Resistance gene homologues in melon are linked to genetic loci conferring disease and pest resistance

Genomic and cDNA fragments with homology to known disease resistance genes (RGH fragments) were cloned from Cucumis melo using degenerate-primer PCR. Fifteen homologues of the NBS-LRR gene family have been isolated. The NBS-LRR homologues show high divergence and, based on the partial NBS-fragment sequences, appear to include members of the two major subfamilies that have been described in dicot plants, one that possesses a TIR-protein element and one that lacks such a domain. Genomic organization of these sequences was explored by DNA gel-blot analysis, and conservation among other Cucurbitaceae was assessed. Two mapping populations that segregate for several disease and pest resistance loci were used to map the RGH probes onto the melon genetic map. Several NBS-LRR related sequences mapped to the vicinity of genetic loci that control resistance to papaya ringspot virus, Fusarium oxysporum race 1, F. oxysporum race 2 and to the insect pest Aphis gossypii. The utility of such markers for breeding resistant melon cultivars and for cloning the respective R-genes is discussed.

An unexpected cause of muscle pain in diabetes

Diabetic muscle infarction is a rare condition which may present to a rheumatologist. It was first reported in 1965. Two illustrative cases are described here and the mechanisms of pathogenesis discussed. Analysis of the published data, results of the muscle biopsies, and a technetium-99m sestamibi scan suggest that the condition, which occurs against a background of diabetic microangiopathy, can be triggered by an ischaemic event and causes extensive muscle necrosis through hypoxia-reperfusion injury and compartment syndrome.

Myositis, polyserositis with a large pericardial effusion and constrictive pericarditis as manifestations of chronic graft-versus-host disease after non-myeloablative peripheral stem cell transplantation and subsequent donor lymphocyte infusion

The clinical features of chronic graft-versus-host disease (cGVHD) following a non-myeloablative peripheral blood stem cell (PBSC) transplant may differ from those that occur after a conventional allograft. We describe a man with Hodgkin's disease refractory to chemotherapy and radiotherapy who was transplanted from an HLA-identical brother, who developed cGVHD characterised, in particular, by polymyositis, polyserositis with a large pericardial effusion and constrictive pericarditis, 1 month after donor lymphocyte infusion for relapsed disease. Constrictive pericarditis has not been previously reported after a conventional allograft, and none of these features have been reported after a non-myeloablative transplant. The course of cGVHD necessitated potent immunosuppression leading to the presumed loss of graft-versus-lymphoma (GVL) effect.

The role of HIV-related chemokine receptors and chemokines in human erythropoiesis in vitro

In order to better define the role of HIV-related chemokines in human erythropoiesis we studied: A) the expression of chemokine receptors, both on human CD34(+) cells which include erythroid progenitors and on more mature erythroid cells; B) the functionality of these receptors by calcium flux, chemotaxis assay and phosphorylation of mitogen-activated protein kinases (MAPK) p42/44 (ERK1/ERK2) and AKT, and finally C) the influence of chemokines on BFU-E formation. We found that HIV-related chemokine receptor CXCR4, but not CCR5, is detectable on human CD34(+) BFU-E cells. CXCR4 surface expression decreased during erythroid maturation, although CXCR4 mRNA was still present in cells isolated from differentiated erythroid colonies. SDF-1, a CXCR4 ligand, induced calcium flux and phosphorylation of MAPK (p42/44) and AKT in CD34(+)KIT(+) bone marrow mononuclear cells which contain BFU-E, as well as chemotactic activity of both human CD34(+) BFU-E progenitors and erythroid cells isolated from day 2-6 BFU-E colonies. Responsiveness to SDF-1 decreased when the cells differentiated to the point of surface expression of the erythroid-specific marker Glycophorin-A. In contrast, the CCR5 ligands (macrophage inflammatory protein-1alpha [MIP-1alpha], MIP-1beta, and RANTES) did not activate calcium flux, MAPK and AKT phosphorylation or chemotaxis of CD34(+)KIT(+) cells or cells isolated from the BFU-E colonies. Interestingly, none of the chemokines tested in this study had any effect on BFU-E colony formation. In conclusion, only CXCR4 is functional, and its specific ligand SDF-1 may therefore play an important role in the homing and/or retention of early erythroid precursors in the bone marrow environment.

