Myosin Heavy Chain Isoform Genes Research Articles

Effects of various levels of dietary fiber on carcass traits, meat quality and myosin heavy chain I, IIa, IIx and IIb expression in muscles in Erhualian and Large White pigs

This study evaluated the effects of bran fiber levels on carcass traits, meat quality and expression of myosin heavy chain isoform genes in muscles in Erhualian (Er-HL) and Large White pig (LW). Our results showed that fiber level did not affect carcass weight of Er-HL, while carcass weight of LW decreased with the increase of fiber level. Fiber level did not influence meat quality traits of LW, whereas increased fiber level led to an increase in pH45 min of Er-HL, and Er-HL fed 7% bran fiber (BRC) increased redness of meat compared with control diet (CON). We observed a decreased MyHCIIb and MyHCIIx mRNAs and protein levels in Er-HL fed 7% BRC compared with those in other groups, accompanying with a tendency for increased mRNA abundance of MyHCI. The slow-twitch oxidative fiber (MyHCI) is rich in myoglobin and mitochondrial oxidative metabolic enzymes, and the increased expression of MyHCI fiber in pork has resulted in higher redness value. In summary, bran fiber had no adverse effect on the meat quality of LW and appropriate fiber level addition in diets could improve meat quality of Er-HL through regulation the expression of myofiber types.

Differential expression of lipid metabolism-related genes and myosin heavy chain isoform genes in pig muscle tissue leading to different meat quality

The aim of this study was to investigate the variations in meat quality, lipid metabolism-related genes, myosin heavy chain (MyHC) isoform genes and peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) gene mRNA expressions in longissimus dorsi muscle (LM) of two different pig breeds. Six Rongchang and six Landrace barrows were slaughtered at 161 days of age. Subsequently, meat quality traits and gene expression levels in LM were observed. Results showed that Rongchang pigs not only exhibited greater pH, CIE a*24 h and intramuscular fat content but also exhibited lower body weight, carcass weight, dressing percentage, LM area and CIE b*24 h compared with Landrace pigs (P<0.05). Meanwhile, the mRNA expression levels of the lipogenesis (peroxisome proliferator-activated receptor gamma, acetyl-CoA carboxylase and fatty acid synthase) and fatty acid uptake (lipoprotein lipase)-related genes were greater in the Rongchang (P<0.05), whereas the lipolysis (adipose triglyceride lipase and hormone sensitive lipase) and fatty acid oxidation (carnitine palmitoyltransferase-1B)-related genes were better expressed in the Landrace. Moreover, compared with the Landrace, the mRNA expression levels of MyHCI, MyHCIIa and MyHCIIx were greater, whereas the mRNA expression levels of MyHCIIb were lower in the Rongchang pigs (P<0.05). In addition, the mRNA expression levels of PGC-1α were greater in Rongchang pigs than in the Landrace (P<0.05), which can partly explain the differences in MyHC isoform gene expressions between Rongchang and Landrace pigs. Although the small number of samples does not allow to obtain a definitive conclusion, we can suggest that Rongchang pigs possess better meat quality, and the underlying molecular mechanisms responsible for the better meat quality in fatty pigs may be partly due to the higher mRNA expression levels of lipogenesis and fatty acid uptake-related genes, as well as the oxidative and intermediate muscle fibers, and due to the lower mRNA expression levels of lipolysis and fatty acid oxidation-related genes, as well as the glycolytic muscle fibers.

Molecular changes in detrained &amp; retrained adult jaw muscle

A hypofunctional masticatory system was developed in 21-day-old male rats by feeding them a soft diet for 27 weeks. Retraining of a parallel group for 6 weeks was achieved by switching back to a hard diet after 21 weeks. A control group was fed a hard diet for 27 weeks. At the end of the experimental period, the expression levels of the myosin heavy chain isoform genes MYH 1 and 2 (fast), 3 (embryonic) and 7 (slow) in the deep masseter were compared using qRT-PCR analysis. The gene expressions of MYH 3 and MYH 7 were significantly higher in the rehabilitation group compared with the normal and hypofunctional group, but no significant differences were found in regards to the gene expression of MYH 1 and 2. Retraining made it possible for the slow (MYH 7) isoform levels to adapt to the increased mechanical load. The increased level of embryonic (MYH 3) isoform could be due to the need of creation of new MYH isoforms.

