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Mechanisms underlying deviant cell size fluctuations among clonal bacterial siblings are generally considered to be cryptic and stochastic in nature. However, by scrutinizing heat-stressed populations of the model bacterium Escherichia coli , we uncovered the existence of a deterministic asymmetry in cell division that is caused by the presence of intracellular protein aggregates (PAs). While these structures typically locate at the cell pole and segregate asymmetrically among daughter cells, we now show that the presence of a polar PA consistently causes a more distal off-center positioning of the FtsZ division septum. The resulting increased length of PA-inheriting siblings persists over multiple generations and could be observed in both E. coli and Bacillus subtilis populations. Closer investigation suggests that a PA can physically perturb the nucleoid structure, which subsequently leads to asymmetric septation.

A critical step in bacterial cytokinesis is the activation of septal peptidoglycan synthesis at the Z ring. Although FtsN is the trigger and acts through FtsQLB and FtsA to activate FtsWI the mechanism is unclear. Spatiotemporal regulation of septal peptidoglycan (PG) synthesis is achieved by coupling assembly and activation of the synthetic enzymes (FtsWI) to the Z ring, a cytoskeletal element that is required for division in most bacteria. In Escherichia coli , the recruitment of the FtsWI complex is dependent upon the cytoplasmic domain of FtsL, a component of the conserved FtsQLB complex. Once assembled, FtsWI is activated by the arrival of FtsN, which acts through FtsQLB and FtsA, which are also essential for their recruitment. However, the mechanism of activation of FtsWI by FtsN is not clear. Here, we identify a region of FtsL that plays a key role in the activation of FtsWI which we designate AWI ( a ctivation of Fts WI ) and present evidence that FtsL acts through FtsI. Our results suggest that FtsN switches FtsQLB from a recruitment complex to an activator with FtsL interacting with FtsI to activate FtsW. Since FtsQLB and FtsWI are widely conserved in bacteria, this mechanism is likely to be also widely conserved. IMPORTANCE A critical step in bacterial cytokinesis is the activation of septal peptidoglycan synthesis at the Z ring. Although FtsN is the trigger and acts through FtsQLB and FtsA to activate FtsWI the mechanism is unclear. Here, we find an essential role for FtsL in activating septal peptidoglycan (PG) synthesis and find that it acts on FtsI. Our results suggest a model where FtsWI is recruited in an inactive form by FtsQLB, and upon the arrival of FtsN, FtsQLB undergoes a conformational change so that a region of FtsL, which we designate the AWI domain, becomes available to interact with FtsI and activate the FtsWI complex. This mechanism for activation of the divisome has similarities to the activation of the elongasome and is likely to be widely conserved in bacteria.

A 50-year-old man presented with shortness of breath. The patient underwent ventricular septation for a single ventricle with L-malposition of the great arteries at 6 years of age. Examinations revealed that the calcified patch for septation was torn and perforated, resulting in a left-to-right shunt. We report a rare case of a single ventricle who survived after septation 40 years ago and underwent the reoperation due to a torn calcified patch.

In vertebrate hearts, the ventricular trabecular myocardium develops as a sponge-like network of cardiomyocytes that is critical for contraction and conduction, ventricular septation, papillary muscle formation and wall thickening through the process of compaction 1 . Defective trabeculation leads to embryonic lethality 2 – 4 or non-compaction cardiomyopathy (NCC) 5 . There are divergent views on when and how trabeculation is initiated in different species. In zebrafish, trabecular cardiomyocytes extrude from compact myocardium 6 , whereas in chicks, chamber wall thickening occurs before overt trabeculation 7 . In mice, the onset of trabeculation has not been described, but is proposed to begin at embryonic day 9.0, when cardiomyocytes form radially oriented ribs 2 . Endocardium–myocardium communication is essential for trabeculation, and numerous signalling pathways have been identified, including Notch 2 , 8 and Neuregulin (NRG) 4 . Late disruption of the Notch pathway causes NCC 5 . Whereas it has been shown that mutations in the extracellular matrix (ECM) genes Has2 and Vcan prevent the formation of trabeculae in mice 9 , 10 and the matrix metalloprotease ADAMTS1 promotes trabecular termination 3 , the pathways involved in ECM dynamics and the molecular regulation of trabeculation during its early phases remain unexplored. Here we present a model of trabeculation in mice that integrates dynamic endocardial and myocardial cell behaviours and ECM remodelling, and reveal new epistatic relationships between the involved signalling pathways. NOTCH1 signalling promotes ECM degradation during the formation of endocardial projections that are critical for individualization of trabecular units, whereas NRG1 promotes myocardial ECM synthesis, which is necessary for trabecular rearrangement and growth. These systems interconnect through NRG1 control of Vegfa , but act antagonistically to establish trabecular architecture. These insights enabled the prediction of persistent ECM and cardiomyocyte growth in a mouse NCC model, providing new insights into the pathophysiology of congenital heart disease. A new model of cardiac trabeculation in mice is presented in which NOTCH1 and NRG1 have opposing roles in extracellular matrix degradation and synthesis that are essential for defining trabecular architecture.

