Biology subjects

Sato, S.

Publications and source records attributed to Sato, S..

60 records · Page 4Linked to original sources

bioRxiv2018

SIX1 cooperates with RUNX1 and SMAD4 in cell fate commitment of Müllerian duct epithelium

During female mammal reproductive tract development, epithelial cells of the lower Mullerian duct are committed to become stratified squamous epithelium of vagina and ectocervix, when the expression of {Delta}Np63 transcription factor is induced by mesenchymal cells. The absence of {Delta}Np63 expression leads to adenosis, the putative precursor of vaginal adenocarcinoma. Our previous studies with genetically engineered mouse models have established that fibroblast growth factor (FGF)/mitogen-activated protein kinase (MAPK), bone morphogenetic protein (BMP)/SMAD, and activin A/runt related transcription factor 1 (RUNX1) signaling pathways are independently required for {Delta}Np63 expression in Mullerian duct epithelium (MDE). Here we report that sine oculis homeobox homolog 1 (SIX1) plays a critical role in the activation of {Delta}Np63 locus in MDE as a downstream transcription factor of mesenchymal signals. In mouse developing reproductive tract, SIX1 expression was restricted to MDE of the future cervix and vagina. SIX1 expression was totally absent in SMAD4 null MDE and was reduced in RUNX1 null and FGFR2 null MDE, indicating that SIX1 is under the control of vaginal mesenchymal factors, BMP4, activin A and FGF7/10. Furthermore, Six1, Runx1 and Smad4 gene-dose-dependently activated {Delta}Np63 expression in MDE within vaginal fornix. Using a mouse model of diethylstilbestrol (DES)-associated vaginal adenosis, we found DES action through epithelial estrogen receptor (ESR1) down-regulates SIX1 and RUNX1 in MDE within the vaginal fornix. This study establishes that the vaginal/ectocervical cell fate of MDE is regulated by a collaboration of multiple transcription factors including SMAD4, SIX1 and RUNX1, and the down-regulation of these key transcription factors leads to vaginal adenosis.\n\nAuthor SummaryIn embryogenesis, differentiation fate of cells is specified through constant communication between neighboring cells. In this study, we investigated the molecular mechanism of epithelial cell fate commitment in the lower female reproductive organs utilizing mouse genetic models. The cell fate of epithelial cells in the uterus, cervix and vagina is directed by signaling from mesenchymal cells. We demonstrated that within the epithelial cells of the developing vagina, signals from mesenchymal cells are integrated into activities of transcription factors including SMAD4, RUNX1 and SIX1, which dose-dependently co-operate in the determination of vaginal epithelial cell fate. Disruption of these processes alters the cell fate from vaginal to uterine epithelium, resulting in a condition called vaginal adenosis, a putative precursor of vaginal adenocarcinoma. Women exposed to diethylstilbestrol (DES) in the womb have about 40 times the risk of developing vaginal adenocarcinoma. We determined that developmental exposure to DES induces vaginal adenosis by repressing SIX1 and RUNX1 through ESR1 in the epithelial cells. This discovery enhances the understanding of how early-life events, such as exposure to endocrine disruptors, causes vaginal adenosis, and thus may contribute to the prevention and therapeutic treatment of idiopathic vaginal adenocarcinoma.

developmental biology↗

bioRxiv2018

Basal level of p53 regulates cell population homeostasis

The tumor suppressor p53 regulates various stress responses via increasing its cellular levels. The lowest p53 levels occur in unstressed cells; however, the functions of these low levels remain unclear. To investigate the functions, we used empirical single-cell tracking of p53-expressing (Control) cells and cells in which p53 expression was silenced by RNA interference (p53 RNAi). Here we show that p53 RNAi cells underwent more frequent cell death and cell fusion, which further induced multipolar cell division to generate aneuploid progeny. Those results suggest that the low levels of p53 in unstressed cells indeed have a role in suppressing the induction of cell death and the formation of aneuploid cells. We further investigated the impact of p53 silencing by developing an algorithm to simulate the fates of individual cells. Simulation of the fate of aneuploid cells revealed that these cells could propagate to create an aneuploid cell population. In addition, the simulation also revealed that more frequent induction of cell death in p53 RNAi cells under unstressed conditions conferred a disadvantage in terms of population expansion compared with Control cells, resulting in faster expansion of Control cells compared with p53 RNAi cells, leading to Control cells predominating in mixed cell populations. In contrast, the expansion of Control cells, but not p53 RNAi cells, was suppressed when the damage response was induced, allowing p53 RNAi cells to expand their population compared with the Control cells. These results suggest that, although p53 could suppress the formation of aneuploid cells, which could have a role in tumorigenesis, it could also allow the expansion of cells lacking p53 expression when the damage response is induced. p53 may thus play a role in both the suppression and the promotion of malignant cell formation during tumorigenesis.

cell biology↗

bioRxiv2018

A member of the ferlin calcium sensor family is essential for Toxoplasma gondii rhoptry secretion

