Indispensability of Iron-bound Chick Transferrin for Chick Myogenesis in Vitro. (myogenesis/transfrrin/iron)

The roles of growth factors and hormones in the regulation of muscle satellite cells for cultured meat production

Cultured meat is a potential sustainable food generated by the in vitro myogenesis of muscle satellite (stem) cells (MSCs). The self-renewal and differentiation properties of MSCs are of primary interest for cultured meat production. MSC proliferation and differentiation are influenced by a variety of growth factors such as insulin-like growth factors (IGF-1 and IGF-2), transforming growth factor beta (TGF-β), fibroblast growth factors (FGF-2 and FGF-21), platelet-derived growth factor (PDGF) and hepatocyte growth factor (HGF) and by hormones like insulin, testosterone, glucocorticoids, and thyroid hormones. In this review, we investigated the roles of growth factors and hormones during cultured meat production because these factors provide signals for MSC growth and structural stability. The aim of this article is to provide the important idea about different growth factors such as FGF (enhance the cell proliferation and differentiation), IGF-1 (increase the number of myoblasts), PDGF (myoblast proliferation), TGF-β1 (muscle repair) and hormones such as insulin (cell survival and growth), testosterone (muscle fiber size), dexamethasone (myoblast proliferation and differentiation), and thyroid hormones (amount and diameter of muscle fibers and determine the usual pattern of fiber distributions) as media components during myogenesis for cultured meat production.

Transferrin as a muscle trophic factor

Muscle cells grow by proliferation and protein accumulation. During the initial stages of development the participation of nerves is not always required. Myoblasts and satellite cells proliferate, fusing to form myotubes which further differentiate to muscle fibers. Myotubes and muscle fibers grow by protein accumulation and fusion with other myogenic cells. Muscle fibers finally reach a quasi-steady state which is then maintained for a long period. The mechanism of maintenance is not well understood. However, it is clear that protein metabolism plays a paramount role. The role played by satellite cells in the maintenance of muscle fibers is not known. Growth and maintenance of muscle cells are under the influence of various tissues and substances. Among them are Tf and the motor nerve, the former being the main object of this review and essential for both DNA and protein synthesis. Two sources of Tf have been proposed, i.e., the motor nerve and the tissue fluid. The first proposal is that the nervous trophic influence on muscle cells is mediated by Tf which is released from the nerve terminals. In this model, the sole source of Tf which is donated to muscle cells should be the nerve, and Tf should not be provided for muscle fiber at sites other than the synaptic region; otherwise, denervation atrophy would not occur, since Tf provided from TfR located at another site would cancel the effect of denervation. The second proposal is that Tf is provided from tissue fluid. This implies that an adequate amount of Tf is transferred from serum to tissue fluid; in this case TfR may be distributed over the entire surface of the cells. The trophic effects of the motor neuron have been studied in vivo, but its effects of myoblast proliferation have not been determined. There are few experiments on its effects on myotubes. Most work has been made on muscle fibers, where innervation is absolutely required for their maintenance. Without it, muscle fibers atrophy, although they do not degenerate. In contrast, almost all the work on Tf has been performed in vitro. Its effects on myoblast proliferation and myotube growth and maintenance have been established; myotubes degenerate following Tf removal. But its effects on mature muscle fibers in vivo are not well understood. Muscle fibers possess TfR all over on their cell surface and contain a variety of Fe-binding proteins, such as myoglobin. It is entirely plausible that muscle fibers require an amount of Tf, and that this is provided by TfR scattered on the cell surface.(ABSTRACT TRUNCATED AT 400 WORDS)

Trace mineral metabolism in the avian embryo

Trace mineral metabolism in the developing avian embryo begins with the formation of the egg and the trace mineral stores contained within it. Vitellogenin, the yolk precursor protein, serves as a trace mineral transporting protein that mediates the transfer of these essential nutrients from stores within the liver of the hen to the ovary and developing oocyte, and hence, to the yolk of the egg. Lipovitellin and phosvitin, derived from intraoocytic proteolytic processing of vitellogenin, are also trace mineral binding proteins that form important storage sites within the granule subfraction of yolk. The mobilization and uptake of egg trace mineral stores is mediated by the extra-embryonic membranes, principally the yolk sac membrane. The yolk sac also serves as a short-term storage site for trace minerals. Because it is an important site of plasma protein synthesis, the yolk sac has the ability to regulate the export of trace minerals to the embryo during development. Within the embryo, specific metaloproteins function in the interorgan transport cellular uptake, and intracellular storage of trace minerals. Thus, embryonic trace mineral homeostasis is established through the coordinated actions of the yolk sac, which mobilizes and exports trace minerals derived from egg stores; the vitelline circulation, which transports them to the embryo; and the liver, which accumulates trace minerals and distributes them to the rest of the tissues of the embryo via the embryonic circulation.