Coordination of outer membrane constriction with septation is critical to faithful division in Gram-negative bacteria and vital to the barrier function of the membrane. This coordination requires the recruitment of the peptidoglycan-binding outer-membrane lipoprotein Pal at division sites by the Tol system. Here, we show that Pal accumulation at Escherichia coli division sites is a consequence of three key functions of the Tol system. First, Tol mobilises Pal molecules in dividing cells, which otherwise diffuse very slowly due to their binding of the cell wall. Second, Tol actively captures mobilised Pal molecules and deposits them at the division septum. Third, the active capture mechanism is analogous to that used by the inner membrane protein TonB to dislodge the plug domains of outer membrane TonB-dependent nutrient transporters. We conclude that outer membrane constriction is coordinated with cell division by active mobilisation-and-capture of Pal at division septa by the Tol system. The lipoprotein Pal participates in the coordination of outer-membrane constriction with septation in Gram-negative bacteria. Here, the authors show that this coordination is mediated by active mobilisation-and-capture of Pal at division septa by the Tol system.

Disruption of cardiac neural crest cells (CNCCs) results in congenital heart disease, yet we do not understand the cell fate dynamics as these cells differentiate to vascular smooth muscle cells. Here we performed single-cell RNA-sequencing of NCCs from the pharyngeal apparatus with the heart in control mouse embryos and when Tbx1 , the gene for 22q11.2 deletion syndrome, is inactivated. We uncover three dynamic transitions of pharyngeal NCCs expressing Tbx2 and Tbx3 through differentiated CNCCs expressing cardiac transcription factors with smooth muscle genes. These transitions are altered non-autonomously by loss of Tbx1 . Further, inactivation of Tbx2 and Tbx3 in early CNCCs results in aortic arch branching defects due to failed smooth muscle differentiation. Loss of Tbx1 interrupts mesoderm to CNCC cell-cell communication with upregulation and premature activation of BMP signaling and reduced MAPK signaling, as well as alteration of other signaling, and failed dynamic transitions of CNCCs leading to disruption of aortic arch artery formation and cardiac outflow tract septation. Cardiac neural crest must differentiate and migrate correctly to achieve proper cardiovascular development. Here, the authors use single cell analyses to show how these cells are altered non-autonomously by loss of Tbx1 , the major gene for 22q11.2 deletion syndrome.

Abstract Introduction/Objective Mesenteric cysts are rare intra-abdominal lesions in adults. However, with the advanced imaging techniques and laparoscopic techniques, they are more often being identified and resected when clinically significant. There is a lack of detailed information in histopathology (except as case reports) since mesentery is generally neglected in our organ-based textbooks. The aim of our study is to highlight the importance of identifying and classifying mesenteric cystic lesions; they are not all that simple. Methods We performed a retrospective search on all mesenteric cysts submitted as excisions in our electronic database from 2013-2019. We classified them as per the de Perrot (PMID: 11053936) classification with modification. Results Our search showed: A. Lymphatic origin-11 (lymphangioma-10, Lymphangioma hamartomatous-1, associated with LAM-0), B. Mesothelial origin-68 (Benign mesothelial cysts-57, multilocular mesothelial cyst-11), C. Enteric origin- 3, D. Urogenital origin (Urachal cyst, mullerian inclusion cyst)-9, E. Mature cystic teratom-2, F. Pseudocyst-12, G. Epithelial cyst (not urogenital)- 11 (a/w LAMN-3, MCN-4, Mucinous cystadenoma-4), H. Associated with carcinoma-2. Case illustration: A 61-year-old male presented with worsening dysphagia, emesis and hiccups. A CT scan showed a 21.2 cm cystic mass with at least one septation (Fig 1). The cyst was resected. On gross pathological examination, the cyst measured 18 cm in greatest dimension with a thick, rough, tan-brown capsule. Microscopic examination showed a fibrous capsule, and cyst wall composed of numerous lymphatic vessels (CD31 positive) and prominent smooth muscle proliferation (Desmin positive). Scattered lymphoid aggregates were also present throughout the cyst wall. No definite epithelial lining was identified and was suspected to have been denuded. HMB-45 immunostain was negative, ruling out association with LAM. The final diagnosis of a Lymphangiomyoma, hamartomatous was rendered. Conclusion Though most of the mesenteric cysts are benign, some of them are significantly important such as Lymphangiomyoma (esp secondary to LAM), MCN, those associated with LAMN etc. and identifying and differentiating from their mimics has distinct clinical implications.