Bone marrow CD34(+) cells and megakaryoblasts secrete beta-chemokines that block infection of hematopoietic cells by M-tropic R5 HIV

CD34(+) cells are nonpermissive to infection by HIV strains X4 and R5, despite the fact that many CD34(+) cells express high levels of the viral receptor protein CD4 and the coreceptor CXCR4 on their surface. In these cells, the co-receptor CCR5 protein, which, like CXCR4, is a chemokine receptor, is detected mainly intracellularly. We hypothesized that CD34(+) cells secrete CCR5-binding chemokines and that these factors interfere with HIV R5 interactions with these cells, possibly by binding CCR5 or by inducing its internalization. We found that human CD34(+) cells and CD34(+)KIT(+) cells, which are enriched in myeloid progenitor cells, expressed and secreted the CCR5 ligands RANTES, MIP-1alpha, and MIP-1beta and that IFN-gamma stimulated expression of these chemokines. In contrast, SDF-1, a CXCR4 ligand, was not detectable in the CD34(+)KIT(+) cells, even by RT-PCR. Conditioned media from CD34(+) cell culture significantly protected the T lymphocyte cell line PB-1 from infection by R5 but not X4 strains of HIV. Interestingly, the secretion of endogenous chemokines decreased with the maturation of CD34(+) cells, although ex vivo, expanded megakaryoblasts still secreted a significant amount of RANTES. Synthesis of CCR5-binding chemokines by human CD34(+) cells and megakaryoblasts therefore largely determines the susceptibility of these cells to infection by R5 HIV strains. We postulate that therapeutic agents that induce the endogenous synthesis of chemokines in human hematopoietic cells may protect these cells from HIV infection.

Expression of ACC oxidase genes differs among sex genotypes and sex phases in cucumber

Ethylene has been implicated as a sex-determining hormone in cucumber: its exogenous application increases femaleness, and gynoecious genotypes were reported to produce more ethylene. In this study, three full-length ACC oxidase cDNAs were isolated from cucumber floral buds. RFLP analysis of a population that segregates for the F(femaleness) locus indicated that CS-ACO2 is linked to F at a distance of 8.7 cM. Expression of two of the genes, CS-ACO2 and CS-ACO3, was monitored in flowers, shoot tips and leaves of different sex genotypes. In situ mRNA hybridization indicated different patternsof tissue- and stage-specific expression of CS-ACO2 and CS-ACO3 in developing flowers. CS-ACO3 expression in mid-stage female flowers was localized to the nectaries, pistil and in the arrested staminoids, whereas CS-ACO2 transcript levels accumulated later and were found in placental tissue, ovary and staminoids. In male flowers, petals and nectaries expressed both genes, whereas ACO2 expression was strong in pollen of mature flowers. In young buds, strong expression was observed along developing vascular bundles. Four sex genotypes were compared for CS-ACO2 and CS-ACO3 expression in the shoot apex and young leaf. FF genotypes had higher transcript levels in leaves but lower levels in the shoot apex and in young buds, as compared to ff genotypes; the shoot-tip pattern is, therefore, inversely correlated with femaleness, and the possibility of a feedback inhibition mechanism underlying such correlation is discussed. The two CS-ACO genes studied displayed a differential response to ethrel treatment in different organs and sex genotypes, further demonstrating the complexity of the mechanisms controlling ethylene production during cucumber floral development.

Expression of multiple AGAMOUS-like genes in male and female flowers of cucumber (Cucumis sativus L.)

Members of the MADS-box gene family control reproductive development in higher plants. In cucumber, floral development exhibits several interesting features related to a genetically determined sex-expression mechanism, that affects the differentiation of male and female flowers. In this study, three cDNA homologues of the homeotic gene AGAMOUS have been cloned from early-stage floral buds of Cucumis sativus and fully sequenced. Their expression was studied by Northern analysis using two contrasting sex genotypes, an androecious line and a gynoecious one. The three genes are expressed at low levels at earlier bud stages, the levels rising as the bud matures. Two of the clones, CAG1 and CAG3, are expressed in the third and fourth whorl of mature flowers, while CAG2 is restricted to the carpel; none is expressed in leaves. The transcript levels do not appear to be modulated by gibberellin or ethephon, two treatments that alter sex expression in cucumber. While MADS-box genes probably play an essential role in cucumber floral development, as they do in other plants, our findings may imply that the pathway leading to reproductive organ arrest in cucumber unisexual buds acts independently of MADS-box gene expression.

Prenatal analysis of rhesus CcDEe blood groups by heteroduplex generator

OBJECTIVE

Our purpose was to determine the efficacy of the heteroduplex generator in the prenatal analysis of rhesus CcDEe blood groups.

