Abundance, efficiency, and stability of reference transcript expression in a seasonal rodent: The Siberian hamster.

Quantitative PCR (qPCR) is a common molecular tool to analyse the expression of transcripts in non-traditional animal models. Most animals experience tissue-specific seasonal changes in cell structure, growth, and cellular function. As a consequence, the choice of reference or 'house-keeping' genes is essential to standardize expression levels of target transcripts of interest for qPCR analyses. This study aimed to determine the abundance, efficiency and stability of several reference genes commonly used for normalisation of qPCR analyses in a model of seasonal biology: the Siberian hamster (Phodopus sungorus). Liver, brown-adipose tissue (BAT), white adipose tissue (WAT), testes, spleen, kidney, the hypothalamic arcuate nucleus, and the pituitary gland from either long or short photoperiod Siberian hamsters were dissected to test tissue-specific and photoperiod effects on reference transcripts. qPCR was conducted for common reference genes including 18s ribosomal RNA (18s), glyceraldehyde 3-phosphate dehydrogenase (Gapdh), hypoxanthine-guanine phosphoribosyltransferase (Hprt), and actin-ß (Act). Cycling time (Ct), efficiency (E) and replicate variation of Ct and E measured by percent coefficient of variance (CV%) was determined using PCR miner. Measures of stability were assessed using a combined approach of NormFinder and BestKeeper. 18s and Act did not vary in Ct across photoperiod conditions. Splenic, WAT and BAT Gapdh Ct was higher in long compared to short photoperiod. Splenic Hprt Ct was higher in long photoperiods. There was no significant effect of photoperiod, tissue or interaction on measures of efficiency, Ct CV%, or efficiency CV%. NormFinder and BestKeeper confirmed that 18s, Gapdh and Hprt were highly stable, while Act showed low stability. These findings suggest that 18s and Hprt show the most reliable stability, efficiency, and abundance across the tissues. Overall, the study provides a comprehensive and standardised approach to assess multiple reference genes in the Siberian hamster and help to inform molecular assays used in studies of photoperiodism.

Transcriptome analyses of nine endocrine tissues identifies organism-wide transcript distribution and structure in the Siberian hamster.

Temperate zone animals exhibit seasonal variation in multiple endocrine systems. In most cases, peripheral organs display robust switches in tissue involution and recrudescence in mass. Our understanding of the molecular control of tissue-specific changes in seasonal function remains limited. Central to this problem is the lack of information on the nucleic acid structure, and distribution of transcripts across tissues in seasonal model organisms. Here we report the transcriptome profile of nine endocrine tissues from Siberian hamsters. Luteinizing hormone receptor expression was localized to gonadal tissues and confirmed previous distribution analyses. Assessment of the prolactin receptor reveal relatively high abundance across tissues involved in reproduction, energy, and water homeostasis. Neither melatonin receptor-1a, nor -1b, were found to be expressed in most tissues. Instead, the closely related G-protein coupled receptor Gpr50 was widely expressed in peripheral tissues. Epigenetic enzymes such as DNA methyltransferase 3a, was widely expressed and the predominant DNA methylation enzyme. Quantitative PCR analyses revealed some sex- and tissue-specific differences for prolactin receptor and DNA methyltransferase 3a expression. These data provide significant information on the distribution of transcripts, relative expression levels and nucleic acid sequences that will facilitate molecular studies into the seasonal programs in mammalian physiology.

The Evolution of Widespread Recombination Suppression on the Dwarf Hamster (Phodopus) X Chromosome.

The X chromosome of therian mammals shows strong conservation among distantly related species, limiting insights into the distinct selective processes that have shaped sex chromosome evolution. We constructed a chromosome-scale de novo genome assembly for the Siberian dwarf hamster (Phodopus sungorus), a species reported to show extensive recombination suppression across an entire arm of the X chromosome. Combining a physical genome assembly based on shotgun and long-range proximity ligation sequencing with a dense genetic map, we detected widespread suppression of female recombination across ∼65% of the Phodopus X chromosome. This region of suppressed recombination likely corresponds to the Xp arm, which has previously been shown to be highly heterochromatic. Using additional sequencing data from two closely related species (P. campbelli and P. roborovskii), we show that recombination suppression on Xp appears to be independent of major structural rearrangements. The suppressed Xp arm was enriched for several transposable element families and de-enriched for genes primarily expressed in placenta, but otherwise showed similar gene densities, expression patterns, and rates of molecular evolution when compared to the recombinant Xq arm. Phodopus Xp gene content and order was also broadly conserved relative to the more distantly related rat X chromosome. These data suggest that widespread suppression of recombination has likely evolved through the transient induction of facultative heterochromatin on the Phodopus Xp arm without major changes in chromosome structure or genetic content. Thus, substantial changes in the recombination landscape have so far had relatively subtle influences on patterns of X-linked molecular evolution in these species.

