Figure 1.
Graph showing body temperature tracings (solid line) of a thirteen-lined ground squirrel inside an environmental chamber beginning in September and ending in April.
Body temperature was measured using a surgically implanted transmitter. The dashed blue line represents the ambient (environmental) temperature, which is lowered to 5°C on November 1 and raised back to 23°C in March or April depending on the experiment. Periodic interbout arousals (IBAs) are seen as regular spikes in body temperature despite a constant ambient temperature of 5°C. Photographs of animals at four different points during the year are indicated and shown above the graph [70]. Characteristic measurements of body temperature (Tb), oxygen consumption (VO2), and heart rate (HR) during torpor and IBA are shown above the respective photographs.
Figure 2.
Twenty most abundant mRNAs in ground squirrel BAT (black) shown along with their respective levels in WAT (gray).
Measurements shown on the x-axis are the mean of the upper-quartile normalized counts of reads from the four collection points. Abbreviations: ACAA2, acetyl-CoA acyltransferase 2; ACADL, acyl-CoA dehydrogenase, long chain; ACADVL, acyl-CoA dehydrogenase, very long chain; ADCK3, aarF domain containing kinase 3; ACO2, aconitase 2; ATP5A1, ATP synthase, alpha subunit 1; ATP5B, ATP synthase, beta polypeptide; CLASP2, cytoplasmic linker associated protein 2; DGAT2, diacylglycerol O-acyltransferase 2; EEF1A1, eukaryotic translation elongation factor 1 alpha 1; FABP4, fatty acid binding protein 4; GNAS, G-protein subunit Gsα; HADHA and HADHB, hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase (trifunctional protein), alpha subunit and beta subunit; MEF2D, myocyte enhancer factor 2D; PCK1, phosphoenolpyruvate carboxykinase 1; PNPLA2, patatin-like phospholipase domain containing protein 2; RAD50, RAD50 homolog (S. cerevisiae); UBR5, ubiquitin protein ligase E3 component n-recognin 5; UCP1, uncoupling protein 1.
Figure 3.
Seasonal expression of four genes that are highly enriched in BAT versus WAT.
Error bars represent standard error of the mean. Abbreviations: ADCY3, Adenylate cyclase 3; GNAS, G-protein subunit Gsα; MEF2D, myocyte enhancer factor 2D; PYGL, phosphorylase, glycogen, liver.
Figure 4.
Differentially expressed genes encoding representative mitochondrial proteins in BAT.
Error bars represent standard error of the mean. Transcript levels for all genes shown have an FDR<0.05. The letters above each bar represent post hoc pair-wise comparisons to determine significance between collection points. Any collection point not connected by the same letter is significantly different (FDR<0.05). Abbreviations: ACSL1, acyl-CoA synthetase long-chain family member 1; HADHA and HADHB, hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase (trifunctional protein), alpha subunit and beta subunit; KMO, kynurenine 3-monooxygenase; UCP1 and UCP3, uncoupling protein 1 and 3.
Figure 5.
Differentially expressed genes encoding representative proteins in the adrenergic signaling pathway in BAT.
Error bars represent standard error of the mean. Transcript levels for all genes shown have an FDR<0.05. The letters above each bar represent post hoc pair-wise comparisons to determine significance between collection points. Any collection point not connected by the same letter is significantly different (FDR<0.05). Abbreviations: ADORA1, adenosine A1 receptor; ADBR1 and ADBR3, beta-adrenergic receptors 1 and 3; PDE3B, phosphodiesterase 3B, cGMP-inhibited; PRKACA, protein kinase A catalytic subunit; PRKAR2B, protein kinase A, cAMP-dependent, regulatory subunit, type II, beta.
Figure 6.
Differentially expressed genes encoding representative proteins involved in lipolysis or fatty acid transport in BAT.
Error bars represent standard error of the mean. Transcript levels for all genes shown have an FDR<0.05. The letters above each bar represent post hoc pair-wise comparisons to determine significance between collection points. Any collection point not connected by the same letter is significantly different (FDR<0.05). Abbreviations: CPT1A, carnitine palmitoyltransferase 1A; FABP3, fatty acid binding protein 3; PLIN2 and PLIN4, perilipin 2 and 4; PNPLA2, patatin-like phospholipase domain containing protein 2; SLC25A20, mitochondrial carnitine/acylcarnitine translocase.
Figure 7.
Model highlighting differentially expressed genes involved in fuel utilization and heat generation in BAT during hibernation.
The role of the gene products in various metabolic processes in a brown adipocyte is shown. Genes with abbreviations in red meet the criteria for differential expression showing highest mRNA levels during the hibernation phases of torpor or interbout arousal. Abbreviations of genes that are not differentially expressed but are highly expressed, and/or tissue-specific genes in BAT, are shown in black. Molecules that serve as sources of fuel are labeled in green. Gene name abbreviations are defined in Table S1. Abbreviations: Ad, adenosine; NE, norepinepherine; NEFA, non-esterified fatty acids; TAG, triacylglycerol.
Figure 8.
Differentially expressed genes encoding BAT transcription factor/regulator mRNAs that are low in torpor.
Error bars represent standard error of the mean. Transcript levels for all genes shown have an FDR<0.05. The letters above each bar represent post hoc pair-wise comparisons to determine significance between collection points. Any collection point not connected by the same letter is significantly different (FDR<0.05). Abbreviations: BHLHE40, class E basic helix-loop-helix protein 40; EGR1, early growth response 1; FOS, FBJ murine osteosarcoma viral oncogene homolog; NFIL3, nuclear factor, interleukin 3 regulated; NR4A1, nuclear receptor subfamily 4, group A, member 1; SIK1, salt-inducible kinase 1.
Figure 9.
Differentially expressed genes with very high expression in April compared to all other collection points.
Error bars represent standard error of the mean. Transcript levels for all genes shown have an FDR<0.05. The letters above each bar represent post hoc pair-wise comparisons to determine significance between collection points. Any collection point not connected by the same letter is significantly different (FDR<0.05). Abbreviations: ALDH1A1 aldehyde dehydrogenase 1 family member A1; ASS1, argininosuccinate synthase 1; CCDC80, coiled-coil domain-containing protein 80; GSTM5 glutathione S-transferase mu 5; IGFBP5, insulin-like growth factor binding protein 5; NNAT, neuronatin.