The very many faces of presenilins and the γ-secretase complex

Presenilin is a central, catalytic component of the γ-secretase complex which conducts intramembrane cleavage of various protein substrates. Although identified and mainly studied through its role in the development of amyloid plaques in Alzheimer disease, γ-secretase has many other important functions. The complex seems to be evolutionary conserved throughout the Metazoa, but recent findings in plants and Dictyostelium discoideum as well as in archeons suggest that its evolution and functions might be much more diversified than previously expected. In this review, a selective survey of the multitude of functions of presenilins and the γ-secretase complex is presented. Following a brief overview of γ-secretase structure, assembly and maturation, three functional aspects are analyzed: (1) the role of γ-secretase in autophagy and phagocytosis; (2) involvement of the complex in signaling related to endocytosis; and (3) control of calcium fluxes by presenilins

Structural and functional analysis of γ-secretase complex subunits in Arabidopsis thaliana

Wydział Biologii: Instytut Biologii Molekularnej i BiotechnologiiGamma-sekretaza jest kompleksem transbłonowym o aktywności proteazy, zdolnym do cięcia substratów w obrębie błon biologicznych. Odkryto go w trakcie badań nad chorobą Alzheimera. Jego substratem jest między innymi białko prekursorowe amyloidu oraz receptor Notch. W skład kompleksu wchodzą 4 białka: presenilina, nikastryna, oraz APH-1 i PEN-2. Jedną z funkcji gamma-sekretazy u zwierząt jest udział w regulowanej proteolizie wewnątrzbłonowej wielu białek sygnałowych. Pewne dane wskazują, że u zwierząt kompleks może być także zaangażowany w proces krążenia pęcherzyków. U roślin istnienie oraz funkcja kompleksu gamma-sekretazy są całkowicie nieznane. W rozprawie doktorskiej przedstawiono analizę strukturalną oraz funkcjonalną kompleksu gamma-sekretazy u Arabidopsis thaliana. Na podstawie danych bioinformatycznych ustalono, że w genomie roślin obecne są homologi wszystkich podjednostek kompleksu. Wykorzystując techniki mikroskopii fluorescencyjnej stwierdzono, że wszystkie podjednostki kompleksu gamma-sekretazy są zlokalizowane w obrębie systemu błon wewnętrznych. Analiza kolokalizacji, połączona z oceną oddziaływań metodą FLIM-FRET, pozwoliła zaproponować model składania i organizacji kompleksu gamma-sekretazy u roślin. Analiza funkcjonalna wykazała, że rośliny pozbawione presenilin wykazują zaburzenia rozwojowe. Poznanie dokładnego mechanizmu tych zmian wymaga dalszych badań.Gamma-secretase is an intramembrane protease complex that carries out proteolysis inside diverse membranes. It was discovered though the genetic linkage with an Alzheimer disease. It is involved in the Notch signaling pathway. The complex consists of 4 proteins: presenilin, nicastrin, PEN-2 and APH-1. In animals gamma-secretase is involved in Regulated Intramembrane Proteolysis of many proteins. It might also play a role in endocytosis and vesicle trafficking regulation. In plants the existence and function of the gamma-secretase complex is completely unknown. The aim of research was to investigate structural and functional aspects of gamma-secretase complex in plants. Sequence analyses indicated that all four components of gamma-secretase complex are present in Arabidopsis genome. Confocal microscopy approach was used to determine the sub-cellular localization of distinct gamma-secretase components in plants. It was revealed that all subunits localize to endomembrane system. Colocalization studies, combined with FLIM-FRET analyses, have proven that gamma-secretase subunits interact with each other. These data were sufficient, to propose a simplified model of gamma-secretase assembly and maturation. Functional analyses showed that plants devoid of presenilins exhibit developmental abnormalities. However, the mechanism of these changes needs to be further investigated

Formative cell divisions: principal determinants of plant morphogenesis

Formative cell divisions utilizing precise rotations of cell division planes generate and spatially place asymmetric daughters to produce different cell layers. Therefore, by shaping tissues and organs, formative cell divisions dictate multicellular morphogenesis. In animal formative cell divisions, the orientation of the mitotic spindle and cell division planes relies on intrinsic and extrinsic cortical polarity cues. Plants lack known key players from animals, and cell division planes are determined prior to the mitotic spindle stage. Therefore, it appears that plants have evolved specialized mechanisms to execute formative cell divisions. Despite their profound influence on plant architecture, molecular players and cellular mechanisms regulating formative divisions in plants are not well understood. This is because formative cell divisions in plants have been difficult to track owing to their submerged positions and imprecise timings of occurrence. However, by identifying a spatiotemporally inducible cell division plane switch system applicable for advanced microscopy techniques, recent studies have begun to uncover molecular modules and mechanisms for formative cell divisions. The identified molecular modules comprise developmentally triggered transcriptional cascades feeding onto microtubule regulators that now allow dissection of the hierarchy of the events at better spatiotemporal resolutions. Here, we survey the current advances in understanding of formative cell divisions in plants in the context of embryogenesis, stem cell functionality and post-embryonic organ formation

