Molecular cloning and characterization of porcine Na⁺/K⁺-ATPase isoform α4.

Na+/K+-ATPase is responsible for maintaining electrochemical gradients of Na+ and K+, which is essential for a variety of cellular functions including neuronal activity. The α-subunit of the Na+/K+-ATPase is composed of four different polypeptides (α1-α4) encoded by different genes. Na,K-ATPase α4, encoded by the ATP1A4 gene, is expressed in testis and in male germ cells of humans, rats and mice. The α4 polypeptide has an important role in sperm motility, and is essential for male fertility. Here we present the RT-PCR cloning and characterization of the porcine ATP1A4 cDNA coding for Na⁺/K⁺-ATPase polypeptide α4. The Na⁺/K⁺-ATPase polypeptide α4, consisting of 1030 amino acids, displays a high homology with its human counterpart (86%). Phylogenetic analysis demonstrated that porcine Na⁺/K⁺-ATPase polypeptide α4 is closely related to other mammalian counterparts. In addition, the genomic structure of the porcine ATP1A4 gene was determined, and the intron-exon organization was found to be similar to that of the human ATP1A4 gene. The promoter sequence for the porcine ATP1A4 gene was also identified. Investigation of the genetic variation in the porcine ATP1A4 gene revealed a missense A/G SNP in exon 18. This A/G polymorphism results in a substitution of a methionine to a glycine residue (M888G). A very high overall DNA methylation rate of the ATP1A4 gene, 70-80%, was observed in both brain and liver. Expression analysis demonstrated that the porcine ATP1A4 gene is predominantly expressed in testis. The sequence of the porcine ATP1A4 cDNA encoding the Na⁺/K⁺-ATPase α4 protein has been submitted to GenBank under the accession number GenBank Accession No. MG587082.

Molecular cloning and characterization of porcine Na⁺/K⁺-ATPase isoforms α1, α2, α3 and the ATP1A3 promoter.

Na⁺/K⁺-ATPase maintains electrochemical gradients of Na⁺ and K⁺ essential for a variety of cellular functions including neuronal activity. The α-subunit of the Na⁺/K⁺-ATPase exists in four different isoforms (α1-α4) encoded by different genes. With a view to future use of pig as an animal model in studies of human diseases caused by Na⁺/K⁺-ATPase mutations, we have determined the porcine coding sequences of the α1-α3 genes, ATP1A1, ATP1A2, and ATP1A3, their chromosomal localization, and expression patterns. Our ATP1A1 sequence accords with the sequences from several species at five positions where the amino acid residue of the previously published porcine ATP1A1 sequence differs. These corrections include replacement of glutamine 841 with arginine. Analysis of the functional consequences of substitution of the arginine revealed its importance for Na⁺ binding, which can be explained by interaction of the arginine with the C-terminus, stabilizing one of the Na⁺ sites. Quantitative real-time PCR expression analyses of porcine ATP1A1, ATP1A2, and ATP1A3 mRNA showed that all three transcripts are expressed in the embryonic brain as early as 60 days of gestation. Expression of α3 is confined to neuronal tissue. Generally, the expression patterns of ATP1A1, ATP1A2, and ATP1A3 transcripts were found similar to their human counterparts, except for lack of α3 expression in porcine heart. These expression patterns were confirmed at the protein level. We also report the sequence of the porcine ATP1A3 promoter, which was found to be closely homologous to its human counterpart. The function and specificity of the porcine ATP1A3 promoter was analyzed in transgenic zebrafish, demonstrating that it is active and drives expression in embryonic brain and spinal cord. The results of the present study provide a sound basis for employing the ATP1A3 promoter in attempts to generate transgenic porcine models of neurological diseases caused by ATP1A3 mutations.

Porcine synapsin 1: SYN1 gene analysis and functional characterization of the promoter.

Synapsin 1 (SYN1) is a phosphoprotein involved in nerve signal transmission. The porcine SYN1 promoter orthologue was cloned and characterized to provide a means of expressing a transgene specifically in neurons. The nucleotide sequence of the promoter displayed a high degree of conservation of elements responsible for neuron-specific expression. Expression analysis of SYN1 demonstrated presence of transcript during embryonic development. Analysis of GFP expression in transgenic zebrafish embryos suggests that the pig SYN1 promoter directs expression in neuronal cells. Thus, the SYN1 promoter is a good candidate for use in the generation of pig models of human neurodegenerative disorders.

Characterization of the porcine TOR1A gene: The first step towards generation of a pig model for dystonia.

The TOR1A (also named DYT1) gene encodes a protein, TorsinA, a member of the AAA+ superfamily of ATPases. The AAA+ proteins have diverse functions such as organelle biogenesis, proteosome function, chaperone function, membrane trafficking and microtubule regulation. However, the molecular function of TorsinA is still largely unknown. Mutations in the TOR1A gene, primarily a 3-bp (GAG) deletion are associated with early-onset autosomal dominant torsion dystonia. Animal models may help to provide information about the underlying cellular and molecular mechanism of early-onset generalized dystonia. The close anatomical, physiological, genetic and biochemical resemblance between man and pig suggest that this animal may constitute an excellent model for this disease. This work reports the cloning and analysis of the porcine (Sus scrofa) homologue of TOR1A. Two porcine TOR1A cDNAs were amplified by reverse transcriptase polymerase chain reaction (RT-PCR), using oligonucleotide primers derived from in silico sequences. The porcine TOR1A cDNAs both encode a protein of 333 amino acids which shows a very high similarity to human (92%) TorsinA. Protein structure comparison of human and porcine TorsinA sequences revealed that there were few differences in the amino acid sequences between the two species and these are not likely to alter TorsinA structure and function. Quantitative real-time RT-PCR detection exhibited TOR1A mRNA expression in all analyzed porcine tissues, although at different levels. The TOR1A gene was demonstrated to be localized on porcine chromosome 1. Single nucleotide polymorphism (SNP) analysis revealed several SNPs in the porcine TOR1A gene, both in the coding region and also in the 3' UTR region. Overexpression of mutant (DeltaE303-304) porcine TorsinA in neuroblastoma cells leads to a more perinuclear localization compared with a cytoplasmatic localization for wildtype TorsinA. Furthermore, inclusion-like structures were observed. In conclusion, the results obtained for porcine TOR1A suggest that the pig could be an ideal model for early-onset generalized dystonia.