Neurotrophic effects of transferrin on embryonic chick brain and neural retinal cell cultures

The viability and differentiation promoting effects of various transferrins [iron-saturated (holo) and iron-depleted (apo) human and chick ovo (conalbumin)-transferrins, and bovine apo-transferrin] were studied, using serum-free, flat-sedimented cell cultures of embryonic chick brain and neural retina. The effects of transferrin (Tf) on the cell cultures depended on the type of Tf used and the parameter measured. Significant differences between brain and neural retina cultures in the effects of apo-ovoTf and iron [supplemented as ammonium-iron (III) citrate] were detected. Maximal levels of mitochondrial activity were observed in the presence of 2 mg/l apo-ovoTf in neural retina cell cultures. In brain cell cultures, 40 mg ovoTf/l were needed to achieve maximal levels. In brain, but not in neural, retina cell cultures ovoTf and optimal concentrations of Fe3+ exhibited similar effects on biochemical parameters of cell function and differentiation. Although, in the absence of ovoTf, neuronal outgrowth on areas not covered by glial cells was inhibited in both cell cultures, the differences were more prominent in neural retina cell cultures. Our data strongly suggest that Tf plays a key role in processes not connected directly with its iron transport capability.

Suppression of transferrin internalization in myogenic L6 cells by dibucaine

Dibucaine, a potent local anesthetic, is known to suppress myogenesis. The promotion of myogenesis requires transferrin (Tf) which transports Fe to the cells. Therefore, the effects of dibucaine on Fe uptake and Tf internalization were studied using myogenic cell line L6. Dibucaine at 200 microM suppressed 55Fe accumulation which was transported by 55Fe-transferrin to the cells. The anesthetic changed neither the number of Tf receptors nor the affinity of Tf to Tf receptors on the cell membrane. Dibucaine retarded the endocytosis and exocytosis cycle of Tf, and this retardation acted to suppress Fe accumulation.

Scleral fibroblasts of the chick embryo proliferate by an autocrine mechanism in protein-free primary cultures: differential secretion of growth factors depending on the growth state

Scleral fibroblasts of the chick embryo in primary culture proliferated in a protein-free medium. Conditioned medium (CdM) from the culture contained plural growth-promoting factors, which were active to the same cell type. The activity of one of the growth-promoting factors (SAF-I) was heat-resistant and the rest (SAF-II) were heat-sensitive. SAF-I accumulated in the CdM only during the growing phase; on the other hand, SAF-II accumulated in the CdM during the stationary phase. SAF-I showed the same time course of DNA synthesis-promoting activity as human PDGF. However, the activity of the SAF-I was not neutralized by anti-human PDGF. On the other hand, a part of the SAF-II (SAF-II a) showed a strong affinity for heparin.

Monoclonal antibody detects embryonic epitope specific for nerve-derived transferrin

Monoclonal antibodies were generated against transferrin purified from chick embryo extract by fusing spleen cells from BALB/c mice immunized against embryonic transferrin, with myeloma cells. Antibodies produced by the selected hybridoma clones were all type IgG. Twelve clones were selected for secretion of antibodies to the embryo extract-derived transferrin, and three clones were studied extensively. Immunoblotting was used to demonstrate antibody binding to several avian transferrin proteins derived from adult chicken serum, adult chicken peripheral nerves, and ovotransferrin. Screening and detailed epitope analysis were accomplished by solid-phase immunoassay. The results indicated that two clones, 2G9.1 and 2B11.1, recognized the embryonic and egg antigens in preference to the adult proteins. However, a third clone, 6H2.1, recognized the nerve-derived transferrin preferentially to both the embryonic and adult serum antigens. None of the clones recognized the serum-derived transferrin in preference to the other antigens. These results indicate that embryonic epitope(s) are conserved in the nerve- but not the serum-derived transferrin. They also show that the neural antigen has site(s) distinct from the embryonic proteins. No changes in displacement curves were observed after these proteins were digested with neuraminidase, indicating that the epitope differences discovered are not intimately related to sialic acid residues on the various transferrins.