Myosinopathies: pathology and mechanisms

The myosin heavy chain (MyHC) is the molecular motor of muscle and forms the backbone of the sarcomere thick filaments. Different MyHC isoforms are of importance for the physiological properties of different muscle fiber types. Hereditary myosin myopathies have emerged as an important group of diseases with variable clinical and morphological expression depending on the mutated isoform and type and location of the mutation. Dominant mutations in developmental MyHC isoform genes (MYH3 and MYH8) are associated with distal arthrogryposis syndromes. Dominant or recessive mutations affecting the type IIa MyHC (MYH2) are associated with early-onset myopathies with variable muscle weakness and ophthalmoplegia as a consistent finding. Myopathies with scapuloperoneal, distal or limb-girdle muscle weakness including entities, such as myosin storage myopathy and Laing distal myopathy are the result of usually dominant mutations in the gene for slow/β cardiac MyHC (MYH7). Protein aggregation is part of the features in some of these myopathies. In myosin storage myopathy protein aggregates are formed by accumulation of myosin beneath the sarcolemma and between myofibrils. In vitro studies on the effects of different mutations associated with myosin storage myopathy and Laing distal myopathy indicate altered biochemical and biophysical properties of the light meromyosin, which is essential for thick filament assembly. Protein aggregates in the form of tubulofilamentous inclusions in association with vacuolated muscle fibers are present at late stage of dominant myosin IIa myopathy and sometimes in Laing distal myopathy. These protein aggregates exhibit features indicating defective degradation of misfolded proteins. In addition to protein aggregation and muscle fiber degeneration some of the myosin mutations cause functional impairment of the molecular motor adding to the pathogenesis of myosinopathies.

CDNA cloning and structural analysis of the globular head for myosin heavy chain from silver carp (&lt;I&gt;Hypophthalmichthys molitrix&lt;/I&gt;)

In the previous study,we reported that two types of myosin heavy chain isoform genes were isolated from fast skeletal muscles of silver carp(Hypophthalmichthys molitrix) acclimatized in winter and summer,and named the low temperature-type(sc-w) and the high temperature-type(sc-s),respectively. In this study,two gene-specific reverse primers were designed according to the striking differences in the nucleotide sequences of 3′-terminals between the two types of silver carp myosin heavy chain isoform,and a forward primer was designed with reference to conserved nucleotide sequences in 5′-terminal of cyprinidae. Long-PCR was performed to amplify the complete cDNAs encoding myosin subfragment-1(S1) heavy chains for the two types of isoform. DNA sequencing of both strands was carried out,and the amino acid sequences for the two types of myosin S1 heavy chain were deduced. The results showed that the primary structure of myosin S1 heavy chain produced 80.5% identity between sc-w and sc-s. Whereas a high sequence identity of 97.2% was found between sc-w and gc10,which was reported to be isolated from 10 ℃-acclimated grass carp. In contrast,the amino acid sequence of S1 heavy chain for sc-s revealed much higher identity to those of gcI(98.4%) and gc30(97.1%),which were isolated from 30 ℃-acclimated grass carp. Compared with the other myosin S1 heavy chain isoforms,isoform-specific differences for sc-w and gc10 were clearly observed in 43 amino acid residues. Furthermore,among these amino acid mutations,15 mutations occurred at the conserved residue sites. Additionally,sc-w and gc10 showed striking differences compared with the other S1 heavy chain isoforms in the two surface loops,loop 1 located near the ATP-binding domain and loop 2,which is one of the actin binding domains,suggesting that the changes in the flexibility of two surface loops were caused by modulations in length,amino acid composition and charge can play an important role in adaptation of motor function to low environmental temperature. Phylogenetic analysis further demonstrated the effects of environmental temperature on genomic divergence and functional evolution of fish myosin isoforms.

