mInsc coordinates Par3 and NuMA condensates for assembly of the spindle orientation machinery in asymmetric cell division.

As a fundamental process governing the self-renewal and differentiation of stem cells, asymmetric cell division is controlled by several conserved regulators, including the polarity protein Par3 and the microtubule-associated protein NuMA, which orchestrate the assembly and interplay of the Par3/Par6/mInsc/LGN complex at the apical cortex and the LGN/Gαi/NuMA/Dynein complex at the mitotic spindle to ensure asymmetric segregation of cell fate determinants. However, this model, which is well-supported by genetic studies, has been challenged by evidence of competitive interaction between NuMA and mInsc for LGN. Here, the solved crystal structure of the Par3/mInsc complex reveals that mInsc competes with Par6ß for Par3, raising questions about how proteins assemble overlapping targets into functional macromolecular complexes. Unanticipatedly, we discover that Par3 can recruit both Par6ß and mInsc by forming a dynamic condensate through phase separation. Similarly, the phase-separated NuMA condensate enables the coexistence of competitive NuMA and mInsc with LGN in the same compartment. Bridge by mInsc, Par3/Par6ß and LGN/NuMA condensates coacervate, robustly enriching all five proteins both in vitro and within cells. These findings highlight the pivotal role of protein condensates in assembling multi-component signalosomes that incorporate competitive protein-protein interaction pairs, effectively overcoming stoichiometric constraints encountered in conventional protein complexes.

Cell autocloning as a pathway to their real rejuvenation.

The article gives a brief description of geroprotection and rejuvenation methods known to date, presenting their main mechanisms and limitations. To overcome the main limitations of the process of rejuvenation, it is possible to use a process called "cell autocloning." The principle of the proposed method of rejuvenation is as follows: a periodic process of autocloning of the cell nucleus is initiated in the cellular genome with the formation of one unstable daughter copy and its subsequent self-elimination. In this case, the process of cell division stops in the phase of nuclei divergence without subsequent physical separation of the cell itself. This is especially important for postmitotic cells, where the looping of the "unidirectional" line of the ontogenesis program into a "ring" will mean their transition into renewable cells. The prototype for autocloning mechanisms could be the already known ways in which cells adapt to the increasing amount of their damage over time. These are polyploidy and asymmetric cell division, relying on which it is possible to obtain a renewable process of cell nuclei division, when only the original nucleus remains as a result of division. Although this is not a simple task, there are possible pathways to its solution using approaches that can suggest modern knowledge from the field of molecular and cell biology and genetics. The realization of such a goal will require a lot of work, but the expected result justifies it.

Spatio-Temporal Regulation of Notch Activation in Asymmetrically Dividing Sensory Organ Precursor Cells in Drosophila melanogaster Epithelium.

The Notch communication pathway, discovered in Drosophila over 100 years ago, regulates a wide range of intra-lineage decisions in metazoans. The division of the Drosophila mechanosensory organ precursor is the archetype of asymmetric cell division in which differential Notch activation takes place at cytokinesis. Here, we review the molecular mechanisms by which epithelial cell polarity, cell cycle and intracellular trafficking participate in controlling the directionality, subcellular localization and temporality of mechanosensitive Notch receptor activation in cytokinesis.

LncRNAs and asymmetric cell division: the epigenetic mechanisms.

Asymmetric cell division (ACD) plays a pivotal role in development, tissue homeostasis, and stem cell maintenance. Emerging evidence suggests that long non-coding RNAs (lncRNAs) are key regulators of ACD, orchestrating the intricate molecular machinery that governs cell fate determination. This review summarizes current literature to elucidate the diverse roles of lncRNAs in modulating ACD across various biological contexts. The regulatory mechanisms of asymmetric cell division mediated by lncRNAs, including their interactions with protein effectors, epigenetic regulation, and subcellular localization are explored. Additionally, we discuss the implications of dysregulated lncRNAs in mediating ACD that lead to tumorigenesis. By integrating findings from diverse experimental models and cell types, this review provides insights into the multifaceted roles of lncRNAs in governing asymmetric cell division, shedding light on fundamental biological processes. Further research in this area may lead to the development of novel therapies targeting dysregulated lncRNAs to restore proper cell division and function. The knowledge of lncRNAs regulating ACD could potentially revolutionize the field of regenerative medicine and cancer therapy by targeting specific lncRNAs involved in ACD. By unraveling the complex interactions between lncRNAs and cellular processes, the potential novel opportunities for precision medicine approaches may be uncovered.

