Cellular Memory of HipA-Induced Growth Arrest: The Length of Cell Growth Arrest Becomes Shorter for Each Successive Induction

Toxin–antitoxin (TA) systems are genetic modules found commonly in bacterial genomes. HipA is a toxin protein encoded from the hipBA TA system in the genome of Escherichia coli. Ectopic expression of hipA induces cell growth arrest. Unlike the cell growth arrest caused by other TA toxins, cells resume growth from the HipA-induced cell growth arrest phase after a defined period of time. In this article, we describe the change in the length of growth arrest while cells undergo repeated cycles of hipA induction, growth arrest and regrowth phases. In the multiple conditions tested, we observed that the length of growth arrest became successively shorter for each round of induction. We verified that this was not due to the appearance of HipA-resistant mutants. Additionally, we identified conditions, such as the growth phase of the starting culture and growth vessels, that alter the length of growth arrest. Our results showed that the length of HipA-induced growth arrest was dependent on environmental factors—in particular, the past growth environment of cells, such as a previous hipA induction. These effects lasted even after multiple rounds of cell divisions, indicating the presence of cellular “memory” that impacts cells’ response to HipA-induced toxicity.

Cellular inertia

It has been experimentally reported that chemotactic cells exhibit cellular memory, that is, a tendency to maintain the migration direction despite changes in the chemoattractant gradient. In this study, we analyzed a phenomenological model assuming the presence of cellular inertia, as well as a response time in motility, resulting in the reproduction of the cellular memory observed in the previous experiments. According to the analysis, the cellular motion is described by the superposition of multiple oscillative functions induced by the multiplication of the oscillative polarity and motility. The cellular intertia generates cellular memory by regulating phase differences between those oscillative functions. By applying the theory to the experimental data, the cellular inertia was estimated at $$m=3-6$$ m = 3 - 6 min. In addition, physiological parameters, such as response time in motility and intracellular processing speed, were also evaluated. The agreement between the experiemental data and theory suggests the possibility of the presence of the response time in motility, which has never been biologically verified and should be explored in the future.

Assessment of the cellular immunity response to the new coronavirus infection COVID-19

In December 2019 humanity faced a new coronavirus infection caused by SARS-CoV-2 virus and the disease referred to as COVID-19 has spread globally.Specially adapted for the detection of SARS-CoV-2 RNA tests based on polymerase chain reaction are used to identify infected patients by processing nasal and oropharyngeal swabs. However, often it may not be sufficient to use polymerase chain reaction only, but in many cases it is very important to assess the humoral and cellular immune reactions to the infection.The present review aims to summarize and analyze the available literature data on the formation of the immune response and diagnostic methods used for characteristics of the immune reactions in patients who recovered from COVID-19 or received an anti-COVID-19 vaccine.Currently, the effectiveness of anti-COVID-19 vaccination and the developing immunity after a previous illness are assessed by detecting specific antibodies. A number of observations show that anti-S and anti-RDB IgG titers significantly decline within 6–8 months after diagnosis. It is important to note that although the antibody levels in the blood of recovered patients decrease, the memory cells can be determined by the appropriate tests.The ELISPOT (Enzyme-linked immunospot) method, which is a variation of the ELISA (Enzyme-linked immunosorbent assay), allows estimation the T- and B-cells that release activation factors such as cytokines and antibodies in response to the presented antigens.The assessment of the generation and effective function of the immune memory to SARS-CoV-2 requires the evaluation of the content and functional activity of its various components, including B-lymphocytes, CD8+, CD4+T-lymphocytes, since they have rather independent mechanisms of action of cellular memory.Therefore, it is crucially important to have tools for evaluating the immunity to SARS-CoV-2 when the level of antibodies is insufficient for determination by the available registered tests, and the introduction of test systems into clinical diagnostic practice, allowing to identify markers of long-term cellular memory, are relevant.

