Growth factors and their receptors are important for cellular migration as well as axonal guidance and myelination in the brain. They also play a key role in programmed cell death, and are implicated in a number of mental illnesses. Recently, we reported that healthy young adults who carry the T allele variant in the growth factor gene, NTRK1 (at location rs6336), had lower white matter integrity than non-carriers on diffusion images of the brain. Diffusion tensor imaging (DTI) revealed how this single nucleotide polymorphism affects white matter microstructure in human populations; DTI is also used to identify characteristic features of brain connectivity in typically developing children and in patients. Newly discovered links between neuroimaging measures and growth factors whose molecular neuroscience is well known offer an important step in understanding mechanisms that contribute to brain connectivity. Altered fiber connectivity may mediate the relationship between some genetic risk factors and a variety of mental illnesses.
neurotrophin; growth factor; tropomyosin-related kinase receptor A; neurotrophic tyrosine kinase receptor 1; myelin; development; fractional anisotropy; radial diffusivity; diffusion tensor imaging; schizophrenia
We recently identified the atypical myosin, Myosin VI, as a component of epithelial cell-cell junctions that interacts with E-cadherin. Recombinant proteins bearing the cargo-binding domain of Myosin VI (Myo VI-CBD) or the cytoplasmic tail of E-cadherin can interact directly with one another. In this report we further investigate the molecular requirements of the interaction between Myo VI-CBD and E-cadherin combining truncation mutation analysis with in vitro binding assays. We report that a short (28 amino acid) juxtamembrane region of the cadherin cytoplasmic tail is sufficient to bind Myo VI-CBD. However, central regions of the cadherin tail adjacent to the juxtamembrane sequence also display binding activity for Myo VI-CBD. It is therefore possible that the cadherin tail bears two binding sites for Myosin VI, or an extended binding site that includes the juxtamembrane region. Nevertheless, our biochemical data highlight the capacity for the juxtamembrane region to interact with functionally-significant cytoplasmic proteins.
E-cadherin; myosin VI; cytoskeleton; protein-protein interaction; Epithelia
Lymphocytes such as T cells, B cells and natural killer (NK) cells form specialized contacts, called immunological synapses, with other cells in order to engage in specific intercellular communication and killing. Synapse formation is associated with the polarization of the microtubule-organizing center (MTOC) toward the contact site, which enables the directional secretion of cytokines and lytic factors. Although MTOC reorientation to the synapse is crucial for lymphocyte function, it has been difficult to study because of technical constraints. We have developed a photoactivation and imaging strategy that enables high-resolution analysis of cytoskeletal dynamics in individual T cells. Using this approach, we have demonstrated that the lipid second messenger diacylglycerol plays a crucial role in promoting MTOC reorientation by recruiting three members of the protein kinase C family to the synapse. Here, I will discuss these results along with studies from other labs, which have explored the role of polarity-inducing protein complexes after synapse formation. I will also propose a two-step model for MTOC reorientation in lymphocytes that reflects what we now know about the subject. Finally, I will consider the extent to which lymphocyte polarity resembles analogous cell polarity systems in other cell types.
polarity; T cell; microtubule; cytoskeleton; signaling; lymphocyte; chemical biology
Skeletal muscle exhibits strikingly regular intracellular sorting of actin and tropomodulin (Tmod) isoforms, which are essential for efficient muscle contraction. A recent study from our laboratory demonstrates that the skeletal muscle sarcoplasmic reticulum (SR) is associated with cytoplasmic γ-actin (γcyto-actin) filaments, which are predominantly capped by Tmod3. When Tmod3 is experimentally induced to vacate its SR compartment, the cytoskeletal organization of SR-associated γcyto-actin is perturbed, leading to SR swelling, depressed SR Ca2+ release and myofibril misalignment. Based on these findings, Tmod3-capped γcyto-actin filaments mechanically stabilize SR structure and regulate SR function via a novel lateral linkage. Furthermore, by placing these findings in the context of studies in nonmuscle cells, we conclude that Tmodcapped actin filaments are emerging as critical regulators of membrane stability and physiology in a broad assortment of cell types.
