New opportunities from the isolation and utilization of whey proteins

Management of dairy whey has often involved implementation of the most economical disposal methods, including discharge into waterways and onto fields or simple processing into low value commodity powders. These methods have been, and continue to be, restricted by environmental regulations and the cyclical variations in price associated with commodity products. In any modern regimen for whey management, the focus must therefore be on maximizing the value of available whey solids through greater and more varied utilization of the whey components. The whey protein constituents offer tremendous opportunities. Although whey represents a rich source of proteins with diverse food properties for nutritional, biological, and functional applications, commercial exploitation of these proteins has not been widespread because of a restricted applications base, a lack of viable industrial technologies for protein fractionation, and inconsistency in product quality. These shortcomings are being addressed through the development of novel and commercially relevant whey processing technologies, the preparation of new whey protein fractions, and the exploitation of the properties of these fractions in food and in nontraditional applications. Examples include the following developments: 1) whey proteins as physiologically functional food ingredients, 2) alpha-lactalbumin and beta-lactoglobulin as nutritional and specialized physically functional food ingredients, and 3) minor protein components as specialized food ingredients and an important biotechnological reagents. Specific examples include the isolation and utilization of lactoferrin and the replacement of fetal bovine serum in tissue cell culture applications with a growth factor extract isolated from whey.

Decreased muscle cell proliferation in chicks with a deletion in the GH receptor gene

The increase in muscle weight in neonatal animals is a consequence of increased protein accretion and DNA content. GH increases protein accretion but direct effects of GH on myogenic cell proliferation have not been demonstrated. Sex-linked dwarfism in the chick is caused by mutation or deletion in the GH receptor gene and has provided a useful model to study the physiological consequences of GH insensitivity. This study determined the consequences of GH receptor gene mutation on muscle cell proliferation in vivo. Northern and Southern blotting and PCR analysis revealed restriction fragment length polymorphism patterns and a 1.7 kb deletion of the intracellular domain of the GH receptor gene in commercial dwarf broiler chicks, similar to the Connecticut strain in which there is a dysfunctional GH receptor. Cell proliferation was measured in muscle sections from normal and dwarf chicks after incorporation of 5-bromo-2'-deoxyuridine (BrdU; 25 mg/kg) in vivo at 2, 5 and 13 days of age. Incorporation of BrdU into nuclei was measured in frozen sections, counterstained with propidium iodide to estimate the total number of nuclei by quantitative image analysis, and the labelling index was calculated. Paraffin-embedded sections of breast muscle were stained using an anti-human IGF-I polyclonal antibody. Expression of IGF-I mRNA in muscle from each genotype at 5 days of age was measured by RNAse protection assay. The labelling index was similar in 2-day-old chicks from both genotypes (normal, 20.14 +/- 2.39%; dwarf, 19.79 +/- 5.83%). By day 5 the labelling index had decreased but was significantly higher (P < 0.02) in normal (12.53 +/- 3.36%) compared with the dwarf (6.25 +/- 1.39%). By 13 days of age, there was a further decrease in labelling index but no difference between the groups (normal, 4.92 +/- 1.28%; dwarf, 4.96 +/- 1.51%). IGF-I mRNA was expressed and IGF-I peptide was identified in muscle sections but there was no difference between genotypes. The results show that cell division in breast muscle in vivo is high in neonatal chicks but it declines with increasing age. The absence of a functional GH receptor in the dwarf is associated with a greater decline in DNA synthesis and suggests that GH may directly affect a proportion of cells, since there was no difference in IGF-I mRNA or peptide.

Production of a human epidermal growth factor fusion protein and its degradation in rat gastrointestinal flushings

