Biology subjects

Allen, M. C.

Publications and source records attributed to Allen, M. C..

4 recordsLinked to original sources

bioRxiv2024

Sex-dependent latent chilling injury changes estimates of thermal tolerance in a model insect

Thermal tolerance limits are closely associated with insect distribution. Thermal injury sets limits to mobility or survival after removal from the stress, and these limits are frequently integrated into models describing or predicting climate suitability for species of interest. Cold stress severity, sex, and prior thermal acclimation status can all influence lower thermal limits. There is a growing understanding of chilling injuries initially manifest, but we poorly understand repair or further injury that may happen after rewarming. We exposed male and female Drosophila melanogaster to an acute or chronic cold stress before assessing their mobility over a 24 h period. Females progressively worsened under both conditions, but male mobility neither worsened nor improved. Female mobility declined slower in flies recovering at cooler temperatures, and cold acclimation significantly mitigated latent injury in females following the same degree of initial injury, regardless of recovery temperature. We conclude that latent chilling injury can be sex-specific, occurs independently from mechanisms driving tissue damage in the cold, is temperature-dependent, and is mitigated by prior thermal acclimation. We argue that latent chilling injury and the factors that influence it should be more carefully considered in estimating tolerance limits.

physiology↗

bioRxiv2023

Effects of a high cholesterol diet on Drosophila chill tolerance are highly context-dependent

Chill susceptible insects are thought to be injured through different mechanisms depending on the duration and severity of chilling. While chronic chilling causes "indirect" injury through disruption of metabolic and ion homeostasis, acute chilling is suspected to cause "direct" injury, in part through phase transitions of cell membrane lipids. Dietary supplementation of cholesterol can reduce acute chilling injury in Drosophila melanogaster, but the generality of this effect and the mechanisms underlying it remain unclear. To better understand how and why cholesterol has this effect, we assessed how a high cholesterol diet and thermal acclimation independently and interactively impact several measures of chill tolerance in both male and female flies. Cholesterol supplementation positively affected tolerance to acute chilling in warm-acclimated flies (as reported previously). Conversely, feeding on the high-cholesterol diet negatively affected tolerance to chronic chilling in both cold and warm acclimated flies, as well as tolerance to acute chilling in cold acclimated flies. Cholesterol had no effect on the ability of flies to remain active in the cold or recover movement after a cold stress. Our findings support the idea that dietary cholesterol reduces mechanical injury to membranes caused by direct chilling injury, and that acute and chronic chilling are associated with distinct mechanisms of injury. Feeding on a high-cholesterol diet may interfere with mechanisms involved in cold acclimation, leaving cholesterol augmented flies more susceptible to chilling injury under some conditions. HighlightsO_LICholesterol improves cold shock tolerance of warm-acclimated flies C_LIO_LICold acclimation and chronic cold instead lead to negative effects of cholesterol on chill tolerance C_LIO_LICholesterol did not affect the ability of flies to remain active in the cold C_LIO_LIBoth sexes were similarly affected by a high cholesterol diet C_LI

physiology↗

bioRxiv2022

Learning of probabilistic punishment as a model of anxiety produces changes in action but not punishment encoding in the dmPFC and VTA

Previously, we developed a novel model for anxiety during motivated behavior by training rats to perform a task where actions executed to obtain a reward were probabilistically punished and observed that after learning, neuronal activity in the ventral tegmental area (VTA) and dorsomedial prefrontal cortex (dmPFC) encode the relationship between action and punishment risk (Park & Moghaddam, 2017). Here we used male and female rats to expand on the previous work by focusing on neural changes in the dmPFC and VTA that were associated with the learning of probabilistic punishment, and with anxiolytic treatment with diazepam after learning. We find that adaptive neural responses of dmPFC and VTA during the learning of anxiogenic contingencies are independent from the punishment experience and occur primarily during the peri-action period. Our results further identify peri-action ramping of VTA neural activity, and VTA-dmPFC correlated activity, as potential markers for the anxiolytic properties of diazepam.

neuroscience↗

bioRxiv2020

In situ differentiation of iridophore crystallotypes underlies zebrafish stripe patterning

Skin color patterns are ubiquitous in nature, evolve rapidly, and impact social behavior1, predator avoidance2, and protection from ultraviolet irradiation3. A leading model system for vertebrate skin patterning is the zebrafish4-7; its alternating blue stripes and yellow interstripes depend on guanine crystal-containing cells called iridophores that reflect light. It was suggested that the zebrafishs alternating color pattern arises from a single type of iridophore migrating differentially to stripes and interstripes7-9. When we tracked iridophores, however, we found they did not migrate between stripes and interstripes but instead differentiated and proliferated in place based on their micro-environment. RNA seq analysis further revealed stripe and interstripe iridophores had different transcriptomic states, while cryogenic scanning electron microscopy and micro-X-ray diffraction showed they had different guanine crystal organizations and responsiveness to norepinephrine, all indicating that stripe and interstripe iridophores are different cell types. Based on these results, we present a new model of skin patterning in zebrafish in which distinct iridophore crystallotypes containing specialized, physiologically responsive, subcellular organelles arise in stripe and interstripe zones by in situ differentiation. In this model, pattern phenotype depends not only on interactions among pigment cells that affect their arrangements, but also on factors that specify subcellular organization and physiological responsiveness of specialized organelles.

developmental biology↗