Cloning and expression of the porcineobesegene

Board-invited review: the biology and regulation of preadipocytes and adipocytes in meat animals

The quality and value of the carcass in domestic meat animals are reflected in its protein and fat content. Preadipocytes and adipocytes are important in establishing the overall fatness of a carcass, as well as being the main contributors to the marbling component needed for consumer preference of meat products. Although some fat accumulation is essential, any excess fat that is deposited into adipose depots other than the marbling fraction is energetically unfavorable and reduces efficiency of production. Hence, this review is focused on current knowledge about the biology and regulation of the important cells of adipose tissue: preadipocytes and adipocytes.

Effect of Acute Administration of Recombinant Human Leptin during the Neonatal Period on Body Temperature and Endocrine Profile of the Piglet

BACKGROUND

Leptin is produced predominantly by white adipocytes; in adults it regulates appetite and energy expenditure but its role in the neonate remains to be fully established.

OBJECTIVES

To examine the effects of acute administration of recombinant human leptin on the endocrine profile and thermoregulation of neonatal pigs.

METHODS

24 pairs of siblings (n = 48) were administered with either a single dose (4 microg ml(-1) kg(-1) body weight) of leptin (L: n = 24) or a placebo (P: n = 24) on day 6 of neonatal life. Rectal temperature was recorded, and tissue samples were taken at 1 (n = 12), 2 (n = 12), 4 (n = 12) or 6 (n = 12) hours post-administration. Plasma concentrations of hormones and metabolites were determined in conjunction with messenger RNA (mRNA) for leptin and uncoupling protein-2.

RESULTS

Plasma leptin increased following leptin administration, and differences in concentrations of insulin, thyroxine and non-esterified fatty acids were observed between the two groups. Initially, rectal temperature decreased in L pigs but returned to start values by 1.5 h. This decline in rectal temperature was delayed in placebo animals, resulting in differences between treatments at 1.5 and 2 h.

CONCLUSIONS

Acute leptin administration alters the endocrine profile of pigs and influences the thermoregulatory ability of the neonate.

Adipocytes, myofibers, and cytokine biology: new horizons in the regulation of growth and body composition

Muscle growth in meat animals is a complex process governed by integrated signals emanating from multiple endocrine and immune cells. A generalized phenomenon among meat animal industries is that animals commonly fail to meet their genetic potential for growth in commercial production settings. Therefore, understanding the impact of stress and disease on muscle growth is essential to improving production efficiency. The adipocyte in particular seems to be well positioned as an interface between energy status and immune function, and may thus influence nutrient partitioning and growth through a combination of signals that influence fat metabolism, glucose uptake, and insulin sensitivity. Adipocytes and myofibers are active participants in the innate immune response, and as such, produce a number of metabolic regulators, including leptin, adiponectin, and proinflammatory cytokines. Specifically, adipocytes and muscle cells respond directly to bacterial lipopolysaccharide (LPS) by producing interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNFalpha). However, adipocytes are also the predominant source of the antiinflammatory hormone adiponectin, which regulates the nuclear factor kappa-B transcription factor. The ability to recognize antigens and produce regulatory molecules strategically positions adipocytes and myofibers to regulate growth locally, and to reciprocally regulate metabolism peripherally.

Associations of leptin gene polymorphisms with production traits in pigs

The associations of leptin (LEP) gene polymorphisms C798T, T2411C, T3266G and T3469C with production traits were investigated in a F2 pig population produced by divergent crosses. The statistical model included genotype, sex, batch and genotype by sex interaction as fixed effects and sire as random effect. Polymorphism C798T was associated with variation in total teat number (p < 0.02) and left teat number (p < 0.03), and polymorphism T3469C was associated with weight at 21 days (p < 0.03), 42 days (p < 0.05), 63 days (p < 0.02) and 77 days of age (p < 0.04) as well as feed intake (p < 0.01), average daily gain (p < 0.01), feed conversion (p < 0.01), bacon depth (p < 0.03) and slaughter weight (p < 0.03). Phenotypic associations were also performed by combining T3469C and C798T genotypes. Interaction between C798T genotypes and sex was observed for some traits. LEP genotypes had significant influence on performance traits, and can be considered as potential genetic markers for selection. However, these results have to be validated in commercial herds.