STUDY DESIGN

A cross-sectional study was performed evaluating fetal samples from 85 women undergoing prenatal diagnosis and comparing the results with standard immunologic serotyping on cord blood delivery.

RESULTS

Of the 85 samples, 64 were tested, for all CcDEe alleles: one case was discrepant. Twenty-one cases were tested solely for the D antigen. Two novel genotypes were detected in the population by heteroduplex generator and confirmed by deoxyribonucleic acid sequencing. Five cases were indeterminate because of an indistinct banding pattern.

CONCLUSIONS

Heteroduplex analysis can identify rhesus blood group alleles and is inexpensive, rapid, and does not use radioactive isotopes.

4-Hydroperoxycyclophosphamide purged autologous bone marrow transplantation in non-Hodgkin's lymphoma patients at high risk of bone marrow involvement

Between June 1990 and January 1994, 19 patients with non-Hodgkin's lymphoma (NHL) at high risk for bone marrow involvement underwent 4-hydroperoxycyclophosphamide (4-HC) purged bone marrow transplantation. Eleven patients had low grade, seven intermediate grade and one high grade NHL and 7/19 patients had received three or more previous chemotherapeutic regimens. Four patients were transplanted in first partial remission (PR) and the remainder in responsive relapse. Fourteen patients had bone marrow (BM) involvement at diagnosis and/or at relapse. The median times to granulocyte and platelet recovery were 26 and 29 days, respectively. There were two toxic deaths and one complete responder developed secondary AML at 31 months post-BMT. Seventeen of 18 evaluable patients achieved a complete remission (CR) and one patient a PR. Fourteen patients (74%) are progression-free at a median follow-up of survivors of 34 months (range 29-55). The 3 year event-free (EFS) and overall survival (OS) probabilities are both 67%. No statistically significant difference was seen between EFS or OS and BM involvement or histologic grade at diagnosis. At 29 months, 4/7 patients with a morphologically involved BM harvest had relapsed or died compared to 1/12 patients with negative BM (P = 0.03). These results are encouraging and warrant further investigation of 4-HC purging in NHL.

Immunohistochemical localization of ORL-1 in the central nervous system of the rat

A novel member of the opioid receptor family (ORL-1) has been cloned from a variety of vertebrates. ORL-1 does not bind any of the classical opioids, although a high affinity endogenous agonist with close homology to dynorphin has recently been identified. We have generated a monoclonal antibody to the N-terminus of ORL-1 to map areas of receptor expression in rat central nervous system (CNS). Intense and specific immunolabeling was observed in multiple areas in the diencephalon, mesencephalon, pons/medulla, and spinal cord. In the telencephalon, intense labeling was observed in the neuropil throughout layers II-V in the neocortex, the anterior olfactory nuclear complex, the pyriform cortex, the CA1-CA4 fields and dentate gyrus of the hippocampus, and in many of the septal and basal forebrain areas. In contrast to other members of the opioid receptor family, light labeling for ORL-1 was observed in telencephalic areas such as caudate-putamen. In the cerebellum, ORL-1 immunoreactivity was only observed in the deep nuclei. Throughout the CNS the majority of labelling was localized to fiber processes and fine puncta, although labeled scattered perikarya were observed in a few brain areas such as the hilus dentate in the hippocampus and some nuclei in the brainstem and spinal cord. The present mapping study is consistent with the reported distribution of ORL-1 mRNA and provides the first immunohistochemical report on anatomical and cellular distribution of ORL-1 receptor in the rat CNS.

Three slow myosin heavy chains sequentially expressed in developing mammalian skeletal muscle

Myosin heavy chain (MyHC) isoforms show a striking diversity of expression patterns during mammalian development. Using a set of monoclonal antibodies that recognize different epitopes on myosin heavy chain isoforms we show that there exist in human and rat skeletal muscle at least three isoforms of slow twitch myosin heavy chain. To facilitate a comparison of our results to others obtained using different antibodies or species, we have identified cDNAs encoding the epitopes recognized by the three slow antibodies. Using these reagents, we show that the onset of expression of three slow MyHC isoforms is temporally distinct during early gestation. This result suggests that a sequence of MyHC transitions plays an important role in determining muscle fiber function at fetal, neonatal, and adult stages.

