The SUN41 and SUN42 genes are essential for cell separation in

Institut Pasteur, Lutetia Parisorum, Île-de-France, France
Molecular Microbiology (Impact Factor: 4.42). 11/2007; 66(5):1256 - 1275. DOI: 10.1111/j.1365-2958.2007.06011.x


Completion of the yeast cell cycle involves extensive remodelling of the cell wall upon separation of mother and daughter cells. We have studied two members of the ascomycete-specific SUN gene family in Candida albicans. Inactivation of SUN41 yields defects in cell separation and hyphal elongation while inactivation of SUN42 results in minor phenotypic alterations. Simultaneous inactivation of SUN41 and SUN42 is synthetically lethal due to lysis of mother cells after septation. Electronic microscopy reveals cell wall defects mainly localized in the region surrounding the septa. This phenotype is osmoremediable and the conditional double mutants show increased sensitivity to cell wall or cell membrane perturbing agents. The essential function shared by Sun41p and Sun42p is conserved among yeasts because UTH1, a Saccharomyces cerevisiae SUN gene, suppresses the lethality of SUN41 and SUN42 conditional mutants. Investigation of functional genomic data obtained in S. cerevisiae reveals links between members of the SUN gene family and the RAM pathway regulating cell wall-degrading enzymes specifically involved during cell separation. Thus, the main function of ascomycetous Sun proteins appears linked to cell wall remodelling, with a probable role in counter-balancing cell wall degradation to avoid cell lysis upon cell separation.

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Available from: Guilhem Janbon, Oct 03, 2014
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    • "The SUN family is comprised of a group of fungus-specific proteins exhibiting high similarity, especially in their C-terminal domain (Table 1) [13], [16]. SUN family members have been predicted to be involved in various unrelated cellular processes, such as mitochondrial biogenesis and autophagy (mitophagy), cytokinesis, cell wall structure and DNA replication [7], [8], [17]. "
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    ABSTRACT: The SUN family is comprised of proteins that are conserved among various yeasts and fungi, but that are absent in mammals and plants. Although the function(s) of these proteins are mostly unknown, they have been linked to various, often unrelated cellular processes such as those connected to mitochondrial and cell wall functions. Here we show that three of the four Saccharomyces cerevisiae SUN family proteins, Uth1p, Sim1p and Sun4p, are efficiently secreted out of the cells in different growth phases and their production is affected by the level of oxygen. The Uth1p, Sim1p, Sun4p and Nca3p are mostly synthesized during the growth phase of both yeast liquid cultures and colonies. Culture transition to slow-growing or stationary phases is linked with a decreased cellular concentration of Sim1p and Sun4p and with their efficient release from the cells. In contrast, Uth1p is released mainly from growing cells. The synthesis of Uth1p and Sim1p, but not of Sun4p, is repressed by anoxia. All four proteins confer cell sensitivity to zymolyase. In addition, Uth1p affects cell sensitivity to compounds influencing cell wall composition and integrity (such as Calcofluor white and Congo red) differently when growing on fermentative versus respiratory carbon sources. In contrast, Uth1p is essential for cell resistance to boric acids irrespective of carbon source. In summary, our novel findings support the hypothesis that SUN family proteins are involved in the remodeling of the yeast cell wall during the various phases of yeast culture development and under various environmental conditions. The finding that Uth1p is involved in cell sensitivity to boric acid, i.e. to a compound that is commonly used as an important antifungal in mycoses, opens up new possibilities of investigating the mechanisms of boric acid's action.
    Preview · Article · Sep 2013 · PLoS ONE
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    • "They also reported defects in biofilm formation and enhanced sensitivity against caspofungin, confirming the defects in glucan synthesis observed by us. In a third approach Firon et al. (2007) identified Fig. 2. Schematic representation of the TLR signaling pathway with the link to the NF-␬B-dependent reporter gene SEAP (secreted alkaline phosphatase): Stimulation of the receptor combination TLR2/6, e.g. with zymosan, results in initiation of the signaling cascade activating the transcription factor NF-␬B. The TLR signaling is visualized by an integrated reporter gene containing an NF-␬B-binding site, resulting in NF-␬B-mediated activation of the promoter. "
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    • "Transcript profiling has identified genes that show increased or decreased expression in biofilms relative to planktonic cells and it has been hypothesized that these genes might play some role in biofilm formation. For instance, C. albicans SUN41 was among the genes that showed high upregulation upon biofilm growth (Garcia- Sanchez et al., 2004) and was subsequently shown to be required for biofilm formation, possibly through its contribution to morphogenesis and/or matrix production (Firon et al., 2007; Hiller et al., 2007; Norice et al., 2007). Yet, other examples showed no strict correlation between differential regulation in biofilm versus planktonic growth and contribution to biofilm formation (Moreno-Ruiz et al., 2009; Sellam et al., 2009). "
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    ABSTRACT: The fungal pathogen Candida albicans forms therapeutically challenging biofilms on biomedical implants. Using a transcript profiling approach genes whose expression is favoured upon biofilm growth compared with planktonic growth have been previously identified. Knock-out mutants for 38 of these genes were constructed, six of which showed a specific defect in biofilm formation. Among these genes, TYE7 that encodes a transcriptional activator of glycolytic genes in planktonic and biofilm growth conditions was identified as being required for the cohesiveness of biofilms. Biofilms formed by the tye7Δ knock-out mutant showed a hyperfilamentous morphology, and growth of this mutant on solid medium under hypoxia was also associated with the production of hyphae. Similar to TYE7 inactivation, inhibition of glycolysis or ATP synthesis using oxalate or an uncoupler, respectively, triggered morphogenesis when a wild-type strain was grown under hypoxia. These treatments also induced the formation of weakly cohesive, hyper-filamentous biofilms by a wild-type strain. Our data indicate that a hypoxic environment is generated within C. albicans biofilms and that continued biofilm development requires a Tye7p-dependent upregulation of glycolytic genes necessary to adapt to hypoxia and prevent uncontrolled hyphal formation. Thus, adaptation to hypoxia is an integral component of biofilm formation in C. albicans.
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