A Matrix Associated Region Localizes the Human SOCS-1 Gene to Chromosome 16p13.13

The MarFinder algorithm was applied to a newly sequenced segment of 16p13.13 abutting the 3 end of the human PRM1 PRM2 TNP2 locus. A candidate region of matrix attached was identified. Subsequent biophysical analysis showed that this region was attached to the somatic nuclear matrix. Nucleotide sequence analysis also revealed the presence of a CpG island. Data base queries showed that this region contained the SOCS-1 gene. Thus, the SOCS-1 gene is bounded by a somatic MAR and is just 3 of the spermatid-expressed PRM1 PRM2 TNP2 domain at position 16p13.13.     

Spectrum of spontaneous missense mutations causing cyclic AMP-resistance phenotypes in cultured S49 mouse lymphoma cells differs markedly from those of mutations induced by alkylating mutagens

Mutants of S49 mouse lymphoma cells resistant to cytolysis by analogs of cyclic AMP (cAMP) generally have missense mutations in the gene encoding the regulatory subunit of cAMP-dependent protein kinase. We have compared the mutations in 95 spontaneous isolates with those in 60 mutagen-induced isolates by sequence analysis of amplified cDNAs. Twenty-nine single basepair substitutions in 19 codons produced selectable phenotypes. The spontaneous mutant spectrum was dominated by a CpG transition hotspot in the codon for Arg334. This and other nearby CpG sites were found to be methylated in genomic S49 cell DNA by restriction enzyme analyses. Most of the remaining spontaneous mutants had either G-CC-G or T-AG-C transversions, which have been associated with damage caused by oxygen radicals. In contrast, the majority of mutants induced with the alkylating mutagens ethyl methanesulfonate (EMS) and N-methyl-N-nitro-N-nitrosoguanidine had G-CA-T mutations at non-CpG sites; in addition, EMS induced several A-TG-C, A-TT-A, and G-CT-A substitutions. A single ICR191-induced mutant analyzed had a unique A-TG-C lesion. A number of spontaneous and mutagen-induced isolates had closely linked double or triple substitutions, and two isolates had tandem triple substitutions.     

Spatial properties of the visual detectability of moving spatial white noise

Summary We determined the spatial parameters that describe the visual detection of spatio-temporal correlation in moving two-dimensional noise patterns. The target field (5.21×5.31 deg of visual angle) was divided into horizontal stripes of equal width D. Adjacent bars alternately contained noise patterns moving with velocity v₁ and v₂. We varied D, v₁ and v₂.Roughly three different percepts occurred. If the stripes were very broad the different movements in alternate stripes were perceived together with the division of the field into stripes. If the stripes were very narrow the division into stripes was not seen, but the moving noise patterns with velocities v₁ and v₂ were perceived as transparent sheets moving through each other. For intermediate stripe widths the target field looked incoherent and the subject was not clear about the percept. In this region the subject found it difficult and sometimes impossible to discriminate these patterns from a completely uncorrelated spatiotemporal white noise pattern (snow).To quantify the detectability, the patterns were masked with snow (spatio-temporal white noise). The r.m.s. contrast of the total stimulus was kept at a constant value, whereas the subject set the signal-to-noise ratio (SNR) to a threshold value. At certain barwidths the thresholds reached a maximum value. These critical barwidths depended on the velocities v₁ and v₂.These critical barwidths were interpreted in terms of a simple general model for the detection of spatiotemporal correlation. In these terms the span of the elementary correlators rose monotonically with the velocity to which the correlator is most sensitive.Supported in part by the Netherlands Organization for the Advancement of Pure Research (Z.W.O.)     

The role of acidic residues in the “fusion segment” of influenza A virus hemagglutinin in low-pH-dependent membrane fusion

Summary To clarify the role of acidic amino acid residues in the fusion segment of hemagglutinin (HA) of influenza A virus (H1N1) in pH-dependent membrane fusion, we have constructed and expressed five mutant HA cDNAs in CV-1 cells by SV40-HA virus vectors (SVHA). Fusion activities of the five mutant HAs were examined by lipid mixing and polykaryon formation assays. In spite of the substitution of Gly and Lys for the acidic residues, all the mutants were found to retain their low-pH-dependent fusion activity by lipid mixing assay. Although SVHA-G19(HA₂19D G), –K11 (HA₂11E K) and –K19(HA₂19D K) induced polykaryon formation at low pH as wild type HA did, SVHA-G11(HA₂11E G) induced limited polykaryon formation and SVHA-G11,19 (HA₂11E G, 19D G) did not. The substitution of Gly for Glu at position 11 inhibited widening of the initial fusion pore. However, Lys mutants induced the formation of an initial fusion pore and widened it at low pH where Lys residues might have positive charges. These results suggest that the neutralization of the charges on acidic residues in the fusion segment at low pH is not important for interaction of the fusion segment with the target lipid bilayer or for triggering the membrane fusion.     