An anti-B cell autoantibody from Wiskott-Aldrich syndrome which recognizes i blood group specificity on normal human B cells

We previously identified IgM autoantibodies in the sera of patients with Wiskott-Aldrich syndrome (WAS) that react with a subset of normal human B lymphocytes and induce B cell differentiation in vitro. From splenocytes of a patient with WAS we generated heterohybridomas (HY18 and HY21) and a lymphoblastoid cell line (LWA10) that produce human IgM lambda or IgM kappa anti-B lymphocyte autoantibodies, respectively. Immunohistochemical and multiparameter flow cytometric analyses demonstrate that these autoantibodies are specific for lymphocytes of the B lineage and preferentially stain B cells that reside in the mantle zone of secondary follicles and that constitutively co-express the CD5 surface antigen and most major autoantibody-associated cross-reactive idiotypes; in addition, these antibodies stain most pre-B cells in adult bone marrow. Molecular studies show that these anti-B lymphocyte autoantibodies are encoded by a highly conserved VH4 gene, designated VH4.21. The gene encodes a number of autoantibodies, especially anti-i and anti-I IgM cold agglutinins. Hemagglutination and surface labeling studies reveal that HY18 and LWA10 recognize the "i" carbohydrate antigenic determinant(s) which is classically found on human cord red blood cells and, as shown now by this study, on a subpopulation of human B cells which expresses it early in B cell development. These studies raise the possibility that the gene product encoded by this highly conserved germ-line VH4 gene may play a physiological role in B cell development and/or differentiation.

Localization of epitopes and functional effects of two novel monoclonal antibodies against skeletal muscle myosin

Two skeletal myosin monoclonal antibodies, raised against human skeletal myosin, were used to study the correlation between function, primary and tertiary structure of S-1 prepared from rabbit skeletal myosin. The heavy chain of S-1 is cleaved into three fragments by trypsin--27 kDa, 50 kDa and 20 kDa--aligned in this order from the N-terminus. The epitope of the first antibody was assigned to the N-terminal 1-23 amino acid stretch of S-1, since it reacted with the 27 kDa N-terminal tryptic fragment of S-1 but not with a derivative of the 27 kDa fragment, which lacks the above amino acid stretch. The epitope of the second antibody was assigned to the 3 kDa N-terminal region of the central 50 kDa domain of S-1. This assignment was based on proteolytic and photochemical cleavage of S-1 and on the labelling of its N-terminus by a specific antibody. The antibodies were visualized binding to the myosin head on electron micrographs of rotary-shadowed complexes of antibodies with myosin. Measurements on the micrographs indicated that the distances between the head-tail junction of myosin and the 'anti-27 K' and 'anti-50 K' epitopes are 14 nm and 17 nm, respectively. Both antibodies have a high affinity to S-1. The affinity of the 'anti-50 K' to S-1 decreased upon actin binding, while that of the 'anti-27 K' was not affected by binding of S-1 to F-actin. The 'anti-50 K' antibody inhibited the K+ (EDTA) and the actin-activated ATPase activity of S-1, while the 'anti-27 K' had no effect. The results indicate that either the epitope of the 'anti-50 K' is near to the actin or to the ATP-binding sites of S-1, or that there is communication, expressed as propagated conformational changes, between these sites and the epitope.

Trisomy 3 in cold agglutinin disease

Cold agglutinin disease (CAD) is a form of autoimmune hemolytic anemia generally considered to result from an antibody-producing clonal expansion of B lymphocytes. We studied 16 patients with CAD and demonstrated a chromosomally abnormal clone in the peripheral blood (PB) of six. Trisomy 3 was the only abnormality in two patients, trisomy 12 the only abnormality in one, and both trisomy 3 and trisomy 12 were present in three patients. A lymphoma was subsequently diagnosed in two of these six patients and in none of the patients without a karyotypic abnormality. The results suggest that trisomy 3 confers a slight growth advantage in the B-cell lineage, particularly at a relatively late stage of differentiation. The resultant clone may present clinically as CAD and, in some cases, progress to a clinical lymphoma.