A 3D micro-printed single cell micro-niche with asymmetric niche signals - An in vitro model for asymmetric cell division study.

Intricate microenvironment signals orchestrate to affect cell behavior and fate during tissue morphogenesis. However, the underlying mechanisms on how specific local niche signals influence cell behavior and fate are not fully understood, owing to the lack of in vitro platform able to precisely, quantitatively, spatially, and independently manipulate individual niche signals. Here, microarrays of protein-based 3D single cell micro-niche (3D-SCµN), with precisely engineered biophysical and biochemical niche signals, are micro-printed by a multiphoton microfabrication and micropatterning technology. Mouse embryonic stem cell (mESC) is used as the model cell to study how local niche signals affect stem cell behavior and fate. By precisely engineering the internal microstructures of the 3D SCµNs, we demonstrate that the cell division direction can be controlled by the biophysical niche signals, in a cell shape-independent manner. After confining the cell division direction to a dominating axis, single mESCs are exposed to asymmetric biochemical niche signals, specifically, cell-cell adhesion molecule on one side and extracellular matrix on the other side. We demonstrate that, symmetry-breaking (asymmetric) niche signals successfully trigger cell polarity formation and bias the orientation of asymmetric cell division, the mitosis process resulting in two daughter cells with differential fates, in mESCs.

A CDK1 phosphorylation site on Drosophila PAR-3 regulates neuroblast polarisation and sensory organ formation.

The generation of distinct cell fates during development depends on asymmetric cell division of progenitor cells. In the central and peripheral nervous system of Drosophila, progenitor cells respectively called neuroblasts or sensory organ precursors use PAR polarity during mitosis to control cell fate determination in their daughter cells. How polarity and the cell cycle are coupled, and how the cell cycle machinery regulates PAR protein function and cell fate determination is poorly understood. Here, we generate an analog sensitive allele of CDK1 and reveal that its partial inhibition weakens but does not abolish apical polarity in embryonic and larval neuroblasts and leads to defects in polarisation of fate determinants. We describe a novel in vivo phosphorylation of Bazooka, the Drosophila homolog of PAR-3, on Serine180, a consensus CDK phosphorylation site. In some tissular contexts, phosphorylation of Serine180 occurs in asymmetrically dividing cells but not in their symmetrically dividing neighbours. In neuroblasts, Serine180 phosphomutants disrupt the timing of basal polarisation. Serine180 phosphomutants also affect the specification and binary cell fate determination of sensory organ precursors as well as Baz localisation during their asymmetric cell divisions. Finally, we show that CDK1 phosphorylates Serine-S180 and an equivalent Serine on human PAR-3 in vitro.

Reduced Levels of Lagging Strand Polymerases Shape Stem Cell Chromatin.

Stem cells display asymmetric histone inheritance while non-stem progenitor cells exhibit symmetric patterns in the Drosophila male germline lineage. Here, we report that components involved in lagging strand synthesis, such as DNA polymerase α and δ (Polα and Polδ), have significantly reduced levels in stem cells compared to progenitor cells. Compromising Polα genetically induces the replication-coupled histone incorporation pattern in progenitor cells to be indistinguishable from that in stem cells, which can be recapitulated using a Polα inhibitor in a concentration-dependent manner. Furthermore, stem cell-derived chromatin fibers display a higher degree of old histone recycling by the leading strand compared to progenitor cell-derived chromatin fibers. However, upon reducing Polα levels in progenitor cells, the chromatin fibers now display asymmetric old histone recycling just like GSC-derived fibers. The old versus new histone asymmetry is comparable between stem cells and progenitor cells at both S-phase and M-phase. Together, these results indicate that developmentally programmed expression of key DNA replication components is important to shape stem cell chromatin. Furthermore, manipulating one crucial DNA replication component can induce replication-coupled histone dynamics in non-stem cells in a manner similar to that in stem cells.