Comparative transcriptomics of the Djungarian hamster hypothalamus during short photoperiod acclimation and spontaneous torpor.

The energy-saving strategy of Djungarian hamsters (Phodopus sungorus, Cricetidae) to overcome harsh environmental conditions comprises of behavioral, morphological, and physiological adjustments, including spontaneous daily torpor, a metabolic downstate. These acclimatizations are triggered by short photoperiod and orchestrated by the hypothalamus. Key mechanisms of long-term photoperiodic acclimatizations have partly been described, but specific mechanisms that acutely control torpor remain incomplete. Here, we performed comparative transcriptome analysis on hypothalamus of normometabolic hamsters in their summer- and winter-like state to enable us to identify changes in gene expression during photoperiodic acclimations. Comparing nontorpid and torpid hamsters may also be able to pin down mechanisms relevant for torpor control. A de novo assembled transcriptome of the hypothalamus was generated from hamsters acclimated to long photoperiod or to short photoperiod. The hamsters were sampled either during long photoperiod normothermia, short photoperiod normothermia, or short photoperiod-induced spontaneous torpor with a body temperature of 24.6 ± 1.0 °C, or. The mRNA-seq analysis revealed that 32 and 759 genes were differentially expressed during photoperiod or torpor, respectively. Biological processes were not enriched during photoperiodic acclimatization but were during torpor, where transcriptional and metabolic processes were reinforced. Most extremely regulated genes (those genes with |log2(FC)| > 2.0 and padj < 0.05 of a pairwise group comparison) underpinned the role of known key players in photoperiodic comparison, but these genes exhibit adaptive and protective adjustments during torpor. Targeted analyses of genes from potentially involved hypothalamic systems identified gene regulation of previously described torpor-relevant systems and a potential involvement of glucose transport.

Photoperiod regulates hypothalamic miR-155 gene expression in female, but not male, Siberian hamsters (Phodopus sungorus).

In many species, seasonal changes in photoperiod regulate several behaviors and physiological systems, including reproduction, energy balance, and immune function. MicroRNAs (miRs) regulate numerous physiological processes and developmental transitions through translational repression and mRNA degradation. Their role in seasonal transitions has been vastly understudied, with only a few reports in animals. Furthermore, no study has assessed whether there are sex differences in seasonal regulation of miRs. miR-155 is a primary candidate for seasonal regulation because it influences immune responses, energetics, and reproductive function. In this study, we tested the hypothesis that photoperiod regulates miR-155 gene expression in Siberian hamsters and whether there were sex differences in this photoperiod regulation. miR-155 gene expression levels were measured in hypothalamus, hippocampus, and spleen of male and female Siberian hamsters reared in short days (SDs) or long days (LDs). As expected, SD-reared hamsters had significantly reduced body mass, lightened pelage color, and lower reproductive organ size than LD-reared hamsters. Notably, SDs increased hypothalamic miR-155 gene expression in females but not in males. No differences were observed in hippocampus and spleen of either sex. These findings demonstrate sex-specific photoperiod regulation of miR-155 gene expression. Future studies should consider possible sex differences in miR contributions to seasonal changes in physiology and behavior. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Reduced adiposity attenuates FGF21 mediated metabolic improvements in the Siberian hamster.

FGF21 exerts profound metabolic effects in Siberian hamsters exposed to long day (LD) photoperiods that increase appetite and adiposity, however these effects are attenuated in short day (SD) animals that display hypophagia and reduced adiposity. The aim of this study was to investigate whether the beneficial effects of a novel mimetic of FGF21 in the LD state are a consequence of increased adiposity or of the central photoperiodic state. This was achieved by investigating effects of FGF21 in aged hamsters, which is associated with reduced adiposity. In LD hamsters with increased adiposity, FGF21 lowered body weight as a result of both reduced daily food intake and increased caloric expenditure, driven by an increase in whole-body fat oxidation. However, in LD animals with reduced adiposity, the effect of FGF21 on body weight, caloric intake and fat oxidation were significantly attenuated or absent when compared to those with increased adiposity. These attenuated/absent effects were underpinned by the inability of FGF21 to increase the expression of key thermogenic genes in interscapular and visceral WAT. Our study demonstrates the efficacy of a novel FGF21 mimetic in hamsters, but reveals attenuated effects in the animal model where adiposity is reduced naturally independent of photoperiod.

