The role of the transcription factor JAGGED in early floral organogenesis

Initiation of organ primordia from pools of undifferentiated cells requires coordinated cytoplasmic growth, oriented cell wall extension, and cell cycle progression. It is debated which of these processes are primary drivers for organ morphogenesis and directly targeted by developmental regulators. The single zinc finger transcription factor JAGGED (JAG) is a direct target of several floral organ identity genes and is expressed in early organ primordia (Dinneny et al., 2004; Ohno et al., 2004; Gomez et al., 2005; Kaufmann et al., 2009). Loss of function jag mutants have narrow floral organs with reduced distal growth. Quantitative 3D imaging has revealed that JAG is required for the transition from meristematic to organ primordium cell behaviour. The transition involves an increase in the rates of cell division and cell growth, a shift from isotropic to anisotropic growth, and modifications in cell size homeostasis in primordia (Schiessl et al., 2012). In this project, ChIP-Seq was combined with transcriptome analysis to identify global direct target genes of JAG. Consistent with the roles of JAG during organ initiation and organ growth, I found that JAG directly repressed genes involved in meristem development, such as the TALE PROTEIN BELL1 and genes involved in organ boundaries specification such as PETAL LOSS. In addition, JAG directly regulated genes involved in growth regulatory pathways, tissue polarity, cell wall modification, and cell cycle progression. For example, JAG directly repressed the cell cycle inhibitors KIP RELATED PROTEIN 2 and 4 (KRP2/4). The krp2 and krp4 mutations suppressed jag loss of function defects in organ growth and cell type patterning. In particular, loss of KRP4 rescued the defects of cell size homeostasis in the primordia of the jag loss of function mutant. In summary, this work revealed that JAG directly coordinates organ patterning with cellular processes required for tissue growth

On the biodegradation of fosfomycin and phosphaisoserine

Organophosphonate, Verbindungen mit einer direkten P-C-Bindung, spielen in der Medizin, Landwirtschaft und Industrie eine wichtige Rolle. Sie können von Mikroorganismen, einige pathogene eingeschlossen, nicht aber von Wirbeltieren, mineralisiert und als zusätzliche oder alleinige Phosphorquelle verwendet werden. Ihr biologischer Abbau ist von entscheidender Bedeutung, da er hilft, ihre Rolle im globalen Phosphor-Redox-Zyklus zu verstehen und ein tieferes Verständnis ihrer Wirkungweise zu gewinnen. Verschiedene Arbeitsgruppen haben sich bereits mit der Aufklärung der Biosynthese einiger spezieller Phosphonate beschäftigt und dabei bemerkenswerte und gleichzeitig erstaunliche Ergebnisse erhalten. Die Biodegradation von Phosphonsäuren ist hingegen noch immer kaum erforscht. Im Rahmen meiner Masterarbeit habe ich verschiedene Phosphonate synthetisiert, die bei Studien zur Aufklärung der Biodegradation von Fosfomycin und der 2-Amino-1-Hhydroxyethylphosphonsäure eingesetzt werden sollen. Das 3,3,3-Trifluor-substituierte Analogon der (1R*,2R*)-1,2-Dihydroxypropylphosphonsäure wurde ausgehend von Trifluoracetaldehyd-Hydrat synthetisiert, das in das Cyanhydrin überführt wurde. Seine Hydroxygruppe wurde TIPS-geschützt und das resultierende alpha-silyloxy-substituierte Nitril wurde mit DIBAl-H zum Aldehyd reduziert. Dann wurde Diethyltrimmethylsilylphosphit an die Carbonylgruppe addiert, um die P-C-Bindung zu bilden. Die beiden resultierenden Diastereomere wurden mittels Flash-Chromatography getrennt und vollständig deblockiert. Die gewünschte Verbindung entstand als Racemat, dessen Synthese in sechs Schritten in einer Gesamtausbeute von 6% gelang. Des Weiteren wurde racemische und enantiomerenreine (S)-1-Hydroxy-2-oxopropylphosphonsäure in drei bzw. fünf Schritten synthetisiert. Ausgehend von Methancrolein wurde racemisches Dimethyl 1-hydroxy-2-methyl-2-propenylphoshonat hergestellt. Seine beiden Enantiomere wurden durch chemische Racematspaltung mit Noe Reagentien erhalten. Das Racemat und das (S)-Enantiomer dieses alpha-Hydroxyphosphonats wurden in die Natriumsalze der Säuren überführt, die mittels Ozonolyse die alpha-Oxophosphonate lieferten. Durch Messung des H/D-Austausches am C-1 und des Drehwerts wurde gefunden, dass die Racemisierung bei neutralem pH innerhalb von 24 h unbedeutend ist. Darüber hinaus wurde eine neue zweistufige Synthese für (±)-2-Amino-1-hydroxyethylphosphonsäure ausgehend von kommerziell erhältlicher Vinylphosphonsäure optimiert. Diese wurde epoxidiert und das entstandene Epoxid anschließend mit Ammoniak regioselektiv geöffnet. Dies liefert die gewünschte Zielverbindung mit einer 40%igen Ausbeute. Schließlich wurde (R)-2-Amino-1-hydroxyethylphosphonsäure in einer sechsstufigen Synthesesequenz mit einer Gesamtausbeute von 49% und einem ee von 81% hergestellt. Das Ausgangmaterial, die Phthalimidoessigsäure, die aus Glycin hergestellt und in das Säurechlorid überführt wurde, wurde mit Triisopropylphosphit umgesetzt. Der Schlüsselschritt dieser Synthese ist die enantioselective Reduktion des alpha-Oxophosphonates mit Catecholboran und (R)-2-Methyloxazaborolidin als Katalysator. Abspaltung der Schutzgruppen schloss die Synthese der Verbindung, die in Gramm-Mengen für Abbaustudien benötigt wird, ab

