Biology subjects

Oyama, Y.

Publications and source records attributed to Oyama, Y..

3 recordsLinked to original sources

bioRxiv2025

Tetraploid Caenorhabditis elegans embryos exhibit enhanced tolerance to osmotic stress

Polyploidy is a widespread phenomenon in development and evolution and is often associated with altered cellular physiology and developmental robustness. However, the influence of genome doubling on embryonic robustness to environmental stress remains poorly understood. Here, we investigated developmental traits and osmotic responses in tetraploid Caenorhabditis elegans embryos. Tetraploid animals exhibited enlarged body and tissue sizes and produced embryos with approximately 1.6-fold greater volume than diploids, accompanied by moderately delayed development and partial embryonic arrest. When exposed to a range of osmotic environments, both diploid and tetraploid embryos swelled or shrank in response to external osmolarity. Strikingly, tetraploid embryos at the early stage maintained normal cell division across a broader range of osmotic conditions than diploids. Quantitative analyses further revealed that tetraploid embryos exhibit reduced cytoplasmic mass density, largely reflecting lower protein concentration, while lipid and RNA levels remain unaffected. These compositional differences likely buffer volume fluctuations and underlie the enhanced osmotic tolerance of tetraploid embryos. Our findings demonstrate that genome doubling reshapes embryonic cellular physiology in a non-proportional manner to ploidy, thereby enhancing robustness during early development.

developmental biology↗

bioRxiv2021

Visualization of ecological successions in lakes subdivided by volcanic eruption at Akan Caldera, Hokkaido, Japan

It is not feasible to continuously observe ecological succession in lakes because of the long time-scales generally involved. Thus, the process has been inductively deduced by comparing many lakes with different succession states, or indirectly simulated by tracking studies of smaller water bodies, experiments using microcosms or mesocosms, and reconstruction of lake history by sediment analysis. However, the reality of succession processes in large lakes with slow succession is not well understood, and new approaches are needed. Theoretically, in a group of large and small lakes of similar ages and with similar initial and watershed environments, the rate of nutrient accumulation in each lake depends on the ratio of watershed area to lake size, and the lakes are predicted to evolve to different trophic levels over time. Here, we tested this hypothesis on the 10 lakes of varying sizes in Akan Caldera, Japan, which were formed thousands of years ago by fragmentation due to volcanic eruptions within the caldera. Topographic and water quality studies showed that the ratio of accumulated watershed area to lake size (area and volume), expressed logarithmically, had a positive linear regression with the total phosphorus concentration, an indicator of trophic level. The trophic levels of the lakes were diverse, including oligotrophic, mesotrophic, and eutrophic types in the traditional "lake type" classification based on total phosphorus and chlorophyll-a concentrations. Furthermore, 21 species of aquatic macrophytes were observed by a diving survey, and the plant species composition was classified into five groups corresponding to the trophic status of the lakes, indicating a conventional "hydrarch succession". The diversity of water quality and aquatic vegetation in a group of lakes with similar origins paves the way for new comparative studies of lakes, including large lakes.

ecology↗

bioRxiv2019

Endothelial specific PER2 at the crossroads of light elicited circadian amplitude enhancement as novel cardioprotective strategy and transcriptional regulation of HIF1A-dependent metabolic adaptation to myocardial ischemia

Consistent daylight oscillations and abundant oxygen availability are fundamental to human health. While both are connected from an evolutionary and cellular perspective, only oxygen is an established therapy in cardiovascular medicine. Here, we probe the mechanistic intersection between light-(Period 2, PER2) and oxygen-(hypoxia inducible factor, HIF1A) sensing pathways in cellular adaptation to low oxygen conditions with respect to myocardial ischemia. Using a whole genome array from daylight exposed wildtype or Per2-/- mice, an affinity purification-mass spectrometry-based proteomics screen for PER2 targets in hypoxic human endothelial cells, and targeted metabolomics from human healthy volunteers after daylight therapy, we investigated the intersection of light and hypoxia elicited pathways. Housing mice under daylight conditions prior to myocardial ischemia and reperfusion (IR)-injury, uncovered circadian PER2 amplitude enhancement as novel cardioprotective strategy, mimicking HIF1A metabolic adaptation to myocardial ischemia in a PER2 regulated manner. Whole genome array analysis from daylight exposed wildtype and Per2-/- mice or myocardial IR-injury in endothelial specific PER2 deficient mice (Per2loxP/loxP-VE-Cadherin -Cre) revealed a critical role for light elicited PER2 in maintaining the endothelial barrier function during myocardial ischemia. Mechanistic studies in human endothelia pointed towards a master transcriptional regulatory role for endothelial PER2 in metabolic reprograming to hypoxia via HIF1A, which was mimicked during normoxic PER2 stabilization. Translational investigation of light elicited pathways in human healthy volunteers found similar increases of PER2 or mimicking of HIF1A dependent metabolism. These studies identify light elicited circadian amplitude enhancement of endothelial PER2 as a novel cardioprotective strategy. Furthermore, these studies identify PER2 as critical control point of endothelial metabolic reprograming to maintain vascular integrity during myocardial IR-injury and implicate the use of daylight therapy to increase endothelial PER2 signaling as a strategy for the treatment of coronary artery disease.

cell biology↗