Biology subjects

Nord, A.

Publications and source records attributed to Nord, A..

23 records · Page 2Linked to original sources

bioRxiv2022

A whole blood approach improves speed and accuracy when measuring mitochondrial respiration in avian hematocytes

Understanding mitochondrial biology and pathology is key to understanding the evolution of animal form and function. However, mitochondrial measurement often involves invasive, or even terminal, sampling, which can be difficult to reconcile in wild models or in longitudinal studies. Non-mammal vertebrates contain mitochondria in their red blood cells, which can be exploited for minimally invasive mitochondrial measurement. Several recent bird studies have measured mitochondrial function using isolated blood cells. Isolation adds time in the laboratory and might be associated with physiological complications. Inference may also be constrained on biological grounds by lack of tissue context. We developed and validated a protocol to measure mitochondrial respiration in bird whole blood. Endogenous respiration was comparable between isolated blood cells and whole blood. However, oxidative respiration was higher in whole blood, and whole blood mitochondria were better coupled and had higher maximum working capacity. Whole blood measurement was also more reproducible than measurement on isolated cells for all traits considered. Measurements were feasible over a 10-fold range of sample volumes, though both small and large volumes were associated with changes to respiratory traits. The protocol was compatible with long-term storage: after 24 h at 5 {degrees}C without agitation all respiration traits but maximum working capacity remained unchanged, the latter decreasing by 14%. Our study suggests that whole blood measurement provides faster, more reproducible, and more biologically (tissue context) and physiologically (mitochondrial integrity) relevant assessment of mitochondrial respiration. We recommend future studies to take a whole blood approach unless specific circumstances require the use of isolated blood cells.

physiology↗

bioRxiv2022

Plasticity of mitochondrial function restores fuel production during rest-phase hypothermia in a winter bird

Many animals downregulate body temperature to save energy when resting (rest-phase hypothermia). Small birds that winter at high latitude have comparatively limited capacity for hypothermia and so pay large energy costs for thermoregulation during cold nights. Available evidence suggests this process is fuelled by adenosine triphosphate (ATP)-dependent mechanisms. Most ATP is produced by oxidative phosphorylation in the mitochondria, but mitochondrial respiration can be lower during hypothermia because of the temperature-dependence of biological processes. This can create conflict between increased organismal ATP demand and a lower mitochondrial capacity to provide it. We studied this in blood cell mitochondria of wild great tits (Parus major) by simulating rest-phase hypothermia via a 6{degrees}C reduction in assay temperature in vitro. The birds had spent the night preceding the experiment in thermoneutrality or in temperatures representing mild or very cold winter nights. Night temperature did not affect mitochondrial respiration. Across treatments, endogenous respiration was 14% lower in hypothermia. This did not reflect general thermal suppression because phosphorylating respiration was unaffected by thermal state. Instead, hypothermia was associated with a threefold reduction of leak respiration, from 17% in normothermia to 4% in hypothermia. Thus, coupling of total respiration to ATP production was 96% in hypothermia, compared to 83% in normothermia. Our study shows that thermal insensitivity of phosphorylation combined with short-term plasticity of leak respiration may safeguard ATP production when endogenous respiration is suppressed. This casts new light on the process by which small birds endure harsh winter cold and warrants future tests across tissues in vivo.

physiology↗

bioRxiv2021

Autism risk gene POGZ promotes chromatin accessibility and expression of clustered synaptic genes

De novo mutations in POGZ, which encodes the chromatin regulator Pogo Transposable Element with ZNF Domain protein, are strongly associated with autism spectrum disorder (ASD). Here we find that in the developing mouse and human brain POGZ binds predominantly euchromatic loci and these are enriched for human neurodevelopmental disorder genes and transposable elements. We profile chromatin accessibility and gene expression in Pogz-/- mice and find that POGZ promotes chromatin accessibility of candidate regulatory elements (REs) and the expression of clustered synaptic genes. We further demonstrate that POGZ forms a nuclear complex and co-occupies loci with HP1{gamma} and ADNP, another high-confidence ASD risk gene. In Pogz+/- mice, Adnp expression is reduced. We postulate that reduced POGZ dosage disrupts cortical function through alterations in the POGZ-ADNP balance which modifies neuronal gene expression.

neuroscience↗

bioRxiv2019

Ambient temperature effects on stress-induced hyperthermia in Svalbard ptarmigan

Stress-induced hyperthermia (SIH) is commonly observed during handling in homeotherms. However, in birds, handling in cold environments typically elicits hypothermia. It is unclear whether this indicates that SIH is differently regulated in this taxon or if it is due to size, because body temperatures changes during handling in low temperature have only been measured in small birds [≤] 0.03 kg (that are more likely to suffer high heat loss when handled). We have, therefore, studied thermal responses to handling stress in the intermediate-sized (0.5-1.0 kg) Svalbard ptarmigan (Lagopus muta hyperborea) in 0{degrees}C and -20{degrees}C, in winter and spring. Handling caused elevated core body temperature, and peripheral vasoconstriction that reduced back skin temperature. Core temperature increased less and back skin temperature decreased more in -20{degrees}C than in 0{degrees}C, probably because of higher heat loss rate at the lower temperature. Responses were qualitatively consistent between seasons, despite higher body condition/insulation in winter and dramatic seasonal changes in photoperiod, possibly affecting stress responsiveness. Our study supports the notion that SIH is a general thermoregulatory reaction to acute stressors in endotherms, but also suggests that body size and thermal environment should be taken into account when evaluating this response in birds.

physiology↗

bioRxiv2018

Kinetic analysis methods applied to single motor protein trajectories

Molecular motors convert chemical or electrical energy into mechanical displacement, either linear or rotary. Under ideal circumstances, single-molecule measurements can spatially and temporally resolve individual steps of the motor, revealing important properties of the underlying mechanochemical process. Unfortunately, steps are often hard to resolve, as they are masked by thermal noise. In such cases, details of the mechanochemistry can nonetheless be recovered by analyzing the fluctuations in the recorded traces. Here, we expand upon existing statistical analysis methods, providing two new avenues to extract the motor step size, the effective number of rate-limiting chemical states per translocation step, and the compliance of the link between the motor position and the probe particle. We first demonstrate the power and limitations of these methods using simulated molecular motor trajectories, and we then apply these methods to experimental data of kinesin, the bacterial flagellar motor, and F1-ATPase.

biophysics↗