cell membrane; cytoskeletal connections; muscle contraction; sarcomere; sarcoplasmic reticulum; thin filament
Mechanoelectrical transduction (MET), the conversion of mechanical stimuli into electrical signals operated by the sensory cells of the inner ear, enables hearing and balance perception. Crucial to this process are the tip-links, oblique fibrous filaments that interconnect the actin-filled stereocilia of different rows within the hair bundle, and mechanically gate MET channels. In a recent study, we observed a complete regression of stereocilia from the short and medium but not the tall row upon the disappearance of the tip-links caused by the loss of one of their components, cadherin-23, or of one of their anchoring proteins, sans, in the auditory organs of engineered mutant mice. This indicates the existence of a coupling between the MET and F-actin polymerization machineries at the tips of the short and medium stereocilia rows in cochlear hair bundles. Here, we first present our findings in the mutant mice, and then discuss the possible effects of the tip-link tension on stereocilia F-actin polymerization, acting either directly or through Ca2+-dependent mechanisms that involve the gating of MET channels.
hair cell; hair bundle; stereocilia; mechanoelectrical transduction (MET); tip-link; sans protein; actin polymerization
Tropomyosins are rod-like dimers which form head-to-tail polymers along the length of actin filaments and regulate the access of actin binding proteins to the filaments.1 The diversity of tropomyosin isoforms, over 40 in mammals, and their role in an increasing number of biological processes presents a challenge both to experienced researchers and those new to this field. The increased appreciation that the role of these isoforms expands beyond that of simply stabilizing actin filaments has lead to a surge of reagents and techniques to study their function and mechanisms of action. This report is designed to provide a basic guide to the genes and proteins and the availability of reagents which allow effective study of this family of proteins. We highlight the value of combining multiple techniques to better evaluate the function of different tm isoforms and discuss the limitations of selected reagents. Brief background material is included to demystify some of the unfortunate complexity regarding this multi-gene family of proteins including the unconventional nomenclature of the isoforms and the evolutionary relationships of isoforms between species. Additionally, we present step-by-step detailed experimental protocols used in our laboratory to assist new comers to the field and experts alike.
tropomyosin; isoforms; cytoskeleton; reagents; antibodies; multi-gene family
Aspects of cellular architecture, such as cytoskeletal asymmetry cues, play critical roles in directing the placement of organelles and establishing the sites of their formation. In the model green alga Chlamydomonas, the photosensory eyespot occupies a defined position in relation to the flagella and microtubule cytoskeleton. Investigations into the cellular mechanisms of eyespot placement and assembly have aided our understanding of the interplay between cytoskeletal and plastid components of the cell. The eyespot, which must be assembled anew after each cell division, is a multi-layered organelle consisting of stacks of carotenoid-filled pigment granules in the chloroplast and rhodopsin photoreceptors in the plasma membrane. Placement of the eyespot is determined on both the latitudinal and longitudinal axes of the cell by the daughter four-membered (D4) microtubule rootlet. Recent findings have contributed to the hypothesis that the eyespot photoreceptor molecules are directed from the Golgi to the daughter hemisphere of the cell and trafficked along the D4 microtubule rootlet. EYE2, a chloroplast-envelope protein, forms an elliptical patch together with the photoreceptors and establishes the site for assembly of the pigment granule arrays in the chloroplast, connecting the positioning information of the cytoskeleton to assembly of the pigment granule arrays in the chloroplast.
Chlamydomonas; eyespot; organelle placement; organelle assembly; microtubule rootlet; asymmetry; photoreception
Metastasis involves tumor cells moving through tissues and crossing tissue boundaries, which requires cell migration, remodeling of cell-to-cell contacts and interactions with the extracellular matrix. Individual tumor cells move in three-dimensional environments with either a rounded “ameboid” or an elongated “mesenchymal” morphology. These two modes of movement are tightly regulated by Rho family GTPases: elongated movement requires activation of Rac1, whereas rounded movement engages specific Cdc42 and Rho signaling pathways. It has been known for some time that events unfolding downstream of Ras GTPases are also involved in regulating multiple aspects of cell migration and invasion. More recently, RasGRF2—a Ras activator—has been identified as a suppressor of rounded movement, by inhibiting the activation of Cdc42, independently of its capacity to activate Ras. Here, we discuss how Rho and Ras signals can either cooperate or oppose each other in the regulation of cell migration and invasion.
