Meat animals are raised for their carcasses, and carcasses are composed from muscle, fat and bone. Enhancing muscle growth and reducing fat accumulation improve the efficiency of animal production. Fetal stage is crucial for skeletal muscle development. Due to extensive efforts to increase lean growth, marbling (intramuscular fat) is reducing in beef, pork and chicken breast, which impairs the eating quality of meat. Because fat is the major contributor to meat flavor, the presence of intramuscular fat is indispensible for the high eating quality of meat. However, up to now, our understanding of adipogenesis (formation of fat cells) in skeletal muscle is limited. Adipocyte differentiation in skeletal muscle initiates from mesenchymal multipotent cells, which are abundant in skeletal muscle at early developmental stages. In this review, the known cellular mechanisms regulating adipogenesis from multipotent cells are summarized, which include hedgehog, Wingless and Int (Wnt)/α-catenin, and bone morphogenesis protein (BMP) mediated signaling pathways, as well as AMP-activated protein kinase. Promoting adipogenesis inside skeletal muscle will dramatically increase intramuscular fat, improving the quality of meat.

AMP-activated protein kinase (AMPK) is a key regulator of energy metabolism; its activity is regulated by a plethora of physiological conditions, exercises and many anti-diabetic drugs. Recent studies show that AMPK involves in cell differentiation but the underlying mechanism remains undefined. Wingless Int-1 (Wnt)/β-catenin signaling pathway regulates the differentiation of mesenchymal stem cells through enhancing β-catenin/T-cell transcription factor 1 (TCF) mediated transcription. The objective of this study was to determine whether AMPK cross-talks with Wnt/β-catenin signaling through phosphorylation of β-catenin. C3H10T1/2 mesenchymal cells were used. Chemical inhibition of AMPK and the expression of a dominant negative AMPK decreased phosphorylation of β-catenin at Ser 552. The β-catenin/TCF mediated transcription was correlated with AMPK activity. In vitro, pure AMPK phosphorylated β-catenin at Ser 552 and the mutation of Ser 552 to Ala prevented such phosphorylation, which was further confirmed using γ-32 P ATP autoradiography. In conclusion, AMPK phosphorylates β-catenin at Ser 552, which stabilizes β-catenin, enhances β-catenin/TCF mediated transcription, expanding AMPK from regulation of energy metabolism to cell differentiation and development via cross-talking with the Wnt/β-catenin signaling pathway.

AMP-activated protein kinase (AMPK) is a key regulator of energy metabolism; it is inhibited under obese conditions and is activated by exercise and by many anti-diabetic drugs. Emerging evidence also suggests that AMPK regulates cell differentiation, but the underlying mechanisms are unclear. We hypothesized that AMPK regulates cell differentiation via altering ␤-catenin expression, which involves phosphorylation of class IIa histone deacetylase 5 (HDAC5). In both C3H10T1/2 cells and mouse embryonic fibroblasts (MEFs), AMPK activity was positively correlated with ␤-catenin content. Chemical inhibition of HDAC5 increased ␤-catenin mRNA expression. HDAC5 overexpression reduced and HDAC5 knockdown increased H3K9 acetylation and cellular ␤-catenin content. HDAC5 formed a complex with myocyte enhancer factor-2 to down-regulate ␤-catenin mRNA expression. AMPK phosphorylated HDAC5, which promoted HDAC5 exportation from the nucleus; mutation of two phosphorylation sites in HDAC5, Ser-259 and -498, abolished the regulatory role of AMPK on ␤-catenin expression. In conclusion, AMPK promotes ␤-catenin expression through phosphorylation of HDAC5, which reduces HDAC5 interaction with the ␤-catenin promoter via myocyte enhancer factor-2. Thus, the data indicate that AMPK regulates cell differentiation and development via cross-talk with the wingless and Int (Wnt)/ ␤-catenin signaling pathway. AMP-activated protein kinase (AMPK),2 a heterotrimeric enzyme composed of ␣, ␤, and ␥ subunits, is recognized as a critical regulator of energy metabolism (1-3). In addition to its capacity to acutely regulate the activity of metabolic enzymes through phosphorylation, AMPK also regulates gene expression (4 -9). Emerging evidence also suggests that AMPK regulates cell differentiation and tissue development (10 -12). Recently, it was shown that double knock-out of AMPK ␣1 and ␣2 subunits is lethal to mice at embryonic stage 10.5 (13), further confirming the important role of AMPK in early development. Mechanisms linking AMPK to cell differentiation and animal development, however, remain poorly defined.␤-Catenin is a key mediator of Wingless and Int (Wnt)/␤-catenin signaling pathway, which is required for early embryonic development (14, 15), cell proliferation, and differentiation (16 -18). We postulate that AMPK regulates cell differentiation through cross-talk with the Wnt/␤-catenin signaling pathway. We previously observed that AMPK phosphorylates ␤-catenin, which enhances ␤-catenin stability (19). In this study we further observed that the mRNA expression of ␤-catenin was promoted by AMPK and suggested that histone deacetylase 5 (HDAC5) has an essential role in linking AMPK with ␤-catenin expression.Epigenetic modifications including histone acetylation and methylation and DNA methylation regulate gene transcription (20,21). Histone acetylation is regulated by histone acetyltransferase and HDAC (22). HDAC5 belongs to the class IIa HDAC family and acts as a conserved transcriptional repressor. HDAC5 interacts with myocyte enhancer fact...

