through the cell cycle presents a number of structural challenges to the cell. Inceptive studies carried out in the last five years have produced clear evidence of modulations in the lipid profile (sometimes referred to as the lipidome) of eukaryotes as a function of the cell cycle. This mounting body of evidence indicates that lipids play key roles in the structural transformations seen across the cycle. The accumulation of this evidence coincides with a revolution in our understanding of how lipid composition regulates a plethora of biological processes ranging from protein activity through to cellular signalling and membrane compartmentalisation. In this review, we discuss evidence from biological, chemical and physical studies of the lipid fraction across the cell cycle that demonstrate that lipids are well-developed cellular components at the heart of the biological machinery responsible for managing progress through the cell cycle. Furthermore, we discuss the mechanisms by which this careful control is exercised.

Regulation of cytokinesis during corticogenesis: focus on the midbody

Development of the cerebral cortices depends on tight regulation of cell divisions. In this system, stem and progenitor cells undergo symmetric and asymmetric divisions to ultimately produce neurons that establish the layers of the cortex. Cell division culminates with the formation of the midbody, a transient organelle that establishes the site of abscission between nascent daughter cells. During cytokinetic abscission, the final stage of cell division, one daughter cell will inherit the midbody remnant, which can then maintain or expel the remnant, but mechanisms and circumstances influencing this decision are unclear. This review describes the midbody and its constituent proteins, as well as the known consequences of their manipulation during cortical development. The potential functional relevance of midbody mechanisms is discussed.

Phosphoinositide-mediated ring anchoring resists perpendicular forces to promote medial cytokinesis

Altering phosphoinositide composition through deletion of efr3, a PI4 kinase scaffold, results in type V myosin-dependent cytokinetic ring sliding in Schizosaccharomyces pombe. Membrane-binding proteins contribute to ring anchoring to resist perpendicular forces and thereby promote medial cytokinesis.

Many eukaryotic cells divide by assembling and constricting an actin- and myosin-based contractile ring (CR) that is physically linked to the plasma membrane (PM). In this study, we report that Schizosaccharomyces pombe cells lacking efr3, which encodes a conserved PM scaffold for the phosphatidylinositol-4 kinase Stt4, build CRs that can slide away from the cell middle during anaphase in a myosin V–dependent manner. The Efr3-dependent CR-anchoring mechanism is distinct from previously reported pathways dependent on the Fes/CIP4 homology Bin-Amphiphysin-Rvs167 (F-BAR) protein Cdc15 and paxillin Pxl1. In efr3Δ, the concentrations of several membrane-binding proteins were reduced in the CR and/or on the PM. Our results suggest that proper PM lipid composition is important to stabilize the central position of the CR and resist myosin V–based forces to promote the fidelity of cell division.

Membrane remodeling during embryonic abscission in Caenorhabditis elegans

Abscission is the final step of cytokinesis and results in the physical separation of two daughter cells. In this study, we conducted a time-resolved series of electron tomographic reconstructions to define the steps required for the first embryonic abscission in Caenorhabditis elegans Our findings indicate that membrane scission occurs on both sides of the midbody ring with random order and that completion of the scission process requires actomyosin-driven membrane remodeling, but not microtubules. Moreover, continuous membrane removal predominates during the late stages of cytokinesis, mediated by both dynamin and the ESCRT (endosomal sorting complex required for transport) machinery. Surprisingly, in the absence of ESCRT function in C. elegans, cytokinetic abscission is delayed but can be completed, suggesting the existence of parallel membrane-reorganizing pathways that cooperatively enable the efficient severing of cytoplasmic connections between dividing daughter cells.

Anaphase asymmetry and dynamic repositioning of the division plane during maize meiosis

The success of an organism is contingent upon its ability to transmit genetic material through meiotic cell division. In plant meiosis I, the process begins in a large spherical cell without physical cues to guide the process. Yet, two microtubule-based structures, the spindle and phragmoplast, divide the chromosomes and the cell with extraordinary accuracy. Using a live-cell system and fluorescently labeled spindles and chromosomes, we found that the process self- corrects as meiosis proceeds. Metaphase spindles frequently initiate division off-center, and in these cases anaphase progression is asymmetric with the two masses of chromosomes traveling unequal distances on the spindle. The asymmetry is compensatory, such that the chromosomes on the side of the spindle that is farthest from the cell cortex travel a longer distance at a faster rate. The phragmoplast forms at an equidistant point between the telophase nuclei rather than at the original spindle mid-zone. This asymmetry in chromosome movement implies a structural difference between the two halves of a bipolar spindle and could allow meiotic cells to dynamically adapt to errors in metaphase and accurately divide the cell volume.

MICAL3 Flavoprotein Monooxygenase Forms a Complex with Centralspindlin and Regulates Cytokinesis

During cytokinesis, the antiparallel array of microtubules forming the central spindle organizes the midbody, a structure that anchors the ingressed cleavage furrow and guides the assembly of abscission machinery. Here, we identified a role for the flavoprotein monooxygenase MICAL3, an actin disassembly factor, in organizing midbody-associated protein complexes. By combining cell biological assays with cross-linking mass spectrometry, we show that MICAL3 is recruited to the central spindle and the midbody through a direct interaction with the centralspindlin component MKLP1. Knock-out of MICAL3 leads to an increased frequency of cytokinetic failure and a delayed abscission. In a mechanism independent of its enzymatic activity, MICAL3 targets the adaptor protein ELKS and Rab8A-positive vesicles to the midbody, and the depletion of ELKS and Rab8A also leads to cytokinesis defects. We propose that MICAL3 acts as a midbody-associated scaffold for vesicle targeting, which promotes maturation of the intercellular bridge and abscission.