Ras GTPases; Rho GTPases; RasGRF; cell migration and invasion; metastasis
The actin cytoskeleton plays essential roles in cell polarization and cell morphogenesis of the budding yeast Saccharomyces cerevisiae. Yeast cells utilize formin-generated actin cables as tracks for polarized transport, which forms the basis for a positive feedback loop driving Cdc42-dependent cell polarization. Previous studies on cable organization mostly focused on polarized actin cables in budded cells and their role as relatively static tracks for myosin-dependent organelle transport. Using quantitative live cell imaging, we have recently characterized the dynamics of cortical actin cables throughout the yeast cell cycle. Surprisingly, randomly oriented actin cables in G1 cells exhibited the highest level of dynamics, while cable dynamics was markedly slowed down upon cell polarization. We further demonstrated that the rapid dynamics of randomly oriented cables were driven by the formin Bni1 and Myosin V. Our data suggested a precise spatio-temporal regulation of the two yeast formins, as well as an unexpected mechanism of actin cable rearrangement through myosins. Here we discuss the immediate significance of these findings, which illustrates the importance of generating randomness for cellular organization.
actin; formin; myosin; polarity; self organization
Adherens junctions (AJs) and tight junctions (TJs) represent key adhesive structures that regulate the apico-basal polarity and barrier properties of epithelial layers. AJs and TJs readily undergo disassembly and reassembly during normal tissue remodeling and disruption of epithelial barriers in diseases. Such junctional plasticity depends on the orchestrated dynamics of the plasma membrane with its underlying F-actin cytoskeleton, however the interplay between these cellular structures remains poorly understood. Recent studies highlighted the spectrin-adducin-based membrane skeleton as an emerging regulator of AJ and TJ integrity and remodeling. Here we discuss new evidences implicating adducin, spectrin and other membrane skeleton proteins in stabilization of epithelial junctions and regulation of junctional dynamics. Based on the known ability of the membrane skeleton to link cortical actin filaments to the plasma membrane, we hypothesize that the spectrin-adducin network serves as a critical signal and force transducer from the actomyosin cytoskeleton to junctions during remodeling of AJs and TJs.
adherens junctions; tight junctions; permeability; membrane skeleton; actomyosin; contractility; calcium switch
The function of nuclear actin is poorly understood. It is known to be a discrete component of several chromatin-modifying complexes. Nevertheless, filamentous forms of actin are important for various nuclear processes as well. Nuclear actin is often associated with nuclear actin-related protein Arp4 and other actin-related proteins like Arp8 in the INO80 chromatin remodeler. We recently determined the crystal structure of S. cerevisiae Arp4 that explains why Arp4 is unable to form actin like filaments and shows that it is constitutively bound to an ATP nucleotide. More interestingly, in vitro activities of Arp4 and Arp8 seem to be directed towards stabilizing monomeric actin and to integrate it stoichiometrically into the INO80 complex. Based on this activity, we discuss possible roles of nuclear Arps in chromatin modifying complexes and in regulating more general aspects of nuclear actin dynamics.
actin-related proteins; chromatin remodeling; INO80 complex; nuclear actin
Cilia are protrusions on the surface of cells. They are frequently motile and function to propel cells in an aqueous environment or to generate fluid flow. Equally important is the role of immotile cilia in detecting environmental changes or in sensing extracellular signals. The structure of cilia is supported by microtubules, and their formation requires microtubule-dependent motors, kinesins, which are thought to transport both structural and signaling ciliary proteins from the cell body into the distal portion of the ciliary shaft. In multicellular organisms, multiple kinesins are known to drive ciliary transport, and frequently cilia of a single cell type require more than one kinesin for their formation and function. In addition to kinesin-2 family motors, which function in cilia of all species investigated so far, kinesins from other families contribute to the transport of signaling proteins in a tissue-specific manner. It is becoming increasingly obvious that functional relationships between ciliary kinesins are complex, and a good understanding of these relationships is essential to comprehend the basis of biological processes as diverse as olfaction, vision, and embryonic development.
C. elegans; cilia; flagella; intraflagellar; kinesin; motor; mouse; photoreceptor; zebrafish
The PCI fold is based on a stack of α-helices topped with a winged-helix domain and is found in a range of proteins that form central parts of large complexes such as the proteasome lid, the COP9 signalosome, elongation factor eIF3, and the TREX-2 complex. Recent structural determinations have given intriguing insight into how these folds function both to facilitate the generation of larger proteinaceous assembles and also to interact functionally with nucleic acids.