Further purification of a fibroblast growth factor-like factor from chick embryo extract by heparin-affinity chromatography

A mitogenic factor which promotes quail myoblast proliferation has been purified some 10(5)-fold from chick embryo extract by a combination of cation-exchange chromatography and heparin-affinity chromatography. The factor is eluted from heparin-Sepharose with 2 M NaCl and is a single-chain polypeptide with an apparent molecular weight of 15,000 to 17,000. It is active at subnanogram level in triggering the proliferation and thereby delaying temporarily fusion of myoblasts. It also stimulates the proliferation of quail fibroblasts in a similar effective concentration range. For both myoblasts and fibroblasts the dose-response to the factor is quantitatively and qualitatively comparable with that of bovine pituitary fibroblast growth factor. These observations strongly suggest that the factor very probably corresponds to chicken fibroblast growth factor or to a closely related molecule(s) and that it is possibly involved in the regulation of myogenesis.

Transferrin concentration and location during formation of chick retina: developmental correlates

The amount of transferrin in chick retina was measured during development and compared to transferrin location seen immunocytochemically. Between embryonic day 6 (E6), and 5 days post hatching, two periods occur in which transferrin concentrations rise sharply and decline. During the first, transferrin concentration rises 5-fold between E6 and 10, then rapidly declines by E14. A second increase begins on E17 and peaks by E19-20. Immunocytochemical findings demonstrate that during the first rise in concentration, transferrin is located primarily in neuritic layers. Later in development, when levels again increase, newly forming photoreceptor outer segments are strongly transferrin positive. These findings are discussed in light of developmental events occurring during retinal maturation.

Transferrin and iron requirements of embryonic mesoderm cells cultured in hydrated collagen matrices

Very early embryonic mesoderm cells were taken from the primitive streak-stage chick embryo and cultured in a matrix of type I collagen in the presence of serum. Previous work has shown that under these conditions cells do not leave the explant and move in the collagen in the absence of supplemented avian transferrin. Cells explanted onto tissue culture plastic in the presence of serum do not require this transferrin supplement. These observations were investigated further by culturing cells in collagen in the presence of the lipophilic iron chelator, ferric pyridoxal isonicotinoyl hydrazone (FePIH), which can replace transferrin as an iron-delivery agent. Under conditions in which FePIH could effectively stimulate chick embryo myoblast growth, no such long-term stimulation was obtained with the early mesoderm cells in collagen. This suggested that for mesoderm cells, FePIH could not replace transferrin. Antibody to the transferrin receptor and to transferrin itself inhibited growth of myoblasts in collagen and on plastic, and of mesoderm cells in collagen. Mesoderm cells on plastic, however, were refractory to the presence of the antibody directed to the receptor and seemed to show a low dependency on transferrin-delivered iron under these conditions, inasmuch as antiserum to transferrin itself only caused a partial inhibition of outgrowth. The results suggest that mesoderm cells in collagen require transferrin for both iron uptake and for another unspecified function. It is consistent with the results to propose that transferrin binding might modulate the cells' attachment to collagen, thus influencing outgrowth. The distribution of the actin cytoskeleton in mesoderm cells actively migrating in collagen, such as in the presence of transferrin, suggests a stronger attachment to the collagen than nonmigrating cells.

Transferrin and iron in cultured chick embryonic neurons: a comparison between human and chick transferrins

Transferrin was not required for the short-term survival of cultured chick retinal neurons. Both human and chick transferrin failed to enhance the in vitro survival of 8- or 11-day embryonic chick retinal neurons when cultured in a defined medium. Furthermore, maintenance of neurons in the presence of chick transferrin antibody did not alter in vitro survival. Retinal neurons, however, could bind and internalize human or chick transferrin when assayed for by fluorescence immunohistochemical techniques. Binding and internalization of chick transferrin appeared to be greater than human transferrin. Iron uptake was measured in cultures maintained in the absence of transferrin. After incubation with 59FeCl3, iron uptake was 3.5 +/- 1.1 fmoles/cell. The presence of chick transferrin antibody did not significantly alter the amount of iron uptake occurring in this assay. In a comparison of human and chick transferrin mediated iron uptake, chick transferrin was 50% more effective than human transferrin in transporting iron. This study demonstrates that cultured embryonic retinal neurons are not dependent on transferrin for survival or iron uptake, although they actively bind and internalize transferrin. Results also demonstrate that whereas cultured chick retinal neurons can bind and utilize human transferrin, they do so with less efficiency than chick transferrin.

