No abstract

The objective of the current research was to investigate the pattern of subcutaneous adipose tissue growth during Peking duck (Anas platyrhynchos) early development and to determine the reasons for regional differences. The morphological characteristics in 5 regions of subcutaneous tissue, including the neck area (NSF), chest area (CSF), lower abdomen area (ASF), back area (BSF), and leg area (LSF), were analyzed by comparing the morphology of the sections, adipocyte volume and number, and lipid content from wk 1 to 8. Moreover, the mRNA expression of several molecular marker genes, including 47-kDa tail interacting protein (TIP47), adipose differentiation-related protein (ADRP), and perilipin, were detected from wk 1 to 8 using quantitative real-time PCR. Our results revealed that the average cell number declined greatly as fattening proceeded (except in the NSF) and changed very little after wk 4 in all 5 regions. In contrast, the average cell volume and triglyceride content per cell increased gradually during early duck growth. The BSF and LSF lipid content had a different pattern of change than the other regions. The NSF, CSF, and ASF regions had the highest lipid content values at all stages, the BSF was intermediate, and the LSF was the lowest at all weeks except wk 3. The highest TIP47 expression level was found in the NSF from wk 1 to 2 and BSF at wk 1. The relative expression level of TIP47 was higher in the CSF than in the ASF and BSF at wk 4, and was higher in the NSF than in the ASF at wk 6. The highest levels of ADRP and perilipin were detected in the LSF. These results suggest that a combination of adipocyte hyperplasia and hypertrophy is mainly responsible for the development of duck adipose tissue before wk 4, after which adipose expansion is accomplished by adipocyte hypertrophy only. Adipocyte hyperplastic and hypertrophic capacity, fat storage capacity, and metabolic activity may be partial explanations for the regional differences during duck growth.

Low-density lipoprotein receptor-related protein 8 (LRP8) is a member of the low-density lipoprotein receptor gene family that functions in body lipoprotein homeostasis. In this study, reverse transcription-polymerase chain reaction, rapid amplification of cDNA ends, and real-time PCR were performed to characterize the duck LRP8 gene. The cDNA of duck LRP8 contained a 14-bp 5' UTR, a 2754-bp open reading frame, and a 189-bp 3' UTR. The duck LRP8 encoded a protein of 917 amino acid residues composed of five functional domains and resembling other members of the LDLR family, and it displayed high nucleotide and amino acid homology to the LRP8 sequences in other avian species. The mRNA expression level of LRP8 was greater in duck extra-hepatic adipose tissue than in the liver. The peak expression values of LRP8 in both liver and adipose tissues occurred at week 1 and were significantly higher than the values observed during any other week (p < 0.05). Differences in the expression patterns of LRP8 mRNA from weeks 2 to 8 of growth were observed in different organs. A consistent low expression was observed in the liver, and fluctuating expression was observed in the subcutaneous adipose tissue (up- and then down-regulated) and abdominal adipose tissue (down-, then up-, then down-regulated). These findings suggest that LRP8 might play more important roles in regulating lipid metabolism in extra-hepatic adipose tissues than in the liver during early growth after hatching in the duck.

TLR4 is a member of the toll-like receptor family and can recognize lipopolysaccharide (LPS), the main component of gram-negative bacteria. To investigate how TLR4 responds to LPS, the TLR4 transcription levels in duck liver, spleen and bursa of Fabricius were examined after a model for immune stress was implemented through LPS injection in Peking ducks. The results from this assay suggested that LPS injection significantly increased the concentration of tumor necrosis factor-α (TNF-α) in bursa of Fabricius (P<0.05), along with an increase in the concentrations of immunoglobulin-G (IgG) and interleukin-12 (IL-12) in the serum of ducks at 1 day and 7 days after LPS injection (P<0.05). However, there were no apparent changes in organ index or the relative expression of TLR4 and IgM (P>0.05). Furthermore, correlation analysis showed a positive relationship between the mRNA expression of TLR4 and concentrations of TNF-α and IL-12. These results revealed that although there were no significant effects of LPS injection on TLR4 mRNA expression in lymphoid organs, the response to LPS may not mainly rely on the transcription of TLR4, and the downstream molecular response in the immune system may contribute more to the TLR4 signaling cascade.

Angiopoietin-like protein 3 and -4 (ANGPTL-3 and -4) are generally related to lipid metabolism as well as angiogenesis in animals, however very less was known about their mRNA expression characterizations in tissue development. In this study, the mRNA expressions of ANGPTL-3 and ANGPTL-4 (ANGPTL-3 and -4) and tissue distribution in Peking duck (Anas platyrhynchos) of 1 to 8 weeks of age were analyzed using quantitative real-time PCR methods. It was observed that ANGPTL-3 and -4 mRNAs were broadly expressed in duck liver and adipose tissues and were most abundant in intra-abdominal adipose tissue (AD). ANGPTL-3 and -4 had different expression patterns in tissues. These data suggested that both duck ANGPTL-3 and -4 could be related to the development of tissues, and ANGPTL-4 may contribute to the development of adipose tissue through promoting adipocyte differentiation.