Balance between asymmetric allocation and repair of somatic damage in unicellular life forms as an ancient form of r/K selection.

Over the course of multiple divisions, cells accumulate diverse nongenetic, somatic damage including misfolded and aggregated proteins and cell wall defects. If the rate of damage accumulation exceeds the rate of dilution through cell growth, a dedicated mitigation strategy is required to prevent eventual population collapse. Strategies for somatic damage control can be divided into two categories, asymmetric allocation and repair, which are not, in principle, mutually exclusive. We explore a mathematical model to identify the optimal strategy, maximizing the total cell number, over a wide range of environmental and physiological conditions. The optimal strategy is primarily determined by extrinsic, damage-independent mortality and the physiological model for damage accumulation that can be either independent (linear) or increasing (exponential) with respect to the prior accumulated damage. Under the linear regime, the optimal strategy is either exclusively repair or asymmetric allocation, whereas under the exponential regime, the optimal strategy is a combination of asymmetry and repair. Repair is preferred when extrinsic mortality is low, whereas at high extrinsic mortality, asymmetric damage allocation becomes the strategy of choice. We hypothesize that at an early stage of life evolution, optimization over repair and asymmetric allocation of somatic damage gave rise to r and K selection strategists.

Spatio-temporal control of asymmetric septum positioning during sporulation in Bacillus subtilis.

During sporulation, Bacillus subtilis forms an asymmetric septum, dividing the cell into two compartments, a mother cell and a forespore. The site of asymmetric septation is linked to the membrane where FtsZ and SpoIIE initiate the formation of the Z-ring and the E-ring, respectively. These rings then serve as a scaffold for the other cell division and peptidoglycan synthesizing proteins needed to build the septum. However, despite decades of research, not enough is known about how the asymmetric septation site is determined. Here, we identified and characterized the interaction between SpoIIE and RefZ. We show that these two proteins transiently colocalize during the early stages of asymmetric septum formation when RefZ localizes primarily from the mother cell side of the septum. We propose that these proteins and their interplay with the spatial organization of the chromosome play a role in controlling asymmetric septum positioning.

The Drosophila neuroblast polarity cycle at a glance.

Drosophila neural stem cells, or neuroblasts, rapidly proliferate during embryonic and larval development to populate the central nervous system. Neuroblasts divide asymmetrically to create cellular diversity, with each division producing one sibling cell that retains the neuroblast fate and another that differentiates into glia or neurons. This asymmetric outcome is mediated by the transient polarization of numerous factors to the cell cortex during mitosis. The powerful genetics and outstanding imaging tractability of the neuroblast make it an excellent model system for studying the mechanisms of cell polarity. This Cell Science at a Glance article and the accompanying poster explore the phases of the neuroblast polarity cycle and the regulatory circuits that control them. We discuss the key features of the cycle - the targeted recruitment of proteins to specific regions of the plasma membrane and multiple phases of highly dynamic actomyosin-dependent cortical flows that pattern both protein distribution and membrane structure.

The contribution of an X chromosome QTL to non-Mendelian inheritance and unequal chromosomal segregation in Auanema freiburgense.

Auanema freiburgense is a nematode with males, females, and selfing hermaphrodites. When XO males mate with XX females, they typically produce a low proportion of XO offspring because they eliminate nullo-X spermatids. This process ensures that most sperm carry an X chromosome, increasing the likelihood of X chromosome transmission compared to random segregation. This occurs because of an unequal distribution of essential cellular organelles during sperm formation, likely dependent on the X chromosome. Some sperm components are selectively segregated into the X chromosome's daughter cell, while others are discarded with the nullo-X daughter cell. Intriguingly, the interbreeding of 2 A. freiburgense strains results in hybrid males capable of producing viable nullo-X sperm. Consequently, when these hybrid males mate with females, they yield a high percentage of male offspring. To uncover the genetic basis of nullo-spermatid elimination and X chromosome drive, we generated a genome assembly for A. freiburgense and genotyped the intercrossed lines. This analysis identified a quantitative trait locus spanning several X chromosome genes linked to the non-Mendelian inheritance patterns observed in A. freiburgense. This finding provides valuable clues to the underlying factors involved in asymmetric organelle partitioning during male meiotic division and thus non-Mendelian transmission of the X chromosome and sex ratios.

Planctoellipticum variicoloris gen. nov., sp. nov., a novel member of the family Planctomycetaceae isolated from wastewater of the aeration lagoon of a sugar processing plant in Northern Germany.

In the present study, we characterise a strain isolated from the wastewater aeration lagoon of a sugar processing plant in Schleswig (Northern Germany) by Heinz Schlesner. As a pioneer in planctomycetal research, he isolated numerous strains belonging to the phylum Planctomycetota from aquatic habitats around the world. Phylogenetic analyses show that strain SH412T belongs to the family Planctomycetaceae and shares with 91.6% the highest 16S rRNA gene sequence similarity with Planctopirus limnophila DSM 3776T. Its genome has a length of 7.3 Mb and a G + C content of 63.6%. Optimal growth of strain SH412T occurs at pH 7.0-7.5 and 28 °C with its pigmentation depending on sunlight exposure. Strain SH412T reproduces by polar asymmetric division ("budding") and forms ovoid cells. The cell size determination was performed using a semi-automatic pipeline, which we first evaluated with the model species P. limnophila and then applied to strain SH412T. Furthermore, the data acquired during time-lapse analyses suggests a lifestyle switch from flagellated daughter cells to non-flagellated mother cells in the subsequent cycle. Based on our data, we suggest that strain SH412T represents a novel species within a novel genus, for which we propose the name Planctoellipticum variicoloris gen. nov., sp. nov., with strain SH412T (= CECT 30430T = STH00996T, the STH number refers to the Jena Microbial Resource Collection JMRC) as the type strain of the new species.

Imaging and Analysis of Drosophila Neural Stem Cell Asymmetric Division.

Cell division is a conserved process among eukaryotes. It is designed to segregate chromosomes into future daughter cells and involves a complex rearrangement of the cytoskeleton, including microtubules and actin filaments. An additional level of complexity is present in asymmetric dividing stem cells because cytoskeleton elements are also regulated by polarity cues. The neural stem cell system of the fruit fly represents a simple model to dissect the mechanisms that control cytoskeleton reorganization during asymmetric division. In this chapter, we propose to describe protocols that allow accurate analysis of microtubule reorganization during cell division in this model.

The contribution of asymmetric cell division to phenotypic heterogeneity in cancer.

Cells have evolved intricate mechanisms for dividing their contents in the most symmetric way during mitosis. However, a small proportion of cell divisions results in asymmetric segregation of cellular components, which leads to differences in the characteristics of daughter cells. Although the classical function of asymmetric cell division (ACD) in the regulation of pluripotency is the generation of one differentiated daughter cell and one self-renewing stem cell, recent evidence suggests that ACD plays a role in other physiological processes. In cancer, tumor heterogeneity can result from the asymmetric segregation of genetic material and other cellular components, resulting in cell-to-cell differences in fitness and response to therapy. Defining the contribution of ACD in generating differences in key features relevant to cancer biology is crucial to advancing our understanding of the causes of tumor heterogeneity and developing strategies to mitigate or counteract it. In this Review, we delve into the occurrence of asymmetric mitosis in cancer cells and consider how ACD contributes to the variability of several phenotypes. By synthesizing the current literature, we explore the molecular mechanisms underlying ACD, the implications of phenotypic heterogeneity in cancer, and the complex interplay between these two phenomena.

Conserved CKI1-mediated signaling is required for female germline specification in Marchantia polymorpha.