Doppler sonography of the uterine and the cubital arteries in normal pregnancies, preeclampsia and intrauterine growth restriction: evidence for a systemic vessel involvement

Aims: The decrease in uterine resistance during normal pregnancy is known to be related to invading trophoblast cells which derive from placental tissue. Uterine and peripheral resistance is elevated in preeclampsia. The aim of the present study was to prospectively examine uterine and peripheral resistance in pregnancies complicated by preeclampsia (PE), fetal intrauterine growth restriction (IUGR) and pregnancy induced hypertension (PIH). Methods: Sixty-seven women with normal pregnancies, 17 with PE, 12 with IUGR underwent Doppler sonographic investigation of the uterine and the cubital arteries. The Pulsatility Index (PI) was calculated for each vessel. Statistical analysis was performed and a P-value < 0.05 was considered significant. Results: Patients with preeclampsia and IUGR showed a significant higher resistance at the placental (mean PI 1.267 and 1.063), nonplacental (mean PI 1.631 and 1.124) and cubital artery (mean PI 3,777 and 3.995) compared to the normal pregnancy group (mean PI 0.678; 0.859 and 2.95 respectively). Mean birth weight in the PE group was 1409 g, in the IUGR group 1649 g and 3419 g in the normal pregnancy group. Conclusions: Pregnancies with IUGR are associated with elevated peripheral resistance in the maternal arterial system as seen in pregnancies with preeclampsia. Our findings encourage to further investigate the maternal vascular system in high risk pregnancies

Active Control of Cell Size Generates Spatial Detail during Plant Organogenesis

SummaryHow cells regulate their dimensions is a long-standing question [1, 2]. In fission and budding yeast, cell-cycle progression depends on cell size, although it is still unclear how size is assessed [3–5]. In animals, it has been suggested that cell size is modulated primarily by the balance of external signals controlling growth and the cell cycle [1], although there is evidence of cell-autonomous control in cell cultures [6–9]. Regardless of whether regulation is external or cell autonomous, the role of cell-size control in the development of multicellular organisms remains unclear. Plants are a convenient system to study this question: the shoot meristem, which continuously provides new cells to form new organs, maintains a population of actively dividing and characteristically small cells for extended periods [10]. Here, we used live imaging and quantitative, 4D image analysis to measure the sources of cell-size variability in the meristem and then used these measurements in computer simulations to show that the uniform cell sizes seen in the meristem likely require coordinated control of cell growth and cell cycle in individual cells. A genetically induced transient increase in cell size was quickly corrected by more frequent cell division, showing that the cell cycle was adjusted to maintain cell-size homeostasis. Genetically altered cell sizes had little effect on tissue growth but perturbed the establishment of organ boundaries and the emergence of organ primordia. We conclude that meristem cells actively control their sizes to achieve the resolution required to pattern small-scale structures

Molecular mechanism of cytokinin-activated cell division in Arabidopsis

Mitogens trigger cell division in animals. In plants, cytokinins, a group of phytohormones derived from adenine, stimulate cell proliferation. Cytokinin signalling is initiated by membrane-associated histidine kinase receptors and transduced through a phosphorelay system. Here we show, in the Arabidopsis shoot apical meristem (SAM), that cytokinin regulates cell division by promoting nuclear shuttling of Myb-domain protein 3R4 (MYB3R4), a transcription factor that activates mitotic gene expression. Newly synthesized MYB3R4 protein resides predominantly in the cytoplasm. At the G2/M transition, rapid nuclear accumulation of MYB3R4—consistent with an associated transient peak in cytokinin concentration—feeds a positive-feedback loop involving importins, and initiates a transcriptional cascade that drives mitosis and cytokinesis. An engineered nuclear-restricted MYB3R4 mimics the cytokinin effects in enhancement of cell proliferation and meristem growth.Gatsby Charitable Foundatio

Nodule inception recruits the lateral root developmental program for symbiotic nodule organogenesis in Medicago truncatula