Gene expression analysis and microdialysis suggest hypothalamic triiodothyronine (T3) gates daily torpor in Djungarian hamsters (Phodopus sungorus).

Thyroid hormones play an important role in regulating seasonal adaptations of mammals. Several studies suggested that reduced availability of 3,3',5-triiodothyronine (T3) in the hypothalamus is required for the physiological adaptation to winter in Djungarian hamsters. We have previously shown that T3 is involved in the regulation of daily torpor, but it remains unclear, whether T3 affects torpor by central or peripheral mechanisms. To determine the effect of T3 concentrations within the hypothalamus in regulating daily torpor, we tested the hypothesis that low hypothalamic T3 metabolism would favour torpor and high T3 concentrations would not. In experiment 1 gene expression in torpid hamsters was assessed for transporters carrying thyroid hormones between cerebrospinal fluid and hypothalamic cells and for deiodinases enzymes, activating or inactivating T3 within hypothalamic cells. Gene expression analysis suggests reduced T3 in hypothalamic cells during torpor. In experiment 2, hypothalamic T3 concentrations were altered via microdialysis and torpor behaviour was continuously monitored by implanted body temperature transmitters. Increased T3 concentrations in the hypothalamus reduced expression of torpor as well as torpor bout duration and depth. Subsequent analysis of gene expression in the ependymal layer of the third ventricle showed clear up-regulation of T3 inactivating deiodinase 3 but no changes in several other genes related to photoperiodic adaptations in hamsters. Finally, serum analysis revealed that increased total T3 serum concentrations were not necessary to inhibit torpor expression. Taken together, our results are consistent with the hypothesis that T3 availability within the hypothalamus significantly contributes to the regulation of daily torpor via a central pathway.

Photoperiodic and ovarian steroid regulation of histone deacetylase 1, 2, and 3 in Siberian hamster (Phodopus sungorus) reproductive tissues.

Epigenetic modifications in reproductive tissues have predominantly focused on pathological conditions, such as ovarian and uterine cancers. The contribution of DNA methylation and histone acetylation to the timing and control of fertility is not well described. Siberian hamsters provide an important model to investigate the relatively short-term regulation of fertility (e.g. estrous) as well as long-term timing of breeding (e.g. seasonal). Recent work has shown that DNA methyltransferase 3a (dnmt3a) expression is associated with reproductive involution. Here, the objectives were to identify the impact of photoperiod on hdac1-3 expression in hamster testicular, ovarian and uterine tissue. Then, we assessed the effect of E2P4 and estrous cycling on hdac1-3 expression in uterine tissue. Testicular expression of hdac1 was significantly reduced, whereas hdac3 increased in reproductively photoregressed male hamsters; hdac2 expression did not significantly change across photoperiod conditions. There was no significant photoperiodic effect on ovarian expression of hdac1-3. Uterine expression of hdac3 expression was greater in long day hamsters; exposure to short days significantly reduced uterine hdac2 expression. Ovariectomized hamsters administered a single bolus injection of oil were found to have elevated uterine hdac2 compared to E2P4 treated females 12h and 24h post injection. Uterine hdac1-3 expression was relatively constant across the estrous cycle. Altogether these data indicate tissue-dependent photoperiodic regulation of hdac1-3 expression and that E2P4 may inhibit uterine hdac2 over long-term breeding cycles.

Genomic imprinting, disrupted placental expression, and speciation.