In land plants, gametes derive from a small number of dedicated haploid cells.1 In angiosperms, one central cell and one egg cell are differentiated in the embryo sac as female gametes for double fertilization, while in non-flowering plants, only one egg cell is generated in the female sexual organ, called the archegonium.2,3 The central cell specification of Arabidopsis thaliana is controlled by the histidine kinase CYTOKININ-INDEPENDENT 1 (CKI1), which is a two-component signaling (TCS) activator sharing downstream regulatory components with the cytokinin signaling pathway.4,5,6,7 Our phylogenetic analysis suggested that CKI1 orthologs broadly exist in land plants. However, the role of CKI1 in non-flowering plants remains unclear. Here, we found that the sole CKI1 ortholog in the liverwort Marchantia polymorpha, MpCKI1, which functions through conserved downstream TCS components, regulates the female germline specification for egg cell development in the archegonium. In M. polymorpha, the archegonium develops three-dimensionally from a single cell accumulating MpBONOBO (MpBNB), a master regulator for germline initiation and differentiation.8 We visualized female germline specification by capturing the distribution pattern of MpBNB in discrete stages of early archegonium development, and found that MpBNB accumulation is restricted to female germline cells. MpCKI1 is required for the proper MpBNB accumulation in the female germline, and is critical for the asymmetric cell divisions that specify the female germline cells. These results suggest that CKI1-mediated TCS originated during early land plant evolution and participates in female germ cell specification in deeply diverged plant lineages.

Chirality-induced Lineage Enforcement of Mechanosensitive Mesenchymal Stem Cells Across Germ Layer Boundaries.

Mesenchymal to epithelial transition (MET) is instrumental in embryogenesis, tissue repair, and wound healing while the epithelial to mesenchymal transition (EMT) plays role in carcinogenesis. Alteration in microenvironment can modulate cellular signaling and induce EMT and MET. However, modulation of microenvironment to induce MET has been relatively less explored. In this work, effect of matrix stiffness in mediating MET in umbilical cord-derived mesenchymal stem cells (UCMSC) is investigated. Differential segregation of cell fate determinant proteins is one of the key factors in mediating altered stem cell fates through MET even though the genesis of apicobasal polarity remains ambiguous. Herein, it is also attempted to decipher if microenvironment-induced asymmetric cell division has a role to play in driving the cells toward MET. UCMSC cultured on stiffer PDMS matrices resulted in significantly (p < 0.05) higher expression of mechanotransduction proteins. It was also observed that stiffer matrices mediated significant (p < 0.05) upregulation of the polarity proteins and cell fate determinant protein, and epithelial marker proteins over lesser stiff substrates. On the contrary, expression of inflammatory and mesenchymal markers was reduced significantly (p < 0.05) on the stiffer matrices. Cell cycle analysis showed a significant increase in the G1 phase among the cells seeded on stiffer matrices. Transcriptomic studies validated higher expression of epithelial markers genes and lower expression of EMT markers. The transition from mesenchymal to epithelial phenotype depending on the gradation in matrix stiffness is successfully demonstrated. A computational machine learning model was developed to validate stiffness-MET correlation with 94% accuracy. The cross-boundary trans-lineage differentiation capability of MSC on bioengineered substrates can be used as a potential tool in tissue regeneration, organogenesis, and wound healing applications. In our present study, we deciphered the correlation between YAP/TAZ mechanotransduction pathway, EMT signaling pathway, and asymmetric cell division in mediating MET in MSC in a substrate stiffness-dependent manner. It is inferred that the stiffer PDMS matrices facilitate the transition from mesenchymal to epithelial state of MSC. Further, our study also proposed a scoring system to sort MSC from an intermediate hybrid E/M population while undergoing graded MET on matrices of different stiffnesses using a machine learning technique. This proposed scoring system can provide information regarding the E/M state of MSC on different bioengineered constructs based on their biophysical properties which may help in the proper choice of biomaterials in complex tissue-engineering applications.

Lysosomal dynamics regulate mammalian cortical neurogenesis.