COP9 complex; PCI fold; PCI protein; TREX-2 complex; eIF3; proteasome
The unique innovation of the layered neocortex in mammalian evolution is believed to facilitate adaptive radiation of mammalian species to various ecological environments by furnishing high information processing ability. There are no transitional states from the non-mammalian simple brain to the mammalian multilayered neocortex, and thus it is totally a mystery so far how this brain structure has been acquired during evolution. In our recent study, we found the evidence showing that the evolutionary origin of the neocortical neuron subtypes predates the actual emergence of layer structure. Our comparative developmental analysis of the chick pallium, homologous to the mammalian neocortex, revealed that mammals and avians fundamentally share the neocortical neuron subtypes and their production mechanisms, suggesting that their common ancestor already possessed a similar neuronal repertory. We further demonstrated that the neocortical layer-specific neuron subtypes are arranged as mediolaterally separated domains in the chick, but not as layers in the mammalian neocortex. These animal group-specific neuronal arrangements are accomplished by spatial modulation of the neurogenetic program, suggesting an evolutionary hypothesis that the regulatory changes in the neurogenetic program innovated the mammalian specific layered neocortex.
bird; brain patterning; evolution; layer; mammal; neocortex; neural progenitor; neuron subtype; pallium; stem cell
During mitosis, microtubules (MTs) are massively rearranged into three sets of highly dynamic MTs that are nucleated from the centrosomes to form the mitotic spindle. Tight regulation of spindle positioning in the dividing cell and chromosome alignment at the center of the metaphase spindle are required to ensure perfect chromosome segregation and to position the cytokinetic furrow that will specify the two daughter cells. Spindle positioning requires regulation of MT dynamics, involving depolymerase activities together with cortical and kinetochore-mediated pushing and pulling forces acting on astral MTs and kinetochore fibres. These forces rely on MT motor activities. Cortical pulling forces exerted on astral MTs depend upon dynein/dynactin complexes and are essential in both symmetric and asymmetric cell division. A well-established spindle positioning pathway regulating the cortical targeting of dynein/dynactin involves the conserved LGN (Leu-Gly-Asn repeat-enriched-protein) and NuMA (microtubule binding nuclear mitotic apparatus protein) complex.1 Spindle orientation is also regulated by integrin-mediated cell adhesion2 and actin retraction fibres that respond to mechanical stress and are influenced by the microenvironment of the dividing cell.3 Altering the capture of astral MTs or modulating pulling forces affects spindle position, which can impair cell division, differentiation and embryogenesis.
In this general scheme, the activity of mitotic kinases such as Auroras and Plk1 (Polo-like kinase 1) is crucial.4 Recently, the p21-activated kinases (PAKs) emerged as novel important players in mitotic progression. In our recent article, we demonstrated that PAK4 regulates spindle positioning in symmetric cell division.5 In this commentary, and in light of recent published studies, we discuss how PAK4 could participate in the regulation of mechanisms involved in spindle positioning and orientation.
astral microtubules; dynein; p21-activated kinase; spindle orientation and positioning
The THO complex is a nuclear structure whose architecture is conserved among all kingdoms and plays an important role in mRNP biogenesis connecting transcription elongation with mRNA maturation and export. Recent data indicates that the THO complex is necessary for the proper expression of some genes, assurance of genetic stability by preventing transcription-associated recombination. Yeast THO has been described as a heterotetramer (Tho2, Hpr1, Mft1 and Thp2) that performs several functions through the interaction with other proteins like Tex1 or the mRNA export factors Sub2 and Yra1, with which it forms the TRanscription and EXport complex (TREX). In this article we review the cellular role of THO, which we show to be composed of five subunits with Tex1 being also an integral part of the complex. We also show a low-resolution structure of THO and localize some of its components. We discuss the consequences of THO interaction with nucleic acids through the unfolded C-terminal region of Tho2, highlighting the importance of unfolded regions in eukaryotic proteins. Finally, we comment on THO recruitment to active chromatin, a role that is linked to mRNA biogenesis.
THO complex; TREX complex; electron microscopy; mRNA export; mRNP quality control
IQGAP1 is an important cytoskeletal regulator, known to act at the plasma membrane to bundle and cap actin filaments, and to tether the cortical actin meshwork to microtubules via plus-end binding proteins. Here we describe the novel subcellular localization of IQGAP1 at the cytoplasmic face of the nuclear envelope, where it co-located with F-actin. The IQGAP1 and F-actin staining overlapped that of microtubules at the nuclear envelope, revealing a pattern strikingly similar to that observed at the plasma membrane. In detergent-extracted cells IQGAP1 was retained at cytoskeletal structures at the nuclear envelope. This finding has new implications for involvement of IQGAP1 in cell polarization and migration events and potentially in cell cycle-associated nuclear envelope assembly/disassembly.
