Molecular characterization and mutational screening of the PRKAG3 gene in the horse

Gene expression profiling in equine muscle tissues using mouse cDNA microarrays

REASONS FOR PERFORMING STUDY

Progress could be achieved by using microarrays to understand metabolic adaptations and disorders in equine muscle in response to exercise.

OBJECTIVES

To test the feasibility of using mouse cDNA microarrays to analyse gene expression profile in normal equine muscles.

METHODS

Muscular biopsies of dorsal gluteus medius and longissimus lumborum were done in 4 healthy Standardbreds. Total RNA was extracted from the muscle samples. The concentration and quality of RNA were measured before and after amplification. Gene expression profiles were measured using mouse cDNA microarrays including 15,264 unique genes representing about 11,000 documented genes. Three hybridisation tests were performed to check interspecificity, reproducibility and to compare gene expression in these muscles. For each test, a dye-swap hybridisation with Cy3 and Cy5 fluoromarkers were done and the gene list filtered according the signal level.

RESULTS

According to the specificity test, the mouse cDNA microarrays were correctly hybridised by equine muscle cDNA. All positive control genes (GAPDH, HPRT and beta-Actin) and no negative control gene (yeast, plant) hybridised. The reproducibility test demonstrated a good linearity between the duplicate hybridisations: 99.99% of the significant expressed genes have an expression ratio between 1.4 and 1/1.4 = 0.71. These limits can be considered as the thresholds to qualify as up-regulated (ratio >1.4) or downregulated (ratio <0.71). In the muscle comparison test between gluteus medius vs. longissimus lumborum, 63 genes were found up-regulated and 8 genes down-regulated. The range of gene expression ratios in the gluteus medius was 0.61-8.31 x the longissimus lumborum. This list of modulated genes was classified by functions using a gene ontology data basis.

CONCLUSION

Mouse microarrays could be used to hybridise equine RNA extracted from muscle tissues. For many genes there are large sequence identities that allowed interspecific cDNA hybridisation. The sensitivity of the method allowed quantification of up- and down-regulated genes after applying appropriate filters.

POTENTIAL RELEVANCE

Expression profiling could be used to explore the muscle metabolism changes related to exercise, training, pathology and illegal medication in horses.

Gene expression profiling in equine polysaccharide storage myopathy revealed inflammation, glycogenesis inhibition, hypoxia and mitochondrial dysfunctions

Background

Several cases of myopathies have been observed in the horse Norman Cob breed. Muscle histology examinations revealed that some families suffer from a polysaccharide storage myopathy (PSSM). It is assumed that a gene expression signature related to PSSM should be observed at the transcriptional level because the glycogen storage disease could also be linked to other dysfunctions in gene regulation. Thus, the functional genomic approach could be conducted in order to provide new knowledge about the metabolic disorders related to PSSM. We propose exploring the PSSM muscle fiber metabolic disorders by measuring gene expression in relationship with the histological phenotype.

Results

Genotypying analysis of GYS1 mutation revealed 2 homozygous (AA) and 5 heterozygous (GA) PSSM horses. In the PSSM muscles, histological data revealed PAS positive amylase resistant abnormal polysaccharides, inflammation, necrosis, and lipomatosis and active regeneration of fibers. Ultrastructural evaluation revealed a decrease of mitochondrial number and structural disorders. Extensive accumulation of an abnormal polysaccharide displaced and partially replaced mitochondria and myofibrils. The severity of the disease was higher in the two homozygous PSSM horses.

Gene expression analysis revealed 129 genes significantly modulated (p < 0.05). The following genes were up-regulated over 2 fold: IL18, CTSS, LUM, CD44, FN1, GST01. The most down-regulated genes were the following: mitochondrial tRNA, SLC2A2, PRKCα, VEGFα. Data mining analysis showed that protein synthesis, apoptosis, cellular movement, growth and proliferation were the main cellular functions significantly associated with the modulated genes (p < 0.05). Several up-regulated genes, especially IL18, revealed a severe muscular inflammation in PSSM muscles. The up-regulation of glycogen synthase kinase-3 (GSK3β) under its active form could be responsible for glycogen synthase (GYS1) inhibition and hypoxia-inducible factor (HIF1α) destabilization.

Conclusion

The main disorders observed in PSSM muscles could be related to mitochondrial dysfunctions, glycogenesis inhibition and the chronic hypoxia of the PSSM muscles.