Triazoles are widely used to control pathogenic fungi. They inhibit the ergosterol biosynthetic pathway, but the precise mechanisms leading to fungicidal activities in many fungal pathogens are poorly understood. Here, we elucidate the mode of action of epoxiconazole and metconazole in the wheat pathogen Zymoseptoria tritici and the rice blast fungus Magnaporthe oryzae . We show that both azoles have fungicidal activity and reduce fluidity, but not integrity, of the plasma membrane. This impairs localisation of Cdc15-like F-BAR proteins, resulting in defective actin ring assembly and incomplete septation. However, mutant studies and pharmacological experiments in vitro and in planta show that azole lethality is due to a combination of reactive oxygen species-induced apoptosis and macroautophagy. Simultaneous inhibition of both programmed cell death pathways abolishes azole-induced cell death. Other classes of ergosterol biosynthesis inhibitors also induce apoptosis and macroautophagy, suggesting that activation of these two cell death pathways is a hallmark of ergosterol synthesis-targeting fungicides. This knowledge will inform future crop protection strategies. Antifungal azoles inhibit ergosterol biosynthesis, but how that leads to fungistatic or fungicidal activities in many pathogenic fungi is poorly understood. Here, Schuster, Kilaru & Steinberg show that azole lethality in the plant pathogens Zymoseptoria tritici and Magnaporthe oryzae is due to a combination of reactive oxygen species-induced apoptosis and macroautophagy.

Most bacterial cells are surrounded by an essential cell wall composed of the net-like heteropolymer peptidoglycan (PG). Growth and division of bacteria are intimately linked to the expansion of the PG meshwork and the construction of a cell wall septum that separates the nascent daughter cells. Class A penicillin-binding proteins (aPBPs) are a major family of PG synthases that build the wall matrix. Given their central role in cell wall assembly and importance as drug targets, surprisingly little is known about howthe activity of aPBPs is controlled to properly coordinate cell growth and division. Here, we report the identification of MacP (SPD_0876) as a membrane-anchored cofactor of PBP2a, an aPBP synthase of the Gram-positive pathogen Streptococcus pneumoniae. We show that MacP localizes to the division site of S. pneumoniae, forms a complex with PBP2a, and is required for the in vivo activity of the synthase. Importantly, MacP was also found to be a substrate for the kinase StkP, a global cell cycle regulator. Although StkP has been implicated in controlling the balance between the elongation and septation modes of cell wall synthesis, none of its substrates are known to modulate PG synthetic activity. Here we show that a phosphoablative substitution in MacP that blocks StkP-mediated phosphorylation prevents PBP2a activity without affecting the MacP–PBP2a interaction. Our results thus reveal a direct connection between PG synthase function and the control of cell morphogenesis by the StkP regulatory network.

During the transition from elongation to septation, Escherichia coli establishes a ring-like peptidoglycan growth zone at the future division site. This preseptal peptidoglycan synthesis does not require the cell division-specific peptidoglycan transpeptidase PBP3 or most of the other cell division proteins, but it does require FtsZ, its membrane-anchor ZipA and at least one of the bi-functional transglycosylase-transpeptidases, PBP1A or PBP1B. Here we show that PBP1A and PBP1B interact with ZipA and localise to preseptal sites in cells with inhibited PBP3. ZipA stimulates the glycosyltransferase activity of PBP1A. The membrane-anchored cell division protein FtsN localises at preseptal sites and stimulates both activities of PBP1B. Genes zipA and ftsN can be individually deleted in ftsA * mutant cells, but the simultaneous depletion of both proteins is lethal and cells do not establish preseptal sites. Our data support a model according to which ZipA and FtsN-FtsA have semi-redundant roles in connecting the cytosolic FtsZ ring with the membrane-anchored peptidoglycan synthases during the preseptal phase of envelope growth. Proteins FtsZ, ZipA, and either PBP1A or PBP1B are required for the synthesis of preseptal peptidoglycan at the future cell division site in E. coli . Here, Pazos et al. provide evidence that ZipA and FtsA-FtsN connect the cytosolic FtsZ ring with the membrane-anchored PBPs.