Mammalian neocortex formation follows a stereotypical pattern wherein the self-renew and differentiation of neural stem cells are coordinated with diverse organelle dynamics. However, the role of lysosomes in brain development has long been overlooked. Here, we demonstrate the highly dynamic lysosomal quantities, types, and localizations in developing brain. We observed asymmetric endolysosome inheritance during radial glial cell (RGC) division and the increased autolysosomes within intermediate progenitor cells (IPs) and newborn neurons. Disruption of lysosomal function shortens the S phase of the cell cycle and promotes RGC differentiation. Mechanistically, we revealed a post-transcriptional regulation governing ribosome homeostasis and cell-cycle progression through differential lysosomal activity modulation. In the human forebrain organoid, lysosomal dynamics are conserved; specifically, during the mitosis of outer subventricular zone RGCs (oRGs), lysosomes are inherited by the progeny without basal process. Together, our results identify the critical role of lysosomal dynamics in regulating mouse and human brain development.

Phase Separation as a Driver of Stem Cell Organization and Function during Development.

A properly organized subcellular composition is essential to cell function. The canonical organizing principle within eukaryotic cells involves membrane-bound organelles; yet, such structures do not fully explain cellular complexity. Furthermore, discrete non-membrane-bound structures have been known for over a century. Liquid-liquid phase separation (LLPS) has emerged as a ubiquitous mode of cellular organization without the need for formal lipid membranes, with an ever-expanding and diverse list of cellular functions that appear to be regulated by this process. In comparison to traditional organelles, LLPS can occur across wider spatial and temporal scales and involves more distinct protein and RNA complexes. In this review, we discuss the impacts of LLPS on the organization of stem cells and their function during development. Specifically, the roles of LLPS in developmental signaling pathways, chromatin organization, and gene expression will be detailed, as well as its impacts on essential processes of asymmetric cell division. We will also discuss how the dynamic and regulated nature of LLPS may afford stem cells an adaptable mode of organization throughout the developmental time to control cell fate. Finally, we will discuss how aberrant LLPS in these processes may contribute to developmental defects and disease.

Separable Roles for Neur and Ubiquitin in Delta Signalling in the Drosophila CNS Lineages.

The execution of a Notch signal at the plasma membrane relies on the mechanical force exerted onto Notch by its ligand. It has been appreciated that the DSL ligands need to collaborate with a ubiquitin (Ub) ligase, either Neuralized or Mindbomb1, in order to exert this pulling force, but the role of ubiquitylation per se is uncertain. Regarding the Delta-Neur pair, it is documented that neither the Neur catalytic domain nor the Delta intracellular lysines (putative Ub acceptors) are needed for activity. Here, we present a dissection of the Delta activity using the Delta-Notch-dependent expression of Hey in newborn Drosophila neurons as a sensitive in vivo assay. We show that the Delta-Neur interaction per se, rather than ubiquitylation, is needed for activity, pointing to the existence of a Delta-Neur signaling complex. The Neur catalytic domain, although not strictly needed, greatly improves Delta-Neur complex functionality when the Delta lysines are mutated, suggesting that the ubiquitylation of some component of the complex, other than Delta, can enhance signaling. Since Hey expression is sensitive to the perturbation of endocytosis, we propose that the Delta-Neur complex triggers a force-generating endocytosis event that activates Notch in the adjacent cell.

Atypical Protein Kinase C Promotes its own Asymmetric Localisation by Phosphorylating Cdc42 in Polarising Cells.

Atypical protein kinase C (aPKC) is a major regulator of cell polarity. Acting in conjunction with Par6, Par3 and the small GTPase Cdc42, aPKC becomes asymmetrically localised and drives the polarisation of cells. aPKC activity is crucial for its own asymmetric localisation, suggesting a hitherto unknown feedback mechanism contributing to polarisation. Here we show in C. elegans zygotes that the feedback relies on CDC-42 phosphorylation at serine 71 by aPKC, which in turn results in aPKC dissociation from CDC-42. The dissociated aPKC then associates with PAR-3 clusters, which are transported anteriorly by actomyosin-based cortical flow. Moreover, the turnover of aPKC-mediated CDC-42 phosphorylation regulates the organisation of the actomyosin cortex that drives aPKC asymmetry. Given the widespread role of aPKC and Cdc42 in cell polarity, this form of self-regulation of aPKC may be vital for the robust polarisation of many cell types.