Molecular cloning, genomic organization, and expression of three chicken 5'-AMP-activated protein kinase gamma subunit genes

The 5'-AMP-activated protein kinase (AMPK) plays a key role in regulating cellular energy homeostasis. The AMPK is a heterotrimeric enzyme complex that consists of 1 catalytic (alpha) and 2 regulatory (beta and gamma) subunits. Mutations of the gamma subunit genes are known to affect AMPK functioning. In this study, we characterized the genomic organization and expression of 3 chicken AMPK gamma subunit genes (cPRKAG). Alternative splicing of the second exon of the cPRKAG1 gene resulted in 2 transcript variants that code for predicted proteins of 298 and 276 amino acids. Use of an alternate promoter and alternative splicing of the cPRKAG2 gene resulted in 4 transcript variants that code for predicted proteins of 567, 452, 328, and 158 amino acids. Alternative splicing of exon 3 of the cPRKAG3 gene resulted in the production of "long" and "short" transcript variants that code for predicted proteins of 382 and 378 amino acids, respectively. We found evidence for differential expression of individual gamma subunit gene transcript variants and, in some cases, tissue-specific expression was observed. The cPRKAG subunit genes displayed similar structural features and high sequence homology compared with corresponding mammalian gamma subunit gene homologues.

Identification of single-nucleotide polymorphisms in 5' end and exons of the PRKAG3 gene in Hubbard White broiler, Leghorn layer, and three Chinese indigenous chicken breeds

5'-AMP-activated protein kinase plays an important role in regulating the level of ATP in the presence of metabolic stress. Previous studies revealed that polymorphisms in 5'-AMP-activated protein kinase gamma 3 subunit (PRKAG3) gene are associated with meat quality in pigs. In the present study, single-nucleotide polymorphisms (SNPs) in the 5'-end and exons of chicken PRKAG3 gene were identified with the method of single-strand conformation polymorphism in Hubbard ISA White broiler, Leghorn layer, and three Chinese indigenous chicken breeds, Tibet Chicken, Shouguang Chicken and Beijing Yellow Chicken. Two SNPs in the 5'-end of the gene and 10 SNPs in exons 3, 4, 9 and 11, of which three caused amino acid substitutions, were identified in the PRKAG3 gene of the five chicken breeds. The results will facilitate further study on the association between the mutations of PRKAG3 and chicken meat quality.

Molecular cloning and characterization of bovine PRKAG3 gene: structure, expression and single nucleotide polymorphism detection

The protein kinase adenosine monophosphate-activated gamma3-subunit (PRKAG3) gene encodes a muscle-specific isoform of the regulatory gamma-subunit of adenosine monophosphate-activated protein kinase, which plays a key role in regulating energy homeostasis in eucaryotes. It is well known that mutations in the PRKAG3 gene affect high glycogen content in the porcine skeletal muscle and, consequently, meat quality. The genomic structure and sequence of the bovine PRKAG3 were analysed from a Korean cattle BAC clone. The bovine PRKAG3 gene comprises 13 exons and spans approximately 6.8 kb on BTA2. From 5' and 3'-rapid amplification of cDNA ends experiments, the full-length cDNA of bovine PRKAG3 has been identified, encoding a deduced protein of 465 amino acids. Two splice isoforms, generated by the alternative splicing of exon 2, were also identified. Northern blot analysis demonstrated that, similar to other species, the bovine PRKAG3 transcript was only expressed in skeletal muscle. Seven single nucleotide polymorphisms, including two previously identified variants, were detected in four Bos taurus cattle breeds. The bovine PRKAG3 gene described in this study may be involved in muscle-related genetic diseases or meat quality traits in cattle.

Hereditary skeletal muscle diseases in the horse. A review

Since riders nowadays are expecting the highest level of performance from their horses, muscular disorders therefore represent a major problem for the equine athlete. A lot of research has been done to identify muscular disorders and their etiopathogenesis. Both acquired and inherited forms of muscle diseases have been described. In this review only the latter forms will be mentioned. Major signs of all muscle disorders are muscular stiffness, cramping or pain, muscular fasciculations, muscular atrophy and exercise intolerance. Muscle biopsies can help to identify the cause of rhabdomyolysis or muscular atrophy. However, especially in hereditary muscular diseases, a lot of questions are still to be answered. Increasing knowledge of the etiopathogenesis and newer diagnostic tests may lead to a more accurate diagnosis of the individual diseases in future.