Effect of the polymorphism of prolactin receptor (PRLR) and leptin (LEP) genes on litter size in Polish pigs

The aim of the experiment was to use the DNA mutations in the PRLR and LEP genes to determine associations between the genotype and litter size in Polish Large White x Landrace sows. Reproductive traits investigated were: total number of piglets born (TNB), number of piglets born alive (NBA) and number of piglets weaned. The polymorphism in PRLR and LEP genes was detected using the polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) method, with specific primers and the restriction enzymes AluI and HinfI respectively. Two different alleles of PRLR and LEP gene were identified: alleles A (0.62) and B (0.38) of the PRLR gene and alleles C (0.10) and T (0.90) of the LEP gene. The relationships between the PRLR and LEP genotypes and TBN, NBA and NW were analysed. The analysis showed, in first parity sows, statistically significant (p < or = 0.01) differences between sows carrying different PRLR genotypes. In later parities, sows with the AA genotype still had the largest litter size compared with AB and BB sows, but the difference was statistically not significant. Analysis of the interaction PARITY x PRLR showed small and statistically not significant differences. The analysis of relationship between different LEP genotypes and TNB, NBA, NW showed small and statistically non-significant differences.

Novos polimorfismos no gene da obesidade em raças divergentes de suínos

Investigou-se a existência de polimorfismo no gene da leptina (gene da obesidade) entre varrões da raça nativa Piau (porco tipo banha) e matrizes mestiças de raças comerciais (Landrace/Large White e Landrace/Large White com Pietrain), selecionadas para peso e precocidade. Oito pares de primers foram desenhados a partir da seqüência disponível no GenBank (U66254), usada, neste trabalho, como seqüência de referência. Amostras de DNA foram extraídas de células sangüíneas brancas utilizando-se solução de fenol:clorofórmio, após tratamento com proteinase K. Os fragmentos gerados por amplificação da reação em cadeia da polimerase foram purificados e seqüenciados em seqüenciador automático. As seqüências de nucleotídeos, obtidas a partir do DNA das raças comerciais de suíno, apresentaram maior similaridade com a seqüência de referência, e as seqüências geradas a partir do DNA dos animais nativos divergiram de ambas em algumas posições. Dos 28 polimorfismos encontrados, oito foram observados em apenas uma das três seqüências geradas a partir do DNA das raças nativas. Doze estavam presentes em duas seqüências, e os oito polimorfismos restantes foram encontrados nos três animais nativos.

Influence of nutrient intake and body fat on concentrations of insulin-like growth factor-I, insulin, thyroxine, and leptin in plasma of gestating beef cows1

Pregnant Angus x Hereford cows (n = 73) were used to determine the effects of amount of nutrient intake and BCS on concentrations of IGF-I, insulin, leptin, and thyroxine in plasma. At 2 to 4 mo of gestation, cows were blocked by BCS and assigned to one of four nutritional treatments: high (H = a 50% concentrate diet fed ad libitum in a drylot) or adequate native grass pastures and one of three amounts of a 40% CP supplement each day (M = moderate, 1.6 kg; L = low, 1.1 kg; or VL = very low, 0.5 kg; as-fed basis). After 110 d of treatment, all cows grazed dormant native grass pasture and received 1.6 kg/d of a 40% CP supplement. At 68, 109, and 123 d of treatment, cows were gathered, and plasma samples were collected by tail venipuncture (fed sample). After 18 h without feed and water, a second plasma sample was collected (fasted sample). At 109 d of treatment, BCS was greatest (P < 0.05) for H cows, similar for M and L cows, and least for VL cows. Concentrations of insulin and leptin were greater (P < 0.05) for H cows than for M and VL cows at 68 and 109 d, but similar for all groups at 123 d. Thyroxine in plasma was greatest (P < 0.05) for H cows at 68 d and similar for cows on all treatments at 123 d. Concentrations of IGF-I, insulin, and leptin in fed and fasted cows were positively correlated with BCS at 109 d. Body condition was predictive of concentrations of IGF-I, insulin, and leptin when cows had different nutrient intakes, but BCS accounted for less than 12% of the variation in plasma concentrations of IGF-I, insulin, and leptin when nutrient intake was the same for all cows. We conclude that amount of nutrient intake has a greater influence than body energy reserves on IGF-I, insulin, and leptin concentrations in the plasma of gestating beef cows.