The effects of thyroid status on some properties of rat fast-twitch muscle

Summary The effects of different thyroid states on some histochemical and biochemical properties of fast-twitch muscle were studied using rat extensor digitorum longus (EDL) muscle. This muscle was found to be much less responsive to thyroidal influence than the slow-twitch soleus muscle. In EDL muscles of hypothyroid rats, fast slow conversions were observed in fibre type composition, myosin ATPase activity and light chain pattern, and in the subunit composition of lactate dehydrogenase, while the only significant slow fast conversion observed in thyrotoxicosis was a decrease in the proportion of slow-oxidative fibres. Denervation of the hypothyroid muscle produced the highest degree of fast slow transformation. These findings support the view that denervation and dysthyreosis alter gene expression in muscle by independent mechanisms.     

Temporal properties of the visual detectability of moving spatial white noise

Summary We obtained movement detection thresholds for two-dimensional random speck-patterns (Julesz patterns) homogeneously moving over the whole target field (5.21×5.31 degrees of visual angle). We alternated between two uncorrelated but otherwise similar patterns, one moving with velocity v₁, the other with velocity v₂, such that each pattern was on for T ms. We masked this pattern (signal) with spatio-temporal white noise (snow). The total r.m.s. contrast was kept constant, whereas the ratio of the r.m.s. contrasts of signal and noise was varied. The square of this ratio was designated SNR.At low SNR values the pattern was not perceptually different from the snow alone. At high SNR values the subject detected spatio-temporal correlation (e.g., movement). In these experiments we determined the threshold SNR values as a measure of the detectability of spatio-temporal correlation as a function of the parameters T, v₁ and v₂.When v₁ and v₂ were sufficiently dissimilar one of three percepts occurred: for very large T the alternation could be followed, for very small T two transparent, simultaneously moving sheets of noise-pattern with different velocities could be seen. For intermediate T-values no systematic movement at all could be observed. At these T-values the threshold SNR was maximal. This critical T-value decreased with increasing velocity.We found that it was possible to have more than one percept of uniform smooth movement at a single location in the visual field if these movements had velocity vectors with an angular difference of at least 30 deg or if their magnitudes differed by at least a factor of 4.Supported in part by the Netherlands Organization for the Advancement of Pure Research (Z.W.O.)     

Counts of Stromal Precursor Cells in Heterotopic Splenic Transplants in CBA Mice of Different Age

The content of stromal precursor cells in heterotopic splenic transplants from old and young mice changed appreciably after cross transplantation to old and young animals. The content of CFC-F in the youngold transplants decreased almost 1.5 times in comparison with the youngyoung transplants, the counts of CFC-F in oldold transplants were minimum in comparison with all other groups (2.5±0.1), while in the old young group transplants this value increased almost 8-fold (to 19.0±1.3) and surpassed the control level. Age-associated shifts in the splenic stromal tissue were determined by regulatory influences of the host, rather than by decreased count of stromal precursor cells in the tissue.__________Translated from Byulleten Eksperimentalnoi Biologii i Meditsiny, Vol. 139, No. 2, pp. 196–198, February, 2005     

Polymerase chain reaction-single strand conformation polymorphism analysis of the p53 gene in paraffin-embedded surgical material from human renal cell carcinomas

p53 tumour suppressor gene mutations were studied in 118 renal cell carcinomas using paraffin-embedded surgical material. Optimal results were obtained with analysis of exon lengths between 150 and 200 base pairs for polymerase chain reaction. Single strand conformation polymorphism and sequencing analysis revealed only two point mutations (2/118, 2%): one involving codon 135; TGCTTC (cysteinephenylalanine) and the other codon 175; CGCCAC (argininehistidine). Both of these cases were classified as granular cell subtype on microscopic observation. The data suggest that the p53 tumour suppressor gene is not related to tumour initiation, promotion, or progression of renal cell carcinomas. However, there is the possibility that granular cell type carcinomas may have a different genetic background from clear cell type renal neoplasms.     