A thyroid hormone receptor mutation that dissociates thyroid hormone regulation of gene expression in vivo

Resistance to thyroid hormone (RTH) is most often due to point mutations in the beta-isoform of the thyroid hormone (TH) receptor (TR-beta). The majority of mutations involve the ligand-binding domain, where they block TH binding and receptor function on both stimulatory and inhibitory TH response elements. In contrast, a few mutations in the ligand-binding domain are reported to maintain TH binding and yet cause RTH in certain tissues. We introduced one such naturally occurring human RTH mutation (R429Q) into the germline of mice at the TR-beta locus. R429Q knock-in (KI) mice demonstrated elevated serum TH and inappropriately normal thyroid-stimulating hormone (TSH) levels, consistent with hypothalamic-pituitary RTH. In contrast, 3 hepatic genes positively regulated by TH (Dio1, Gpd1, and Thrsp) were increased in R429Q KI animals. Mice were then rendered hypothyroid, followed by graded T(3) replacement. Hypothyroid R429Q KI mice displayed elevated TSH subunit mRNA levels, and T(3) treatment failed to normally suppress these levels. T(3) treatment, however, stimulated pituitary Gh levels to a greater degree in R429Q KI than in control mice. Gsta, a hepatic gene negatively regulated by TH, was not suppressed in R429Q KI mice after T(3) treatment, but hepatic Dio1 and Thrsp mRNA levels increased in response to TH. Cardiac myosin heavy chain isoform gene expression also showed a specific defect in TH inhibition. In summary, the R429Q mutation is associated with selective impairment of TH-mediated gene repression, suggesting that the affected domain, necessary for TR homodimerization and corepressor binding, has a critical role in negative gene regulation by TH.

Myosin proteins identified from masseter muscle using quantitative reverse transcriptase-polymerase chain reaction--a pilot study of the relevance to orthodontics

There is a clearly established relationship between masticatory muscle structure and facial form. Human studies in this area, however, have been limited, especially in consideration of the myosin heavy chain (MyHC) family of contractile proteins. The aim of this pilot study was to assess if differences were detectable between genotype with respect to MyHC isoforms and the vertical facial phenotype in a sample of nine Caucasian female patients, age range 18-49 years, using a novel rapid technique. Masseter muscle biopsies were taken from patients with a range of vertical facial form. The levels of expression of the MyHC isoform genes MYH 1, 2, 3, 6, 7, and 8 were compared with the expression in a female calibrator patient aged 23 years with normal vertical facial form, using quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Statistical analysis was undertaken using Pearson correlation coefficient. The results showed that there were distinct differences in gene expression between patients with a wide range of variation although changes in MYH1 were consistent with one cephalometric variable, the maxillo-mandibular angle. The full procedure, from start to finish, can be completed within half a day. Rapid genotyping of patients in this way could reveal important information of relevance to treatment. This technology has potential as a diagnostic and prognostic aid when considering correction of certain malocclusions.

Temperature-dependent developmental variation in lobster muscle myosin heavy chain isoforms

The temperature- and developmental-regulation of myosin heavy chain (MyHC) expression and primary sequence was investigated in the abdominal musculature of developing Homarus gammarus larvae acclimated to 10, 14 and 19±1 °C. MyHC loop 1 (ATP binding) and loop 2 (actin binding) regions were sequenced and compared. The deduced amino acid sequence of MyHC loop 1 showed a development-related increase in net charge from +1 to +2 between larval stages 1 and 2, which was not temperature-dependent. In post-settled stage 9 larvae, minor shifts in amino acid sequence occurred at 19 °C, and corresponded to a significant up-regulation of fast myosin mRNA expression. However, no temperature-specific loop 1 isoforms were detected. The deduced amino acid sequence of MyHC loop 2 was not affected by temperature, and the net charge remained +4 throughout development. These findings contrast to previous studies using the common carp, in which temperature-specific MyHC isoform genes were expressed in response to disparate thermal regimes. This raises the question as to whether arthropods do not express specific temperature isoforms but instead rely on shifts in fibre type to accommodate alterations in thermal environment.

Coordinate Changes in Myosin Heavy Chain Isoform Gene Expression Are Selectively Associated With Alterations in Dilated Cardiomyopathy Phenotype