The importance of regulatory incompatibilities to the early stages of speciation remains unclear. Hybrid mammals often show extreme parent-of-origin growth effects that are thought to be a consequence of disrupted genetic imprinting (parent-specific epigenetic gene silencing) during early development. Here, we test the long-standing hypothesis that abnormal hybrid growth reflects disrupted gene expression due to loss of imprinting (LOI) in hybrid placentas, resulting in dosage imbalances between paternal growth factors and maternal growth repressors. We analyzed placental gene expression in reciprocal dwarf hamster hybrids that show extreme parent-of-origin growth effects relative to their parental species. In massively enlarged hybrid placentas, we observed both extensive transgressive expression of growth-related genes and biallelic expression of many genes that were paternally silenced in normal sized hybrids. However, the apparent widespread disruption of paternal silencing was coupled with reduced gene expression levels overall. These patterns are contrary to the predictions of the LOI model and indicate that hybrid misexpression of dosage-sensitive genes is caused by other regulatory mechanisms in this system. Collectively, our results support a central role for disrupted gene expression and imprinting in the evolution of mammalian hybrid inviability, but call into question the generality of the widely invoked LOI model.

Resting Metabolic Rate Is Positively Correlated with Parental Care Behavior in a Dwarf Hamster.

Endotherms maintain high and constant body temperatures through the production and maintenance of metabolic heat. Defining the evolutionary history of these thermal adaptations and the selective factors responsible for the evolution of endothermy despite its high metabolic costs have been elusive and controversial topics in evolutionary biology. In this sense, several models have been proposed to explain the evolution of endothermy. Among them, the parental care model explains the increase in resting metabolic rate (RMR) by the action of natural selection favoring parental care. Thus, a positive relationship between parental care behavior and RMR is predicted. However, there appears to be no or little previous work experimentally testing this relationship. In the study presented here, RMR was increased through l-tyrosine injections and parental care behavior was measured. This treatment allowed us to test the relationship between RMR level and parental care behavior in a dwarf hamster. It was found that increased RMR enhanced male parental care. Specifically, male latency time, or the time until contacting and picking up their pups, decreased when RMR increased. This study demonstrates the positive relationship between RMR and the allocation of resources to parental care. This study supports the main assumption of Kotejas's parental care model and accepts Koteja's proposed explanation for the evolution of endothermy as a plausible hypothesis.

Photoperiod- and Triiodothyronine-dependent Regulation of Reproductive Neuropeptides, Proinflammatory Cytokines, and Peripheral Physiology in Siberian Hamsters (Phodopus sungorus).

Seasonal trade-offs in reproduction and immunity are ubiquitous in nature. The mechanisms that govern transitions across seasonal physiological states appear to involve reciprocal switches in the local synthesis of thyroid hormone. In long-day (LD) summer-like conditions, increased hypothalamic triiodothyronine (T3) stimulates gonadal development. Alternatively, short-day (SD) winter-like conditions increase peripheral leukocytes and enhance multiple aspects of immune function. These data indicate that the localized effects of T3 in the hypothalamus and leukocytes are photoperiod dependent. We tested the hypothesis that increased peripheral T3 in SD conditions would increase aspects of reproductive physiology and inhibit immune function, whereas T3 injections in LD conditions would facilitate aspects of immune function (i.e., leukocytes). In addition, we also examined whether T3 regulates hypothalamic neuropeptide expression as well as hypothalamic and splenic proinflammatory cytokine expression. Adult male Siberian hamsters were maintained in LD (15L:9D) or transferred to SD (9L:15D) for 8 weeks. A subset of LD and SD hamsters was treated daily with 5 µg T3 for 2 weeks. LD and SD controls were injected with saline. Daily T3 administration in SD hamsters (SD+T3) resulted in a rapid and substantial decrease in peripheral leukocyte concentrations and stimulated gonadal development. T3 treatment in LD (LD+T3) had no effect on testicular volumes but significantly increased leukocyte concentrations. Molecular analyses revealed that T3 stimulated interleukin 1ß messenger RNA (mRNA) expression in the spleen and inhibited RFamide Related Peptide-3 mRNA expression in the hypothalamus. Moreover, there was a photoperiod-dependent decrease in splenic tumor necrosis factor-α mRNA expression. These findings reveal that T3 has tissue-specific and photoperiod-dependent regulation of seasonal rhythms in reproduction and immune function.

Continental Refugium in the Mongolian Plateau during Quaternary Glacial Oscillations: Phylogeography and Niche Modelling of the Endemic Desert Hamster, Phodopus roborovskii.