Transient expression of myosin heavy chain MHCIα in rabbit muscle during fast-to-slow transition

The expression of an -cardiac-like myosin heavy chain, MHCI, was investigated at both the mRNA and protein levels in rabbit tibialis anterior muscle undergoing fast-to-slow transition by continuous chronic low-frequency stimulation (CLFS). According to sequence analyses of the PCR product, the MHCI isoform was found to be identical to the -cardiac MHC expressed in rabbit atrium. In muscles at different degrees of transformation, the upregulation of MHCI mRNA preceded that of the MHCI mRNA. At more advanced stages of the transformation, MHCI mRNA decayed while MHCI mRNA persisted at high levels. The expression of MHCI, therefore, was transitory. Studies at the protein level were based on immunoblotting using a monoclonal antibody (F88 12F8,1), characterized to be specific to MHCI in rabbit muscle. These studies revealed a similar relationship between initial increase and successive decline of the MHCI protein as seen at themRNA level. Immunohistochemistry of 30-day stimulated muscle revealed that up to 65% of the fibres expressed the MHCI isoform in combination with other adult MHC isoforms. The most frequent patterns of coexistence were MHCIIa+MHCI + MHCI (28%), MHCI+MHCI (18%), and MHCIIa + MHCI (11%). According to these combinations, the upregulation of MHCI may be assigned as an intermediate step in the transformation of existing fibres during theMHCIIa MHCI transition. A small fraction of fibres contained, in addition to the MHCI + MHCI and MHCIIa + MHCI combinations, developmental myosin, suggesting that MHCI was also expressed in regenerating fibres originating from satellite cell-derived myotubes.     

DNA fingerprinting involving fluorescence-labeled termini of any enzymatically generated fragments of DNA

Summary We have developed a new fluorescence-based method for DNA fingerprinting that does not require a fluorescent linker or a synthetic oligonucleotide primer, both of which are normally used for labeling of DNA. Cosmid DNAs are digested with appropriate restriction enzymes and the 3 termini of DNA fragments are labeled with the corresponding, fluorescent dye-conjugated dideoxynucleotide triphosphate terminator (dye-ddNTP) by the Klenow fragment of DNA polymerase I fromEscherichia coli, which has 35 exonuclease and replacement activities as well as its main 53 polymerase activity. Samples are separated on a DNA-sequencing gel and data are analyzed by application of both the Version 0.3.8a mapper program (Applied Biosystem Inc., Foster City, CA) and our Overlap I program that facilitate rapid analysis of the frequency of overlapping of cosmid DNAs. Using this method we have determined the overlap frequency of DNA fragments of each cosmid clone from the mouse MHC class I gene cluster.     

Identification of genetic alterations associated with the process of human experimental colon cancer liver metastasis in the nude mouse

Understanding the genetic elements controlling the process of tumor metastasis to distant organ sites such as the liver may be the key to improving survivorship from colon cancer. By using standard cytogenetic techniques in combination with comparative genomic hybridization, multiple genetic imbalances within three human colon cancer cell lines previously selected for differences in liver-metastatic behavior were identified. The entire genome of one poorly metastatic cell line (KM12C) was compared directly with that of two highly metastatic cell lines (KM12SM, KM12L4A) derived from it. A number of chromosomal gains (8q, 12g15, 20q11.2) and losses (5p13, 6p21.3, 18) were common to all three cell lines and are likely related to early tumor development rather than to the selection process used to generate cell lines of increased metastatic potential. Chromosomal imbalances detected only in the highly metastatic cell lines were also observed. KM12SM showed losses of portions of 2p22, 2824.32q32.2, 4p15.3cen, 4q24 without the 13q and 15q22.3 gains noted for KM12C. Both gains (1p31.31p21, 28222q33, 3cen3q26.2, 5q145q23, 6cen6q23) and losses (16p, 17p, 17q, 19p, 19q, 22q) were observed for KM12L4A but not for the other two cell lines. Identification of these alterations provides valuable insight into the process of experimental liver metastasis and is a first step towards mapping genes linked to the terminal phases of human colon cancer progression.     

