The aim of the study was to investigate whether phosphorus (P) transporters, type IIb sodium-dependent phosphate cotransporter (NaP-IIb) and inorganic phosphate transporter 2 (PiT2), were directly involved in P absorption across primary cultured duodenal epithelial cell monolayers of chick embryos.  The siRNAs against NaP-IIb or PiT2 were designed, synthesized and transfected into primary cultured duodenal epithelial cells of chick embryos.  Then, the inhibitory efficiency of siRNAs against NaP-IIb or PiT2 was analyzed, and the most efficacious siRNAs were selected to be used for subsequent P absorption experiments.  Briefly, primary cultured duodenal epithelial cells of chick embryos were transfected with either NaP-IIb or PiT2 siRNAs and grown in confluent monolayers on transwell plates.  The untransfected or transfected cell monolayers were then incubated in an uptake medium containing 0 or 0.25 mmol L^–1 of P as KH₂PO₄ to measure the P absorption across duodenal epithelial cell monolayers.  The results showed that among the siRNAs designed, si-1372 and si-890 were demonstrated to be the most effective in inhibiting the NaP-IIb and PiT2 expressions, respectively.  Supplemental P increased (P=0.065) the protein abundance of PiT2 and enhanced (P<0.0001) P absorption in primary cultured duodenal epithelial cell of chick embryos.  Furthermore, NaP-IIb silencing decreased (P=0.07) P absorption across duodenal epithelial cell monolayers, while PiT2 silencing had no effect (P=0.345).  It is concluded that the NaP-IIb, but not PiT2, might be directly involved in the P absorption of chick duodenal epithelial cells.

Bone marrow mesenchymal stem cells (BMSCs) could differentiate into various cell types including adipocytes and myocytes, which had important scientific significance not only in the field of tissue regeneration, but also in the field of agricultural science. In an attempt to exhibit the characterization and differentiation into adipocytes and myocytes of porcine BMSCs, we isolated and purified porcine BMSCs by red blood cell lysis method and percoll gradient centrifugation. The purified cells presented a stretched fibroblast-like phenotype when adhered to the culture plate. The results of flow cytometry analysis and immunofluorescence staining demonstrated that the isolated cells were positive for mesenchymal surface markers CD29, CD44 and negative for hematopoietic markers CD45 and the adhesion molecules CD31. Cells were induced to differentiate into adipocytes with adipogenic medium containing insulin, dexamethasone, oleate and octanoate. Oil Red O staining demonstrated that the porcine BMSCs successfully differentiated to adipocytes. Moreover, the findings of real-time PCR and Western blotting indicated that the induced cells expressed adipogenic marker genes (PPAR-γ, C/EBP-α, perilipin, aP2) mRNA or proteins (PPAR-γ, perilipin, aP2). On the other hand, porcine BMSCs were induced into myoctyes with myogenic medium supplemented with 5-azacytidine, basic fibroblast growth factor, chick embryo extract and horse serum. Morphological observation by hochest 33342 staining showed that the induced cells presented as multi-nucleus muscular tube structure. And myogenic marker genes (Myf5, desmin) mRNA or proteins (Myf5, MyoD, myogenin, desmin) were found in the induced cells. In addition, the results of immunofluorescence staining revealed that myogenic marker (Myf5, MyoD, myogenin, desmin, S-MyHC) proteins was positive in the induced cells. Above all, these results suggested that the isolated porcine BMSCs were not only consistent with the characterization of mesenchymal stem cells, but also exhibited the multipotential capacity to form adipocytes and myocytes, which provided the basis to investigate the regulation mechanism involved in the selective differentiation of porcine BMSCs.

Intramuscular fat (IMF) content is considered to be a key factor that affects the marbling, tenderness, juiciness and flavor of pork. To investigate the effects of myristic acid (MA) on the differentiation of porcine intramuscular adipocytes, cells were isolated from longissimus dorsi muscle (LDM) and treated with 0, 10, 50 or 100 μmol L-1 MA. The results showed that MA significantly promotes the differentiation of intramuscular adipocytes in a dose-dependent manner. MA also led to a parallel increase in the expression of peroxisome proliferator activated receptor-γ (PPARγ) and adipose-related genes, such as glucose transporter 1 (GLUT1), lipoprotein lipase (LPL), adipocyte fatty acid binding protein 4 (FABP4/aP2), fatty acid translocase (FAT), acetyl-CoA carboxylase α (ACCα), adipose triglyceride lipase (ATGL) and fatty acid synthase (FASN). However, no significant effects of MA were observed on the expression of CAAT enhancer binding protein-α (C/EBPα) or hormone sensitive lipase (HSL). The expression of pyruvate dehydrogenase kinase 4 (PDK4) was increased by MA during the early stages of differentiation (day 1-3). In addition, MA also increased the absolute content of C14 (P<0.001) and saturated fatty acids (SFA) (P<0.05) to varying degrees, but no effects were observed on other fatty acids. These results suggest that MA might be able to enhance the IMF content of pork and increase the accumulation of myristic and myristoleic acid in muscle, which might have beneficial implications for human health.