We utilized the proteomic approach to investigate the proteome of the fifth instar hemolymph during growth and development, and to improve the understanding of this important bioprocess and gene expression situation. A total of 25 μL of hemolymph was used for 2D analysis, and the separated proteins were visualized by silver staining and analyzed using the ImageMaster 2D software. The report showed as many as 241 of protein spots were expressed in the beginning of the fifth instar. Among them, most were concentrated in pI 3.5−6.5, which reached 76% of the total protein spots. As for the protein molecular sizes, 182 protein spots concentrated between 35 and 90 kDa, which comes to 75% of the total spots. When the larvae grow to the seventh day (total fifth instar duration was 9 days), 298 protein spots were visualized through 2D electrophoresis. Fifty-seven spots were newly expressed compared to the image of the first day in fifth instar. The results implied that these proteins are related to biosynthesis of silk protein and metamorphosis preparation from larva to pupa. In total, 19 protein spots including 6 special spots expressed in seventh day were analyzed through MALDI-TOF−MS. The relations between proteins and growth and development of silkworm were discussed. Keywords: silkworm (Bombyx mori L.) • hemolymph • proteomic analysis • 2D electrophoresis • MALDI-TOF−MS

BackgroundShiga toxin (stx) genes have been transferred to numerous bacteria, one of which is E. coli O157:H7. It is a common belief that stx gene is transferred by bacteriophages, because stx genes are located on lambdoid prophages in the E. coli O157:H7 genome. Both E. coli O157:H7 and non-pathogenic E. coli are highly enriched in cattle feedlots. We hypothesized that strong UV radiation in combination with high temperature accelerates stx gene transfer into non-pathogenic E. coli in feedlots.Methodology/Principal Findings E. coli O157:H7 EDL933 strain were subjected to different UV irradiation (0 or 0.5 kJ/m2) combination with different temperature (22, 28, 30, 32, and 37°C) treatments, and the activation of lambdoid prophages was analyzed by plaque forming unit while induction of Stx2 prophages was quantified by quantitative real-time PCR. Data showed that lambdoid prophages in E. coli O157:H7, including phages carrying stx2, were activated under UV radiation, a process enhanced by elevated temperature. Consistently, western blotting analysis indicated that the production of Shiga toxin 2 was also dramatically increased by UV irradiation and high temperature. In situ colony hybridization screening indicated that these activated Stx2 prophages were capable of converting laboratory strain of E. coli K12 into new Shiga toxigenic E. coli, which were further confirmed by PCR and ELISA analysis.Conclusions/SignificanceThese data implicate that high environmental temperature in combination with UV irradiation accelerates the spread of stx genes through enhancing Stx prophage induction and Stx phage mediated gene transfer. Cattle feedlot sludge are teemed with E. coli O157:H7 and non-pathogenic E. coli, and is frequently exposed to UV radiation via sunlight, which may contribute to the rapid spread of stx gene to non-pathogenic E. coli and diversity of shiga toxin producing E. coli.