Biology subjects

Jonas, F.

Publications and source records attributed to Jonas, F..

6 recordsLinked to original sources

bioRxiv2024

The molecular mechanism of on-demand sterol biosynthesis at organelle contact sites

Contact-sites are specialized zones of proximity between two organelles, essential for organelle communication and coordination. The formation of contacts between the Endoplasmic Reticulum (ER), and other organelles, relies on a unique membrane environment enriched in sterols. However, how these sterol-rich domains are formed and maintained had not been understood. We found that the yeast membrane protein Yet3, the homolog of human BAP31, is localized to multiple ER contact sites. We show that Yet3 interacts with all the enzymes of the post-squalene ergosterol biosynthesis pathway and recruits them to create sterol-rich domains. Increasing sterol levels at ER contacts causes its depletion from the plasma membrane leading to a compensatory reaction and altered cell metabolism. Our data shows that Yet3 provides on-demand sterols at contacts thus shaping organellar structure and function. A molecular understanding of this proteins functions gives new insights into the role of BAP31 in development and pathology.

cell biology↗

bioRxiv2022

Histone exchange sensors reveal variant specific dynamics in mouse embryonic stem cells

Eviction of histones from nucleosomes and their exchange with newly synthesized or alternative variants is a central epigenetic determinant. Here, we define the genome-wide incorporation and exchange pattern of canonical and non-canonical histone variants in mouse embryonic stem cells by implementing a recently established, genetically encoded exchange sensor. While exchange of all measured variants scales with transcription, we describe variant-specific associations with transcription elongation and Polycomb binding. We found considerable exchange of H3.1 and H2B variants in heterochromatin and repeat elements, contrasting the stable incorporation and little exchange of H3.3 in these regions. This unexpected association between H3.3 incorporation and exchange of canonical variants is also evident in active promoters and enhancers, and further validated by reduced H3.1 dynamics following depletion of the HIRA H3.3-specific chaperone. The sensor system provides a powerful tool for studying regulation of histone dynamics toward understanding its role in shaping the epigenetic landscape in vivo.

genomics↗

bioRxiv2022

Rtt109 promotes nucleosome replacement ahead of the replicating fork

DNA replication perturbs chromatin by triggering the eviction, replacement and incorporation of nucleosomes. How this dynamic is orchestrated in time and space is poorly understood. Here, we apply a recently established sensor for histone exchange to follow the time-resolved histone H3 exchange profile in budding yeast cells undergoing synchronous replication. We find that new histones are incorporated not only behind, but also ahead of the replication fork. We provide evidence that Rtt109, the S phase-specific acetyltransferase, stabilizes nucleosomes behind the fork, but promotes H3 replacement ahead of the fork. Unexpectedly, increased replacement ahead of the fork is independent of the primary Rtt109 acetylation target H3K56, and rather results from Rtt109 activity towards the H3 N-terminus. Our results suggest that selective incorporation of differentially modified H3s behind and ahead of the replication fork results in opposing effects on histone exchange, which may contribute to genome stability by overcoming replication-associated challenges.

genomics↗

bioRxiv2021

Evolution of binding preferences among whole-genome duplicated transcription factors

Throughout evolution, new transcription factors (TFs) emerge by gene duplication, promoting growth and rewiring of transcriptional networks. How TF duplicates diverge is known for only a few studied cases. To provide a genome-scale view, we considered the 35% of budding yeast TFs, classified as whole-genome duplication (WGD)-retained paralogs. Using high-resolution profiling, we find that ~60% of paralogs evolved differential binding preferences. We show that this divergence results primarily from variations outside the DNA binding domains (DBDs), while DBD preferences remain largely conserved. Analysis of non-WGD orthologs revealed that ancestral preferences are unevenly split between duplicates, while new targets are acquired preferentially by the least conserved paralog (biased sub/neo-functionalization). Dimer-forming paralogs evolved mostly one-sided dependency, while other paralogs interacted through low-magnitude DNA-binding competition that minimized paralog interference. We discuss the implications of our findings for the evolutionary design of transcriptional networks.

genomics↗

bioRxiv2021

Generation and timing of graded responses to morphogen gradients

Morphogen gradients are known to subdivide a naive cell field into distinct zones of gene expression. Here we examine whether morphogens can also induce a graded response within such domains. To this end we explore the role of the Dorsal protein nuclear gradient along the dorso-ventral axis in defining the graded pattern of actomyosin constriction that initiates gastrulation in early Drosophila embryos. Two complementary mechanisms for graded accumulation of mRNAs of critical zygotic target genes were identified. First, activation of target-gene expression expands over time from the ventral-most region of high nuclear Dorsal to lateral regions where the levels are lower, due to a Dorsal-dependent priming probability of transcription sites. Thus, sites that are activated earlier will lead to more mRNA accumulation. Second, once the sites are primed, the rate of Pol II loading is also dependent on Dorsal levels. Morphological restrictions require that translation of the graded mRNA be delayed until completion of embryonic cell formation. Such timing is achieved by large introns, that provide a delay in production of the mature mRNAs.

developmental biology↗

bioRxiv2020

Mapping the architecture of regulatory variation provides insights into the evolution of complex traits

BackgroundOrganisms evolve complex traits by recruiting existing programs to new contexts, referred as co-option. Within a species, single upstream regulators can trigger full differentiation programs. Distinguishing whether co-option of differentiation programs results from variation in single regulator, or in multiple genes, is key for understanding how complex traits evolve. As an experimentally accessible model for studying this question we turned to budding yeast, where a differentiation program (filamentous) is activated in S. cerevisiae only upon starvation, but used by the related species S. paradoxus also in rich conditions. ResultsTo define expression variations associated with species-specific activation of the filamentous program, we profiled the transcriptome of S. cerevisiae, S. paradoxus and their hybrid along two cell cycles at 5-minutes resolution. As expected in cases of co-option, expression of oscillating genes varies between the species in synchrony with their growth phenotypes and was dominated by upstream trans-variations. Focusing on regulators of filamentous growth, we identified gene-linked variations (cis) in multiple genes across regulatory layers, which propagated to affect expression of target genes, as well as binding specificities of downstream transcription factor. Unexpectedly, variations in regulators essential for S. cerevisiae filamentation were individually too weak to explain activation of this program in S. paradoxus. ConclusionsOur study reveals the complex architecture of regulatory variation associated with species-specific use of a differentiation program. Based on these results, we suggest a new model in which evolutionary co-option of complex traits is stabilized in a distributed manner through multiple weak-effect variations accumulating throughout the regulatory network.

evolutionary biology↗