Species specificity of transferrin binding, endocytosis and iron internalization by cultured chick myogenic cells

The ability of unlabelled heterologous transferrin to interact with transferrin receptors on developing chick myogenic cells was investigated by measuring their capacity to inhibit the surface-binding and internalization of 125I- and 59Fe-labelled ovotransferrin. Transferrins from rat, rabbit, human, and a species of kangaroo (Macropus fuliginosus) were unable to inhibit either surface-binding or internalization of labelled ovotransferrin even at concentrations ten times the molar concentration of the ovotransferrin. Transferrins isolated from the serum of a toad (Bufo marinus) and a lizard (Teliqua rugosa), when added at high concentrations, were found to reduce surface-binding of 125I-Tf by 20-25% but did not inhibit internalization of either 125I-Tf or 59Fe. This suggests that the effects of toad and lizard transferrins are due to non-specific binding to the myogenic cells. In contrast, inhibition of both surface-binding and internalization of labelled ovotransferrin was found when myogenic cells were incubated in the presence of the homologous transferrin (ovotransferrin). The species-specificity of transferrin binding, endocytosis and iron internalization did not vary with the state of proliferation or differentiation of the myogenic cells. However, the intracellular iron utilization was found to differ between differentiating presumptive and terminally differentiated myotubes. Internalized 59Fe was fractioned by gel filtration. In dividing and non-dividing presumptive myoblasts 59Fe was found to elute in three peaks, two with elution volumes corresponding to ferritin and transferrin and one at greater elution volume than that of myoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)

Domain-specific monoclonal antibodies to ovotransferrin indicate conservation of determinants involved in avian transferrin receptor recognition

1. Three of five monoclonal antibodies produced to chicken ovotransferrin bound quail ovotransferrin but none of the antibodies bound human, bovine or equine serum transferrin. 2. Equilibrium binding experiments indicate that both quail and chicken ovotransferrin bind to transferrin receptors on chick reticulocytes although the quail protein binds to 40% fewer sites with an affinity which is three times lower than chicken ovotransferrin. 3. The antibodies that recognize quail ovotransferrin block binding of both radiolabelled chicken and quail ovotransferrin to chick reticulocytes. 4. Quail NH2-terminal half-molecule domain appears to be unable to form a functional hybrid holo-ovotransferrin with chicken C-terminal half-molecule domain.

Transferrin in chick retina: distribution and location during development

Chick retinas from embryonic day 6 (E6) to 3 weeks post-hatching were examined for the presence and location of endogenous transferrin. Immunocytochemistry revealed that transferrin was differentially distributed in retinal layers. Furthermore, the pattern of transferrin distribution changed with developmental age. At day E6, transferrin was found in 2 distinct bands which were located in the area of the Müller cell end-feet. By day E9, additional regions of transferrin immunoreactivity could be found in the inner and outer plexiform layers (IPL, OPL) and the nerve fiber layer (NFL). These latter 3 bands (IPL, OPL and NFL) became more prominent from E9 until E17 as the synaptic layers and nerve fiber layer increased in density and maturation. Perikarya in the nuclear layers size, density and maturation. Perikarya in the nuclear layers were negative. At day E17 and later, the newly forming outer segments of photoreceptor cells were strongly reactive for transferrin while the somas of the photoreceptor cells, in the ONL, were negative. Retinas from chicks 1 day to 3 weeks post-hatching retained strong immunoreactivity for transferrin in the photoreceptor cell outer segments and OPL, lessened immunoreactivity in the IPL and loss of immunoreactivity in the NFL. Iron distribution in the retina for all ages examined showed only 2 bands that locally corresponded to the Müller cell end-feet. Iron stores were not found in the synaptic layers or photoreceptor cell outer segments. These studies suggest an iron storage function for retinal glia and a role for transferrin in neuronal development and differentiation.

Hormonal control of muscle growth

In muscle of whole animals, pituitary growth hormone, the thyroid hormones, and insulin are major growth-promoting hormones, and the glucocorticoids have significant catabolic actions. At the cellular level the primary anabolic hormones for cultured myoblasts are the somatomedins (insulin-like growth factors) and fibroblast growth factor. In these cells physiological concentrations of growth hormone, thyroid hormones, and insulin have no growth-promoting effect; some of the reported actions of insulin probably result from cross-reaction with the somatomedin receptor. Results with purified proteins do not support the view that mitogens block myoblast differentiation; transforming growth factor-beta and interferon are nonmitogenic proteins that inhibit differentiation, insulin-like growth factors are mitogens that stimulate differentiation, and fibroblast growth factor is the only purified mitogen that inhibits differentiation. At least six serum-free media have now been devised for the growth of various kinds of muscle cells under closely defined conditions.