Effect of Administration of Recombinant Human Leptin during the Neonatal Period on the Plasma Concentration and Gene Expression of Leptin in the Piglet

Leptin is produced predominantly by white adipocytes and in adults it regulates both appetite and energy expenditure but its role in the neonate remains to be fully established. The aim of this, the first study of leptin administration to Meishan piglets, was to examine the effects of chronic leptin administration to neonatal pigs on their endocrine profile, growth and development. Six Meishan sows gave birth normally at term and 6 pairs of siblings (n = 12), matched by birth weight and gender (male, n = 6; female, n = 6) were randomly allocated to leptin (L: n = 6) or placebo (P: n = 6) administration groups. Piglets remained with their mother throughout the study and from day 3 to 8 of neonatal life each pig received either 4 microg ml(-1) kg(-1) body weight recombinant human leptin or a saline placebo. Plasma concentrations of key hormones and metabolites were determined in conjunction with messenger RNA (mRNA) for leptin, which was assessed by PCR. Recombinant leptin treatment improved growth performance and promoted skeletal growth in favour of adipose tissue accretion. Circulating plasma leptin concentrations were higher on days 4 and 7 in L pigs. Leptin administration altered the endocrine profile of the neonatal pig, although these changes were not maintained. There were no relationships between plasma leptin and body weight or mRNA leptin abundance, irrespective of treatment. Chronic leptin administration appeared to have a beneficial influence on growth rate and body conformation, which may in part be attributed to alterations in metabolism and nutrient partitioning.

A new mutation in the coding region of the bovine leptin gene associated with feed intake

An experimental cattle population was screened for polymorphisms in the leptin gene and five SNPs were found in the regions containing the coding sequences. The association of these polymorphisms with feed intake and fat-related traits was evaluated. The results suggest an association between a polymorphism in exon 2, described here for the first time, and feed intake. Individuals with genotype A/T at this position had 19% greater mean feed intake than individuals with genotype A/A. There was also evidence for a link between leptin haplotypes and some fat-related traits.

Nutritionally induced adipose hypertrophy in young pigs is transient and independent of changes in the expression of the obese and peroxisome proliferator activated receptor genes