The most common cause of chronic heart failure in the US is secondary or primary dilated cardiomyopathy (DCM). The DCM phenotype exhibits changes in the expression of genes that regulate contractile function and pathologic hypertrophy. However, it is unclear if any of these alterations in gene expression are disease producing or modifying. One approach to providing evidence for cause-effect of a disease-influencing gene is to quantitatively compare changes in phenotype to changes in gene expression by employing serial measurements in a longitudinal experimental design. We investigated the quantitative relationships between changes in gene expression and phenotype n 47 patients with idiopathic DCM. In endomyocardial biopsies at baseline and 6 months later, we measured mRNA expression of genes regulating contractile function (beta-adrenergic receptors, sarcoplasmic reticulum Ca(2) + ATPase, and alpha- and beta-myosin heavy chain isoforms) or associated with pathologic hypertrophy (beta-myosin heavy chain and atrial natriuretic peptide), plus beta-adrenergic receptor protein expression. Left ventricular phenotype was assessed by radionuclide ejection fraction. Improvement in DCM phenotype was directly related to a coordinate increase in alpha- and a decrease in beta-myosin heavy chain mRNA expression. In contrast, modification of phenotype was unrelated to changes in the expression of beta(1)- or beta(2)-adrenergic receptor mRNA or protein, or to the mRNA expression of sarcoplasmic reticulum Ca(2) + ATPase and atrial natriuretic peptide. We conclude that in human DCM, phenotypic modification is selectively associated with myosin heavy chain isoform changes. These data support the hypothesis that myosin heavy chain isoform changes contribute to disease progression in human DCM.

Changes in Mass and Performance in Rabbit Muscles after Muscle Damage with or without Transplantation of Primary Satellite Cells.

Changes in morphology, metabolism, myosin heavy chain gene expression, and functional performances in damaged rabbit muscles with or without transplantation of primary satellite cells were investigated. For this purpose, we damaged bilaterally the fast muscle tibialis anterior (TA) with either 1.5 or 2.6 ml cardiotoxin 10-5 M injections. Primary cultures of satellite cells were autotransplanted unilaterally 5 days after muscle degeneration. Two months postoperation, the masses of damaged TAs, with or without transplantation, were significantly larger than those of the controls. Furthermore, damaged transplanted muscles weighed significantly more than damaged muscles only. The increase in muscle mass was essentially due to increased fiber size. These results were independent of the quantity of cardiotoxin injected into the muscles. Maximal forces were similar in control and 2.6 ml damaged TAs with or without satellite cell transfer. In contrast, 1.5 ml damaged TAs showed a significant decrease in maximal forces that reached the level of controls after transplantation of satellite cells. Fatigue resistance was similar in control and 1.5 ml damaged TAs independently of satellite cell transfer. Fatigue index was significantly higher in 2.6 ml damaged muscles with or without cell transplantation. These changes could be explained in part by muscle metabolism, which shifted towards oxidative activities, and by gene expression of myosin heavy chain isoforms, which presented an increase in type IIa and a decrease in type I and IIb in all damaged muscles with or without cell transfer. Under our experimental conditions, these results show that muscle damage rather than satellite cell transplantation changes muscle metabolism, myosin heavy chain isoform gene expression, and, to a lesser extent, muscle contractile properties. In contrast, muscle weight and fiber size are increased both by muscle damage and by satellite cell transfer.

Reversible Ca2+-induced fast-to-slow transition in primary skeletal muscle culture cells at the mRNA level.

1. The adult fast character and a Ca2+-inducible reversible transition from a fast to a slow type of rabbit myotube in a primary culture were demonstrated at the mRNA level by Northern blot analysis with probes specific for different myosin heavy chain (MyHC) isoforms and enzymes of energy metabolism. 2. No non-adult MyHC isoform mRNA was detected after 22 days of culture. After 4 weeks of culture the fast MyHCIId mRNA was strongly expressed while MyHCI mRNA was virtually absent, indicating the fast adult character of the myotubes in the primary skeletal muscle culture. 3. The data show that a fast-to-slow transition occurred in the myotubes at the level of MyHC isoform gene expression after treatment with the Ca2+ ionophore A23187. The effects of ionophore treatment were decreased levels of fast MyHCII mRNA and an augmented expression of the slow MyHCI gene. Changes in gene expression started very rapidly 1 day after the onset of ionophore treatment. 4. Levels of citrate synthase mRNA increased and levels of glyceraldehyde 3-phosphate dehydrogenase mRNA decreased during ionophore treatment. This points to a shift from anaerobic to oxidative energy metabolism in the primary skeletal muscle culture cells at the level of gene expression. 5. Withdrawal of the Ca2+ ionophore led to a return to increased levels of MyHCII mRNA and decreased levels of MyHCI mRNA, indicating a slow-to-fast transition in the myotubes and the reversibility of the effect of ionophore on MyHC isoform gene expression.