Distribution of glycoconjugates in the optic vesicle and optic cup

Summary Lectin histochemical methods and immunohistochemical techniques have been utilized to investigate and partially characterize glycoconjugates in the developing eye. Peanut-lectin-binding sites associated with radial glial cells were found in the diencephalon. In the optic primordia, binding sites associated with radial glia were masked by terminal sialic acid, and only reacted with peanut lectin when pretreated with sialidase. This finding indicates that glycoconjugates associated with diencephalic radial glia contain terminal galactose--(13)N-acetyl galactosamine, but glycoconjugates associated with radial glia in the optic primordia contain sialic acidgalactose-(13)N-acetyl galactosamine. The selective distribution of galactose, N-acetyl galactosamine and fucose associated with radial glial cells has also been demonstrated. We postulate that these distributions mediate the shaping of the developing eye.This work was supported by NIH Grants # NS 11066 and # DE 05832     

Altered expression of the steroid bioconverting pathway in pAN 7-1 transformants of Cochliobolus lunatus

Summary The filamentous fungus C. lunatus converts progesterone mainly to its 11-hydroxy derivative. C. lunatus transformed with the plasmid pAN 7-1, which contains the E. coli hph gene expressed under the control of the A. nidulans gpd and trpC expression signals, lacks this activity, but exhibits acetyl side chain degradation of progesterone through the reaction scheme progesterone20-hydroxy-progesterone ⁴-androstene-3,17-dione testolactone+testosterone. The main partof this metabolic pathway is not expressed in the non-transformed strain. It was determined that the site-specific integration of the plasmid into the genome directly influences the expression of genes involved in the bioconversion of steroids.     

Die s?ulenchromatographische Fraktionierung der sauren Mucopolysaccharide im Harn

Zusammenfassung Es wurde eine säulenchromatographische Methode beschrieben, die es gestattet, Heparitinsulfat (Heparansulfat) (HMS), Chondroitinsulfat A und C [Chondroitin-4-Sulfat (CSA), Chondroitin-6-Sulfat (CSC)], Chondroitinsulfat B (Dermatansulfat) (CSB) und Keratosulfat (Keratansulfat) (KS) deutlich voneinander zu trennen und einzeln colorimetrisch (z. B. mit der Carbazol- und/oder Anthron-Reaktion) zu bestimmen. Als Trägersubstanz diente Dowex 1 × 2. Die Elution erfolgte mit NaCl-Lösungen steigender Konzentration: 0,5 m, 1,25 m (HMS); 1,5 m (CSA, CSC); 2,0 m (CSB); 3,0 m (KS).Die Vollständigkeit der Trennung wurde durch Bausteinanalyse der erhaltenen Elutionsgipfel (Bestimmung des Hexuronsäure-, Hexosamin-, Neutralzukkergehaltes) und Papierchromatographie geprüft und mit gereinigten sauren Mucopolysacchariden (SMP) verglichen.Für die Anwendung der Dowex-Säulenchromatographie zur Ermittlung des SMP-Musters im menschlichen Harn wurde folgender Arbeitsgang vorgeschlagen: Dialyse des 24 h-Harnes gegen 0,9%ige NaCl-Lösung Fällung der Gesamt-SMP mittels Cetyltrimethylammoniumbromid Waschen des Präcipitates mit NaCl-gesättigten 95%igen Äthanol DowexSäulenchromatographie colorimetrische Bestimmung des Hexuronsäure- und Hexosegehaltes jeder Fraktion.Bei Normalpersonen konnte mit dieser Methode HMS, CSA, CSB und KS im Harn nachgewiesen werden. CSA stellte die Hauptmenge dar.

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Summary A column chromatographic method using Dowex 1 × 2 is described which clearly separates heparitin sulfate (HMS), chondroitin sulfate A and C (CSA and CSC), chondroitin sulfate B (CSB) and keratosulfate (KS) from a mixture of acid mucopolysaccharides (AMPS). Subsequently, these compounds are individually measured by colorimetric assays.The elution of AMPS is achieved by NaCl-solutions of increasing concentrations: 0,5 M, 1,25 M (HMS); 1,5 M (CSA, CSC); 2,0 M (CSB); 3,0 M (KS).In order to examine the completeness of chromatographic separation aliquots of each peak were subjected to paper chromatography. The contents of hexuronic acid, hexosamine and neutral sugar were determined by appropriate color reactions and compared to values obtained with purified AMPS.For the determination of AMPS patterns in normal human urine on the basis of the described Dowex column chromatography the following procedure was used: dialysis of 24h urine against normal saline precipitation of total AMPS material with cetyltrimethylammoniumbromide washing of precipitate with 95% ethanol saturated with NaCl column chromatography on Dowex 1 × 2 colorimetric determination of hexuronic acid and neutral sugar contents of each fraction.Normal persons reveled an urinary excretion of HMS, CSA, CSB and KS, with CSA being the main compound.

