SELMA - das ERAD-ähnliche Präproteintranslokationssystem der zweiten Plastidenmembran von Phaeodactylum tricornutum

Diatomeen spielen bei der globalen Kohlenstofffixierung eine maßgebliche Rolle und stellen als Hauptbestandteil des Phytoplanktons einen Großteil der marinen Biomasse dar. Wie viele andere Algengruppen, aber auch beispielsweise humanpathogene Organismen, wie der Malariaerreger P. falciparum, sind Diatomeen im Rahmen einer sekundären Endosymbiose entstanden, bei der eine Rotalge von einer eukaryoten Wirtszelle aufgenommen und zur komplexen Plastide reduziert wurde. Vergleichbar mit der Entstehung primärer Plastiden mussten in der Folge Transportmechanismen entwickelt werden, um Präproteine zurück in die Plastide über nun allerdings nicht zwei, sondern drei bzw. vier Membranen zu transportieren. Wie die Zelle dieses Problem mechanistisch gelöst hat, war lange Zeit unklar und wurde im Rahmen verschiedenster Modelle diskutiert. 2007 wurde auf theoretischer Basis postuliert, dass der Präproteintransport an der zweiten Plastidenmembran von Heterokontophyten, Haptophyten, Cryptophyten und Apikomplexen durch ein ERAD-ähnliches Transportsystem vermittelt wird. Im Rahmen dieser Arbeit konnte diese Hypothese in der Diatomee P. tricornutum erstmals experimentell untermauert werden. Es wurde gezeigt, dass die symbiontenspezifischen ERAD-Faktoren sDer1-1 und sDer1-2 einen oligomeren Komplex in der zweiten Plastidenmembran bilden und mit den Transitpeptiden periplastidärer Präproteine interagieren. Der sDer1-Komplex spielt dabei als potentiell kanalbildende Komponente eine zentrale Rolle des symbiontenspezifischen ERAD-ähnlichen Systems SELMA. Zusätzlich findet am sDer1-Komplex eine Unterscheidung stromaler und periplastidärer Präproteine statt. So wurde im Rahmen dieser Arbeit gezeigt, dass Transitpeptide periplastidärer nicht aber stromaler Präproteine mit den Proteinen sDer1- 1 und sDer1-2 interagieren. Untersuchungen mit mutagenisierten Transitpeptiden zeigten zudem, dass alleine die +1 Position des Transitpeptids, besetzt mit einer aromatischen bzw. nicht-aromatischen Aminosäure, für diese Unterscheidung am sDer1-Komplex kritisch ist. Mit der symbiontenspezifischen Ubiquitin-Ligase s-E3 wurde ein Kandidat für ein weiteres Schlüsselelement von SELMA identifiziert. Im Ganzen zeigt sich damit, dass das symbiontenspezifische ERAD-Translokationssystem im Zuge der Endosymbiose von der ER-Membran in die zweite Plastidenmembran relokalisiert und zum Präproteintranslokator SELMA umfunktioniert wurde

Immune Gene Expression in Bombus terrestris: Signatures of Infection Despite Strong Variation among Populations, Colonies, and Sister Workers

Ecological immunology relies on variation in resistance to parasites. Colonies of the bumblebee Bombus terrestris vary in their susceptibility to the trypanosome gut parasite Crithidia bombi, which reduces colony fitness. To understand the possible origin of this variation in resistance we assayed the expression of 28 immunologically important genes in foraging workers. We deliberately included natural variation of the host “environment” by using bees from colonies collected in two locations and sampling active foraging workers that were not age controlled. Immune gene expression patterns in response to C. bombi showed remarkable variability even among genetically similar sisters. Nevertheless, expression varied with parasite exposure, among colonies and, perhaps surprisingly, strongly among populations (collection sites). While only the antimicrobial peptide abaecin is universally up regulated upon exposure, linear discriminant analysis suggests that the overall exposure effect is driven by a combination of several immune pathways and further immune functions such as ROS regulation. Also, the differences among colonies in their immune gene expression profiles provide clues to the mechanistic basis of well-known inter-colony variation in susceptibility to this parasite. Our results show that transcriptional responses to parasite exposure can be detected in ecologically heterogeneous groups despite strong background noise

Zusammenarbeit der sächsischen Hochschulen im Bereich Tutorienarbeit und Tutor_innen-Qualifizierung

Tutorienarbeit und Tutor_innen-Qualifizierung haben an deutschen Hochschulen Konjunktur. Dies zeigt sich u.a. in hochschulpolitischen Programmen zur Verbesserung der Lehre, die neben Lehrenden auch studentische Tutor_innen als Akteure universitärer Lehre verstärkt in den Blick nehmen

Didaktische Qualifizierung studentischer Tutor_innen: eine Aufgabe der Hochschuldidaktik

Spätestens seit dem Bologna-­Prozess wird in der universitären Ausbildung ein Wandel vom Lehren zum Lernen (shift from teaching to learning) forciert. Diese Perspektivverschiebung – in der Lehren und Lehrkompetenz aus der Perspektive des Lernens neu gedacht werden und Lehrenden (inkl. studentischer Tutor_innen, Anm. d. Verf.) die Aufgabe zukommt, Lehre lernförderlich zu gestalten (vgl. Wildt 2004, S. 169) – bildet „die zentrale Denk-­ und Entwicklungsli-­ nie der Hochschuldidaktik“ (Welbers 2005, S. 358). Zudem wird sie seit einiger Zeit auch von hochschulpolitischen Institutionen wie der Europäischen Rektorenkonferenz und der Hochschulrektorenkonferenz gefordert

