ER-to-Golgi trafficking of procollagen in the absence of large carriers

AbstractSecretion and assembly of collagen is fundamental to the function of the extracellular matrix. Defects in the assembly of a collagen matrix lead to pathologies including fibrosis and osteogenesis imperfecta. Owing to the size of fibril-forming procollagen molecules it is assumed that they are transported from the endoplasmic reticulum to the Golgi in specialised large COPII-dependent carriers. Here, analysing endogenous procollagen and a new engineered GFP-tagged form, we show that transport to the Golgi occurs in the absence of large carriers. Large GFP-positive structures are observed occasionally but these are non-dynamic, are not COPII-positive, and label with markers of the ER. We propose a “short-loop” model of COPII-dependent ER-to-Golgi traffic that, while consistent with models of ERGIC-dependent expansion of COPII carriers, does not invoke long-range trafficking of large vesicular structures. Our findings provide an important insight into the process of procollagen trafficking and reveal a short-loop pathway from the ER to the Golgi, without the use of large carriers.SummaryTrafficking of procollagen is essential for normal cell function. Here, imaging of GFP-tagged type I procollagen reveals that it is transported from the endoplasmic reticulum to the Golgi, without the use of large carriers.</jats:sec

New factors for protein transport identified by a genome-wide CRISPRi screen in mammalian cells

Protein and membrane trafficking pathways are critical for cell and tissue homeostasis. Traditional genetic and biochemical approaches have shed light on basic principles underlying these processes. However, the list of factors required for secretory pathway function remains incomplete, and mechanisms involved in their adaptation poorly understood. Here, we present a powerful strategy based on a pooled genome-wide CRISPRi screen that allowed the identification of new factors involved in protein transport. Two newly identified factors, TTC17 and CCDC157, localized along the secretory pathway and were found to interact with resident proteins of ER-Golgi membranes. In addition, we uncovered that upon TTC17 knockdown, the polarized organization of Golgi cisternae was altered, creating glycosylation defects, and that CCDC157 is an important factor for the fusion of transport carriers to Golgi membranes. In conclusion, our work identified and characterized new actors in the mechanisms of protein transport and secretion, and opens stimulating perspectives for the use of our platform in physiological and pathological contexts.Includes Wellcome Trust, MRC and H202

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Protein transport by vesicles and tunnels

Palade's corpus placed small vesicles as the sole means to transport proteins across stable distinct compartments of the secretory pathway. We suggest that cargo, spatial organization of secretory compartments, and the timing of fission of cargo-filled containers dictate the design of transport intermediates that can be vesicles and transient direct tunnels.We acknowledge support from the Spanish Ministry of Economy and Competitiveness through the Program “Centro de Excelencia Severo Ochoa 2013-2017” (SEV-2012-0208), support from the CERCA Program/Generalitat de Catalunya and fellowship IJCI-2017-34751 (to I. Raote). V. Malhotra is an Institució Catalana de Recerca i Estudis Avançats professor at the Centre for Genomic Regulation and the work in his laboratory is funded by grants from MINECO’s Plan Nacional (BFU2013-44188-P) and Consolider (CSD2009-00016). The project has received research funding from the European Union. This paper reflects only the authors’ views. The European Union is not liable for any use that may be made of the information contained therein

TANGO1 marshals the early secretory pathway for cargo export

TANGO1 protein facilitates the endoplasmic reticulum (ER) export of large cargoes that cannot be accommodated in 60 nm transport vesicles. It assembles into a ring in the plane of the ER membrane to create a distinct domain. Its lumenal portion collects and sorts folded cargoes while its cytoplasmic domains collar COPII coats, recruit retrograde COPI-coated membranes that fuse within the TANGO1 ring, thus opening a tunnel for cargo transfer from the ER into a growing export conduit. This mode of cargo transfer bypasses the need for vesicular intermediates and is used to export the most abundant and bulky cargoes. The evolution of TANGO1 and its activities defines the difference between yeast and animal early secretory pathways.Vivek Malhotra thanks Felix Goñi for keeping him sane in Spain. We acknowledge the Spanish Ministry of Science and Innovation for its support of the European Molecular Biology Laboratory partnership, the Centro de Excelencia Severo Ochoa, and the Centres de Recerca de Catalunya (CERCA) Programme/Generalitat de Catalunya. We acknowledge financial support from the following sources: Ministerio de Economía y Competitividad (SEV-2012-0208, BFU2013-44188-P, and CSD2009- 00016 to V.M. and IJCI-2017-34751 to I.R.). FC acknowledges support from the Government of Spain (RYC-2017-22227, PID2019-106232RB-I00/10.13039/501100011033; Severo Ochoa CEX2019-000910-S), Fundació Cellex, Fundació Mir-Puig, and Generalitat de Catalunya (CERCA, AGAUR)

Biallelic TANGO1 mutations cause a novel syndromal disease due to hampered cellular collagen secretion

The transport and Golgi organization 1 (TANGO1) proteins play pivotal roles in the secretory pathway. Full length TANGO1 is a transmembrane protein localised at endoplasmic reticulum (ER) exit sites, where it binds bulky cargo within the ER lumen and recruits membranes from the ER Golgi intermediate compartment to create an exit route for their export. Here we report the first TANGO1-associated syndrome in humans. A synonymous substitution that results in exon eight skipping in most mRNA molecules, ultimately leading to a truncated TANGO1 protein was identified as disease-causing mutation. The four homozygously affected sons of a consanguineous family display severe dentinogenesis imperfecta, short stature, various skeletal abnormalities, insulin-dependent diabetes mellitus, sensorineural hearing loss, and mild intellectual disability. Functional studies in HeLa and U2OS cells revealed that the corresponding truncated TANGO1 protein is dispersed in the ER and its expression in cells with intact endogenous TANGO1 impairs cellular collagen I secretion

Protein transport by vesicles and tunnels

Palade's corpus placed small vesicles as the sole means to transport proteins across stable distinct compartments of the secretory pathway. We suggest that cargo, spatial organization of secretory compartments, and the timing of fission of cargo-filled containers dictate the design of transport intermediates that can be vesicles and transient direct tunnels.We acknowledge support from the Spanish Ministry of Economy and Competitiveness through the Program “Centro de Excelencia Severo Ochoa 2013-2017” (SEV-2012-0208), support from the CERCA Program/Generalitat de Catalunya and fellowship IJCI-2017-34751 (to I. Raote). V. Malhotra is an Institució Catalana de Recerca i Estudis Avançats professor at the Centre for Genomic Regulation and the work in his laboratory is funded by grants from MINECO’s Plan Nacional (BFU2013-44188-P) and Consolider (CSD2009-00016). The project has received research funding from the European Union. This paper reflects only the authors’ views. The European Union is not liable for any use that may be made of the information contained therein