This study describes the biosynthesis of a human epidermal growth factor fusion protein, Long EGF, that has a 53 amino acid extension peptide derived from the 46 N-terminal amino acids of porcine GH. The approach allowed the production of Long EGF at high efficiency due to the expression of the fusion protein in high yield as inclusion bodies in Escherichia coli. Long EGF had a slightly lower potency compared with native EGF in a range of assays, including binding to anti-EGF antibodies or the EGF receptor, stimulation of Balb/3T3 fibroblast and rat intestinal epithelial cell growth, as well as counteracting the inhibition of mink lung epithelial cell proliferation by transforming growth factor-beta 1. Degradation of Long EGF and native EGF was compared in gastrointestinal flushings as an indication of whether the EGF domain of the fusion protein would be protected from proteolytic cleavage and be useful as a trophic agent in the gut. Incubation with flushings from the stomach or jejunum of rats caused rapid cleavage of the extension peptide, releasing native EGF. A C-terminal truncation of Arg53 in the stomach and a removal of the C-terminal pentapeptide (49 Trp-Trp-Glu-Leu-Arg53) in the small bowel was demonstrated by N-terminal sequencing and mass spectrometry. The degradation patterns were reflected by changes in migration of products on SDS-PAGE and in subsequent binding activities to the EGF receptor and anti-EGF antibodies. The data show that a human EGF fusion protein can be produced efficiently in a bacterial expression system and that it retains biological activity in vitro. Although the extension peptide was rapidly cleaved from Long EGF in both stomach and small bowel producing similar biological activity to native EGF, it could not prevent subsequent degradation of the EGF domain. Other strategies are being investigated to develop an effective oral form of EGF that resists digestion by proteases in the gastrointestinal tract.

Porcine osteochondrosis: deficiencies in transforming growth factor-beta and insulin-like growth factor-I

Osteochondrosis and dyschondroplasia are common multifocal disturbances of endochondral ossification in many species of domestic animals, and are characterized by the retention of avascular cartilage. These cartilage disorders are characterized by a failure of chondrocyte differentiation, matrix mineralisation and its replacement by bone. Rabbit polyclonal antibodies to transforming growth factor-beta (TGF-beta) and to insulin-like growth factor-I (IGF-I) were used to detect the two growth factors in normal and osteochondrotic porcine epiphyses. In the normal pig epiphyses IGF-I and TGF-beta were present in the chondrocytes of the epiphyseal hyaline cartilage and IGF-I was readily localised to the hypertrophic chondrocytes in the growth cartilage adjacent to the epiphyseal ossification centre. Both growth factors were found to be deficient in chondrocytes at sites of osteochondrosis. Both these growth factors are thought to be involved in the cascade of events associated with chondrocyte function during endochondral ossification. Deficiencies in TGF-beta and IGF-I demonstrated in porcine osteochondrosis and previously shown in avian dyschondroplasia suggest further similarities in the pathogenesis of these conditions.

Regulation of chick muscle satellite cells by fibroblast growth factors: interaction with insulin-like growth factor-I and heparin

This study describes the effect of acidic and basic fibroblast growth factor (FGF) on DNA synthesis in chick satellite cells in vitro and interactions with insulin-like growth factor-I (IGF-I) and exogenous heparin. Basic bFGF stimulated incorporation of [3H]thymidine into DNA with a half-maximum concentration (ED50) of 3.23 +/- 0.33 pmol/l, more than 500-fold more potent than acidic FGF (ED50 = 2.13 +/- 0.5 nmol/l). Both bFGF and IGF-I allowed the cells to traverse the cell cycle with an approximate length of the G1 phase of 12 h. When cells were incubated with bFGF and IGF-I together their effects on DNA synthesis were additive rather than synergistic throughout the full concentration range. Incubation of satellite cells with low concentrations of heparin (ng/ml) to mimic the effect of endogenous heparan sulphate proteoglycan caused a small increase in DNA synthesis, whereas higher concentrations (microgram/ml) inhibited DNA synthesis in a dose-related manner. A low concentration of heparin increased DNA synthesis at the highest concentration of bFGF, but high doses of heparin inhibited the response to bFGF throughout the dose-response curve but without altering the ED50. RNAse protection assay showed the expression of bFGF mRNA in proliferating cells which appeared to decrease on differentiation. The results suggest that aspects of neonatal muscle development are regulated by interactions between autocrine/paracrine growth factors such as IGF-I and bFGF, perhaps IGF-I derived from the circulation, and components of the extracellular matrix. Concentrations of the matrix components may change throughout the neonatal period and into adulthood and have an important effect on the regulatory role played by the growth factors.