To overcome nitrogen deficiencies in the soil, legumes enter symbioses with rhizobial bacteria that convert atmospheric nitrogen into ammonium. Rhizobia are accommodated as endosymbionts within lateral root organs called nodules that initiate from the inner layers of Medicago truncatula roots in response to rhizobial perception. In contrast, lateral roots emerge from predefined founder cells as an adaptive response to environmental stimuli, including water and nutrient availability. CYTOKININ RESPONSE 1 (CRE1)-mediated signaling in the pericycle and in the cortex is necessary and sufficient for nodulation, whereas cytokinin is antagonistic to lateral root development, with cre1 showing increased lateral root emergence and decreased nodulation. To better understand the relatedness between nodule and lateral root development, we undertook a comparative analysis of these two root developmental programs. Here, we demonstrate that despite differential induction, lateral roots and nodules share overlapping developmental programs, with mutants in LOB-DOMAIN PROTEIN 16 (LBD16) showing equivalent defects in nodule and lateral root initiation. The cytokinin-inducible transcription factor NODULE INCEPTION (NIN) allows induction of this program during nodulation through activation of LBD16 that promotes auxin biosynthesis via transcriptional induction of STYLISH (STY) and YUCCAs (YUC). We conclude that cytokinin facilitates local auxin accumulation through NIN promotion of LBD16, which activates a nodule developmental program overlapping with that induced during lateral root initiation

Molecular mechanism of cytokinin-activated cell division in Arabidopsis

Mitogens trigger cell division in animals. In plants, cytokinins, a group of phytohormones derived from adenine, stimulate cell proliferation. Cytokinin signalling is initiated by membrane-associated histidine kinase receptors and transduced through a phosphorelay system. Here we show, in the Arabidopsis shoot apical meristem (SAM), that cytokinin regulates cell division by promoting nuclear shuttling of Myb-domain protein 3R4 (MYB3R4), a transcription factor that activates mitotic gene expression. Newly synthesized MYB3R4 protein resides predominantly in the cytoplasm. At the G2/M transition, rapid nuclear accumulation of MYB3R4—consistent with an associated transient peak in cytokinin concentration—feeds a positive-feedback loop involving importins, and initiates a transcriptional cascade that drives mitosis and cytokinesis. An engineered nuclear-restricted MYB3R4 mimics the cytokinin effects in enhancement of cell proliferation and meristem growth.Gatsby Charitable Foundatio

Renal Interstitial Platelet-Derived Growth Factor Receptor-β Cells Support Proximal Tubular Regeneration

Background The kidney is considered to be a structurally stable organ with limited baseline cellular turnover. Nevertheless, single cells must be constantly replaced to conserve the functional integrity of the organ. PDGF chain B (PDGF-BB) signaling through fibroblast PDGF receptor-beta (PDGFR beta) contributes to interstitial-epithelial cell communication and facilitates regenerative functions in several organs. However, the potential role of interstitial cells in renal tubular regeneration has not been examined. Methods In mice with fluorescent protein expression in renal tubular cells and PDGFR beta-positive interstitial cells, weablated single tubular cells by high laser exposure. We then used serial intravital multiphoton microscopy with subsequent three-dimensional reconstruction and ex vivo histology to evaluate the cellular and molecular processes involved in tubular regeneration. Results Single-tubular cell ablation caused the migration and division of dedifferentiated tubular epithelial cells that preceded tubular regeneration. Moreover, tubular cell ablation caused immediate calcium responses in adjacent PDGFR beta-positive interstitial cells and the rapid migration thereof toward the injury. These PDGFR beta-positive cells enclosed the injured epithelium before the onset of tubular cell dedifferentiation, and the later withdrawal of these PDGFR beta-positive cells correlated with signs of tubular cell redifferentiation. Intraperitoneal administration of trapidil to block PDGFR beta impeded PDGFR beta-positive cell migration to the tubular injury site and compromised the recovery of tubular function. Conclusions Ablated tubular cells are exclusively replaced by resident tubular cell proliferation in a process dependent on PDGFR beta-mediated communication between the renal interstitium and the tubular system

Cell size controlled in plants using DNA content as an internal scale

How eukaryotic cells assess and maintain sizes specific for their species and cell type remains unclear. We show that in the Arabidopsis shoot stem cell niche, cell size variability caused by asymmetric divisions is corrected by adjusting the growth period before DNA synthesis. KIP-related protein 4 (KRP4) inhibits progression to DNA synthesis and associates with mitotic chromosomes. The F BOX-LIKE 17 (FBL17) protein removes excess KRP4. Consequently, daughter cells are born with comparable amounts of KRP4. Inhibitor dilution models predicted that KRP4 inherited through chromatin would robustly regulate size, whereas inheritance of excess free KRP4 would disrupt size homeostasis, as confirmed by mutant analyses. We propose that a cell cycle regulator, stabilized by association with mitotic chromosomes, reads DNA content as a cell size-independent scale.European Commission (ERC-2018-AdG_833617) and the Ministry of Science and Innovation (RTI2018-094793-B-I00) and institutional grants from Fundación Ramón Areces and Banco de Santander to the Centro de Biologia Molecular Severo Ocho