Biology subjects

Sanchez, J. S.

Publications and source records attributed to Sanchez, J. S..

3 recordsLinked to original sources

bioRxiv2024

A conserved function of corepressors is to nucleate assembly of the transcriptional preinitiation complex.

The plant corepressor TPL is recruited to diverse chromatin contexts, yet its mechanism of repression remains unclear. Previously, we have leveraged the fact that TPL retains its function in a synthetic transcriptional circuit in the yeast model Saccharomyces cerevisiae to localize repressive function to two distinct domains. Here, we employed two unbiased whole genome approaches to map the physical and genetic interactions of TPL at a repressed locus. We identified SPT4, SPT5 and SPT6 as necessary for repression with the SPT4 subunit acting as a bridge connecting TPL to SPT5 and SPT6. We also discovered the association of multiple additional constituents of the transcriptional preinitiation complex at TPL-repressed promoters, specifically those involved in early transcription initiation events. These findings were validated in yeast and plants through multiple assays, including a novel method to analyze conditional loss of function of essential genes in plants. Our findings support a model where TPL nucleates preassembly of the transcription activation machinery to facilitate rapid onset of transcription once repression is relieved.

molecular biology↗

bioRxiv2022

A conserved sequence in Drosophila Argonaute1 mRNA contributes to stress response via inducing miR-999 degradation

MicroRNAs (miRNAs) load onto Argonaute (AGO) proteins and target messenger RNAs (mRNA) to directly suppress gene expression at the post-transcriptional level. However, miRNA degradation can be triggered when there is extended base-pairing between miRNAs and the target RNAs. Such base-pairing can induce confirmational change of AGO and recruitment of ZSWIM8 ubiquitin ligase to mark AGO for proteasomal degradation, while the miRNAs are subsequently degraded. This target RNA-directed miRNA degradation (TDMD) mechanism appears to be an evolutionary conserved mechanism, but recent studies have focused on identifying endogenous TDMD events in the mammalian systems. Here, we performed AGO1-CLASH (crosslinking and sequencing of miRNA-mRNA hybrids) in Drosophila S2 cells, with Dora (ortholog of vertebrate ZSWIM8) knockout (KO) mediated by CRISPR-Cas9 to identify five TDMD triggers (sequences that can induce miRNA degradation). Interestingly, one trigger residing in the 3' UTR of AGO1 mRNA induces miR-999 degradation. CRISPR-Cas9 KO of the AGO1 trigger in S2 cells and in Drosophila elevates miR-999 abundance, with concurrent repression of the miR-999 targets. AGO1 trigger-KO flies respond poorly to hydrogen peroxide-induced stress, demonstrating the physiological importance of a single TDMD event.

molecular biology↗

bioRxiv2020

Amplification, not spreading limits rate of tau aggregate accumulation in Alzheimer's disease

Both the replication of protein aggregates and their spreading throughout the brain are implicated in the progression of Alzheimers disease (AD). However, the rates of these processes are unknown and the identity of the rate-determining process in humans has therefore remained elusive. By bringing together chemical kinetics with measurements of tau seeds and aggregates across brain regions, we are able to quantify their replication rate in human brains. Remarkably, we obtain comparable rates in several different datasets, with 5 different methods of tau quantification, from seed amplification assays in vitro to tau PET studies in living patients. Our results suggest that the overall rate of accumulation of tau in neocortical regions is limited not by spreading between brain regions but by local replication, which doubles the number of seeds every ~5 years. Thus, we propose that limiting local replication constitutes the most promising strategy to control tau accumulation during AD.

biophysics↗