Increased expression and activity of ornithine decarboxylase in chicks genetically selected for rapid growth rate

Polyamines are essential requirements for cell proliferation and their role in stimulation of RNA, DNA, and protein synthesis is clearly established. Ornithine decarboxylase is a key enzyme in the biosynthesis of the polyamines and its activity is regulated in response to factors that stimulate cell proliferation. Steady-state ODC mRNA levels and enzyme activity were measured in muscle of chicks genetically selected for increased growth rate or for egg production. In muscle, muscle satellite cells and myotubes, two ODC mRNA transcripts are present of molecular size 2.05 and 1.75 kb. Northern blotting analysis suggest that these transcripts are produced as a result of using different polyadenylation sites. Between day 1 and day 6 after hatching, a period of rapid muscle growth in these animals, a peak in muscle ODC mRNA levels is followed by a peak in enzyme activity in both lines. Significantly higher ODC mRNA levels and enzyme activity are associated with selection for rapid growth in the broiler line. The results are consistent with other data showing that ODC is a major factor in cell growth and provide further evidence that it is a candidate 'trait-gene' for growth.

Identification of tricyclic analogs related to ellagic acid as potent/selective tyrosine protein kinase inhibitors

The plant-derived natural product ellagic acid (1) has recently been identified as a potent, though nonselective, inhibitor of the tyrosine-specific protein kinase pp60src. This report details efforts directed toward the identification of tricyclic structures related to ellagic acid, with enhanced specificity for inhibition of pp60src over other protein kinases. Phenanthridinone and carbazole core structures were selected for investigation, since N-functionalization allows for the synthesis of numerous analogs which can be utilized to probe enzyme-inhibitor interactions. These ring systems were prepared via a general sequence of biaryl bond formation followed by cyclization to form the desired tricyclic ring systems. N-Alkylation, -acylation, or -sulfonylation and deprotection with boron tribromide afford the target tetraphenolic phenanthridinones 5 and carbazoles 9. Several analogs from both of these series have potencies comparable to that of 1 and exhibit substantially enhanced selectivities for inhibition of pp60src relative to protein kinase A (PKA), a serine/threonine protein kinase. Carbazole-based analogs 9j,m,p are submicromolar inhibitors of pp60src, with potency for the target tyrosine kinase comparable to that of ellagic acid (1), however with 2 orders of magnitude greater selectivity versus that for PKA. As seen for ellagic acid, members of the phenanthridinone-based series (e.g., 5a) exhibited inhibition of pp60src in a manner which is partial mixed noncompetitive with respect to ATP, while analogs in the carbazole series (e.g., 9a) inhibit pp60src in an ATP competitive manner.

Plasma concentrations of growth hormone and insulin-like growth factor-I in chickens developing tibial dyschondroplasia

The concentrations of plasma growth hormone (GH) and insulin-like growth factor-I (IGF-I) were measured in broilers during the initial development of tibial dyschondroplasia. Chicks were fed a standard starter ration, or a diet imbalanced in calcium and phosphorus to increase the incidence of dyschondroplasia. At 14 days of age four blood samples were collected and assayed for GH and IGF-I. The chicks were killed at three weeks of age and sections of bone were assessed histologically for evidence of dyschondroplasia. All the chicks displayed a pulsatile pattern of GH secretion. Eight of the group fed the imbalanced diet developed dyschondroplasia which was accompanied by a significant increase in the mean and peak GH concentrations compared with the control group but no increase in basal concentrations. The chicks fed the imbalanced diet which did not develop dyschondroplasia were not different from the control birds. There were no differences in IGF-I concentrations between the groups.

Plasma growth hormone and insulin-like growth factor-I (IGF-I) concentrations at the onset of lay in ad libitum and restricted broiler breeder fowl

1. Plasma concentrations of growth hormone (GH) and insulin-like growth factor I(IGF-I) were determined in individually caged broiler breeder females from 17 to 30 weeks of age. The birds were fed ad libitum or restricted during rearing in a randomised block design. Restricted birds were fed ad libitum after laying an egg and egg production was recorded to 54 weeks. 2. GH concentrations were higher in restricted compared with ad libitum-fed birds at 17 to 21 weeks of age and were similar thereafter. Plasma IGF-I concentrations were higher in restricted compared with ad libitum-fed birds throughout the sampling period of the experiment. 3. The age at first egg was delayed by about two weeks in restricted birds. At 54 weeks of age they had laid 114 compared with 67 eggs in birds fed ad libitum throughout and had produced less than half the number of eggs with defective shells. 4. It was suggested that differences in egg production between ad libitum and restricted broiler breeder females could be related to changes in the pattern of GH and/or IGF-I secretion.