Protein kinase C activity regulates slow myosin heavy chain 2 gene expression in slow lineage skeletal muscle fibers.

Expression of the slow myosin heavy chain (MyHC) 2 gene defines slow versus fast avian skeletal muscle fiber types. Fetal, or secondary, skeletal muscle fibers express slow MyHC isoform genes in developmentally regulated patterns within the embryo, and this patterning is at least partly dependent on innervation in vivo. We have previously shown that slow MyHC 2 gene expression in vitro is regulated by a combination of innervation and cell lineage. This pattern of gene expression was indistinguishable from the pattern observed in vivo in that it was restricted to innervated muscle fibers of slow muscle origin. We show here that slow MyHC 2 gene expression in the slow muscle fiber lineage is regulated by protein kinase C (PKC) activity. Inhibition of PKC activity induced slow MyHC 2 gene expression, and the capacity to express the slow MyHC 2 gene was restricted to muscle fibers of slow muscle (medial adductor) origin. Fast muscle fibers derived from the pectoralis major did not express significant levels of slow MyHC 2 with or without inhibitors of PKC activity. This differential expression pattern coincided with different inherent PKC activities in fast versus slow muscle fiber types. Furthermore, over-expression of an unregulated PKCalpha mutant suppressed slow MyHC 2 gene expression in muscle fibers of the slow lineage. Lastly, denervation of skeletal muscles caused an increase in PKC activity, particularly in the slow medial adductor muscle. This increase in PKC activity was associated with lack of slow MyHC 2 gene expression in vivo. These results provide a mechanistic link between innervation, an intracellular signaling pathway mediated by PKC, and expression of a muscle fiber type-specific contractile protein gene. Dev Dyn 1999;216:177-189.

Expression of fast myosin heavy chain transcripts in developing and dystrophic chicken skeletal muscle

The expression of fast myosin heavy chain (MyHC) genes was examined in vivo during fast skeletal muscle development in the inbred White Leghorn chicken (line 03) and in adult muscles from the genetically related dystrophic White Leghorn chicken (line 433). RNA dotblot and northern hybridization was employed to monitor MyHC transcript levels utilizing specific oligonucleotide probes. The developmental pattern of MyHC gene expression in the pectoralis major (PM) and the gastrocnemius muscles was similar during embryonic development with three embryonic MyHC isoform genes, Cemb1, Cemb2, and Cemb3, sequentially expressed. Following hatching, MyHC expression patterns in each muscle differed. The expression of MyHC genes was also studied in muscle cell cultures derived from 12-day embryonic pectoralis muscles. In vitro, Cvent, Cemb1, and Cemb2 MyHC genes were expressed; however, little if any Cemb3 MyHC gene expression could be detected, even though Cemb3 was the predominant MyHC gene expressed during late embryonic development in vivo. In most adult muscles other than the PM and anterior latissimus dorsi (ALD), the Cemb3 MyHC gene was the major adult MyHC isoform. In addition, two general patterns of expression were identified in fast muscle. The fast muscles of the leg expressed neonatal (Cneo) and Cemb3 MyHC genes, while other fast muscles expressed adult (Cadult) and Cemb3 MyHC genes. MyHC gene expression in adult dystrophic muscles was found to reflect the expression patterns found in corresponding normal muscles during the neonatal or early post-hatch developmental period, providing additional evidence that avian muscular dystrophy inhibits muscle maturation.

Expression of fast myosin heavy chain transcripts in developing and dystrophic chicken skeletal muscle