The Mongolian Plateau (MP), which is situated in the interior of Asia and possesses a typical continental climate, experienced harsh climatic conditions during the Quaternary glacial fluctuations. Although these events likely had huge impacts on the local animal populations, the current effects have hardly been explored. To investigate whether the MP supported a refugium along an oceanic-continental gradient (ROCG), and whether this refugium was glacial or interglacial, we investigated the demographic and phylogeographic history of an endemic mammal species, the desert hamster Phodopus roborovskii. We reconstructed the demographic variation, the phylogeographic diffusion, and modelled the potential habitat during historical periods. The genetic diversity in the MP was the highest among all the localities, and the MP was a suitable habitat throughout the modelled historical periods. A phylogeographic diffusion analysis emphasized the importance of the MP as the centre of origin, preservation and spread for P. roborovskii. The homogeneous landscape provided the opportunity for a wide gene flow, which resulted in low resolution of the phylogenetic relationships. Moreover, P. roborovskii was favoured by the interglacial condition, with both its demographical and geographical ranges expanded within the interglacial periods. The range variation from the Last Glacial Maximum to the current condition reflects a distinct longitudinal shift, while both ranges largely contracted from that of the Last Interglacial. Our results support that the MP served as a refugium and spread centre for P. roborovskii during the Quaternary climate fluctuations. The interglacial expansion and the longitudinal shifts highlighted the important effects of precipitations on the distribution range of species adapted to arid and semi-arid during glacial oscillations.

Thyroid hormone status affects expression of daily torpor and gene transcription in Djungarian hamsters (Phodopus sungorus).

Thyroid hormones (TH) play a key role in regulation of seasonal as well as acute changes in metabolism. Djungarian hamsters (Phodopus sungorus) adapt to winter by multiple changes in behaviour and physiology including spontaneous daily torpor, a state of hypometabolism and hypothermia. We investigated effects of systemic TH administration and ablation on the torpor behaviour in Djungarian hamsters adapted to short photoperiod. Hyperthyroidism was induced by giving T4 or T3 and hypothyroidism by giving methimazole (MMI) and sodium perchlorate via drinking water. T3 treatment increased water, food intake and body mass, whereas MMI had the opposite effect. Continuous recording of body temperature revealed that low T3 serum concentrations increased torpor incidence, lowered Tb and duration, whereas high T3 serum concentrations inhibited torpor expression. Gene expression of deiodinases (dio) and uncoupling proteins (ucp) were analysed by qPCR in hypothalamus, brown adipose tissue (BAT) and skeletal muscle. Expression of dio2, the enzyme generating T3 by deiodination of T4, and ucps, involved in thermoregulation, indicated a tissue specific response to treatment. Torpor per se decreased dio2 expression irrespective of treatment or tissue, suggesting low intracellular T3 concentrations during torpor. Down regulation of ucp1 and ucp3 during torpor might be a factor for the inhibition of BAT thermogenesis. Hypothalamic gene expression of neuropeptide Y, propopiomelanocortin and somatostatin, involved in feeding behaviour and energy balance, were not affected by treatment. Taken together our data indicate a strong effect of thyroid hormones on torpor, suggesting that lowered intracellular T3 concentrations in peripheral tissues promote torpor.

The puzzling character of repetitive DNA in Phodopus genomes (Cricetidae, Rodentia).

Three novel repetitive DNA sequences are described, presenting a similar heterochromatic chromosomal location in two hamster species: Phodopus roborovskii and Phodopus sungorus (Cricetidae, Rodentia). Namely, two species-specific repetitive sequences (PROsat from P. roborovskii and PSUchr1sat from P. sungorus) surrounding a third one (PsatDNA), that is shared by both hamster genomes. Fiber-FISH analyses revealed that PROsat intermingles with PsatDNA in P. roborovskii and PSUchr1sat intermingles with PsatDNA in P. sungorus. A model explaining the evolution of this intricate chromosomal distribution is proposed, which can explain better the evolution of these very derivative genomes (in comparison to the ancestral Muroidea). The most plausible evolutionary scenario seems to be the expansion of a number of repeats into other's domain, most probably resulting in its intermingling, followed by the subsequent spread of these complex repeats from a single chromosomal location to other chromosomes. Evidences of an association between repetitive sequences and the chromosome evolution process were observed, namely for PROsat. Most probably, the evolutionary breakpoints that shaped PRO and PSU chromosomes (pericentric inversions and fusions) occurred within the boundaries of PROsat blocks in the ancestor. The repeats high diversity at the heterochromatic regions of Phodopus chromosomes, together with its complex organization, suggests that these species are important models for evolutionary studies, namely in the investigation of a possible relationship between repetitive sequences and the occurrence of chromosomal rearrangements and consequently, in genome evolution.

