Influence of torpor on cardiac expression of genes involved in the circadian clock and protein turnover in the Siberian hamster (Phodopus sungorus).

The Siberian hamster exhibits the key winter adaptive strategy of daily torpor, during which metabolism and heart rate are slowed for a few hours and body temperature declines by up to 20 degrees C, allowing substantial energetic savings. Previous studies of hibernators in which temperature drops by >30 degrees C for many days to weeks have revealed decreased transcription and translation during hypometabolism and identified several key physiological pathways involved. Here we used a cDNA microarray to define cardiac transcript changes over the course of a daily torpor bout and return to normothermia, and we show that, in common with hibernators, a relatively small proportion of the transcriptome (<5%) exhibited altered expression over a torpor bout. Pathways exhibiting significantly altered gene expression included transcriptional regulation, RNA stability and translational control, globin regulation, and cardiomyocyte function. Remarkably, gene representatives of the entire ubiquitylation pathway were significantly altered over the torpor bout, implying a key role for cardiac protein turnover and translation during a low-temperature torpor bout. The circadian clock maintained rhythmic transcription during torpor. Quantitative PCR profiling of heart, liver, and lung and in situ hybridization studies of clock genes in the hypothalamic circadian clock in the suprachiasmatic nucleus revealed that many circadian regulated transcripts exhibited synchronous alteration in expression during arousal. Our data highlight the potential importance of genes involved in protein turnover as part of the adaptive strategy of low-temperature torpor in a seasonal mammal.

Components of litter size in gilts with different prolactin receptor genotypes.

Behavioral estrus and components of litter size at Day 35/36 of pregnancy were studied in gilts with prolactin receptor (PRLR) genotype AA (n=9), AB (n=25), and BB (n=22). This PRLR polymorphism (two alleles, A and B) has been associated with litter size, although it is not known whether the polymorphism itself causes differences in litter size or whether it is a marker for a closely linked causative gene. Estrus length in three successive estrous cycles was not affected by genotype, but estrous cycle length tended (P<0.1) to be longer for AA gilts compared to AB and BB gilts. AA gilts had a significantly (P<0.05) higher ovulation rate (21.5+/-0.9) than BB gilts (18.7+/-0.6), resulting in a numerically higher number of embryos at Day 35/36 (17.0+/-1.3, 15.6+/-0.8, and 13.7+/-0.9 for AA, AB, and BB gilts, respectively) which may lead to a subsequent difference in litter size. Ovulation rate of AB gilts (20.0+/-0.5) was intermediate. Genotype affected the total weight of the ovaries (P<0.05). Even after subtraction of the total weight of corpora lutea, ovarian weight in AA gilts was highest (16.6+/-1.0 g), in BB lowest (13.4+/-0.6g), and in AB gilts intermediate (15.0+/-0.6g; P<0.05). Unlike AB gilts, in AA and BB gilts uterine length was adapted to litter size, which led to longer (P<0.05) uteri for AA gilts (669+/-28 cm) compared to BB gilts (566+/-18 cm). Furthermore, embryos of AA gilts had heavier placentae (52.5+/-3.4 g) and larger implantation surface areas (309+/-19 cm(2)) than embryos of BB (42.0+/-2.3g, P<0.05; 256+/-12 cm(2), P<0.1) or AB (43.2+/-2.0 g, P<0.1; 257+/-11 cm(2), P<0.05) gilts. Results of this experiment show that the PRLR gene or a very closely linked gene affects porcine ovaries, uterus, and placenta in a way that might lead to differences in litter size. Since other genes and also environmental factors, however, might change the effect within the 112 days to parturition, it is preferable to state that the PRLR gene is a candidate gene for ovulation rate rather than for litter size.