Insulin-like growth factor-I in the ovary of the laying hen: gene expression and biological actions on granulosa and thecal cells

Concentrations of insulin-like growth factor-I (IGF-I) were measured in granulosa and thecal tissue dissected from the three largest follicles in the ovaries of laying hens. The higher concentration was found in extracts of granulosa (0.82 +/- 0.01 pmol/g wet wt) and theca (0.36 +/- 0.02), both of which were greater than that in liver extracts (0.25 +/- 0.01). RNA was extracted from these tissues, and by using reverse transcription and the polymerase chain reaction with primers specific for chicken IGF-I, both granulosa and thecal tissue were shown to express chicken IGF-I mRNA. Granulosa and thecal cell cultures were established and used to measure IGF binding sites and the response to exogenous IGF peptides in terms of DNA synthesis. Both cell types bound [125I]IGF-I, which was displaced by IGF-I, IGF-II, and insulin in descending order of potency, characteristic of a type-I IGF receptor. Treatment of granulosa and thecal cell cultures with IGF-I resulted in a dose-dependent increase in [3H]thymidine incorporation into DNA by both cell types. LH, but not FSH, stimulated DNA synthesis in cultured granulosa cells but not in cultured thecal cells. This effect was enhanced in granulosa cells by the addition of IGF-I to the culture medium. These data are consistent with an autocrine or paracrine role for IGF-I within the developing ovarian follicle of the domestic hen.

Rapidly growing broiler (meat-type) chickens: their origin and use for comparative studies of the regulation of growth

1. Rapidly growing (meat-type) chickens have been intensively selected for over 50 years and grow up to four times faster than "layer" strains selected for reproductive traits. 2. Comparison between these lines are increasingly being used to study mechanisms underlying lean tissue growth. 3. Selection for increased growth has resulted in some undesirable consequences such as poor reproductive performance, excessive fatness, increased skeletal abnormalities and ascites. 4. The biochemistry, physiology and molecular biology of these changes are reviewed.

Regulation of amino acid transport and protein metabolism in myotubes derived from chicken muscle satellite cells by insulin-like growth factor-I

The effects of insulin and insulin-like growth factor-I (IGF-I) on amino acid transport and protein metabolism were compared in myotubes derived from chicken breast muscle satellite cells. Protein synthesis was assessed by continuous labelling with [3H]-tyrosine. Protein degradation was estimated by the release of trichloroacetic acid (TCA) soluble radioactivity by cells which had been previously labelled with [3H]-tyrosine for 3 days. Amino acid transport was measured in myotubes incubated in Dulbecco's modified Eagle's medium (DMEM) 0.5% bovine serum albumin (BSA) with or without insulin or IGF-I. Subsequent [3H]-aminoisobutyric acid (AIB) uptake was then measured in amino acid-free medium. IGF-I was more efficient than insulin at equimolar concentration (3.2 nmol/l) in stimulating protein synthesis (127 and 113% of basal, respectively) and inhibiting protein degradation (32% and 13% inhibition of protein degradation following 4 h incubation). Half maximal effective concentrations for stimulation of AIB uptake were 0.27 +/- 0.03 nmol/l and 34.8 +/- 3.1 nmol/l for IGF-I and insulin respectively, with maximal stimulation of about 340% of basal. Cycloheximide (3.6 mumol/l) diminished IGF-I-stimulated AIB uptake by 55%. Chicken growth hormone had no effect on basal AIB uptake in these cells and neither glucagon nor dexamethasone had an effect on basal or IGF-I-stimulated AIB uptake. This study demonstrates an anabolic effect for IGF-I in myotubes derived from primary chicken satellite cells which is mediated by the type I IGF receptor, since the cation-independent mannose 6-phosphate receptor does not bind IGF-II in chicken cells.