Previous studies have shown that piglets weaned to a liquid milk replacer (MR), rather than a typical dry diet (DD) regimen, have improved growth rates and deposit more energy as body fat. In the present study, we used this model to determine whether changes in the expression of genes linked to the regulation of adiposity were related to the accelerated fat accretion. We also determined whether the increase in body fat was sustained throughout a substantial proportion of the growth curve. At weaning (19 plus minus 2 days of age), 96 piglets were placed in 12 replicate pens per diet (4 pigs per pen, 2 barrows and 2 gilts), and fed a liquid MR or conventional DD regimen for 5 weeks. Thereafter, 6 barrows and 6 gilts pigs from each diet were killed for determination of whole body chemical composition (less gastrointestinal contents). The remaining pigs were assigned randomly to weight target groups (60, 85, and 110 kg), placed in individual pens, and fed a conventional dietary regimen until killed at their respective weight targets for tissue sampling and determination of whole body chemical composition. Over the 5-week period in which the MR was fed, the growth rate of the pigs consuming the MR exceeded that of the pigs fed the DD by 36% (P <.05). Fat gain in these pigs was increased to 1.8 times that of the pigs fed the DD, and percentage body fat was 45% greater (P <.05). Acetyl Co-A carboxylase (ACC) activity (per mg of adipose extract protein) was not different between the two diet groups at the conclusion of the 5-week period, or at 110 kg body weight. During the MR period, actual protein gain was increased (P <.05) 22% in the pigs fed the MR as well. By 110 kg of body weight, body fat was reduced (P <.05) by 7.7% (total fat mass) and 8.3% (percentage of body weight basis) in the pigs fed MR vs. the DD group. The expression of the peroxisome proliferator activated receptors (PPAR) alpha and gamma was not influenced by diet or by body weight. Expression of the obese gene was independent of diet, but was greater (P <.09) in pigs at 110 kg body weight than at 60 kg. These data provide additional evidence that piglets weaned to liquid diets have greater rates of growth and deposit more body fat, but that this difference subsides quickly when a typical dry dietary regimen is imposed. Furthermore, the biochemical changes responsible for the increased adiposity are independent of changes in the expression of the obese or PPAR genes, at least at the mRNA level.

Leptin and the regulation of food intake, energy homeostasis and immunity with special focus on periparturient ruminants

The biology of leptin has been studied most extensively in rodents and in humans. Leptin is involved in the regulation of food intake, energy homeostasis and immunity. Leptin is primarily produced in white adipose tissue and acts via a family of membrane bound receptors, including an isoform with a long intracellular domain (OB-Rb), and many isoforms with short intracellular domains (Ob-Rs). OB-Rb is predominantly expressed in the hypothalamic regions involved in the regulation of food intake and energy homeostasis. The other isoforms are distributed ubiquitously and are found in most peripheral tissues in far greater abundance than OB-Rb. The effects of leptin on food intake and energy homeostasis are central and are mediated via a network of orexigenic neuropeptides (neuropeptide Y, galanin, galanin-like peptide, melanin-concentrating hormone, orexins, agouti-related peptide) and anorexigenic neuropeptides (corticotropin-releasing hormone, pro-opiomelanocortin, alpha-melanocyte stimulating hormone and cocaine- and amphetamine-regulated transcript). In addition, leptin acts directly on immune cells to stimulate hematopoesis, T-cell immunity, phagocytosis, cytokine production, and to attenuate susceptibility to infectious insults. Emerging data in ruminants suggest that leptin is dynamically regulated by many factors and physiological states. Thus, leptin is secreted in a pulsatile fashion, but without a marked diurnal rhythm. A positive relationship between adiposity and plasma leptin concentration exists in growing and lactating ruminants. The concentration of plasma leptin increases during pregnancy, starts to decline 1--2 wk before parturition, and reaches a nadir in early lactation. The reduction of plasma leptin at parturition is likely to promote centrally mediated adaptations required in periods of energy deficit, but could have negative effects on immune cell function. Future research is needed in ruminants to address the roles played by leptin and the central nervous system in orchestrating metabolism during the periparturient period and during infectious diseases.

Characterization of swine leptin (LEP) polymorphisms and their association with production traits

Four polymorphisms in the swine leptin (LEP) gene were characterized and evaluated for association with economically important production traits in Yorkshire, Landrace and Duroc pigs. Our results show that these polymorphisms are generally of low frequency or are absent in pig populations. Two polymorphisms (A2845T and T3469C) may be associated (P < 0.0078) with feed intake and growth rate traits in Landrace pigs.

Porcine leptin receptor: molecular structure and expression in the ovary

The porcine leptin receptor complementary DNA was cloned and sequenced and the leptin receptor gene expression evaluated in the porcine ovary. An open reading frame of 3498 nt cDNA was amplified from pig liver mRNA by RT-PCR. Sequence homology with the extracellular, transmembrane, and cytoplasmic domains of human, mouse, rat, sheep, and cow leptin receptors varied between 45% and 90%. Leptin receptor mRNA was present in porcine kidney, liver, spleen, lung, brain, testis, uterus, ovary, corpus luteum (CL), theca, and granulosa cells. The abundance of leptin receptor transcripts and protein varied during luteinization of granulosa cells in vitro and in the CL during the pig luteal phase. In the postovulatory CL, both mRNA and protein were low but detectable, maximal expression was observed in the midcycle CL, and lowest abundance occurred in regressed CL. Leptin receptor mRNA was present in granulosa cells at isolation and increased in abundance as the cells luteinized over 96 hr in culture. Leptin receptor protein was detectable after 12 hr of in vitro luteinization. We conclude that leptin receptor is expressed in granulosa and luteal cells, and varies during pig ovarian cell differentiation.

Expression of porcine adipocyte transcripts during differentiation in vitro and in vivo

Transcript concentrations for the transcription factors, CCAAT enhancer binding protein beta and alpha (C/EBPbeta and C/EBPalpha), plus the adipocyte-characteristic proteins, fatty acid synthase (FAS), glucose transporter 4 (Glut 4), hormone-sensitive lipase (HSL), insulin receptor (InsR), lipoprotein lipase (LPL), and leptin were measured during differentiation of porcine stromal-vascular (S/V) cells in vitro. These same transcripts, excluding FAS and InsR, were measured in porcine adipose tissue from birth to 7 weeks of age. In S/V cells, C/EBPbeta and InsR were continuously elevated. At day 0, C/EBPalpha was approximately 20% of the day 9 value. The LPL increased gradually from day 0 to 9, whereas most other transcripts had a lag period of several days. In tissue, C/EBPbeta was substantial at birth and increased gradually. The C/EBPalpha was relatively low at birth and increased at day 17. The LPL and leptin increased continuously. The Glut 4 was low at birth and increased at day 28. The HSL was relatively low at birth, increased at day 10, and plateaued at day 28. Transcripts in porcine S/V cells develop somewhat differently from adipocyte differentiation models established in clonal cells, but the porcine cells represent a model that should be more applicable to pigs.

Integration of metabolism and intake regulation: a review focusing on periparturient animals

There has been great interest in dry matter intake regulation in lactating dairy cattle to enhance performance and improve animal health and welfare. Predicting voluntary dry matter intake (VDMI) is complex and influenced by numerous factors relating to the diet, management, housing, environment and the animal. The objective of this review is to identify and discuss important metabolic factors involved in the regulation of VDMI and their integration with metabolism. We have described the adaptations of intake and metabolism and discussed mechanisms of intake regulation. Furthermore we have reviewed selected metabolic signals involved in intake regulation. A substantial dip in VDMI is initiated in late pregnancy and continues into early lactation. This dip has traditionally been interpreted as caused by physical constraints, but this role is most likely overemphasized. The dip in intake coincides with changes in reproductive status, fat mass, and metabolic changes in support of lactation, and we have described metabolic signals that may play an equally important role in intake regulation. These signals include nutrients, metabolites, reproductive hormones, stress hormones, leptin, insulin, gut peptides, cytokines, and neuropeptides such as neuropeptide Y, galanin, and corticotrophin-releasing factor. The involvement of these signals in the periparturient dip in intake is discussed, and evidence supporting the integration of the regulation of intake and metabolism is presented. Still, much research is needed to clarify the complex regulation of VDMI in lactating dairy cows, particularly in the periparturient animal.

Physiological response to acute endotoxemia in swine: effect of genotype on energy metabolites and leptin

Certain high lean gain swine genotypes have greater sensitivity to pathogen and nonpathogen stressors evident by reduced productivity and increased mortality during disease stress or in suboptimal production environments. Saline (control) and an immunologic challenge (LPS; 25 microg lipopolysaccharide/kg BW) were administered to three genetic populations (each pig used as its own control): high lean (H), moderate lean terminal cross (MT), and moderate lean maternal cross (MM). LPS induced anorexia, and significantly increased body temperature and circulating TNF-alpha, cortisol, and NEFA in all genotypes (P < 0.0004). LPS reduced circulating glucose, insulin, and IGF-1 in all genotypes (P < 0.05). The LPS-induced hypoglycemia was significantly greater in MM versus MT and H pigs (P < 0.03). The hypoinsulinemia was significantly greater in MM versus H pigs (P < 0.02). MM pigs recovered from hypoinsulinemia slower than MT pigs (P < 0.03). Control insulin was higher in H versus MT pigs (P < 0.08), but relative to basal, the insulin response to LPS was similar. Plasma haptoglobin response to LPS was lower for MM versus MT and H pigs (P < 0.02), and tended to be lower in MT versus H pigs (P < 0.09). LPS treatment caused similar decreases in plasma IGF-1 concentrations among genotypes. Ten hours after LPS treatment, leptin mRNA abundance in adipose tissue was significantly reduced (relative to control) in MM and H pigs (P < 0.02) but not in MT pigs (P > 0.05). Physiological differences in leptin, a potent regulator of food intake and energy metabolism, may be important factors in the genetic variation in sensitivity to environmental stress.

Leptin expression is reduced with acute endotoxemia in the pig: correlation with glucose, insulin, and insulin-like growth factor-1 (IGF-1)

Leptin has been implicated in the regulation of anorexia associated with cachexia in rodents and humans. Regulation of leptin expression is under complex endocrine and metabolic control. To determine if leptin expression is regulated by acute inflammation and to define the endocrine and metabolic factor(s) that regulates leptin expression during acute inflammation, castrate male pigs (ad libitum fed, used as their own controls) were treated with saline (control period) and endotoxin (lipopolysaccharide [LPS] period). Frequent blood samples were collected to identify dynamic changes in hormones and metabolites that are known to regulate leptin expression. LPS caused fever and elevated plasma cortisol (p < 0.0004), tumor necrosis factor-alpha (TNF-alpha) (p < 0.0001), and plasma nonesterified fatty acids (NEFA) (p < 0.001) compared with control. Circulating insulin (p < 0.01), glucose (p < 0.003), and insulin-like growth factor-1 (IGF-1) (p < 0.0001), as well as adipose leptin mRNA abundance (p < 0.01), were profoundly reduced following LPS treatment compared with control. Our data indicate that during acute endotoxemia (1-10 h after injection), leptin gene expression is decreased compared with ad libitum fed animals and is more closely related to energy homeostasis than cytokine profiles in plasma.

Expression of leptin mRNA and CCAAT-enhancer binding proteins in response to insulin deprivation during preadipocyte differentiation in primary cultures of porcine stromal-vascular cells

The aim of this study was to examine the correlation between CCAAT-enhancer binding proteins (C/EBPs) and leptin gene expression in response to insulin deprivation in preadipocytes and adipocytes. Adipose tissue from 7 d-old pigs was digested enzymatically and stromal-vascular (S-V) cells were seeded and plated for 3 d in fetal bovine serum (FBS) with dexamethasone (DEX) followed by 6 d (Days 3-9) in serum-free medium with insulin (850 nM or 10 nM), transferrin, and selenium. During FBS+DEX treatment (Days 0-3) a large number of preadipocytes develop with no lipid accretion. In contrast, preadipocyte number does not change with lipid accretion during insulin treatment (Days 3-9). Total RNA and cells were harvested from S-V cultures after periods with and without insulin after FBS+DEX. Northern-blotting and Western blot analysis were used to study leptin mRNA and C/EBP protein expression in cultures, respectively. Insulin deprivation from Days 3-4 reduced leptin mRNA and C/EBP-alpha protein expression. Treatment with 850 nM or 10 nM insulin from Days 3-9 induced leptin mRNA and C/EBP-alpha expression at a similar level. In cultures treated with 10 nM insulin from Days 3-7, leptin and C/EBP-alpha expression were reduced markedly by insulin deprivation from Days 7-9, but were restored by insulin treatment for 6 hr before harvesting. The restoration of leptin expression by insulin was blocked by cycloheximide treatment. However, C/EBP-beta protein levels did not change regardless of insulin deprivation. Insulin deprivation from Days 7-9 in cultures treatedwith 850 nM insulin from Days 3-7 did not influence C/EBP-alpha or leptin mRNA expression, whereas C/EBP-alpha and leptin expression were reduced after treating these cultures with 1.5 uM okadaic acid for 45 min before harvesting on Day 9. However, cycloheximide treatment for 6 hr before harvesting did not reduce leptin mRNA expression. These results suggest that 1) leptin expression is positively correlated with C/EBP-alpha expression, and 2) the maintenance of leptin expression after insulin deprivation in 850 nM insulin-treated cultures on Day 9 may be associated with the presence of C/EBP-alpha expression and/or activation.

The chicken leptin gene: has it been cloned?

The DNA sequence of a chicken leptin gene that shares 95% nucleotide similarity with the mouse leptin sequence has been recently reported (Taouis et al., 1998, Gene 208, 239-242). Experiments have been performed independently in two laboratories to try to confirm this finding. Fourteen PCR primers based on the mouse leptin sequence were designed to amplify the avian leptin gene. Four of the primers were identical to the mouse and published chicken leptin sequences. PCR amplification was carried out on genomic DNA and reverse-transcribed mRNA from the fat, liver, and pancreas of several chicken strains and from the domestic turkey, goose, and Japanese quail. No PCR products sharing close similarity to the mouse leptin sequence were generated from any avian templates. Amplification of mouse leptin sequence was consistently obtained when control mouse templates were used. Northern hybridization using a mouse leptin probe failed to produce a signal with poly(A)+ RNA from chicken fat and liver and from the fat and liver of force-fed geese but a strong signal was obtained from control mouse fat total RNA. Southern hybridization under low stringency washing conditions revealed hybridization of a mouse leptin probe to chicken genomic DNA. Under higher stringency washing conditions, the chicken signal disappeared, while those from control mouse and sheep genomic DNA remained. This suggests that the putative chicken leptin sequence shares less than the 83% nucleotide sequence identity between the mouse and sheep genes. It is concluded that a chicken leptin gene sequence with close sequence similarity to mouse leptin is not present in the chicken genome. Furthermore, mRNA sharing high sequence identity with mouse leptin is not present in the fat or liver of the domestic chicken, turkey, goose, or Japanese quail.

Leptin expression in porcine adipose tissue is not increased by endotoxin but is reduced by growth hormone

The physiologic response to infection includes reductions in tissue concentrations of anabolic growth factors as a means of reducing growth and conserving nutrients for immunologic processes. This repartitioning of nutrients is accompanied by anorexia, which has been linked to increased leptin expression. Furthermore, leptin and growth hormone (GH) concentrations are inversely related, with leptin being required for normal GH release. The objective of this study was to determine if pretreatment with GH would influence endotoxin-induced changes in leptin expression or attenuate endotoxin-induced reductions in serum insulin-like growth factor-1 (IGF-1) and IGF-1 expression in liver and longissimus muscle. In experiment 1, 40 pigs were assigned to four treatments (n = 10 per treatment) arranged as a 2x2 factorial with GH (s.c. injection, 2 mg 1 h before challenge and 2 mg 2 h after challenge) and endotoxin (single i.m. injection, 25 microg/kg body weight) as main effect variables. Pretreatment with GH resulted in a marked increase (p<0.001) in serum GH within 1 h that was sustained throughout the study. Endotoxin challenge reduced (p<0.003) serum IGF-1 independent of GH (GH x endotoxin, p>0.682), and reduced (p<0.05) IGF-1 expression in longissimus muscle but not liver. Leptin mRNA abundance was reduced 56% (p<0.005) by GH but was not affected by endotoxin (p>0.81). In experiment 2, 36 pigs (n = 12 per treatment) were either allowed ad libitum feed consumption with no injection or deprived of feed and injected twice with either saline or endotoxin 24 h apart. Feed deprivation reduced leptin expression (p<0.05). However, endotoxin did not change leptin expression but markedly increased (p<0.05) serum haptoglobin. These data indicate that changes in IGF-1 status in endotoxin-challenged pigs are independent of serum GH and that leptin expression is not increased by endotoxin challenge in the pig. These data also indicate a regulatory linkage between GH and leptin in vivo.

Leptin and its receptors: regulators of whole-body energy homeostasis

Leptin is the adipocyte-specific product of the ob gene. Expression of leptin in fully fed animals reflects adipocyte size and body-fat mass. Leptin signals the status of body energy stores to the brain, where signals emanate to regulate food intake and whole-body energy expenditure. The leptin gene was identified in the leptin-deficient, obese ob/ob mouse by positional cloning techniques. Recently, leptin has been cloned in domestic species including pigs, cattle, and chickens. The leptin receptor has at least five splice variants; the long form of the receptor is primarily expressed in the hypothalamus and is thought to be the predominant signaling isoform. Leptin receptors are members of the cytokine family of receptors and signal via janus-activated kinases (JAK)/signal transducers and activators of transcription (STAT) and mitogen-activated protein kinase (MAPK) pathways. Mutations in the leptin or leptin receptor genes results in morbid obesity, infertility, and insulin resistance in rodents and humans. Leptin regulates food intake and energy expenditure via central and peripheral mechanisms. Leptin receptors are expressed in most tissues, and in vitro evidence suggests that leptin may have direct effects on some tissues such as adipose tissue, the adrenal cortex, and the pancreatic beta-cell. Leptin is thought to influence whole-body glucose homeostasis and insulin action. Studies are underway to determine the role that leptin plays in the biology of domestic animals.

Obese gene expression in porcine adipose tissue is reduced by food deprivation but not by maintenance or submaintenance intake

The relationship between obese gene expression and energy intake was determined in pigs of various body weights. With ad libitum consumption, expression increased (P < 0.001) with body weight from 55 to 163 kg. Obese mRNA relative abundance was correlated with fat mass (r = 0.74, P < 0.0001) and percentage of fat (r = 0.72, P < 0. 0001). Obese expression was also evaluated at 159 kg (initial weight) and ad libitum, maintenance or 23% of maintenance intake for 28 d. Obese mRNA was independent of treatment (P > 0.78) despite considerable weight differences. Obese mRNA abundance was then compared at 136 kg (initial weight) and ad libitum or maintenance intake for 3 or 28 d. Abundance was not influenced by either duration of treatment or intake, despite a small increase (P < 0.01) in serum nonesterified fatty acids (NEFA) and a reduction (P < 0.02) in insulin attributable to maintenance intake. Finally, mRNA abundance was determined at 60 and 136 kg and conditions of food deprivation or ad libitum intake for 3 d. Food deprivation reduced (P < 0.01) serum insulin and increased (4- to 5-fold) NEFA concentrations. Obese mRNA abundance was greater (P < 0.01) in the heavier pigs and was reduced (P < 0.01) by food deprivation. We conclude that obese mRNA abundance in pigs correlates with fat mass and percentage of body fat under conditions of ad libitum intake. Furthermore, obese mRNA abundance is reduced by food deprivation, whereas lesser degrees of intake restriction do not change obese mRNA abundance, even when accompanied by appreciable weight loss.