Inter-laboratory comparison of gene expression biodosimetry for protracted radiation exposures as part of the RENEB and EURADOS WG10 2019 exercise.

Large-scale radiation emergency scenarios involving protracted low dose rate radiation exposure (e.g. a hidden radioactive source in a train) necessitate the development of high throughput methods for providing rapid individual dose estimates. During the RENEB (Running the European Network of Biodosimetry) 2019 exercise, four EDTA-blood samples were exposed to an Iridium-192 source (1.36 TBq, Tech-Ops 880 Sentinal) at varying distances and geometries. This resulted in protracted doses ranging between 0.2 and 2.4 Gy using dose rates of 1.5-40 mGy/min and exposure times of 1 or 2.5 h. Blood samples were exposed in thermo bottles that maintained temperatures between 39 and 27.7 °C. After exposure, EDTA-blood samples were transferred into PAXGene tubes to preserve RNA. RNA was isolated in one laboratory and aliquots of four blinded RNA were sent to another five teams for dose estimation based on gene expression changes. Using an X-ray machine, samples for two calibration curves (first: constant dose rate of 8.3 mGy/min and 0.5-8 h varying exposure times; second: varying dose rates of 0.5-8.3 mGy/min and 4 h exposure time) were generated for distribution. Assays were run in each laboratory according to locally established protocols using either a microarray platform (one team) or quantitative real-time PCR (qRT-PCR, five teams). The qRT-PCR measurements were highly reproducible with coefficient of variation below 15% in ≥ 75% of measurements resulting in reported dose estimates ranging between 0 and 0.5 Gy in all samples and in all laboratories. Up to twofold reductions in RNA copy numbers per degree Celsius relative to 37 °C were observed. However, when irradiating independent samples equivalent to the blinded samples but increasing the combined exposure and incubation time to 4 h at 37 °C, expected gene expression changes corresponding to the absorbed doses were observed. Clearly, time and an optimal temperature of 37 °C must be allowed for the biological response to manifest as gene expression changes prior to running the gene expression assay. In conclusion, dose reconstructions based on gene expression measurements are highly reproducible across different techniques, protocols and laboratories. Even a radiation dose of 0.25 Gy protracted over 4 h (1 mGy/min) can be identified. These results demonstrate the importance of the incubation conditions and time span between radiation exposure and measurements of gene expression changes when using this method in a field exercise or real emergency situation.

Competition for dispersal in ant-dispersed plants.

Two closely related and coexisting plants (Chenopodiaceae) of the Australian arid zone are adapted for seed dispersal by ants. These facultatively perennial shrubs persist in saltbush communities largely as a result of highly directional dispersal to ant mounds, where conditions are favorable for establishment and growth. The two species grow predominantly on mounds and compete for dispersal to these favorable microhabitats.

Myrmecochory in some plants (F. chenopodiaceae) of the Australian arid zone.

Several common plants (Chenopodiaceae) of the Australian arid zone produce diaspores that bear small and inconspicuous food bodies and are adapted for dispersal by ants. For these species, myrmecochory probably represents an adaptation for highly directional dispersal of diaspores to favorable microsites where nutrients are concentrated and possibly more accessible. Dispersal of diaspores by ants can have a pronounced effect on plant dispersion. In habitats characterized by red, crusty alluvial loam soils, myrmecochorous species grow almost exclusively on ant mounds; these same species grow in relatively continuous stands in sandy soil habitats. The flora of the Australia arid zone may contain many plant species that are adapted to use ants as dispersal agents. We consider several factors that may have promoted or facilitated the evolution of myrmecochory in arid zone plants.

Cheek pouch capacity in heteromyid rodents.

Cheek pouch volumes (V in cm3) were positively and significantly related to body mass (M in g) in 12 species and 14 populations of heteromyid rodents by the relationship V=0.065 M 0.887. When genera were considered separately, Microdipodops, Perognathus, and Thomomys conformed closely to the relationship, but Dipodomys did not. All species could obtain sufficient energy to meet their daily requirements from one maximum cheek pouch load, but the larger Dipodomys and Thomomys can carry a greater amount of energy relative to their needs. It is postulated that Thomomys and herbivorous Dipodomys conform to the relationship because they must transport food of low density and nutritional value; other Dipodomys, which feed on seeds of high density and greater nutritional worth, appear to have passed a threshold in size beyond which conformance to an allometric relationship is unnecessary. Thus, the two most important factors governing cheek pouch capacity are body mass and the density of the preferred food.