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Mit dankenswerter Unterstützung der Deutschen Forschungsgemeinschaft, Bad Godesberg.Auszugsweise vorgetragen auf der 3. Arbeitstagung für pädiatrische Forschung, Marburg a. d. Lahn, 25./26. Februar 1966.     

Association of polymorphisms of paraoxonase 1 and 2 genes,alone or in combination,with bone mineral density in community-dwelling Japanese

Oxidative stress may affect cellular functions in various pathological conditions, including osteoporosis. Paraoxonase 1 confers antioxidant properties on high-density lipoprotein, with which it is associated, by reducing the accumulation of lipid peroxidation products. We have now examined whether the 584AG (Gln192Arg) and 172TA (Leu55Met) polymorphisms of the paraoxonase 1 gene and the 959GC (Cys311Ser) polymorphism of the paraoxonase 2 gene are associated with bone mineral density (BMD) in community-dwelling Japanese (1,087–1,094 women and 1,112–1,125 men). The subjects were aged 40 –79 years and were randomly recruited to a population-based prospective cohort study of aging and age-related diseases. BMD for the lumbar spine and right femoral neck was measured by dual-energy X-ray absorptiometry. Genotypes were determined with a fluorescence- or colorimetry-based allele-specific DNA primer-probe assay system. The 584AG and 172TA polymorphisms of the paraoxonase 1 gene and the 959GC polymorphism of the paraoxonase 2 gene were associated with BMD for the lumbar spine or femoral neck in postmenopausal women, with the 584GG, 172TT, and 959CC genotypes representing risk factors for reduced bone mass. None of these three polymorphisms was associated with BMD in premenopausal women or in men. Our results suggest that the paraoxonase 1 and 2 genes are candidate loci for reduced bone mass in postmenopausal Japanese women.     

Gene assignment of α-fucosidase and glucose dehydrogenase to the p21→pter region of chromosome 1 in man

Assignment of human genes coding for -fucosidase (FUC) and glucose dehydrogenase (GDH) to chromosome 1 has been confirmed and a location in the p21pter region demonstrated using man-mouse somatic cell hybrids. The regional location af FUC andGDH was established in cell hybrids using human cells possessing 1/2 translocation chromosomes [46,XX,t(1;2)(p21;q37)]. Hybrids which retained the 2q⁺ chromosome carrying the 1p211pter region concordantly expressed FUC, GDH, and the short-arm markers ENO₁, AK₂, and PGM₁. Hybrids which retained the 1p211qter region only expressed human PEPC and FH. Data obtained from hybrids in which spontaneous breaks in chromosome 1 had occurred indicate that the gene order in 1p21ar1pter is (ENO₁,GDH)-FUC-AK₂-PGM₁.     

Lack of association of polymorphisms of the lymphotoxin α gene with myocardial infarction in Japanese

Vascular inflammation plays an important role in the development of myocardial infarction (MI). Lymphotoxin (LTA) is a cytokine with multiple functions in regulation of the immune system and inflammatory reactions. The aim of this study was to examine whether polymorphisms of the LTA gene are associated with the risk of MI in Japanese men and women. A case-control association study was performed for the 252AG and 804CA polymorphisms of the LTA gene and the prevalence of MI. The study population comprised 3,689 unrelated Japanese individuals (2,486 men, 1,203 women), including 1891 patients with MI (1,493 men, 398 women) and 1798 control subjects (993 men, 805 women). Among the control subjects 257 individuals (108 men, 149 women) who had none of the conventional risk factors for coronary artery disease (CAD) were defined as low-risk controls. Genotypes for the two polymorphisms were determined with a fluorescence-based allele-specific DNA primer assay system. Among all study subjects the 252AG and 804CA polymorphisms exhibited linkage disequilibrium. No association of either polymorphism with MI was detected in men or in women in comparisons with total control or low-risk control subjects. However, each of the two polymorphisms was associated with the prevalence of type 2 diabetes mellitus both in men with MI and in those without MI in a recessive genetic model. No association was detected between the polymorphisms and other conventional risk factors for CAD. The LTA gene thus does not appear to be a susceptibility locus for MI in Japanese men or women, although it might affect susceptibility to type 2 diabetes in Japanese men.Abbreviations BMI Body mass index - CAD Coronary artery disease - HLA Human leukocyte antigen - LTA Lymphotoxin - MI Myocardial infarction - PCR Polymerase chain reaction - TNF Tumor necrosis factor     