Abnormal pairing of X and Y sex chromosomes during meiosis I in interspecific hybrids of Phodopus campbelli and P. sungorus.

Hybrid sterility plays an important role in the maintenance of species identity and promotion of speciation. Male interspecific hybrids from crosses between Campbell's dwarf hamster (Phodopus campbelli) and the Djungarian hamster (P. sungorus) exhibit sterility with abnormal spermatogenesis. However, the meiotic phenotype of these hybrids has not been well described. In the present work, we observed the accumulation of spermatocytes and apoptosis of spermatocyte-like cells in the testes of hybrids between P. campbelli females and P. sungorus males. In hybrid spermatocytes, a high frequency of asynapsis of X and Y chromosomes during the pachytene-like stage and dissociation of these chromosomes during metaphase I (MI) was observed. No autosomal univalency was observed during pachytene-like and MI stages in the hybrids; however, a low frequency of synapsis between autosomes and X or Y chromosomes, interlocking and partial synapsis between autosomal pairs, and γ-H2AFX staining in autosomal chromatin was observed during the pachytene-like stage. Degenerated MI-like nuclei were frequently observed in the hybrids. Most of the spermatozoa in hybrid epididymides exhibited head malformation. These results indicate that the pairing of X and Y chromosomes is more adversely affected than that of autosomes in Phodopus hybrids.

Evolutionary story of a satellite DNA from Phodopus sungorus (Rodentia, Cricetidae).

With the goal to contribute for the understanding of satellite DNA evolution and its genomic involvement, in this work it was isolated and characterized the first satellite DNA (PSUcentSat) from Phodopus sungorus (Cricetidae). Physical mapping of this sequence in P. sungorus showed large PSUcentSat arrays located at the heterochromatic (peri)centromeric region of five autosomal pairs and Y-chromosome. The presence of orthologous PSUcentSat sequences in the genomes of other Cricetidae and Muridae rodents was also verified, presenting however, an interspersed chromosomal distribution. This distribution pattern suggests a PSUcentSat-scattered location in an ancestor of Muridae/Cricetidae families, that assumed afterwards, in the descendant genome of P. sungorus a restricted localization to few chromosomes in the (peri)centromeric region. We believe that after the divergence of the studied species, PSUcentSat was most probably highly amplified in the (peri)centromeric region of some chromosome pairs of this hamster by recombinational mechanisms. The bouquet chromosome configuration (prophase I) possibly displays an important role in this selective amplification, providing physical proximity of centromeric regions between chromosomes with similar size and/or morphology. This seems particularly evident for the acrocentric chromosomes of P. sungorus (including the Y-chromosome), all presenting large PSUcentSat arrays at the (peri)centromeric region. The conservation of this sequence in the studied genomes and its (peri)centromeric amplification in P. sungorus strongly suggests functional significance, possibly displaying this satellite family different functions in the different genomes. The verification of PSUcentSat transcriptional activity in normal proliferative cells suggests that its transcription is not stage-limited, as described for some other satellites.

Evidence for species-specific clock gene expression patterns in hamster peripheral tissues.

Rhythmic oscillations that repeat every 24h can be found in numerous behavioral and physiological functions. Beside the endogenous master clock in the suprachiasmatic nucleus (SCN), peripheral oscillators exist that can disengage from the master clock rhythm by different mechanisms. The fact that core clock genes in peripheral tissues do not always have the same characteristics as in the SCN suggests that their function may vary in different organs. Additionally, suggestions about species-specific variation in expression peak and nadir times, especially in the testis, led to the need for systematical investigations on clock gene expression patterns in different organs and species under standardized methodological conditions. Therefore, daily gene expression patterns of the clock genes Bmal1, Period1, Period2, Clock, Cryptochrome1 and Cryptochrome2 were recorded at each of eight time points during a 24 hour period in the testis, kidney, liver, spleen and heart of three hamster species (Phodopus sungorus, Phodopus roborovskii and Cricetulus griseus; family: Cricetidae). Clock gene expression was found to be rhythmic in all investigated organs, however with inconsistent results in the testis. Complex cosinor analysis revealed species differences in temporal gene expression patterns regarding their orthophase, number of peaks, and amplitude for all genes and organs with most pronounced differences in the testis. The results of this study strongly indicate that clock gene expression in peripheral tissues is species-specific and that their functions might be at least partly connected to clock-unrelated traits that vary between the investigated species. Further studies should aim at clarifying the specific roles of clock genes in the testis.