Development of muscle fiber types in the prenatal rat hindlimb

Immunohistochemistry was used to examine the expression of embryonic, slow, and neonatal isoforms of myosin heavy chain in muscle fibers of the embryonic rat hindlimb. While the embryonic isoform is present in every fiber throughout prenatal development, by the time of birth the expression of the slow and neonatal isoforms occurs, for the most part, in separate, complementary populations of fibers. The pattern of slow and neonatal expression is highly stereotyped in individual muscles and mirrors the distribution of slow and fast fibers found in the adult. This pattern is not present at the early stages of myogenesis but unfolds gradually as different generations of fibers are added. As has been noted by previous investigators (e.g., Narusawa et al., 1987, J. Cell Biol. 104, 447-459), all of the earliest generation (primary) muscle fibers initially express the slow isoform but some of these primary fibers later lose this expression. In this study we show that loss of slow myosin in these fibers is accompanied by the expression of neonatal myosin. This switch in isoform expression occurs in all primary fibers located in specific regions of particular muscles. However, in other muscles primary fibers which retain their slow expression are extensively intermixed with those that switch to neonatal expression. Later generated (secondary) muscle fibers, which are interspersed among the primary fibers, express neonatal myosin, although a few of them in stereotyped locations later switch from neonatal to slow myosin expression. Many of the observed changes in myosin expression occur coincidentally with the arrival of axons in the limb or the invasion of axons into individual muscles. Thus, although both fiber birth date and intramuscular position are grossly predictive of fiber fate, neither factor is sufficient to account for the final pattern of fiber types seen in the rat hindlimb. The possibility that fiber diversification is dependent upon innervation is tested in the accompanying paper (K. Condon, L. Silberstein, H.M. Blau, and W.J. Thompson, 1990, Dev. Biol. 138, 275-295).

Differentiation of fiber types in aneural musculature of the prenatal rat hindlimb

The presynaptic neurotoxin, beta-bungarotoxin, was injected into rat fetuses in utero to destroy the innervation of their hindlimb muscles. These injections were made prior to the invasion of motor axons into the muscles and, in some cases, prior to the cleavage of individual muscles. Examination of the lateral motor column of the spinal cord showed a dramatic reduction (greater than 95%) in the number of motoneuron cell bodies. Staining of sections of the hindlimb with silver and with antibodies to neurofilament proteins and to a synaptic vesicle protein indicated that the muscles were aneural. Anti-myosin antibodies applied to sections of the hindlimb revealed that these aneural muscles by the 20th day of gestation had the same types of fibers as were present in normal muscles of the same age. Moreover, fiber types in most muscles showed their characteristic intramuscular distributions. These findings suggest that fiber types can differentiate in the absence of the nervous system. However, some fibers achieved their ultimate fiber type fate without passing through the normal sequence of myosin expressions. Moreover, some slow fibers lost their slow expression, suggesting that the maintenance of the slow differentiation may require innervation. Muscle growth was dramatically affected by the absence of motoneurons; some muscles were decreased in size and others disappeared completely. In muscles which had not degenerated by the time secondary myogenesis normally begins, secondary muscle fibers were generated indicating that the genesis of these fibers is not strictly nerve dependent. Because fiber types differentiate independently of the nervous system, this study suggests that motoneurons selectively innervate fiber types during normal development.

Transfusion therapy in emergency medicine

Volume replacement is critical to the resuscitation of the hemorrhaging patient, but this usually can be accomplished quickly and safely with crystalloid and/or colloid solutions. Red cells should be used in addition to asanguinous fluids in the treatment of tissue hypoxia due to anemia. The need for whole blood as opposed to packed red blood cells is controversial. However, plasma should not be used as a volume expander, and its use to supplement coagulation factors during the massive transfusion of red cells should be guided by laboratory tests that document a coagulopathy. Similarly, platelet transfusions are indicated to correct documented thrombocytopenia or platelet dysfunction, and routine prophylaxis after fixed volumes of red cells results is unwarranted. Many anticipated complications of massive transfusions, including hemostatic abnormalities, acid-base imbalances, hyperkalemia, and hypocalcemia, are uncommon or of limited clinical significance. The risks of immune hemolysis and transfusion-transmitted diseases, on the other hand, are significant, and argue for judicious use of blood components. In emergencies in which blood is required immediately before compatibility testing can be completed, O-negative uncrossmatched blood can be requested. Careful blood specimen collection and patient identification prior to transfusion are critical. Practices that emphasize blood conservation, including the use of autologous salvaged blood, are always to the patient's advantage.