Transferrin receptor numbers and transferrin and iron uptake in cultured chick muscle cells at different stages of development

The mechanism of iron uptake and the changes which occur during cellular development of muscle cells were investigated using primary cultures of chick embryo breast muscle. Replicating presumptive myoblasts were examined in exponential growth and after growth had plateaued. These were compared to the terminally differentiated cell type, the myotube. All cells, regardless of the state of growth or differentiation, had specific receptors for transferrin. Presumptive myoblasts in exponential growth had more transferrin receptors (3.78 +/- 0.24 X 10(10) receptors/micrograms DNA) than when division had ceased (1.70 +/- 0.14 X 10(10) receptors/micrograms DNA), while myotubes had 3.80 +/- 0.26 X 10(10) receptors/micrograms DNA. Iron uptake occurred by receptor-mediated endocytosis of transferrin. While iron was accumulated by the cells, apotransferrin was released in an undegraded form. There was a close correlation between the molar rates of endocytosis of transferrin and iron. Maximum rates of iron uptake were significantly higher in myotubes than in presumptive myoblasts in either exponential growth or after growth had plateaued. There were two rates of exocytosis of transferrin, implying the existence of two intracellular pathways for transferrin. These experiments demonstrate that iron uptake by muscle cells in culture occurs by receptor-mediated endocytosis of transferrin and that transferrin receptor numbers and the kinetics of transferrin and iron uptake vary with development of the cells.

Iron supports myogenic cell differentiation to the same degree as does iron-bound transferrin

T. Hasegawa, K. Saito, I. Kimura, and E. Ozawa (1981, Proc. Jopan Acad. B 57, 206-210) have shown that Fe ion can promote myogenic cell growth as Fe-bound transferrin. In the present work, the effects of these substances in supporting myogenic cell differentiation were examined. The hallmarks of differentiation adopted were appearance of structural and regulatory proteins, myofibrils, sarcoplasmic reticulum, and Ca-activated activities of myosin B and phosphorylase kinase; isoform transition of creatine kinase; and acquisition of cell membrane excitability and contractility following electrical stimulation of myotubes. The degree of differentiation of myotubes cultured in the presence of Fe ion was almost the same as that of myotubes cultured in the presence of Fe-bound transferrin. These facts suggest that transferrin protein molecules do not play a primary role in differentiation. Further, it has also been shown that myotubes acquire excitation-contraction and metabolism coupling qualitatively similar to that of adult muscle fiber.

Necessity of transferrin for RNA synthesis in chick myotubes

Chick transferrin (Tf) is essential not only for growth and differentiation but also for the maintenance of chick myotubes in culture. Its removal from the culture medium gives rise to degeneration of the myotubes. The analysis of this process revealed that the removal resulted in decrease in total and messenger RNA content in the myotubes; this was mainly due to a decrease in RNA synthesis. Activity of in vitro RNA synthesis in isolated nuclei from myotubes cultured without Tf was lower than the activity in nuclei from myotubes cultured with Tf and increased with the addition of FeCl3. Although RNA degradation in myotubes was also enhanced following Tf removal, the degree was small. The synthesis of most proteins was reduced. In contrast to this, a few new proteins of unknown nature were synthesised in myotubes cultured in Tf-free medium. The role of Fe ion carried into the cells by Tf in promoting myogenic cell growth and differentiation and in preventing the myotubes from degeneration can be explained, at least in part, on the basis of its effect on RNA synthesis. Since we have found that Fe is required for activation of RNA polymerase purified from embryonic muscles (Shoji and Ozawa, 1985b), these effects may be ascribed to this activating effect.

Class specificity of transferrin as a muscle trophic factor

The specificity of transferrin (Tf) in its exertion of a growth-promoting effect on myogenic cells was examined using serum Tfs from chick, dove, goose, turkey, bovine, horse, rabbit, rat, and swine and primary myogenic cells from chick, duck, quail, rabbit, and rat, and rat L6 cells. Avian Tfs were effective on avian cells but not on mammalian cells, while mammalian Tfs were effective on mammalian cells but not on avian cells. Dove and bovine Tfs were exceptional in that they were effective on some class-heterologous cells at higher concentrations and less so or completely ineffective on some class-homologous cells. Despite these exceptions, however, the relationship between Tfs and cells can be summarized as a class specificity. To exert the growth-promoting effect, it is prerequisite for Tf to bind its specific receptor on the cell surface. Using quail and L6 cells, we found that the binding of 125I-labeled chick and rat Tfs to the respective receptors of quail and L6 myoblasts was competitively inhibited by other kinds of effective Tfs, but not by ineffective ones. We conclude that the class specificity in myotrophic activity of Tf is due to the affinity between Tf and Tf receptor.