Dim light at night disrupts the short-day response in Siberian hamsters.

Photoperiodic regulation of physiology, morphology, and behavior is crucial for many animals to survive seasonally variable conditions unfavorable for reproduction and survival. The photoperiodic response in mammals is mediated by nocturnal secretion of melatonin under the control of a circadian clock. However, artificial light at night caused by recent urbanization may disrupt the circadian clock, as well as the photoperiodic response by blunting melatonin secretion. Here we examined the effect of dim light at night (dLAN) (5lux of light during the dark phase) on locomotor activity rhythms and short-day regulation of reproduction, body mass, pelage properties, and immune responses of male Siberian hamsters. Short-day animals reduced gonadal and body mass, decreased spermatid nuclei and sperm numbers, molted to a whiter pelage, and increased pelage density compared to long-day animals. However, animals that experienced short days with dLAN did not show these short-day responses. Moreover, short-day specific immune responses were altered in dLAN conditions. The nocturnal activity pattern was blunted in dLAN hamsters, consistent with the observation that dLAN changed expression of the circadian clock gene, Period1. In addition, we demonstrated that expression levels of genes implicated in the photoperiodic response, Mel-1a melatonin receptor, Eyes absent 3, thyroid stimulating hormone receptor, gonadotropin-releasing hormone, and gonadotropin-inhibitory hormone, were higher in dLAN animals than those in short-day animals. These results suggest that dLAN disturbs the circadian clock function and affects the molecular mechanisms of the photoperiodic response.

The involvement of repetitive sequences in the remodelling of karyotypes: the Phodopus genomes (Rodentia, Cricetidae).

In this work we characterize the Phodopus roborovskii and Phodopus sungorus karyotypes, describing the constitutive heterochromatin and the telomeric repeats distribution in these chromosomes. In the two species, (peri)centromeric, interstitial and (sub)telomeric C-bands were revealed, presenting a very high colocalization with evolutionary breakpoint regions identified in these karyotypes. Also both species present telomeric sequences located interstitially (ITS), as short ITS blocks or as large ITS blocks, mainly at the (peri)centromeric heterochromatic regions. The number and degree of ITSs amplification varies greatly in the two hamsters, indicating independent evolutionary events of these repeats in each genome. The combination of the data provided interesting insights about the genome organization of these hamster species, also allowing establishing evolutionary considerations on their chromosomes. The obtained results clearly suggest an involvement of the repetitive genomic fraction in the reshaping of P. roborovskii and P. sungorus karyotypes.

Hypothalamic gene expression rapidly changes in response to photoperiod in juvenile Siberian hamsters (Phodopus sungorus).

Siberian hamsters are seasonal mammals that survive a winter climate by making adaptations in physiology and behaviour. This includes gonadal atrophy, reduced food intake and body weight. The underlying central mechanisms responsible for the physiological adaptations are not fully established but involve reducing hypothalamic tri-iodthyronine (T3) levels. Juvenile Siberian hamsters born or raised in short days (SD) respond in a similar manner, although with an inhibition of gonadal development and growth instead of reversing an established long day (LD) phenotype. Using juvenile male hamsters, the present study aimed to investigate whether the central mechanisms are similar before the establishment of the mature LD phenotype. By in situ hybridisation, we examined the response of genes involved in thyroid hormone (Dio2 and Dio3, which determine hypothalamic T3 levels) and glucose/glutamate metabolism in the ependymal layer, histamine H3 receptor and VGF as representatives of the highly responsive dorsomedial posterior arcuate nucleus (dmpARC), and somatostatin, a hypothalamic neuropeptide involved in regulating the growth axis. Differential gene expression of type 2 and type 3 deiodinase in the ependymal layer, histamine H3 receptor in the dmpARC and somatostatin in the ARC was established by the eighth day in SD. These changes are followed by alterations in glucose metabolism related genes in the ependymal layer by day 16 and increased secretogranin expression in the dmpARC by day 32. In conclusion, our data demonstrate similar but rapid and highly responsive changes in gene expression in the brain of juvenile Siberian hamsters in response to a switch from LD to SD. The data also provide a temporal definition of gene expression changes relative to physiological adaptations of body weight and testicular development and highlight the likely importance of thyroid hormone availability as an early event in the adaptation of physiology to a winter climate in juvenile Siberian hamsters.