Fast muscle fibers are preferentially affected in Duchenne muscular dystrophy

We show that Duchenne muscular dystrophy (DMD) selectively affects a subset of skeletal muscle fibers specialized for fast contraction. Muscle fiber types were characterized immunohistochemically with monoclonal antibodies that distinguish isoforms of fetal and adult-fast or adult-slow myosin heavy chain present in the same fiber. Fetal myosin expression increased with patient age and was not due to arrested development but rather to de novo synthesis, which served as a sensitive indicator of muscle regeneration. A subset of fast fibers were the first to degenerate (type IIb). Extensive fast fiber regeneration occurred before slow fibers were affected. These results suggest that the DMD gene product has a specific function in a subpopulation of muscle fibers specialized to respond to the highest frequency of neuronal stimulation with maximal rates of contraction.

Benefit of a 37 degree C extracorporeal circuit in plasma exchange therapy for selected cases with cold agglutinin disease

Plasmapheresis is commonly advocated in cold agglutinin disease with life-threatening hemolysis. Some clinicians, however, are reluctant to use this therapy because of perceived technical problems and risks attendant with the temperature of the extracorporeal circulation. In this study we report our experience of two patients with severe life-threatening hemolysis and in whom plasma exchange was not feasible due to red blood cell autoagglutination in the extracorporeal circuit. A method is described involving the use of blood warmers and the Fenwal CS-3000 blood cell separator with its 37 degrees C centrifuge compartment. The use of plasma exchange in this manner is a safe and beneficial form of adjunctive therapy and should be considered for patients with cold agglutinin disease at risk for extracorporeal agglutination or hemolysis.

Reinnervation of muscle fiber types in the newborn rat soleus

We have examined the selectivity of reinnervation of fiber types in rat soleus muscle denervated by crush of the soleus nerve 2 d after birth. The fibers innervated by single, regenerated motor axons were identified by use of glycogen depletion approximately 2 weeks following denervation. The types of fibers were determined by immunohistochemistry employing anti-myosin antibodies and, in some cases, by myofibrillar ATPase staining. Two distinct types of fibers are present in soleus at 2 d and through the next 16 d of normal postnatal development. These fiber types are retained in a denervated muscle for the period of time required for reinnervation. Although 40% of the fibers are lost from the muscle during reinnervation, we find no evidence for interconversion of muscle fiber types. Nonetheless, 10 of the 12 single motor units examined had fiber type compositions that were markedly biased toward one or the other of these 2 types; the bias in these units could not be explained by chance reinnervation. On the basis of the topographical distribution of the muscle fibers in each of these units, the motor axons reinnervated a novel set of fibers. We interpret these findings to mean that neonatal soleus motor neurons reinnervate fiber types in a selective manner. This selective innervation may explain the bias in the fiber type composition of normal motor units during early postnatal development.

Blood transfusions in surgery of the larynx and neck

Effective utilization of blood and blood products is an important consideration in elective surgical procedures. A cost-effective process will maintain availability to the general population while supplying reasonable surgical needs. Removing stored blood from the general pool strains these resources and drastically increases cost. To establish the first clinical model of study and to better predict blood requirements for elective surgery of the larynx and neck, medical records of 137 consecutive patients who underwent laryngeal surgery from January 1, 1981 to June 30, 1984 were reviewed. All patients had one or a combination of one of the following: radical neck dissection, total laryngectomy, hemilaryngectomy, and/or supra-glottic laryngectomy. Data analyzed included estimated allowable blood loss, estimated intraoperative blood loss, as well as preoperative and postoperative blood hemoglobin concentrations. Actual blood utilization was adjusted for individual patient need, and recommendations for appropriate blood screen and crossmatch were derived for each of the above surgical procedures. It was concluded that blood availability for the individual patient is best assessed by the surgeon.

Developmental progression of myosin gene expression in cultured muscle cells

Myosin heavy chains are encoded by distinct members of a multigene family at different stages of muscle development. Study of the underlying regulatory mechanisms has been hindered because transitions in myosin expression have not been readily attained in tissue culture. Here we show a transition from early (fetal) to late (perinatal/adult) myosins defined by two monoclonal antibodies, F1.652 and N3.36, in the myotubes of mouse C2C12 cells. On day 1 of differentiation, essentially all myosin was early myosin. By day 8, early myosin dropped to 25% of its day 1 value and was replaced by late myosin. The transition occurred without neural contact, connective tissue components, or complex substrates, suggesting that its regulation may be intrinsic to the muscle cell. Our results demonstrate that a developmental progression in myosin gene expression, which occurs rapidly, with high frequency, and under relatively simple conditions, is now amenable to molecular analysis in cultured muscle cells.