Fluorescence microscopy techniques in the research on the endomembrane system of plant cells

Gwałtowny rozwój technik mikroskopii fluorescencyjnej, w tym konfokalnej, w połączeniu z wykorzystaniem metod biologii molekularnej znacząco zdynamizowały rozwój molekularnej biologii komórki. Z wielu różnych względów, zwłaszcza znaczącej odmienności strukturalnej i funkcjonalnej, badania komórek roślinnych są nieco opóźnione. Artykuł podsumowuje stan badań systemu błon wewnętrznych komórek roślinnych z wykorzystaniem zróżnicowanych podejść i metod badawczych biologii komórki. Wskazuje na użycie różnego typu znaczników, tak chemicznych, jak i genetycznych, które umożliwiają lokalizację makrocząsteczek i procesów biologicznych. Omawia substancje chemiczne, które zaburzają funkcjonowanie systemu wewnątrzbłonowego, a więc pośrednio pozwalają wnioskować o roli uczestniczących w tych procesach białek. Wreszcie, pokazuje wykorzystanie nowych podejść i technik mikroskopowych do badań komórek roślinnych. Gdzie to jest stosowne, omawia także trudności wynikające ze swoistości składu, struktury i funkcji komórek roślinnych.Rapid development of fluorescence microscopy, including confocal microscopy, combined with the utilization of the methodologies of molecular biology, significantly accelerated the development of molecular cell biology. Research in plant cell biology slightly lags behind, mainly due to marked structural and functional dissimilarity of plant cells. This paper summarizes the current state of research on plant endomembrane system with respect to the utilization of differentiated approaches and methods of cell biology. The use of markers, both chemical and genetic, which enable localization of macromolecules and biological processes is indicated. Chemical substances perturbing the functioning of the endomembrane system and thus enabling to draw conclusions on the role of specific proteins are listed and discussed. Finally, use of novel approaches and microscopic techniques to the research of plant cells is demonstrated. Where applicable, problems arising due to the specific composition, structure and function of plant cells, are also considered

Plant plasma membrane-bound staphylococcal-like DNases as a novel class of eukaryotic nucleases

<p>Abstract</p> <p>Background</p> <p>The activity of degradative nucleases responsible for genomic DNA digestion has been observed in all kingdoms of life. It is believed that the main function of DNA degradation occurring during plant programmed cell death is redistribution of nucleic acid derived products such as nitrogen, phosphorus and nucleotide bases. Plant degradative nucleases that have been studied so far belong mainly to the S1-type family and were identified in cellular compartments containing nucleic acids or in the organelles where they are stored before final application. However, the explanation of how degraded DNA components are exported from the dying cells for further reutilization remains open.</p> <p>Results</p> <p>Bioinformatic and experimental data presented in this paper indicate that two <it>Arabidopsis</it> staphylococcal-like nucleases, named CAN1 and CAN2, are anchored to the cell membrane via N-terminal myristoylation and palmitoylation modifications. Both proteins possess a unique hybrid structure in their catalytic domain consisting of staphylococcal nuclease-like and tRNA synthetase anticodon binding-like motifs. They are neutral, Ca²⁺-dependent nucleaces showing a different specificity toward the ssDNA, dsDNA and RNA substrates. A study of microarray experiments and endogenous nuclease activity revealed that expression of CAN1 gene correlates with different forms of programmed cell death, while the CAN2 gene is constitutively expressed.</p> <p>Conclusions</p> <p>In this paper we present evidence showing that two plant staphylococcal-like nucleases belong to a new, as yet unidentified class of eukaryotic nucleases, characterized by unique plasma membrane localization. The identification of this class of nucleases indicates that plant cells possess additional, so far uncharacterized, mechanisms responsible for DNA and RNA degradation. The potential functions of these nucleases in relation to their unique intracellular location are discussed.</p

Gamma-secretase subunits associate in intracellular membrane compartments in <em>Arabidopsis thaliana</em>

International audienceGamma-secretase is a multisubunit complex with intramembrane proteolytic activity. In humans it was identified in genetic screens of patients suffering from familial forms of Alzheimer's disease, and since then it was shown to mediate cleavage of more than 80 substrates, including amyloid precursor protein or Notch receptor. Moreover, in animals, gamma-secretase was shown to be involved in regulation of a wide range of cellular events, including cell signalling, regulation of endocytosis of membrane proteins, their trafficking, and degradation. Here we show that genes coding for gamma-secretase homologues are present in plant genomes. Also, amino acid motifs crucial for gamma-secretase activity are conserved in plants. Moreover, all gamma-secretase subunits: PS1/PS2, APH-1, PEN-2, and NCT colocalize and interact with each other in Arabidopsis thaliana protoplasts. The intracellular localization of gamma-secretase subunits in Arabidopsis protoplasts revealed a distribution in endomembrane system compartments that is consistent with data from animal studies. Together, our data may be considered as a starting point for analysis of gamma-secretase in plants