Macrophage Stimulator β-(1→3)-D-Carboxymethylglucan Improves the Efficiency of Chemotherapy of Lewis Lung Carcinoma

We studied the effect of macrophage stimulator water-soluble -(13)-D-carboxymethylglucan on the efficiency of cyclophosphamide chemotherapy in Lewis lung carcinoma. Cyclophosphamide inhibited the growth of primary tumor nodes by 57%. The preparation possessed pronounced antimetastatic activity: metastases were found in 40.9% animals. Combination therapy with cyclophosphamide and (13)-beta;-D-glucan inhibited the growth of intramuscular tumors by 75-89% and reduced the incidence of metastases into the lungs by 92-94%. The therapeutic effect was most pronounced after simultaneous administration of these preparations: tumor growth was suppressed by 89.3% and metastases were found in only 7.5% animals (vs. 100% in the control). The potentiating effect of -(13)-D-carboxymethylglucan is related to accumulation of cysteine proteinase inhibitors in the tumor tissue and plasma, but not to changes in blood cell composition.     

Imbalance of purine nucleotides in alanosine-resistant baby hamster kidney cells

Human DNA was used to transform adenosine kinase (AK)-deficient BHK cells followed by selection of AK⁺ cells in medium containing alanosine, adenosine, and uridine (AAV medium). Twenty AAU^r isolates were analyzed, and none of them contained AK activity. Several purine salvage enzymes were, however, found to be affected in these cells. The levels of hypoxanthine-guanine phosphoribosyltransferase and adenylosuccinate synthetase activities were elevated, while the adenylosuccinase activity was reduced. AAU-resistance may be explained by elevated activity of adenylosuccinate synthetase to overcome the alanosine block; thus AAU^r cells were able to convert exogenous adenosine inosine hypoxanthine IMP AMPS AMP. Moreover, these AAU^r cells required exogenous purines for growth. HPLC analyses of endogenous nucleotide pools of AAU^r cells showed that the levels of adenine nucleotides have diminished to less than 10% of the parental levels. These results suggest that the AAU-resistant mutation, which elicits pleiotropic phenotypes in BHK cells, affects an important component in the regulation of adenine nucleotide synthesis. By including erthyro-9-(2-hydroxy-3-nonyl)adenine in the AAU medium (renamed as AAUE medium) to block deamination of adenosine, AK⁺ BHK cells were isolated.     

Partial fast-to-slow conversion of regenerating rat fast-twitch muscle by chronic low-frequency stimulation

Chronic low-frequency stimulation (CLFS) of rat fast-twitch muscles induces sequential transitions in myosin heavy chain (MHC) expression from MHCIIb MHCIId/x MHCIIa. However, the final step of the fast-to-slow transition, i.e., the upregulation of MHCI, has been observed only after extremely long stimulation periods. Assuming that fibre degeneration/regeneration might be involved in the upregulation of slow myosin, we investigated the effects of CLFS on extensor digitorum longus (EDL) muscles regenerating after bupivacaine-induced fibre necrosis. Normal, non-regenerating muscles responded to both 30- and 60-day CLFS with fast MHC isoform transitions (MHCIIb MHCIId MHCIIa) and only slight increases in MHCI. CLFS of regenerating EDL muscles caused similar transitions among the fast isoforms but, in addition, caused significant increases in MHCI (to 30% relative concentration). Stimulation periods of 30 and 60 days induced similar changes in the regenerating bupivacaine-treated muscles, indicating that the upregulation of slow myosin was restricted to regenerating fibres, but only during an early stage of regeneration. These results suggest that satellite cells and/or regenerating fast rat muscle fibres are capable of switching directly to a slow program under the influence of CLFS and, therefore, appear to be more malleable than adult fibres.