Polycomb Requires Chaperonin Containing TCP-1 Subunit 7 for Maintaining Gene Silencing in Drosophila

In metazoans, heritable states of cell type-specific gene expression patterns linked with specialization of various cell types constitute transcriptional cellular memory. Evolutionarily conserved Polycomb group (PcG) and trithorax group (trxG) proteins contribute to the transcriptional cellular memory by maintaining heritable patterns of repressed and active expression states, respectively. Although chromatin structure and modifications appear to play a fundamental role in maintenance of repression by PcG, the precise targeting mechanism and the specificity factors that bind PcG complexes to defined regions in chromosomes remain elusive. Here, we report a serendipitous discovery that uncovers an interplay between Polycomb (Pc) and chaperonin containing T-complex protein 1 (TCP-1) subunit 7 (CCT7) of TCP-1 ring complex (TRiC) chaperonin in Drosophila. CCT7 interacts with Pc at chromatin to maintain repressed states of homeotic and non-homeotic targets of PcG, which supports a strong genetic interaction observed between Pc and CCT7 mutants. Depletion of CCT7 results in dissociation of Pc from chromatin and redistribution of an abundant amount of Pc in cytoplasm. We propose that CCT7 is an important modulator of Pc, which helps Pc recruitment at chromatin, and compromising CCT7 can directly influence an evolutionary conserved epigenetic network that supervises the appropriate cellular identities during development and homeostasis of an organism.

Using a new HSPC senescence model in vitro to explore the mechanism of cellular memory in aging HSPCs

Background Age-associated changes attenuate human blood system functionality through the aging of hematopoietic stem and progenitor cells (HSPCs), manifested in human populations an increase in myeloproliferative disease and even leukemia; therefore, study on HSPC senescence bears great significance to treat hematopoietic-associated disease. Furthermore, the mechanism of HSPC aging is lacking, especially the cellular memory mechanism. Here, we not only reported a new HSPC senescence model in vitro, but also propose and verify the cellular memory mechanism of HSPC aging of the Polycomb/Trithorax system. Methods HSPCs (Lin−c-kit+ cells) were isolated and purified by magnetic cell sorting (MACS). The proportions and cell cycle distribution of cells were determined by flow cytometry; senescence-related β-galactosidase assay, transmission electron microscope (TEM), and colony-forming unit (CFU)-mix assay were detected for identification of the old HSPC model. Proteomic tests and RNA-seq were applied to analyze differential pathways and genes in the model cells. qPCR, Western blot (WB), and chromatin immunoprecipitation PCR (CHIP-PCR) were used to detect the gene expression of cell memory-related proteins. Knockdown of cell memory-related key genes was performed with shRNA interference. Results In the model old HSPCs, β-gal activity, cell cycle, colony-forming ability, aging-related cell morphology, and metabolic pathway were significantly changed compared to the young HSPCs. Furthermore, we found the model HSPCs have more obvious aging manifestations than those of natural mice, and IL3 is the major factor contributing to HSPC aging in the model. We also observed dramatic changes in the expression level of PRC/TrxG complexes. After further exploring the downstream molecules of PRC/TrxG complexes, we found that Uhrf1 and TopII played critical roles in HSPC aging based on the HSPC senescence model. Conclusions These findings proposed a new HSPC senescence model in vitro which we forecasted could be used to preliminary screen the drugs of the HSPC aging-related hemopathy and suggested cellular memory mechanism of HSPC aging.

Polycomb requires Tcp-1η chaperonin for maintaining gene silencing inDrosophila

In metazoans, heritable states of cell type specific gene expression patterns linked with specialization of various cell types constitute transcriptional cellular memory. Evolutionarily conserved Polycomb group (PcG) and trithorax group (trxG) proteins contribute to the transcriptional cellular memory by maintaining heritable patterns of repressed and active expression states, respectively. Although chromatin structure and modifications appear to play a fundamental role in maintenance of repression by PcG, the precise targeting mechanism and the specificity factors that bind PcG complexes to a defined region in chromosomes remain elusive. Here we report a serendipitous discovery that uncovers a direct molecular interaction between Polycomb (PC) and TCP-1 Ring Complex (TRiC) chaperonin subunit, Tcp-1η inDrosophila. Tcp-1η interacts with PC at chromatin to maintain repressed states of homeotic and non-homeotic targets of PcG, which supports a strong genetic interaction observed betweenPcandTcp-1ηmutants. Depletion of Tcp-1η results in dissociation of PC from chromatin and redistribution of an abundant amount of PC in cytoplasm. We propose that Tcp-1η is an important modulator of PC, which helps PC recruitment at chromatin and compromising Tcp-1η can directly influence an evolutionary highly conserved epigenetic network that supervises the appropriate cellular identities during development and homoeostasis of an organism.Significance StatementSilencing of key developmental genes, e.g, Hox genes, by PcG is a hallmark of differential gene expression patterns associated with cell fate determination. Here we describe a previously unknown molecular and genetic interaction of Polycomb (PC) with Tcp-1η subunit of TRiC chaperonin complex inDrosophila. Compromising Tcp-1η function results in de-repression of PcG targets and a concomitant loss of PC from chromatin. Moreover, depletion of Tcp-1η leads to redistribution of PC in cytoplasm. Molecular interaction of PC with Tcp-1η highlights a novel factor which helps PC recruitment at chromatin. We propose that Tcp-1η chaperonin is one of the specificity factors and part of the targeting mechanism that binds PC to specific regions on chromosomes.