Purification to homogeneity and amino acid sequence analysis of two anionic species of human interleukin 1

Two anionic species of human IL-1 have been purified to homogeneity. These molecules were characterized as having pI of 5.4 and 5.2 and molecular weights identical to IL-1/6.8 (17,500). The specific activities of IL-1/5.4 and IL-1/5.2, as measured in the mouse thymocyte co-mitogenic assay, were identical to that of IL-1/6.8, namely 1.2 X 10(7) U/mg, with half-maximal stimulation observed at 2 X 10(-11) M. IL-1/5.4 and IL-1/5.2 were found to be antigenically distinct from IL-1/6.8 in an ELISA. IL-1/5.4 was structurally distinct from IL-1/6.8 based on reverse-phase HPLC or CNBr peptides. Intact IL-1/5.2 and three intact CNBr peptides of IL-1/5.4 were sequenced, with the identification of 74 amino acid residues. These sequences were found to correspond exactly with the amino acid sequence deduced from the IL-1-alpha cDNA reported by March et al.

Plasticity of the differentiated state

Heterokaryons provide a model system in which to examine how tissue-specific phenotypes arise and are maintained. When muscle cells are fused with nonmuscle cells, muscle gene expression is activated in the nonmuscle cell type. Gene expression was studied either at a single cell level with monoclonal antibodies or in mass cultures at a biochemical and molecular level. In all of the nonmuscle cell types tested, including representatives of different embryonic lineages, phenotypes, and developmental stages, muscle gene expression was induced. Differences among cell types in the kinetics, frequency, and gene dosage requirements for gene expression provide clues to the underlying regulatory mechanisms. These results show that the expression of genes in the nuclei of differentiated cells is remarkably plastic and susceptible to modulation by the cytoplasm. The isolation of the genes encoding the tissue-specific trans-acting regulators responsible for muscle gene activation should now be possible.

The effects of a myasthenic serum on the acetylcholine receptors of C2 myotubes. I. Immunological distinction between the two toxin-binding sites of the receptor

We have examined the effect of a serum from a patient with myasthenia gravis on the binding of alpha-bungarotoxin (alpha-BuTx) to the acetylcholine receptors (AChRs) of a mouse muscle cell line, C2. After a 2-hr incubation, antibodies in the serum reduced toxin binding to C2 myotubes to a maximal extent of approximately 50%. The degradation of surface AChRs could account for the loss of only 5% of sites during the incubation; the remainder, therefore, must have been lost by blockage of binding. To investigate whether the antibodies blocked specifically one of the two toxin-binding sites that each AChR possesses, we used an analysis based on that of Sine, S. W., and P. Taylor, [1981) J. Biol. Chem. 255: 10144-10156). Although the two sites could not be distinguished by their rates of binding of alpha-BuTx, d-tubocurarine (dTC) inhibition of the initial rate of toxin binding revealed that the sites had affinities for dTC that differed by approximately 30-fold. Incubation with the myasthenic antibodies reduced the number of high affinity dTC sites, without affecting those of low affinity. We conclude that the two toxin-binding sites of the AChR are immunologically distinct.

A postnatal change in the immunological properties of the acetylcholine receptor at rat muscle endplates

We have used a myasthenic serum that in adult rat muscle is specific for acetylcholine receptors (AChRs) in the extra-junctional membrane to characterize the AChRs at developing endplates. Immunocytochemical experiments show that AChRs at endplates in the rat diaphragm bind the myasthenic antibodies during the first week after birth but lose their reactivity during the second and third postnatal weeks. AChRs at endplates in adult rat diaphragm do not bind the antibodies even after denervation; in contrast, AChRs at endplates in an adult chicken muscle (anterior latissimus dorsi) are recognized by the antibodies. The loss of immunological reactivity thus may be correlated with a change in the channel properties of the AChR and with the appearance of synaptic folds, two postnatal developmental changes that occur at the endplates of rats, but not of chickens.

