Yao Zhang

Publications (3)8.95 Total impact

• Article: Cell Wall Amidase AmiC1 Is Required for Cellular Communication and Heterocyst Development in the Cyanobacterium Anabaena PCC 7120 but Not for Filament Integrity.

  Susanne Berendt, Josef Lehner, Yao Vincent Zhang, Tobias M Rasse, Karl Forchhammer, Iris Maldener
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  ABSTRACT: Filamentous cyanobacteria of the order Nostocales display typical properties of multicellular organisms. In response to nitrogen starvation, some vegetative cells differentiate into heterocysts, where fixation of N(2) takes place. Heterocysts provide a micro-oxic compartment to protect nitrogenase from the oxygen produced by the vegetative cells. Differentiation involves fundamental remodeling of the Gram-negative cell wall by deposition of a thick envelope and by formation of a neck-like structure at the contact site to the vegetative cells. Cell wall-hydrolyzing enzymes, like cell wall amidases, are involved in peptidoglycan maturation and turnover in unicellular bacteria. Recently, we showed that mutation of the amidase homologue amiC2 gene in Nostoc punctiforme ATCC 29133 distorts filament morphology and function. Here, we present the functional characterization of two amiC paralogues from Anabaena sp. strain PCC 7120. The amiC1 (alr0092) mutant was not able to differentiate heterocysts or to grow diazotrophically, whereas the amiC2 (alr0093) mutant did not show an altered phenotype under standard growth conditions. In agreement, fluorescence recovery after photobleaching (FRAP) studies showed a lack of cell-cell communication only in the AmiC1 mutant. Green fluorescent protein (GFP)-tagged AmiC1 was able to complement the mutant phenotype to wild-type properties. The protein localized in the septal regions of newly dividing cells and at the neck region of differentiating heterocysts. Upon nitrogen step-down, no mature heterocysts were developed in spite of ongoing heterocyst-specific gene expression. These results show the dependence of heterocyst development on amidase function and highlight a pivotal but so far underestimated cellular process, the remodeling of peptidoglycan, for the biology of filamentous cyanobacteria.
  Journal of bacteriology 07/2012; 194(19):5218-27. · 3.94 Impact Factor
• Article: The morphogene AmiC2 is pivotal for multicellular development in the cyanobacterium Nostoc punctiforme.

  Josef Lehner, Yao Zhang, Susanne Berendt, Tobias M Rasse, Karl Forchhammer, Iris Maldener
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  ABSTRACT: Filamentous cyanobacteria of the order Nostocales are primordial multicellular organisms, a property widely considered unique to eukaryotes. Their filaments are composed of hundreds of mutually dependent vegetative cells and regularly spaced N(2)-fixing heterocysts, exchanging metabolites and signalling molecules. Furthermore, they may differentiate specialized spore-like cells and motile filaments. However, the structural basis for cellular communication within the filament remained elusive. Here we present that mutation of a single gene, encoding cell wall amidase AmiC2, completely changes the morphology and abrogates cell differentiation and intercellular communication. Ultrastructural analysis revealed for the first time a contiguous peptidoglycan sacculus with individual cells connected by a single-layered septal cross-wall. The mutant forms irregular clusters of twisted cells connected by aberrant septa. Rapid intercellular molecule exchange takes place in wild-type filaments, but is completely abolished in the mutant, and this blockage obstructs any cell differentiation, indicating a fundamental importance of intercellular communication for cell differentiation in Nostoc. AmiC2-GFP localizes in the cell wall with a focus in the cross walls of dividing cells, implying that AmiC2 processes the newly synthesized septum into a functional cell-cell communication structure during cell division. AmiC2 thus can be considered as a novel morphogene required for cell-cell communication, cellular development and multicellularity.
  Molecular Microbiology 01/2011; 79(6):1655-69. · 5.01 Impact Factor
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  Available from: PubMed Central

  Article: In vivo imaging of intact Drosophila larvae at sub-cellular resolution.

  Yao Zhang, Petra Füger, Shabab B Hannan, Jeannine V Kern, Bronwen Lasky, Tobias M Rasse
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  ABSTRACT: Recent improvements in optical imaging, genetically encoded fluorophores and genetic tools allowing efficient establishment of desired transgenic animal lines have enabled biological processes to be studied in the context of a living, and in some instances even behaving, organism. In this protocol we will describe how to anesthetize intact Drosophila larvae, using the volatile anesthetic desflurane, to follow the development and plasticity of synaptic populations at sub-cellular resolution. While other useful methods to anesthetize Drosophila melanogaster larvae have been previously described, the protocol presented herein demonstrates significant improvements due to the following combined key features: (1) A very high degree of anesthetization; even the heart beat is arrested allowing for lateral resolution of up to 150 nm, (2) a high survival rate of >90% per anesthetization cycle, permitting the recording of more than five time-points over a period of hours to days and (3) a high sensitivity enabling us in 2 instances to study the dynamics of proteins expressed at physiological levels. In detail, we were able to visualize the postsynaptic glutamate receptor subunit GluR-IIA expressed via the endogenous promoter in stable transgenic lines and the exon trap line FasII-GFP. (4) In contrast to other methods the larvae can be imaged not only alive, but also intact (i.e. non-dissected) allowing observation to occur over a number of days. The accompanying video details the function of individual parts of the in vivo imaging chamber, the correct mounting of the larvae, the anesthetization procedure, how to re-identify specific positions within a larva and the safe removal of the larvae from the imaging chamber.
  Journal of Visualized Experiments 01/2010;