Using a new HSPC aging model in vitro to explore the mechanism of cellular memory in aging HSPCs

Age-associated changes attenuate human blood system functionality through the aging of hematopoietic stem and progenitor cells (HSPCs). Hematopoietic aging is manifested in human populations in the form of an increase in myeloproliferative disease,therefore, study on hematopoietic stem and progenitor cells (HSPCs) senescence bears great significance to treat hematopoietic associated disease. However, the mechanism of HSPC aging is lacking, especially cellular memory mechanism. Here, we not only reported a new HSPC aging model in vitro, but also propose and verify the cellular memory mechanism of HSPC aging of Polycomb/Trithorax system. In this model cells, the senescence-related β-gal activity, cell cycle, colony-forming ability, aging-related cell morphology and metabolic pathway are significantly changed compare to the young group. Furthermore, we found the model HSPCs have more obvious aging manifestation than those of natural mice and IL3 is the major factor contributing to HSPC aging in the model. We also observed dramatically changes in the expression level of PRC/TrxG complexes. We further identified downstream molecules of PRC/TrxG complexes,Uhrf1 and TopII, which were found to play a critical role in HSPC aging based on the HSPC aging model. So, these findings proposed a new aging HSPC model in vitro which we forecasted could be used to preliminary screen the drugs of the HSPC aging related hemopathy and suggested cellular memory mechanism of HSPC aging.

Sequential development of embryoblast like memory entities in human malignant tumors, an evidence of cancer cell metamorphosis retrodifferentiation.

Every cancer cell can partially or completely return to an embryonic genotype-phenotype: We capture the cycle of the activation of an individual cellular memory, which allowed a group of squamous tumor cells with mutations caused by the Human Papilloma Virus to return collectively to an embryoblast- like entities. Somatic injured cells have the plasticity to transform their morphology into an embryonic phenotype by expression of dormant genes when they enter a state of cellular emergency.

Polycomb suppresses a female gene regulatory network in Sertoli cells

Gonadal sex determination is controlled by the support cells of testes and ovaries. Sexual fate becomes labile and interchangeable with the removal of specific, critical transcription factors from postnatal gonad support cells. In Sertoli cells, the specific support cells for postnatal testes, the epigenetic mechanism that maintains cellular memory to suppress female sexual differentiation remains unknown. Here, we show that, in postnatal Sertoli cells, Polycomb suppresses a female gene regulatory network. Through genetic ablation, we removed Polycomb repressive complex 1 (PRC1) from embryonic Sertoli cells after sex determination. PRC1-depleted postnatal Sertoli cells exhibited defective proliferation and cell death, leading to the degeneration of adult testes. In adult Sertoli cells, PRC1 suppressed the specific, critical genes required for granulosa cells, the support cells of ovaries, thereby inactivating the female gene regulatory network. The underlying chromatin of female genes was coated with Polycomb-mediated repressive modifications: PRC1-mediated H2AK119ub and PRC2-mediated H3K27me3. Taken together, we identify a critical mechanism centered on Polycomb that maintains the male fate in adult testes.SignificanceSex differences in mammals are defined by the reproductive organs, testes and ovaries. In testes and ovaries, sexual fate is determined by Sertoli cells and granulosa cells, respectively, which are supporting cells derived from common somatic progenitors. Critical transcription factors determine sexual fate of Sertoli and granulosa cells, and, remarkably, removal of these factors reverses sexual identity. Therefore, sexual fate is surprisingly plastic. Here we address a long-standing question in developmental biology of how male sexual fate is maintained in testes throughout life. We show that epigenetic machinery of Polycomb repressive complex 1 (PRC1) suppresses a female gene regulatory network in Sertoli cells. Thus, Polycomb preserves cellular memory and sexual identity of Sertoli cells, thereby defining the testicular fate.