Gene Expression Profiling in the Hibernating Primate,Cheirogaleus Medius

Abstract

Hibernation is a complex physiological response that some mammalian species employ to evade energetic demands. Previous work in mammalian hibernators suggests that hibernation is activated not by a set of genes unique to hibernators, but by differential expression of genes that are present in all mammals. This question of universal genetic mechanisms requires further investigation and can only be tested through additional investigations of phylogenetically dispersed species. To explore this question, we use RNA-Seq to investigate gene expression dynamics as they relate to the varying physiological states experienced throughout the year in a group of primate hibernators—Madagascar’s dwarf lemurs (genus Cheirogaleus). In a novel experimental approach, we use longitudinal sampling of biological tissues as a method for capturing gene expression profiles from the same individuals throughout their annual hibernation cycle. We identify 90 candidate genes that have variable expression patterns when comparing two active states (Active 1 and Active 2) with a torpor state. These include genes that are involved in metabolic pathways, feeding behavior, and circadian rhythms, as might be expected to correlate with seasonal physiological state changes. The identified genes appear to be critical for maintaining the health of an animal that undergoes prolonged periods of metabolic depression concurrent with the hibernation phenotype. By focusing on these differentially expressed genes in dwarf lemurs, we compare gene expression patterns in previously studied mammalian hibernators. Additionally, by employing evolutionary rate analysis, we find that hibernation-related genes do not evolve under positive selection in hibernating species relative to nonhibernators.

Transcriptomics in the wild: Hibernation physiology in free‐ranging dwarf lemurs

“…This enzyme inhibits carbohydrate catabolism by preventing the conversion of pyruvate to acetyl‐CoA (Buck et al., ). Shallow torpor under laboratory conditions also induces PDK4 , in agreement with a previous study conducted at the Duke Lemur Center (Durham, NC, USA) with dwarf lemurs of the species Cheirogaleus medius (fat‐tailed dwarf lemurs; Faherty, Villanueva‐Cañas, et al., ). The present study provided a unique opportunity to investigate whether similar changes occurred in dwarf lemurs undergoing torpor in the wild.…”

“…This study demonstrates why some studies, such as those on hibernation physiology, are best conducted in the field under entirely natural conditions, at least in critically endangered lemur species. Although acknowledging the difficulty of tracking animals, variables that cannot be controlled as well as under laboratory settings, and overall challenging working conditions, our field study uncovered more genes that were found to be differentially expressed when comparing our former captive study with dwarf lemurs at the Duke Lemur Center (Faherty, Villanueva‐Cañas, et al., ). In both studies, differential expression was investigated using four individuals.…”

“…In other hibernating species (e.g., American and Japanese black bears; Ursus spp. ; Fedorov et al., ; Shimozuru, Kamine, & Tsubota, ), thirteen‐lined ground squirrels ( I. tridecemlineatus ; Hampton et al., ) and Arctic ground squirrels (Williams et al., ; Xu et al., ; Yan, ) and certainly in captive C. medius at the Duke Lemur Center (Faherty, Villanueva‐Cañas, et al., ), genetic pathways involved in lipid biosynthesis are also upregulated during the transition into the hibernation season.…”

“…We predict that the transcriptomic profiles we uncover during three distinct physiological states will identify the biological processes that are important for maintaining functioning during physiological extremes associated with torpor in free‐ranging Crossley's dwarf lemurs. The impacts of changes in gene expression in WAT on metabolic profiles throughout the circannual cycle have been investigated in only a few model mammalian species, and always under laboratory conditions (Bauer, Squire, Lowe, & Andrews, ; Boyer, Barnes, Lowell, & Grujic, ; Buck, Squire, & Andrews, ; Demas, Bowers, Bartness, & Gettys, ; Eddy, Morin, & Storey, ; Eddy & Storey, ; Hampton et al., ; Herminghuysen, Vaughan, Pace, Bagby, & Cook, ; Kabine et al., ; Wilson, Deeb, & Florant, ), including a captive colony of Cheirogaleus medius (Faherty, Villanueva‐Cañas, Klopfer, Albà, & Yoder, ). Thus, to our knowledge, this is the first study of its kind to focus on the longitudinal transcriptomic changes that drive hibernation physiology in free‐ranging animals under natural conditions, especially in primate heterotherms.…”

Tropical heterothermy is “cool”: The expression of daily torpor and hibernation in primates

“…), [108][109][110][111][112] American black bears (Ursus americanus), 113,114 little brown bats (Myotis lucifugus) 115 and recently in two different species of dwarf lemurs (Cheirogaleus medius and Cheirogaleus crossleyi). 21,116 These studies reveal specific genes that might play a key role in the hibernation phenotype and similar pathways are upregulated in predictable ways in all hibernating species studied to date. Of import are genes involved in lipid and carbohydrate metabolism, blood coagulation, and circadian rhythms.…”