Biology subjects

Wetzel, R.

Publications and source records attributed to Wetzel, R..

4 recordsLinked to original sources

bioRxiv2021

A chemically defined biomimetic surface for enhanced isolation efficiency of high-quality human mesenchymal stromal cells under xeno-/serum-free conditions

Mesenchymal stromal cells (MSCs) are one of the most frequently used cell types in regenerative medicine and cell therapy. Generating sufficient cell numbers for MSC-based therapies is constrained by: 1) their low abundance in tissues of origin, which imposes the need for significant ex vivo cell amplification, 2) donor-specific characteristics including MSC frequency/quality that decline with disease state and increasing age, 3) cellular senescence, which is promoted by extensive cell expansion and results in decreased therapeutic functionality. The final yield of a manufacturing process is therefore primarily determined by the applied isolation procedure and its efficiency in isolating therapeutically active cells from donor tissue. To date, MSCs are predominantly isolated using media supplemented with either serum or its derivatives, which pose safety and consistency issues. To overcome those limitations while enabling robust MSC production with constant high yield and quality, we developed a chemically defined biomimetic surface coating, called isoMATRIX, that facilitates the isolation of significantly higher numbers of MSCs in xeno-/serum-free and chemically defined conditions. The isolated cells display a smaller cell size and higher proliferation rate than those derived from a serum-containing isolation procedure and a strong immunomodulatory capacity. In sum, the isoMATRIX promotes enhanced xeno-, serum-free, or chemically defined isolation of human MSCs and supports consistent and reliable cell performance for improved stem cell-based therapies.

cell biology↗

bioRxiv2021

Correlative light and electron microscopy reveals that mutant huntingtin dysregulates the endolysosomal pathway in presymptomatic Huntington's disease

Huntingtons disease (HD) is a late onset, inherited neurodegenerative disorder for which early pathogenic events remain poorly understood. Here we show that mutant exon 1 HTT proteins are recruited to a subset of cytoplasmic aggregates in the cell bodies of neurons in brain sections from presymptomatic HD, but not wild-type, mice. This occurred in a disease stage and polyglutamine-length dependent manner. We successfully adapted a high-resolution correlative light and electron microscopy methodology, originally developed for mammalian and yeast cells, to allow us to correlate light microscopy and electron microscopy images on the same brain section within an accuracy of 100 nm. Using this approach, we identified these recruitment sites as single membrane bound, vesicle-rich endolysosomal organelles, specifically as (i) multivesicular bodies (MVBs), or amphisomes and (ii) autolysosomes or residual bodies. The organelles were often found in close proximity to phagophore-like structures. Immunogold labeling localized mutant HTT to non-fibrillar, electron lucent structures within the lumen of these organelles. In presymptomatic HD, the recruitment organelles were predominantly MVBs/amphisomes, whereas in late-stage HD, there were more autolysosomes or residual bodies. Electron tomograms indicated the fusion of small vesicles with the vacuole within the lumen, suggesting that MVBs develop into residual bodies. We found that markers of MVB-related exocytosis were depleted in presymptomatic mice and throughout the disease course. This suggests that endolysosomal homeostasis has moved away from exocytosis toward lysosome fusion and degradation, in response to the need to clear the chronically aggregating mutant HTT protein, and that this occurs at an early stage in HD pathogenesis.

neuroscience↗

bioRxiv2019

Structural basis of RNA Polymerase III transcription repression by Maf1

Maf1 is a highly conserved central regulator of transcription by RNA polymerase III (Pol III), and Maf1 activity influences a wide range of phenotypes from metabolic efficiency to lifespan. Here, we present a 3.3 [A] cryo-EM structure of yeast Maf1 bound to Pol III, which establishes how Maf1 achieves transcription repression. In the Maf1-bound state, Pol III elements that are involved in transcription initiation are sequestered, and the active site is sealed off due to ordering of the mobile C34 winged helix 2 domain. Specifically, the Maf1 binding site overlaps with the binding site of the Pol III transcription factor TFIIIB and DNA in the pre-initiation complex, rationalizing that binding of Maf1 and TFIIIB to Pol III are mutually exclusive. We validate our structure using variants of Maf1 with impaired transcription-inhibition activity. These results reveal the exact mechanism of Pol III inhibition by Maf1, and rationalize previous biochemical data.

molecular biology↗

bioRxiv2018

Structural rearrangement of TFIIS- and TFIIF/TFIIE-like subunits in RNA polymerase I transcription complexes

RNA polymerase (Pol) I is a 14-subunit enzyme that solely transcribes pre-ribosomal RNA. Cryo-EM structures of Pol I initiation and elongation complexes have given first insights into the molecular mechanisms of Pol I transcription. Here, we present cryo-electron microscopy structures of yeast Pol I elongation complexes (ECs) bound to the nucleotide analog GMPCPP at 3.2 to 3.4 [A] resolution that provide additional insight into the functional interplay between the TFIIE/TFIIF-like A49-A34.5 heterodimer and the TFIIS-like subunit A12.2 present in Pol I. Strikingly, most of the nucleotide-bound ECs lack the A49-A34.5 heterodimer and adopt a Pol II-like conformation, in which the A12.2 C-terminal domain is bound in a previously unobserved position at the A135 surface. Our work suggests a regulatory mechanism of Pol I transcription where the association of the A49-A34.5 heterodimer to Pol I is regulated by subunit A12.2, thereby explaining in vitro biochemical and kinetic data.

molecular biology↗