Biology subjects

Zaburdaev, V.

Publications and source records attributed to Zaburdaev, V..

3 recordsLinked to original sources

bioRxiv2018

Intracellular mass density increase is accompanying but not sufficient for stiffening and growth arrest of yeast cells

Many organisms, including yeast cells, bacteria, nematodes and tardigrades, endure harsh environmental conditions, such as nutrient scarcity, or lack of water and energy for a remarkably long time. The rescue programs that these organisms launch upon encountering these adverse conditions include reprogramming their metabolism in order to enter a quiescent or dormant state in a controlled fashion. Reprogramming coincides with changes in the macromolecular architecture and changes in the physical and mechanical properties of the cells. However, the cellular mechanisms underlying the physical-mechanical changes remain enigmatic. Here, we induce metabolic arrest of yeast cells by lowering their intracellular pH. We then determine the differences in the intracellular mass density and stiffness of active and metabolically arrested cells using optical diffraction tomography and atomic force microscopy. We show that an increased intracellular mass density is associated with an increase in stiffness when the growth of yeast is arrested. However, increasing the intracellular mass density alone is not sufficient for maintenance of the growth-arrested state in yeast cells. Our data suggest that the cytoplasm of metabolically arrested yeast displays characteristics of solid. Our findings constitute a bridge between the mechanical behavior of the cytoplasm and the physical and chemical mechanisms of metabolically arrested cells with the ultimate aim of understanding dormant organisms.

biophysics↗

bioRxiv2017

Transcription establishes microenvironments that organize euchromatin

Chromatin is organized into heterochromatin, which is transcriptionally inactive, and euchromatin, which can switch between transcriptionally active and inactive states. This switch in euchromatin activity is accompanied by changes in its spatial distribution. How euchromatin rearrangements are established is unknown. Here we use super-resolution and live-cell microscopy to show that transcriptionally inactive euchromatin moves away from transcriptionally active euchromatin. This movement is driven by the formation of RNA-enriched microenvironments that exclude inactive euchromatin. Using theory, we show that the segregation into RNA-enriched microenvironments and euchromatin domains can be considered an active microemulsion. The tethering of transcripts to chromatin via RNA polymerase II forms effective amphiphiles that intersperse the two segregated phases. Taken together with previous experiments, our data suggest that chromatin is organized in the following way: heterochromatin segregates from euchromatin by phase separation, while transcription organizes euchromatin similar to an active microemulsion.

cell biology↗

bioRxiv2017

Competition between histone and transcription factor binding regulates the onset of transcription in zebrafish embryos

SUMMARYUpon fertilization, the genome of animal embryos remains transcriptionally inactive until the maternal-to-zygotic transition. At this time, the embryo takes control of its development and transcription begins. How the onset of zygotic transcription is regulated remains unclear. Here, we show that a dynamic competition for DNA binding between nucleosome-forming histones and transcription factors regulates zebrafish genome activation. Taking a quantitative approach, we found that the concentration of non-DNA bound core histones sets the time for the onset of transcription. The reduction in nuclear histone concentration that coincides with genome activation does not affect nucleosome density on DNA, but allows transcription factors to compete successfully for DNA binding. In agreement with this, transcription factor binding is sensitive to histone levels and the concentration of transcription factors also affects the time of transcription. Our results demonstrate that the relative levels of histones and transcription factors regulate the onset of transcription in the embryo.

developmental biology↗