The expression of fast myosin heavy chain (MyHC) genes was examined in vivo during fast skeletal muscle development in the inbred White Leghorn chicken (line 03) and in adult muscles from the genetically related dystrophic White Leghorn chicken (line 433). RNA dot-blot and northern hybridization was employed to monitor MyHC transcript levels utilizing specific oligonucleotide probes. The developmental pattern of MyHC gene expression in the pectoralis major (PM) and the gastrocnemius muscles was similar during embryonic development with three embryonic MyHC isoform genes, Cemb1, Cemb2, and Cemb3, sequentially expressed. Following hatching, MyHC expression patterns in each muscle differed. The expression of MyHC genes was also studied in muscle cell cultures derived from 12-day embryonic pectoralis muscles. In vitro, Cvent, Cemb1, and Cemb2 MyHC genes were expressed; however, little if any Cemb3 MyHC gene expression could be detected, even though Cemb3 was the predominant MyHC gene expressed during late embryonic development in vivo. In most adult muscles other than the PM and anterior latissimus dorsi (ALD), the Cemb3 MyHC gene was the major adult MyHC isoform. In addition, two general patterns of expression were identified in fast muscle. The fast muscles of the leg expressed neonatal (Cneo) and Cemb3 MyHC genes, while other fast muscles expressed adult (Cadult) and Cemb3 MyHC genes. MyHC gene expression in adult dystrophic muscles was found to reflect the expression patterns found in corresponding normal muscles during the neonatal or early post-hatch developmental period, providing additional evidence that avian muscular dystrophy inhibits muscle maturation. Dev. Dyn. 208:491–504, 1997. © 1997 Wiley-Liss, Inc.

Adaptation of fish to different environmental temperature by qualitative and quantitative changes in gene expression

In fish that coccupy a specific thermal habitat the contractile apparatus has been adapted during evolution for that specific temperature range. In Antarctic fish the myofibrillar ATPase activity is relatively high at temperatures around 0°C, but this is at the expense of enzyme thermostability as this enzyme from antarctic fishes is heat inactivated at comparatively low temperatures (Johnston and Goldspink, 1975c; Johnston and Walesby, 1977). Such thermal characteristics may be a general feature of proteins from Antarctic fish (Somero, 1991) and so may contribute to their extreme cold stenothermy. Some curythermal species of fish have the ability to rebuild their contractile systems by expressing a different set of genes at low temperature to that expressed at warm environmental temperatures. We have cloned and are in the process of characterising warm and cold as well as embryonic myosin heavy chain isoform genes of carp. These genes encode different types of myosin crossbridges (the force generators for muscular contraction) and therefore determine the contractile characteristics of the muscle. The physiological result of the switches in gene expression are that the muscles of fish acclimated to low environmental temperatures develop more force and more power at these temperatures than muscles from fish acclimated to warm environmental temperatures. Carp acclimated to warm temperatures have myosin with a greater thermostability but at a lower myofibrillar ATPase.

Discoordinate regulation of isoforms of Na,K-ATPase and myosin heavy chain in the hypothyroid postnatal rat heart and skeletal muscle.

During postnatal life, many contractile and electrophysiological properties of the rat heart undergo changes. Among the changes is a switch in the expression of Na,K-ATPase catalytic subunit isoforms. Thyroid hormone has been postulated to play an important role in the postnatal transformation of the heart, and its effect on myosin heavy chain isoform gene transcription is well documented. To test whether it controls Na,K-ATPase gene switching in vivo, we made neonatal rats hypothyroid by maternal treatment with methimazole. The expression of Na,K-ATPase catalytic subunit isoforms in cardiac and skeletal muscle membranes was measured with specific antibodies at time points from birth to 4 weeks of age. Postnatal changes in Na,K-ATPase isoform expression in cardiac ventricle and hind limb skeletal muscle were similar in control and hypothyroid animals. In the same hypothyroid animals, the postnatal switch from the V3 (beta) isoform of myosin heavy chain to the V1 (alpha) isoform was blocked. The conclusion is that thyroid hormone may have a modulatory role in Na,K-ATPase gene expression, but it is not the developmental signal that dominates gene switching.

Mechanisms of temperature acclimation in the carp: a molecular biology approach

Most fish are unable to regulate their body temperature. Therefore their muscle power output would be expected to decline markedly with decreased environmental temperature. However, some species including carp show a remarkable ability to acclimate. The nature and significance of changes in enzymatic myosin ATPase activity and the recruitment of different muscle fiber types in relation to acclimation and environmental temperature in carp are reviewed. These changes presumably involve qualitative and quantitative changes in gene expression. To approach the problem, we have constructed a carp genomic library and isolated 28 nonoverlapping clones containing sequences of different myosin heavy chain (MHC) isoforms along with a clone containing carp actin sequences. Plasmids containing probes specific for a carp fast muscle MHC and actin RNA were constructed. Hybridization results suggest that the expression of this MHC isoform RNA is increased in warm- relative to cold-acclimated carp. These data indicate that there are different MHC isoform genes that are expressed at warm and cold environmental temperatures.