From hybridomas to a robust microalgal-based production platform: molecular design of a diatom secreting monoclonal antibodies directed against the Marburg virus nucleoprotein

Background: The ideal protein expression system should provide recombinant proteins in high quality and quantity involving low production costs only. However, especially for complex therapeutic proteins like monoclonal antibodies many challenges remain to meet this goal and up to now production of monoclonal antibodies is very costly and delicate. Particularly, emerging disease outbreaks like Ebola virus in Western Africa in 2014–2016 make it necessary to reevaluate existing production platforms and develop robust and cheap alternatives that are easy to handle. Results: In this study, we engineered the microalga Phaeodactylum tricornutum to produce monoclonal IgG antibodies against the nucleoprotein of Marburg virus, a close relative of Ebola virus causing severe hemorrhagic fever with high fatality rates in humans. Sequences for both chains of a mouse IgG antibody were retrieved from a murine hybridoma cell line and implemented in the microalgal system. Fully assembled antibodies were shown to be secreted by the alga and antibodies were proven to be functional in western blot, ELISA as well as IFA studies just like the original hybridoma produced IgG. Furthermore, synthetic variants with constant regions of a rabbit IgG and human IgG with optimized codon usage were produced and characterized. Conclusions: This study highlights the potential of microalgae as robust and low cost expression platform for monoclonal antibodies secreting IgG antibodies directly into the culture medium. Microalgae possess rapid growth rates, need basically only water, air and sunlight for cultivation and are very easy to handle

Microalgae as bioreactors for bioplastic production

<p>Abstract</p> <p>Background</p> <p>Poly-3-hydroxybutyrate (PHB) is a polyester with thermoplastic properties that is naturally occurring and produced by such bacteria as <it>Ralstonia eutropha </it>H16 and <it>Bacillus megaterium</it>. In contrast to currently utilized plastics and most synthetic polymers, PHB is biodegradable, and its production is not dependent on fossil resources making this bioplastic interesting for various industrial applications.</p> <p>Results</p> <p>In this study, we report on introducing the bacterial PHB pathway of <it>R. eutropha </it>H16 into the diatom <it>Phaeodactylum tricornutum</it>, thereby demonstrating for the first time that PHB production is feasible in a microalgal system. Expression of the bacterial enzymes was sufficient to result in PHB levels of up to 10.6% of algal dry weight. The bioplastic accumulated in granule-like structures in the cytosol of the cells, as shown by light and electron microscopy.</p> <p>Conclusions</p> <p>Our studies demonstrate the great potential of microalgae like the diatom <it>P. tricornutum </it>to serve as solar-powered expression factories and reveal great advantages compared to plant based production systems.</p

ERAD Components in Organisms with Complex Red Plastids Suggest Recruitment of a Preexisting Protein Transport Pathway for the Periplastid Membrane

The plastids of cryptophytes, haptophytes, and heterokontophytes (stramenopiles) (together once known as chromists) are surrounded by four membranes, reflecting the origin of these plastids through secondary endosymbiosis. They share this trait with apicomplexans, which are alveolates, the plastids of which have been suggested to stem from the same secondary symbiotic event and therefore form a phylogenetic clade, the chromalveolates. The chromists are quantitatively the most important eukaryotic contributors to primary production in marine ecosystems. The mechanisms of protein import across their four plastid membranes are still poorly understood. Components of an endoplasmic reticulum-associated degradation (ERAD) machinery in cryptophytes, partially encoded by the reduced genome of the secondary symbiont (the nucleomorph), are implicated in protein transport across the second outermost plastid membrane. Here, we show that the haptophyte Emiliania huxleyi, like cryptophytes, stramenopiles, and apicomplexans, possesses a nuclear-encoded symbiont-specific ERAD machinery (SELMA, symbiont-specific ERAD-like machinery) in addition to the host ERAD system, with targeting signals that are able to direct green fluorescent protein or yellow fluorescent protein to the predicted cellular localization in transformed cells of the stramenopile Phaeodactylum tricornutum. Phylogenies of the duplicated ERAD factors reveal that all SELMA components trace back to a red algal origin. In contrast, the host copies of cryptophytes and haptophytes associate with the green lineage to the exclusion of stramenopiles and alveolates. Although all chromalveolates with four membrane-bound plastids possess the SELMA system, this has apparently not arisen in a single endosymbiotic event. Thus, our data do not support the chromalveolate hypothesis

Nine newly identified individuals refine the phenotype associated with MYT1L mutations

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Algae as Protein Factories: Expression of a Human Antibody and the Respective Antigen in the Diatom Phaeodactylum tricornutum

Microalgae are thought to offer great potential as expression system for various industrial, therapeutic and diagnostic recombinant proteins as they combine high growth rates with all benefits of eukaryotic expression systems. Moreover, microalgae exhibit a phototrophic lifestyle like land plants, hence protein expression is fuelled by photosynthesis, which is CO2-neutral and involves only low production costs. So far, however, research on algal bioreactors for recombinant protein expression is very rare calling for further investigations in this highly promising field. In this study, we present data on the expression of a monoclonal human IgG antibody against the Hepatitis B surface protein and the respective antigen in the diatom Phaeodactylum tricornutum. Antibodies are fully-assembled and functional and accumulate to 8.7% of total soluble protein, which complies with 21 mg antibody per gram algal dry weight. The Hepatitis B surface protein is functional as well and is recognized by algae-produced and commercial antibodies

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives