Abstract
Leptin is the adipocyte-specific product of the obese gene and plays a major role in food intake and energy metabolism. Leptin research was mainly focused on mammalian species, but understanding of leptin and its function in poultry is very poor. In this study, the duck leptin gene was amplified using the reverse transcription-polymerase chain reaction (RT-PCR) from duck liver RNA. The cDNA fragment was inserted into the pET-28a expression vector, and the resulting plasmid was expressed in Escherichia coli BL21 (DE3). Experimental mice were given an intraperitoneal injection of 10 mg/kg leptin dissolved in phosphate buffered saline (PBS), while the control mice were injected with PBS. The effect of leptin on food intake, body weight and fatty deposition in mice was detected. Sequence analysis revealed that duck leptin had a length of 438 nucleotides which encoded a peptide with 146 amino acid residues. The sequence shares highly homology to other animals. The coding sequence of duck leptin was 84 and 86% identical to human and pig leptin nucleotides sequence. Highest identity was with the rat coding sequence (95%). The identity of the amino acid sequence was 84, 82 and 96% respectively compared to that of the human, pig and rat. Results of SDS-PAGE analysis indicated that a fusion protein was specifically expressed in E. coli BL21 (DE3). The purified product was found to be biologically active during tests. Continuous administration of recombinant duck leptin inhibited food intake. Despite the decrease of food intake, leptin significantly induced body weight and fatty deposition. These changes were accompanied by a significant down-secretion of plasma glucose, cholesterol, triglyceride and insulin levels in mice. The observations provide evidence for an inhibitory effect of leptin in the regulation of food intake and for a potential role of duck leptin in the regulation of lipogenesis.
Highlights
IntroductionThe adipocyte-specific product of the obese gene, in the chicken (Taouis et al, 1998; Horev et al, 2000; is a recently discovered (Zhang et al, 1994) peptide Ohkubo et al, 2000)
Leptin shares high conservation in vertebrates (Zhang et al, 1994)
Leptin was initially discovered in mice and is highly conserved in vertebrate species
Summary
The adipocyte-specific product of the obese gene, in the chicken (Taouis et al, 1998; Horev et al, 2000; is a recently discovered (Zhang et al, 1994) peptide Ohkubo et al, 2000). Chicken leptin is not exclusively hormone which regulates food intake Role in the regulation of avian hepatic lipogenesis (Dridi et Leptin is produced and secreted by mammalian adipocytes al., 2005). These observations are thought to be due to the and mediates its central effect through a specific receptor role of the avian liver as the primary source of lipogenesis (Fei et al, 1997; Elmquist et al, 1998), modulating the (Leveille et al, 1968). The decrease in food intake an important signaling factor that reflects body fat level. observed in layer and broiler chickens injected centrally or Leptin research has provided the key to understanding the peripherally with recombinant chicken, ovine or human molecular mechanisms underlying obesity
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