Waking the sleeping dragon: gene expression profiling reveals adaptive strategies of the hibernating reptile Pogona vitticeps

Abstract

Background Hibernation is a physiological state exploited by many animals exposed to prolonged adverse environmental conditions associated with winter. Large changes in metabolism and cellular function occur, with many stress response pathways modulated to tolerate physiological challenges that might otherwise be lethal. Many studies have sought to elucidate the molecular mechanisms of mammalian hibernation, but detailed analyses are lacking in reptiles. Here we examine gene expression in the Australian central bearded dragon ( Pogona vitticeps ) using mRNA-seq and label-free quantitative mass spectrometry in matched brain, heart and skeletal muscle samples from animals at late hibernation, 2 days post-arousal and 2 months post-arousal. Results We identified differentially expressed genes in all tissues between hibernation and post-arousal time points; with 4264 differentially expressed genes in brain, 5340 differentially expressed genes in heart, and 5587 differentially expressed genes in skeletal muscle. Furthermore, we identified 2482 differentially expressed genes across all tissues. Proteomic analysis identified 743 proteins (58 differentially expressed) in brain, 535 (57 differentially expressed) in heart, and 337 (36 differentially expressed) in skeletal muscle. Tissue-specific analyses revealed enrichment of protective mechanisms in all tissues, including neuroprotective pathways in brain, cardiac hypertrophic processes in heart, and atrophy protective pathways in skeletal muscle. In all tissues stress response pathways were induced during hibernation, as well as evidence for gene expression regulation at transcription, translation and post-translation. Conclusions These results reveal critical stress response pathways and protective mechanisms that allow for maintenance of both tissue-specific function, and survival during hibernation in the central bearded dragon. Furthermore, we provide evidence for multiple levels of gene expression regulation during hibernation, particularly enrichment of miRNA-mediated translational repression machinery; a process that would allow for rapid and energy efficient reactivation of translation from mature mRNA molecules at arousal. This study is the first molecular investigation of its kind in a hibernating reptile, and identifies strategies not yet observed in other hibernators to cope stress associated with this remarkable state of metabolic depression. Electronic supplementary material The online version of this article (10.1186/s12864-019-5750-x) contains supplementary material, which is available to authorized users.

Meta-Transcriptomic Discovery of a Divergent Circovirus and a Chaphamaparvovirus in Captive Reptiles with Proliferative Respiratory Syndrome

“…Brumation is an extreme hypometabolic state used by some reptiles to cope with low or unpredictable food availability and unfavorable seasonal conditions for the duration of winter. A number of specific protective measures have been identified during this hibernation in bearded dragons, including increased neuroprotection in the brain, maintenance of heart function through hypertrophy, and upgrading antioxidant capacity and mitochondrial maintenance by skeletal muscle atrophy [ 16 ]. Emergence from brumation may also represent a period of increased disease susceptibility in reptiles, as shown by downregulated transcription of several genes responsible for microbial pathogen defense, cellular and oxidative stress, and cell differentiation and growth [ 17 ].…”

MicroRNA dynamics during hibernation of the Australian central bearded dragon (Pogona vitticeps)

“…The targets of these genes include PPARGC1A, CRTC1, CRTC2, and PRKAG1. These genes were upregulated during hibernation in all tissues with the exception of PPARGC1A, which was downregulated in brain 7 . miRNAs that target two genes important in miRNA-mediated translational repression (AGO3 and CNOT1) were downregulated during hibernation.…”

“…Studies aiming to understand the molecular architecture of hibernation phenotype have demonstrated control at multiple levels of gene regulation: including epigenetic changes (DNA methylation and histone modification), gene silencing by microRNAs (miRNAs), and protein modifications 6,7 . Amongst these, the role of miRNAs in response to stress, such as during hibernation, is becoming increasingly evident [8][9][10][11][12][13][14][15][16][17] .…”

“…Furthermore, RISC is able to repress translation of mRNAs, without degradation, by modulating the binding of ribosomes and their associated proteins 23 . miRNA-mediated translational repression is potentially a rapid and energy efficient means of regulating gene expression during hibernation that may be particularly important for 'kickstarting' normal function after arousal 7 .…”

“…In captivity, hibernation typically occurs uninterrupted, with minimal loss of body weight and muscle mass. Using mRNA sequencing, we found that pathways involved in prevention of atrophy in skeletal muscle and excitotoxicity in brain were enriched during hibernation 7 .…”