Regulation of adipocyte precursor DNA synthesis by acidic and basic fibroblast growth factors: interaction with heparin and other growth factors

The development of adipose tissue is dependent on the growth and differentiation of fibroblast-like adipocyte precursor cells. Culture of adipocyte precursor cells in vitro has provided an ideal system for identifying potential regulators of proliferation and differentiation. We have demonstrated that both acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF) stimulate chicken adipocyte precursor DNA synthesis in a dose-dependent manner up to a concentration of 100 micrograms aFGF/l and 1 microgram bFGF/l. The effect of bFGF was biphasic, so that in incubations with 25 micrograms bFGF/l, DNA synthesis was not significantly different from controls. In the presence of heparin, stimulation of DNA synthesis at 25 micrograms bFGF/l was 1.6-fold greater than at a concentration of 1 microgram bFGF/l. Addition of heparin to incubations containing aFGF reduced the concentration required for maximum stimulation of DNA synthesis to 1 microgram/l. Cells incubated with aFGF (1-100 micrograms/l) in combination with insulin-like growth factor-I (IGF-I), platelet-derived growth factor, transforming growth factor-alpha or transforming growth factor-beta 1 (TGF-beta 1) exhibited a marked synergistic increase in DNA synthesis. This was also the case when 1 microgram bFGF/l was used, but at a concentration of 25 micrograms bFGF/l synergy was only seen with IGF-I and TGF-beta 1. These results suggest that both basic and acidic FGF are potentially important regulators of adipocyte hyperplasia and that their effect is modulated by constituents of the extracellular matrix and the presence of other growth factors.

Insulin-like growth factor-I-stimulated glucose transport in myotubes derived from chicken muscle satellite cells

The effects of insulin and insulin-like growth factor-I (IGF-I) on glucose transport were compared in myotubes derived from chicken breast muscle satellite cells in vitro. Myotubes were incubated (for 0.5 or 4 h) with or without glucose in the presence or absence of insulin or IGF-I. Glucose uptake was subsequently measured by the incorporation of 2-[1,2-3H(N)] deoxy-D-glucose ([3H]2DG) in glucose-free medium (10 min at 20 degrees C). Glucose uptake was almost completely abolished by the addition of cytochalasin B or phloretin. It was increased by a decrease in glucose concentration in the incubation medium. Insulin (5 mg/l) stimulated [3H]2DG uptake to a maximum of 43 +/- 10% above basal after 30-min incubation and 101 +/- 15% after 4-h incubation. IGF-I and insulin at equimolar concentrations (25 micrograms/l and 20 micrograms/l respectively) were almost equipotent after 0.5 h but after 4-h incubation IGF-I was 17-fold more potent, suggesting that this 'late' effect was mediated through the IGF-I receptor. Incubation with cycloheximide suggested that the effect of IGF-I involved increased protein synthesis. The results suggest that chicken myotubes express a glucose transporter which is regulated by IGF-I and glucose concentration. However, they do not appear to express a typical insulin-responsive transport system.

Effects of transforming growth factor-alpha on chicken adipocyte precursor cells in vitro

The hyperplastic capacity of adipose tissue resides in a group of fibroblast-like adipocyte precursor cells. There is evidence to suggest that their proliferation and differentiation is regulated by insulin-like growth factor-I (IGF-I) and transforming growth factor-beta (TGF-beta) but there is less information about other growth factors which may also participate in adipocyte precursor cell hyperplasia. Transforming growth factor-alpha (TGF-alpha) is a 50 amino acid polypeptide which has been shown to stimulate proliferation in both neoplastic and normal cell types acting through the epidermal growth factor (EGF) receptor. We have studied the regulation of DNA synthesis and the activity of lipoprotein lipase by TGF-alpha in chicken adipocyte precursor cells in vitro. Both TGF-alpha and EGF stimulated incorporation of [3H]thymidine into DNA in a dose-dependent manner. TGF-alpha was approximately 180-fold more potent than EGF. Addition of TGF-alpha in combination with IGF-I, TGF-beta 1 or platelet-derived growth factor produced a synergistic increase in DNA synthesis. Short-term incubation with TGF-alpha reduced lipoprotein lipase activity by 23%. These results show that TGF-alpha is a potent mitogen in these adipocyte precursor cells and can inhibit their differentiation in vitro and may participate in the regulation of adipose tissue development in vivo.

