Biology subjects

Meyerowitz, E. M.

Publications and source records attributed to Meyerowitz, E. M..

6 recordsLinked to original sources

bioRxiv2018

Observing the Cell in Its Native State: Imaging Subcellular Dynamics in Multicellular Organisms

True physiological imaging of subcellular dynamics requires studying cells within their parent organisms, where all the environmental cues that drive gene expression, and hence the phenotypes we actually observe, are present. A complete understanding also requires volumetric imaging of the cell and its surroundings at high spatiotemporal resolution without inducing undue stress on either. We combined lattice light sheet microscopy with two-channel adaptive optics to achieve, across large multicellular volumes, noninvasive aberration-free imaging of subcellular processes, including endocytosis, organelle remodeling during mitosis, and the migration of axons, immune cells, and metastatic cancer cells in vivo. The technology reveals the phenotypic diversity within cells across different organisms and developmental stages, and may offer insights into how cells harness their intrinsic variability to adapt to different physiological environments.\n\nOne Sentence SummaryCombining lattice light sheet microscopy with adaptive optics enables high speed, high resolution in vivo 3D imaging of dynamic processes inside cells under physiological conditions within their parent organisms.

cell biology↗

bioRxiv2017

Nitrate modulates stem cell dynamics by regulating WUSCHEL expression through cytokinins

The shoot apical meristem (SAM) is responsible for the generation of all of the aerial parts of plants1. Given its critical role, dynamical changes in SAM activity should play a central role in the adaptation of plant architecture to the environment2. Using quantitative microscopy, grafting experiments and genetic perturbations, we connect the plant environment to the SAM, by describing the molecular mechanism by which cytokinins signal the level of nutrient availability to the SAM. We show that a systemic signal of cytokinin precursors3 mediates the adaptation of SAM size and organogenesis rate to the availability of mineral nutrients by modulating the expression of WUSCHEL, a key regulator of stem cell homeostasis4. In time-lapse experiments, we further show that this mechanism allows meristems to adapt to rapid changes in nitrate concentration, and thereby modulate their rate of organ production to the availability of mineral nutrients within a few days. Our work sheds new light on the role of the stem cell regulatory network, by showing that it does not only maintain meristem homeostasis but also allows plants to adapt to rapid changes in the environment.

plant biology↗

bioRxiv2017

Gene expression dynamics and inter-tissue recognition mechanisms during tissue fusion at the Arabidopsis graft junction

The ability for cut tissues to join together and form a chimeric organism is a remarkable property of many plants, however, grafting is poorly characterized at the molecular level. To better understand this process we monitored genome-wide temporal and spatial gene expression changes in grafted Arabidopsis thaliana hypocotyls. Tissues above and below the graft rapidly developed an asymmetry such that many genes were more highly expressed on one side than the other. This asymmetry correlated with sugar responsive genes and we observed an accumulation of starch above the graft that decreased along with asymmetry once the sugar-transporting vascular tissues reconnected. Despite the initial starvation response below the graft, many genes associated with vascular formation were rapidly activated in grafted tissues but not in cut and separated tissues indicating that a recognition mechanism activated that was independent of functional vascular connections. Auxin which is transported cell-to-cell, had a rapidly elevated response that was symmetric, suggesting that auxin was perceived by the root within hours of tissue attachment to activate the vascular regeneration process. A subset of genes were expressed only in grafted tissues, indicating that wound healing proceeded via different mechanisms depending on the presence or absence of adjoining tissues. Such a recognition process could have broader relevance for tissue regeneration, inter-tissue communication and tissue fusion events.

plant biology↗

bioRxiv2017

Cell Cycle Control by Nuclear Sequestration of CDC20 and CDH1 mRNA in Plant Stem Cells

In eukaryotic cells, most RNA molecules are exported into the cytoplasm after being transcribed in the nucleus. Long noncoding RNAs (lncRNAs) have been found to reside and function primarily inside the nucleus, but nuclear localization of protein-coding messenger RNAs (mRNAs) has been considered rare in both animals and plants. Here we show that two mRNAs, transcribed from the CDC20 and CCS52B (plant orthologue of CDH1) genes, are specifically sequestered inside the nucleus during the cell cycle. CDC20 and CDH1 both function as coactivators of the anaphase-promoting complex or cyclosome (APC/C) E3 ligase to trigger cyclin B (C YCB) destruction. In the Arabidopsis thaliana shoot apical meristem (SAM), we find CDC20 and CCS52B are co-expressed with CYCBs in mitotic cells. CYCB transcripts can be exported and translated, whereas CDC20 and CCS52B mRNAs are strictly confined to the nucleus at prophase and the cognate proteins are not translated until the redistribution of the mRNAs to the cytoplasm after nuclear envelope breakdown (NEBD) at prometaphase. The 5 untranslated region (UTR) is necessary and sufficient for CDC20 mRNA nuclear localization as well as protein translation. Mitotic enrichment of CDC20 and CCS52B transcripts enables the timely and rapid activation of APC/C, while their nuclear sequestration at prophase appears to protect cyclins from precocious degradation.

cell biology↗

bioRxiv2017

Cell type boundaries organize plant development

In plants the dorsoventral boundary of leaves defines an axis of symmetry through the centre of the organ separating the top (dorsal) and bottom (ventral) tissues. Although the positioning of this boundary is critical for leaf morphogenesis, how the boundary is established and how it influences development remains unclear. Using live-imaging and perturbation experiments we show that leaf orientation, morphology and position are pre-patterned by HD-ZIPIII and KAN gene expression in the shoot, leading to a model in which dorsoventral genes coordinate to regulate plant development by localizing auxin response between their expression domains. However we also find that auxin levels feedback on dorsoventral patterning by spatially organizing HD-ZIPIII and KAN expression in the shoot periphery. By demonstrating that the regulation of these genes by auxin also governs their response to wounds, our results also provide a parsimonious explanation for the influence of wounds on leaf dorsoventrality.\n\nOnce sentence summaryCell type boundaries regulate plant development

developmental biology↗

bioRxiv2017

SUPERMAN prevents stamen formation and promotes stem cell termination in the fourth whorl of the Arabidopsis flower

The molecular and genetic networks underlying the determination of floral organ identity are well studied, but much less is known about how the flower is partitioned into four developmentally distinct whorls. The SUPERMAN gene is required for proper specification of the boundary between stamens in whorl 3 and carpels in whorl 4, as superman mutants exhibit supernumerary stamens but usually lack carpels. However, it has remained unclear whether extra stamens in superman mutants originate from an organ identity change in whorl 4 or the overproliferation of whorl 3. Using live confocal imaging, we show that the extra stamens in superman mutants arise from cells in whorl 4, which change their fate from female to male, while floral stem cells proliferate longer, allowing for the production of additional stamens.

developmental biology↗