Developmental regulation of 16S acetylcholinesterase and acetylcholine receptors in a mouse muscle cell line

We have studied the appearance, distribution and regulation of acetylcholinesterase (AChE) and acetylcholine receptors (AChRs) in a mouse skeletal muscle cell line (C2), that was originally isolated and described by Yaffe & Saxel [54]. In culture, cells from this line form spontaneously contracting myotubes, with overshooting action potentials that are TTX-sensitive. After fusion of myoblasts into myotubes, there was a dramatic increase in the amount of both AChE and AChR. Three forms of AChE, distinguished by their sedimentation on sucrose gradients, were synthesized: 4-6S, 10S, and 16S. The 4-6S and 10S forms appeared 1 day after the cells began to fuse, whereas the 16S form appeared only 2 days after fusion began. Maximal levels of the 16S AChE form (25-30% of the total) were obtained by reducing the concentration of horse serum in the fusion medium. Prevention of myoblast fusion by reducing the calcium levels in the medium decreased the total AChE by 70%, and only the 4-6S form was synthesized. Blocking spontaneous contractile activity of the myotubes by tetrodotoxin (TTX) led to a 50% reduction in all three esterase forms. Thus, the 16S, or endplate form of AChE is not specifically regulated by electrical or contractile activity in the C2 cell line. After fusion the number of AChRs increased rapidly for 3-4 days and then stabilized. Receptor clusters, ranging from 10-30 micron in length, appeared 1 day after myoblast fusion began. When cells were grown in medium containing reduced Ca2+, the total number of AChRs was decreased by 20-50%. Reduction of Ca2+ after myotubes and AChR clusters had formed resulted in dispersal of AChR clusters. Inhibition of muscle contractions with TTX did not affect the number of AChRs or their distribution.

Neuronal cultures on microcarriers: dissociated spinal cord cells

Dissociated spinal cord cells from rat fetuses were successfully cultured up to the state of synaptogenesis and myelin formation on DEAE cellulose cylindrical microcarriers. Nerve cells and microcarriers interconnected to form conglomerates offering optimal nutritional conditions which enhanced cell maturation. These conglomerates yielded large amounts of cells which could easily be harvested for biochemical analysis.

Association of the synaptic form of acetylcholinesterase with extracellular matrix in cultured mouse muscle cells

Myotubes of a mouse muscle-cell line (C2) synthesize in culture a 16S form of acetylcholinesterase that is normally found only in regions of adult mouse muscle that contain endplates. The 16S enzyme in C2 cell extracts has the properties expected of acetylcholinesterase forms that have a collagen-like tail. In intact cells, the active site of the 16S acetylcholinesterase is protected by a membrane-impermeable inhibitor, and this form of the enzyme can be removed by treatment of the cells with collagenase. Thus the enzyme is extracellular. Its extraction by high ionic strength solutions lacking detergent suggests that the 16S form is associated with the extracellular matrix by ionic interactions. Histochemical staining shows focal patches of acetylcholinesterase activity on the cell surface. Collagenase treatment, which removes only the 16S form, abolishes this staining pattern, indicating that the patches consist of the 16S enzyme. We conclude that the 16S enzyme in C2 myotubes occurs in focal patches on the cell surface, where it is associated with the extracellular matrix.

DE-52 and DE-53 cellulose microcarriers. I. Growth of primary and established anchorage-dependent cells

DEAE cellulose anion exchangers having small ion exchange capacity (0.5 to 2.0 meq/g dry material) were tested for cell attachment kinetics and capacity to support growth anchorage-dependent cells. It was found that cells from established cell lines (BHK and MDCK) can grow to confluency on DEAE cellulose particles having exchange capacity of 1 and 2 meq/g dry materials, DE-52 and DE-53, respectively. On the other hand, chick embryo fibroblasts (primary cells) can grow only on DE-53 particles.

Investigation of immunological relationships among myosin light chains and troponin C

Two classes of myosin light chains can be distinguished functionally: those that restore calcium regulation to "desensitized" scallop myofibrils, and those that do not (Kendrick-Jones, J., et al. (1976), J. Mol. Biol. 104, 747--775). Despite this functional classification, chemical analyses reveal few patterns unique to regulatory light chains, and, indeed, sequence comparisons suggest structural similarities between both classes of myosin subunits (Collins, J. H. (1977), Nature (London) 259, 699--700; Kendrick-Jones, J., and Jakes, R. (1977), in International Symposium on Myocardial Failure at Tegernsee, Riecker, G., and Boehringer, Ed., Munich, West Germany, Springer-Verlag, pp. 28--40). Immunological assays using antisera to regulatory and to nonregulatory light chains showed no correlation between antigenic activity and the presence or absence of regulatory function. Weak cross-reactivity was observed, however, among myosin light chains and troponin C, consistent with the suggestion made on the basis of sequence homologies that these subunits contain similar structural domains (Weeds, A. G., and McLachlan, A. D. (1974), Nature (London) 252, 646--649). Unexpectedly, the strongest cross-reactivity observed was that between the vertebrate myosin alkali 1 and DTNB light chains.