Regulation of DNA synthesis in chicken adipocyte precursor cells by insulin-like growth factors, platelet-derived growth factor and transforming growth factor-beta

Adipose tissue growth can occur by both hypertrophy and hyperplasia. The capacity for adipocyte hyperplasia in vivo resides in a population of fibroblast-like adipocyte precursor cells but the regulation of the proliferation of these cells by growth factors has not been well characterized. This study was designed to determine the effects of the insulin-like growth factors (IGF-I and IGF-II), platelet-derived growth factor (PDGF) and transforming growth factor-beta 1 (TGF-beta 1) added alone or together on the proliferation of primary adipocyte precursor cells in vitro. Adipocyte precursor cell proliferation measured by [3H]thymidine incorporation into DNA was stimulated by all of these growth factors and was particularly marked with PDGF. IGF-I or IGF-II added together with TGF-beta 1 produced a greater than additive response and the effect of PDGF was synergistic with that of IGF-I at certain concentrations. Stimulation of proliferation of some cell types by TGF-beta has been linked to the secondary production of PDGF but the evidence we have suggests that this is unlikely in chicken adipocyte precursors. DNA synthesis in response to TGF-beta 1 required only a short exposure to the peptide, and conditioned medium from chicken adipocyte precursor cells previously exposed to TGF-beta had no effect on DNA synthesis when added to fresh batches of cells. Addition of TGF-beta 1 together with PDGF produced a synergistic effect whereas an additive effect would be expected if PDGF mediated the effect of TGF-beta 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal antibody based sandwich enzyme-linked immunosorbent assay for chicken growth hormone

1. Monoclonal antibodies which bind to different epitopes of chicken growth hormone (cGH) were used to develop a homologous sandwich enzyme-linked immunosorbent assay (ELISA). 2. The first antibody, which is species specific, was immobilised on microtitre plates and concentrations of cGH in biological fluids were estimated by revealing bound hormone using a second, biotinylated monoclonal antibody. 3. The sensitivity was 0.024 ng/ml, which is at least ten-fold greater than current radioimmunoassays (RIA) and there was no cross-reactivity to other chicken pituitary hormones or to growth hormone from other species. 4. The accuracy and precision of the assay were similar to RIA, and the growth hormone concentrations measured in plasma samples by both RIA and this new ELISA showed a high degree of correlation. 5. The assay takes only 4 h using pre-coated plates which can be stored at 4 degrees C in sucrose. The advantages of being rapid and non-isotopic make this method attractive to both research and industrial laboratories.

Stimulation of DNA synthesis in chicken muscle satellite cells by insulin and insulin-like growth factors: evidence for exclusive mediation by a type-I insulin-like growth factor receptor

Insulin-like growth factors-I and -II (IGF-I and IGF-II) stimulate proliferation, differentiation, nutrient uptake and protein accretion in muscle cells. These effects are thought to be mediated through the type-I IGF receptor although a role for the type-II IGF receptor cannot be ruled out, since it has been found in most cells studied so far. Current evidence suggests that the chicken does not have a type-II IGF receptor and therefore provides a good model to study the function of IGF peptides. We have compared the effects of insulin and insulin-like growth factors on DNA synthesis with the binding of these peptides to receptors in primary chicken muscle satellite cells. Human IGF-I (hIGF-I), hIGF-II and porcine insulin increased thymidine incorporation into DNA by threefold in muscle satellite cells prepared from neonatal chickens. IGF-I and -II were almost equipotent, with half-maximum effective concentrations of 10 micrograms/l, and were 1000-fold more potent than insulin. A combination of maximum effective concentrations of all three peptides was not additive, suggesting that their effect was mediated by the same receptor. Receptor binding studies on satellite cells demonstrated the presence of specific IGF receptors. Human IGF-I inhibited the binding of 125I-labelled hIGF-I with a much higher potency than insulin, as usually observed for a type-IIGF receptor. However, unlabelled hIGF-II exhibited a higher potency than hIGF-I in displacing 125I-labelled hIGF-I. Affinity cross-linking of 125I-labelled hIGF-I and -II, followed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, showed that hIGF-I and -II bound to a receptor with the structural characteristics of a type-I IGF receptor and confirmed the lack of a type-II IGF receptor in these cells. The concentrations of IGF-I, -II and insulin required for biological action and to displace 125I-labelled hIGF-I binding were similar, and support the hypothesis that their effects on proliferation were mediated exclusively through a type-I IGF receptor.