Specificity of chicken and mammalian transferrins in myogenesis

Chicken transferrins isolated from eggs, embryo extract, serum or ischiatic-peroneal nerves are able to stimulate incorporation of [3H]thymidine, and promote myogenesis by primary chicken muscle cells in vitro. Mammalian transferrins (bovine, rat, mouse, horse, rabbit, and human) do not promote [3H]thymidine incorporation or myotube development. Comparison of the peptide fragments obtained after chemical or limited proteolytic cleavage demonstrates that the four chicken transferrins are all indistinguishable, but they differ considerably from the mammalian transferrins. The structural differences between chicken and mammalian transferrins probably account for the inability of mammalian transferrins to act as mitogens for, and to support myogenesis of, primary chicken muscle cells.

Motoneurons purified by cell sorting respond to two distinct activities in myotube-conditioned medium

Spinal motoneurons from chick embryos were purified by retrograde transport and fluorescence-activated cell sorting. Growth conditions for motoneurons were studied, with experiments focused on the effects of conditioned media from chick myotubes, fibroblasts, and spinal cord dividing cells. Motoneurons rapidly extended neurites when plated onto polylysine-coated dishes that had been exposed to these conditioned media. Enzymatic analysis of the substratum-binding, neurite outgrowth-promoting activity from myotube-conditioned medium indicated that it contained heparan sulfate and protein. The neurite outgrowth-promoting activity sedimented as a peak centered at a density of 1.34 in associative cesium chloride gradients, and eluted near the void volume of a Sepharose CL-6B column. Inclusion of myotube conditioned medium in the culture medium of motoneurons also enhanced their survival over periods greater than 2 days in culture. This enhancement of survival could not be explained by myotube-conditioned medium providing motoneurons with a continuous supply of the neurite outgrowth-promoting activity. Media conditioned by spinal cord dividing cells and fibroblasts supported motoneuron survival to some extent, but this effect was not as great as that of myotube-conditioned medium.

There is selective accumulation of a growth factor in chicken skeletal muscle. I. Transferrin accumulation in adult anterior latissimus dorsi

Chick embryo myoblasts in culture will respond to extracts of adult anterior latissimus dorsi muscle with an increase in cell number and an increase in total protein and in myosin heavy chain in fused myotubes. Extracts of adult pectoralis major and of posterior latissimus muscles are only marginally active. The active adult muscle extracts are fractionated by DEAE-cellulose column chromatography and transferrin is identified as the active component based on the following findings: (1) the active fractions are shown to contain an 80K protein that comigrates with chicken transferrin on SDS-PAGE, (2) the active extract from the anterior latissimus dorsi completely replaced embryo extract in the culture medium and supported normal myogenesis, (3) the active extract requires iron for its ability to support myogenesis, (4) the peptide map of the 80K protein is identical to a peptide map of transferrin. Under conditions where the 80K protein is detected in adult anterior latissimus dorsi muscles it is shown that the protein is nevertheless not synthesized in the muscle. These results support the idea that tissues of selective muscles in the adult chicken accumulate transferrin. An accompanying paper shows that transferrin also accumulates in early developmental stages of fast muscle tissue but that accumulation ceases after hatching in these muscles in normal chickens but not in animals of congenic strains with inherited muscular dystrophy.

Trophic effect of iron-bound transferrin on acetylcholine receptors in rat skeletal muscle in vivo

Trophic effect of iron-bound transferrin (FeTf) on the total content of acetylcholine receptors (AChRs) and the specific activity of AChRs in innervated and denervated skeletal muscle was investigated in vivo. The right ischiadic nerves of 15 rats weighing 160 g were transected. FeTf (1.2 mg/ml) was injected daily into bilateral crural muscles of rats for the following 11 days. Control groups received injections of saline or no treatment. FeTf significantly increased the total content of AChRs and the specific activity of AChRs in innervated and denervated muscle compared with control groups (P less than 0.001). This result shows that intramuscular injections of FeTf may be useful for the treatment of disorders of neuromuscular transmission.