Cdc42; IQGAP1; Rac1; actin; cell polarization; nuclear envelope
Chromatin remodeling by the SWI/SNF complex is required to activate the transcription of myogenic-specific genes. Our work addressed the details of how SWI/SNF is recruited to myogenic regulatory regions in response to differentiation signals. Surprisingly, the muscle determination factor MyoD and the SWI/SNF subunit BAF60c form a complex on the regulatory elements of MyoD-targeted genes in myogenic precursor cells. This Brg1-devoid MyoD-BAF60c complex flags the chromatin of myogenic-differentiation genes before transcription is activated. On differentiation, BAF60c phosphorylation on a conserved threonine by p38 α kinase promotes the incorporation of MyoD-BAF60c into a Brg1-based SWI/SNF complex, which remodels the chromatin and activates transcription of MyoD-target genes. Downregulation of BAF60c expression prevents MyoD access to the chromatin and the proper loading of an active myogenic transcriptosome preventing the expression of hundreds of myogenic genes. Our data support an unprecedented two-step model by which (1) pre-assembled BAF60c-MyoD complex poises the chromatin of myogenic genes for rapid transcription; (2) chromatin-bound BAF60c “senses” the myogenic differentiation cues and recruits an active SWI/SNF complex to remodel the chromatin allowing transcriptional activation.
MyoD; BAF60c; SWI/SNF; chromatin; remodeling; transcription; myogenesis; differentiation
Apoptosis is an important biological process required for the removal of unwanted or damaged cells. Mounting evidence implicates the actin cytoskeleton as both a sensor and mediator of apoptosis. Studies also suggest that actin binding proteins (ABPs) significantly contribute to apoptosis and that actin dynamics play a key role in regulating apoptosis signaling. Changes in the organization of the actin cytoskeleton has been attributed to the process of malignant transformation and it is hypothesized that remodeling of the actin cytoskeleton may enable tumor cells to evade normal apoptotic signaling. This review aims to illuminate the role of the actin cytoskeleton in apoptosis by systematically analyzing how actin and ABPs regulate different apoptosis pathways and to also highlight the potential for developing novel compounds that target tumor-specific actin filaments.
actin; apoptosis; actin binding proteins; mitochondria; Bcl-2; cancer; multi-drug resistance
Adult skeletal muscles adapt their fiber size to workload. We show that serum response factor (Srf) is required for satellite cell-mediated hypertrophic muscle growth. Deletion of Srf from myofibers, and not satellite cells, blunts overload-induced hypertrophy, and impairs satellite cell proliferation and recruitment to pre-existing fibers. We reveal a gene network in which Srf within myofibers modulates interleukin-6 and cyclooxygenase-2/interleukin-4 expressions and therefore exerts a paracrine control of satellite cell functions. In Srf-deleted muscles, in vivo overexpression of interleukin-6 is sufficient to restore satellite cell proliferation, but not satellite cell fusion and overall growth. In contrast, cyclooxygenase-2/interleukin-4 overexpression rescues satellite cell recruitment and muscle growth without affecting satellite cell proliferation, identifying altered fusion as the limiting cellular event. These findings unravel a role for Srf in the translation of mechanical cues applied to myofibers into paracrine signals, which in turn will modulate satellite cell functions and support muscle growth.
skeletal muscle; hypertrophy; satellite cells; paracrine; transcription factor
Integrin-linked kinase (ILK), PINCH and Parvin proteins form the IPP-complex that has been established as a core component of the integrin-actin link. Our recent genetic studies on Drosophila parvin, reveal that loss of function mutant defects phenocopy those observed upon loss of ILK or PINCH in the muscle and the wing, strengthening the notion that these proteins function together in the organism. Our work identified that ILK is necessary and sufficient for parvin subcellular localization, corroborating previous data indicating a direct association between these two proteins. Further genetic epistasis analysis of the IPP-complex assembly at integrin adhesion sites reveals that depending on the cell context each component is required differently. At the muscle attachment sites of the embryo, ILK is placed upstream in the hierarchy of genetic interactions required for the IPP-complex assembly. By contrast, in the wing epithelium the three proteins are mutually interdependent. Finally, we uncovered a novel property for the CH1-domain of parvin: its recruitment at the integrin-containing junctions in an ILK-dependent manner. Apparently, this ability of the CH1-domain is controlled by the inter-CH linker region. Thus, an intramolecular interaction within parvin could serve as a putative regulatory mechanism controlling the ILK-Parvin interaction.
