Visualization of Chromatin in the Yeast Nucleus and Nucleolus Using Hyperosmotic Shock

Abstract

Unlike in most eukaryotic cells, the genetic information of budding yeast in the exponential growth phase is only present in the form of decondensed chromatin, a configuration that does not allow its visualization in cell nuclei conventionally prepared for transmission electron microscopy. In this work, we studied the distribution of chromatin and its relationships to the nucleolus using different cytochemical and immunocytological approaches applied to yeast cells subjected to hyperosmotic shock. Our results show that osmotic shock induces the formation of heterochromatin patches in the nucleoplasm and intranucleolar regions of the yeast nucleus. In the nucleolus, we further revealed the presence of osmotic shock-resistant DNA in the fibrillar cords which, in places, take on a pinnate appearance reminiscent of ribosomal genes in active transcription as observed after molecular spreading (“Christmas trees”). We also identified chromatin-associated granules whose size, composition and behaviour after osmotic shock are reminiscent of that of mammalian perichromatin granules. Altogether, these data reveal that it is possible to visualize heterochromatin in yeast and suggest that the yeast nucleus displays a less-effective compartmentalized organization than that of mammals.

Large organellar changes occur during mild heat shock in yeast

“…4 C). EDC is distinct from nuclear structures such as the nucleolus and chromatin ( Hyde, 1965 ; Karreman et al, 2009 ; Thelen et al, 2021 ); at 90 min of heat shock, 90% of EDC in the nucleus was outside the nucleolus ( ).…”

Increasing Complexity of Ribosomes and Their Biogenesis

“…The morphology of this organelle has been extensively explored in metazoan cells, but the analysis of the yeast nucleolus is challenged by the low contrast of its mostly decondensed chromatin. Thelen, Defourny, Lafontaine, and Thiry show that this hurdle can be overcome by subjecting cells to hyperosmotic shock [ 19 ]. Moreover, they find that the organization of the yeast nucleolus into separate domains is less distinct than is the case in mammalian nucleoli.…”

Mechanisms of weak acid and sugar tolerance in Saccharomyces cerevisiae

“…Strikingly, cell viability and growth (Figure S4b) are significantly improved by the addition of sorbitol to the medium. In previous studies, 0.4 ~ 1 M sorbitol was used to induce hyperosmolarity responses [21,55,56]. Here, lower levels of 0.1 to 0.3 M sorbitol sufficed to counteract the maltose induced cell death (Figure 6c).…”

“…Hence, the overexpression of Xks1 combined with the absence of a negative feedback loop could, at high D-xylulose concentrations, potentially lead to rapid ATP consumption and cause substrate accelerated death. Such a phenomenon was observed with D-glucose conversion by Hxk2 which, when the negative feedback loop was deleted (TPS1), showed substrate accelerated death since all D-glucose is instantaneously converted in to D-glucose-6-phosphate thereby draining all ATP (42,54,55). Likewise, reduced activity of L-ribulokinase, converting L-ribulose into L-ribulose 5-phosphate with the consumption of one ATP, is also crucial for efficient L-arabinose utilization in a L-arabinose consuming S. cerevisiae strain (56).…”

“…Short-chain aliphatic acids present in lignocellulosic hydrolysates are effective inhibitors of the growth of yeast. This mainly concerns acetic acid that is formed by the release of hemicellulose acetyl side chains, and formic and levulinic acids that are derived from the degradation of furfural and/or HMF [55]. Formic acid has a very low pKa (i.e., 3.74), and shows the strongest toxic effect of all acids due to the high membrane permeability of this small sized molecule [56].…”