Biology subjects

Stasevich, T.

Publications and source records attributed to Stasevich, T..

3 recordsLinked to original sources

bioRxiv2022

Synonymous codon usage regulates translation initiation

Synonymous codon usage regulates gene expression such that transcripts rich in optimal codons produce significantly more protein than their nonoptimal counterparts. A major unresolved issue has been understanding the mechanisms by which synonymous codons regulate gene expression. We and others have previously shown that nonoptimal codons slow translation elongation speeds and thereby trigger mRNA degradation. However, differences in transcript abundance are not always sufficient to explain differences in protein levels, suggesting there are additional mechanisms by which codon usage regulates gene expression. Using reporter assays in human and Drosophila cells, we found that transcript levels account for less than half of the variation in protein abundance. We demonstrate that the differences at the protein level are not attributable to either protein folding or stability. Instead, we find that mRNAs with nonoptimal codons are bound by fewer ribosomes and that nonoptimal codon usage represses translation initiation. Nonoptimal transcripts are also less bound by the key translation initiation factors eIF4E and eIF4G, providing a mechanistic explanation for their reduced initiation rates. Our results reveal a new mechanism of regulation by codon usage, where nonoptimal codons repress further rounds of translation.

molecular biology↗

bioRxiv2021

A Drosophila Toolkit for Imaging of HA-tagged Proteins Unveiled a Block in Autophagy Flux in the Last Instar Larval Fat Body

For in vivo functional analysis of a protein of interest (POI), multiple transgenic strains with POI harboring different tags are needed but generation of these strains is still labor-intensive work. To overcome this, we developed a versatile Drosophila toolkit with a genetically encoded single-chain variable fragment for the HA epitope tag: "HA Frankenbody". This system allows various analyses of HA-tagged POI in live tissues by simply crossing an HA Frankenbody fly with an HA-tagged POI fly. Strikingly, the GFP-mCherry tandem fluorescent-tagged HA Frankenbody revealed a block in autophagic flux and an accumulation of enlarged autolysosomes in the last instar larval and prepupal fat body. Autophagy was dispensable for the swelling of lysosomes, indicating that lysosomal activity is downregulated at this stage. Furthermore, forced activation of lysosomes by fat body-targeted overexpression of Mitf, the single MiTF/TFE family gene in Drosophila, suppressed the lysosomal swelling and resulted in pupal lethality. Collectively, we propose that downregulated lysosomal function in the fat body plays a role in the metamorphosis of Drosophila.

cell biology↗

bioRxiv2021

Imaging translational control by Argonaute with single-molecule resolution in live cells

A major challenge to our understanding of translational control has been deconvolving the individual impact specific regulatory factors have on the complex dynamics of mRNA translation. MicroRNAs (miRNAs), for example, guide Argonaute and associated proteins to target mRNAs, where they direct gene silencing in multiple ways that are not well understood. To better deconvolve these dynamics, we have developed technology to directly visualize and quantify the impact of human Argonaute2 (Ago2) on the translation and subcellular localization of individual reporter mRNAs in living cells. We show that our combined translation and Ago2 tethering system reflects endogenous miRNA-mediated gene silencing. Using the system, we find that Ago2 association leads to progressive silencing of translation at individual mRNA. The timescale of silencing was similar to that of translation, consistent with a role for Ago2 in blocking translation initiation, leading to ribosome runoff. At early time points, we observed occasional brief bursts of translational activity at Ago2-tethered mRNAs undergoing silencing, suggesting that translational repression may initially be reversible. At later time points, Ago2-tethered mRNAs cluster and coalesce with endogenous P-bodies, where a translationally silent state is maintained. These results provide a framework for exploring miRNA-mediated gene regulation in live cells at the single-molecule level. Furthermore, our tethering-based, single-molecule reporter system will likely have wide-ranging application in studying general RNA-protein interactions.

molecular biology↗