integrin; cell adhesion; PINCH; actin; Drosophila
Tetraspanins regulate the signaling, trafficking and biosynthetic processing of associated proteins, and may link the extracellular domain of α-chain integrins with intracellular signaling molecules, including PI4K and PKC, both of which regulate cytoskeletal architecture. We showed that TSPAN7, a member of tetraspannin-family, promotes filopodia and dendritic spine formation in cultured hippocampal neurons, and is required for spine stability and normal synaptic transmission. TSPAN7 directly interacts with the PDZ domain of protein interacting with C kinase 1 (PICK1), and associates with AMPAR subunit GluA2 and β1-integrin. TSPAN7 regulates PICK1 and GluA2/3 association, and AMPA receptor trafficking. These findings identify TSPAN7 as a key player in the morphological and functional maturation of glutamatergic synapses.
intellectual disability; AMPAR trafficking; synapse function/plasticity; tetrasapanins; TSPAN7; integrins; PICK1
Our recent paper examined how pelvic fins and their musculature form developmentally and how these mechanisms have evolved within the vertebrate lineage, a process fundamental to the tetrapod transition. The transition from the water onto the land is among one of the most well studied steps in the evolutionary history of vertebrates, yet the genetic basis of this evolutionary transition is little studied and ill-defined. The advent of these terrestrial species resulted in a shift in locomotor strategies from the rhythmic undulating muscles of the fish body to a reliance upon powerful weight bearing muscles of the limbs to generate movement. We demonstrated that the pelvic fin muscles of bony fish are generated by a mechanism that has features of both of limb/fin muscle formation in tetrapods and primitive cartilaginous fish. We hypothesize that the adoption of the fully derived mode of hindlimb muscle formation, was a further modification of the mode of development deployed to generate pelvic fin muscles, a shift in overall muscle bioarchitecture we believe was critical to the success of the tetrapod transition.
muscle; evolution; fin; limb; zebrafish; tetrapod
Scaffolding proteins that are associated with glutamate receptors in dendritic spines govern the location and function of receptors to control synaptic transmission. Unraveling the spatio-temporal dynamics of protein-protein interactions within components of the scaffolding complex will bring to light the function of these interactions. Combining bioluminescence resonance energy transfer (BRET) imaging to electrophysiological recordings, we have recently shown that GKAP, a core protein of the scaffolding complex, interacts with DLC2, a protein associated with molecular motors. Synaptic activity-induced GKAP-DLC2 interaction in spines stabilizes the scaffolding complex and enhances the NMDA currents. Interestingly, this work placed emphasis on the bioarchitectural dependence of protein-protein interaction dynamics. Depending on physiological conditions, the modulation in space and time of protein-protein interaction is acutely regulated, engendering a subtle control of synaptic transmission in the state of the individual synapse.
bioluminescence resonance energy transfer (BRET); dendritic spine; dynein light chain 2 (DLC2); glutamate receptors; guanylate kinase-associated protein (GKAP); protein-protein interaction; scaffolding proteins; synaptic transmission
Checkpoint controls, the surveillance pathways that impose “an order of execution” on the major cell cycle events, are critical to the maintenance of genome stability. When cells fail to execute a cellular event or do so erroneously due to misregulation or exposure to genotoxic stresses, these evolutionarily conserved regulatory circuits prevent passage to the subsequent event, thus bringing the cell cycle to a halt. Once the checkpoint stimulus is removed, cells recover from the arrest and eventually resume cell cycle progression. While the activation, execution and maintenance, the three major aspects of the checkpoint controls, have been investigated in detail, the recovery process remains underexplored. It is not clear if cells recover passively upon dissipation of the checkpoint signals or require an active participation by specific effectors. A recent study in the yeast Saccharomyces cerevisiae uncovered two previously unsuspected functions of Cdk1 in efficient recovery from the spindle assembly checkpoint (SAC) imposed arrest. An inability to fulfil these requirements in the absence of Cdk1 makes it virtually impossible for cells to recover from the mitotic arrest. Given the conserved nature of the SAC, these findings may have implications for vertebrate cells.
Cdk1; cell cycle; cell division; checkpoint; mitosis; recovery; spindle; yeast