Invasion of host cells by apicomplexan parasites such as Toxoplasma gondii is critical for their infectivity and pathogenesis. In Toxoplasma, secretion of essential egress, motility and invasion-related proteins from microneme organelles is regulated by oscillations of intracellular Ca2+. Later stages of invasion are considered Ca2+-independent, including the secretion of proteins required for host cell entry and remodeling from the parasites rhoptries. We identified a family of three Toxoplasma proteins with homology to the ferlin family of double C2 domain-containing Ca2+ sensors. In humans and model organisms such Ca2+ sensors orchestrate Ca2+-dependent exocytic membrane fusion with the plasma membrane. One ferlin that is conserved across the Apicomplexa, TgFER2, localizes to the parasites cortical membrane skeleton, apical end, and rhoptries. Unexpectedly, conditionally TgFER2-depleted parasites secreted their micronemes normally and were completely motile. However, these parasites were unable to invade host cells and were therefore not viable. Specifically, knockdown of TgFER2 prevented rhoptry secretion and these parasites failed to form the moving junction on the parasite-host interface necessary for host cell invasion. Collectively, these data demonstrate that the putative Ca2+ sensor TgFER2 is required for the secretion of rhoptries. These findings provide the first regulatory and mechanistic insights into this critical yet poorly understood aspect of apicomplexan host cell invasion.\n\nGraphical abstract\n\nO_FIG O_LINKSMALLFIG WIDTH=199 HEIGHT=200 SRC=\"FIGDIR/small/304048_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (58K):\norg.highwire.dtl.DTLVardef@505202org.highwire.dtl.DTLVardef@138400aorg.highwire.dtl.DTLVardef@1f468beorg.highwire.dtl.DTLVardef@1089d34_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2018

CTD-dependent and -independent mechanisms govern co-transcriptional capping of Pol II transcripts

Co-transcriptional capping of RNA polymerase II (Pol II) transcripts by capping enzyme proceeds orders of magnitude more efficiently than capping of free RNA. Previous studies brought to light a role for the phosphorylated Pol II CTD in activation of co-transcriptional capping; however, CTD phosphorylation alone could not account for the observed magnitude of activation. Here, we exploit a defined Pol II transcription system that supports both CTD phosphorylation and robust activation of capping to dissect the mechanism of co-transcriptional capping. Taken together, our findings identify a novel CTD-independent, but Pol II-mediated, mechanism that functions in parallel with CTD-dependent processes to ensure optimal capping, and they support a \"tethering\" model for the mechanism of activation.

molecular biology↗

bioRxiv2017

Dose-dependent spatiotemporal responses of mammalian cells to an alkylating agent

Cultured cell populations are composed of heterogeneous cells, and previous single-cell lineage tracking analysis of individual HeLa cells provided empirical evidence for significant heterogeneity of cell fates. Nevertheless, such cell lines have been used for investigations of cellular responses to various substances, resulting in incomplete characterizations. This problem caused by heterogeneity within cell lines could be overcome by analyzing the spatiotemporal responses of individual cells to a substance. However, no approach to investigate the responses using spatiotemporal data is currently available. Thus, the current study aimed to analyze the spatiotemporal responses of individual HeLa cells to cytotoxic, sub-cytotoxic, and non-cytotoxic doses of the well-characterized carcinogen, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Although cytotoxic doses of MNNG are known to induce cell death, the single-cell tracking approach revealed that cell death occurred following at least four different cellular events, suggesting that cell death is induced via multiple processes. We also found that HeLa cells exposed to sub-cytotoxic doses of MNNG were in a state of equilibrium between cell proliferation and cell death, with cell death again induced through different processes. However, exposure of cells to non-cytotoxic doses of MNNG promoted growth by reducing the cell doubling time, thus promoting the growth of a sub-population of cells previously recognized as putative cancer stem cells. These results demonstrate that the responses of cells to MNNG can be analyzed precisely using spatiotemporal data, regardless of the presence of heterogeneity among cultured cells, suggesting that single-cell lineage tracking analysis can be used as a novel and accurate analytical method to investigate cellular responses to various substances.

cell biology↗

bioRxiv2017

Galectin-3 and N-acetylglucosamine promote myogenesis and improve skeletal muscle function in the mdx model of Duchenne muscular dystrophy

The muscle membrane, sarcolemma, must be firmly attached to the basal lamina. The failure of proper attachment results in muscle injury, which is the underlying cause of Duchenne muscular dystrophy (DMD), where mutations in the dystrophin gene disrupts the firm adhesion. In DMD patients, even moderate contraction causes damage, leading to progressive muscle degeneration. The damaged muscles are repaired through myogenesis. Consequently, myogenesis is highly active in DMD patients, and the repeated activation of myogenesis leads to the exhaustion of the myogenic stem cells. Therefore, approaches to reducing the risk of the exhaustion are to develop a treatment that strengthens the interaction between the sarcolemma and the basal lamina, and increases the efficiency of myogenesis. Galectin-3 is an oligosaccharide-binding protein and known to be involved in cell-cell interactions and cell-matrix interactions. Galectin-3 is expressed in myoblasts and skeletal muscle while its function in muscle remains elusive. In this study, we found evidence that galectin-3 and the monosaccharide N-acetylglucosamine, which increases the ligands (oligosaccharides) of galectin-3, promotes myogenesis in vitro. Moreover, in the mdx mouse model of DMD, treatment with N-acetylglucosamine increased the muscle force production. Our results demonstrate that treatment with N-acetylglucosamine can mitigate the burden of DMD.

pathology↗