Why are young broiler chickens fatter than layer-strain chicks?

1. The abdominal fat pads of 5 week-old broiler and layer chicks incorporated 6.0 and 3.9% of intravenously-injected 14C-labelled very low density lipoproteins respectively. 2. These proportions of total plasma lipoprotein flux were sufficient to account for about 65-70% of the rate of fat deposition in broilers, but were more than 4-fold greater than that the rate of fat deposition in layers. 3. [14C]Palmitate taken up into adipose tissue of layer chicks had a t1/2 of 2-3 days. 4. There was no significant turnover of adipose tissue triglycerides in broilers and this appears to be a major reason for their relative fatness.

Recombinant transforming growth factor type beta 3: biological activities and receptor-binding properties in isolated bone cells

We have recently cloned the cDNA for transforming growth factor type beta 3 (TGF-beta 3), a new member of the TGF-beta gene family. We examined the biological effects of recombinant TGF-beta 3 protein in osteoblast-enriched bone cell cultures. In this report we demonstrate that TGF-beta 3 is a potent regulator of functions associated with bone formation, i.e., mitogenesis, collagen synthesis, and alkaline phosphatase activity. In a direct comparison between TGF-beta 3 and TGF-beta 1, TGF-beta 3 appeared to be three- to fivefold more potent than TGF-beta 1. Our cross-linking experiments with iodinated TGF-beta showed that in osteoblast-enriched bone cell cultures, both TGF-beta 3 and TGF-beta 1 associated with the same three cell surface binding sites. Scatchard analysis of receptor competition studies indicated the presence of high-affinity binding sites for TGF-beta 3 in the picomolar range. TGF-beta 3 showed an approximately fourfold-higher apparent affinity than TGF-beta 1 in overall binding.

Biological activity of insulin-like growth factor-I purified from chicken serum

This study describes a rapid purification of insulin-like growth factor-I from chicken serum and the immunological, biological and receptor binding activity of the peptide. It was purified after initial extraction, by cation exchange chromatography, hydrophobic interaction chromatography and reverse phase chromatography up to 1.4 x 10(6)-fold with an overall yield ranging from 10-30%. The N-terminal amino acid sequence was the same as predicted from the nucleotide sequence of a chicken IGF-I cDNA and the partial sequence obtained from a previously reported purification. The material was both immunologically and biologically active. It had a 50% potency compared to human IGF-I in a radioimmunoassay using an antiserum raised against human IGF-I, stimulated the incorporation of [3H]-thymidine into DNA in cultured chick embryo myoblasts with a half-maximum effective dose of 5 ng/ml and displaced [125I]-labelled human IGF-I and IGF-II from binding sites in microsomal membranes prepared from both the chicken liver and the lactating rabbit mammary gland in a dose dependent manner.

Insulin-like growth factor receptors in chicken liver membranes: binding properties, specificity, developmental pattern and evidence for a single receptor type

Two distinct receptors for the insulin-like growth factors (IGF-I and IGF-II) have been identified in mammalian tissues, but so far only a receptor structurally related to the type I receptor has been identified in chicken embryonic tissues. This study was designed to characterize binding sites for IGF peptides in chicken liver microsomal membranes prepared from hatch to 10 weeks of age which is the period of most rapid growth. Binding of both human (h) IGF-I and hIGF-II was displaceable by either peptide and exhibited similar pH, time and temperature dependency. Human IGF-II was more potent than hIGF-I in competing for the binding of the iodinated ligands with half-maximum effective concentrations of 3-5 micrograms/l and 7-13 micrograms/l respectively. Porcine insulin was also a potent competitor. Affinity cross-linking studies, followed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis under reducing conditions demonstrated that both IGF peptides were linked to a protein with a molecular weight of about 130,000 Da characteristic of the alpha-subunit of the type I receptor. There was no evidence for the presence of a type II receptor similar to that found in mammals. Specific binding of both peptides was low on the day of hatch, increased about threefold by day 3 of age and remained high for the first 3 weeks of life before returning to a lower steady state level up to 10 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)