Chromosomal localization of human Na+, K+-ATPase alpha- and beta-subunit genes

ATP1A1 de novo Mutation-Related Disorders: Clinical and Genetic Features

Background: ATP1A1 encodes an α1 isoform of Na⁺/K⁺-ATPase, which is expressed abundantly in kidneys and central nervous system. ATP1A1 variants may cause Na⁺/K⁺-ATPase loss of function and lead to a wide spectrum of phenotypes. This study aims to summarize the clinical and genetic features of ATP1A1 de novo mutation-related disorders and explore the potential correlations between phenotypes and genotypes. Methods: We analyzed two new cases harboring novel de novo ATP1A1 variants and reviewed all reported cases. Results: Both our probands had developmental delay, patient 1 accompanied with sleep disorders, irritability, and patient 2 with refractory seizures. They each had a novel de novo heterozygous missense variant, c.2797G>A[p.Asp933Asn] (NM_000701) and c.2590G>A[p.Gly864Arg] (NM_000701) respectively. Four patients with de novo ATP1A1 variants have been reported in two previous papers. Among them, three patients had refractory seizures and one patient had complex hereditary spastic paraplegia (HSP). Therefore, all six patients had developmental delay, and four of them had epilepsy. All variants located in the transmembrane regions M3, M4, M7, and M8 of ATP1A1 protein. Four patients with mutations in M3 and M7 had more severe phenotypes, including developmental delay and epileptic encephalopathy, three of them with hypomagnesemia, whereas two patients with mutations in M4 and M8 had milder phenotypes, only with mild developmental delay, without seizures or hypomagnesemia. Correcting hypomagnesemia had not controlled those seizures. Conclusions: Two novel de novo ATP1A1 variants identified in two patients here enriched the genotypic and phenotypic spectrum of ATP1A1 mutation-related disorder. Our findings suggest that hypomagnesemia in this disorder might relate to more severe phenotype and indicate more severe Na⁺/K⁺-ATPase dysfunction. Variations in M3 and M7 transmembrane regions were related to more severe phenotype than those in M4 and M8, which suggested that variations in M3 and M7 might cause more severe ATP1A1 functional defect.

The Trade-Off between Dietary Salt and Cardiovascular Disease; A Role for Na/K-ATPase Signaling?

It has been postulated for some time that endogenous digitalis-like substances, also called cardiotonic steroids (CTS), exist, and that these substances are involved in sodium handling. Within the past 20 years, these substances have been unequivocally identified and measurements of circulating and tissue concentrations have been made. More recently, it has been identified that CTS also mediate signal transduction through the Na/K-ATPase, and consequently been implicated in profibrotic pathways. This review will discuss the mechanism of CTS in renal sodium handling and a potential "trade-off" effect from their role in inducing tissue fibrosis.

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.

Regulation of Na,K-ATPase subunit abundance by translational repression

The Na,K-ATPase is an alphabeta heterodimer responsible for maintaining fluid and electrolyte homeostasis in mammalian cells. We engineered Madin-Darby canine kidney cell lines expressing alpha(1)FLAG, beta(1)FLAG, or beta(2)MYC subunits via a tetracycline-regulated promoter and a line expressing both stable beta(1)MYC and tetracycline-regulated beta(1)FLAG to examine regulatory mechanisms of sodium pump subunit expression. When overexpression of exogenous beta(1)FLAG increased total beta subunit levels by >200% without changes in alpha subunit abundance, endogenous beta(1) subunit (beta(1)E) abundance decreased. beta(1)E down-regulation did not occur during beta(2)MYC overexpression, indicating isoform specificity of the repression mechanism. Measurements of RNA stability and content indicated that decreased beta subunit expression was not accompanied by any change in mRNA levels. In addition, the degradation rate of beta subunits was not altered by beta(1)FLAG overexpression. Cells stably expressing beta(1)MYC, when induced to express beta(1)FLAG subunits, showed reduced beta(1)MYC and beta(1)E subunit abundance, indicating that these effects occur via the coding sequences of the down-regulated polypeptides. In a similar way, Madin-Darby canine kidney cells overexpressing exogenous alpha(1)FLAG subunits exhibited a reduction of endogenous alpha(1) subunits (alpha(1)E) with no change in alpha mRNA levels or beta subunits. The reduction in alpha(1)E compensated for alpha(1)FLAG subunit expression, resulting in unchanged total alpha subunit abundance. Thus, regulation of alpha subunit expression maintained its native level, whereas beta subunit was not as tightly regulated and its abundance could increase substantially over native levels. These effects also occurred in human embryonic kidney cells. These data are the first indication that cellular sodium pump subunit abundance is modulated by translational repression. This mechanism represents a novel, potentially important mechanism for regulation of Na,K-ATPase expression.

Physical mapping and characterization of the human Na,K-ATPase isoform, ATP1A4

Four isoforms of the catalytic alpha subunit of the Na,K-ATPase have been previously identified. We characterized and mapped a genomic copy of the human ATP1A4 isoform between D1S2707 and WI-9524, telomeric to a nearby isoform ATP1A2, and within a candidate region at 1q23 for familial hemiplegic migraine (FHM). Human ATP1A4 gene shares 84% identity with the mouse Atp1a4 gene, and both consist of 22 exons and 21 introns. The predicted polypeptide is 1029 amino acids and shares 82 and 79.8% identity, respectively, with human ATP1A2 and ATP1A1. ATP1A4 is larger than other isoforms and most divergent at the N-terminus. ATP1A4 and ATP1A2 are paralogous genes with the same number and organization of putative H-transmembrane domains, conserved exon-intron boundaries, and are found approximately 8.5 kb apart. Expression analysis of the ATP1A4 gene revealed a new major approximately 7.5 kb transcript in human skeletal muscle, with expression also shown in mouse muscle. Predictive analysis of promoter regions identified muscle specific regulatory elements for ATP1A4 and Atp1a4. Mutation analysis among eight affected individuals from a single large, highly penetrant FHM family was negative in ATP1A4 and ATP1A2 although multiple polymorphisms were identified.

Segmental localization of mRNAs encoding Na(+)-K(+)-ATPase alpha(1)- and beta(1)-subunits in diabetic rat kidneys using RT-PCR

The present study evaluated renal Na(+)-K(+)-ATPase activity and mRNA in rats with diabetes mellitus. To localize the segmental alpha(1)- and beta(1)-mRNAs of Na(+)-K(+)-ATPase 1 and 8 days after induction of diabetes, we used the polymerase chain reaction after reverse transcription of the mRNA in microdissected nephron segments. Na(+)-K(+)-ATPase activity in the proximal convoluted tubule (PCT) rose on days 1 and 8 by 42 and 23%, respectively. In the medullary thick ascending limb (MTAL), it remained unchanged on day 1 and increased on day 8 by 55%. In the cortical collecting duct (CCD), activity rose by 81 and 45% on days 1 and 8, respectively. In parallel, alpha(1)-mRNA in the PCT increased by 52 and 22% on days 1 and 8, respectively. In the MTAL, alpha(1)-mRNA remained unchanged on day 1 and rose by 47% on day 8. In the CCD, alpha(1)-mRNA increased by 140 and 110% on days 1 and 8, respectively. beta(1)-mRNA was unchanged in the PCT throughout the study and was elevated in the MTAL and CCD on days 1 and 8. Thus there was a temporal dissociation between alpha(1)- and beta(1)-subunit expression. There was a highly significant linear correlation between Na(+)-K(+)-ATPase activity and alpha(1)-mRNA in all nephron segments throughout the experiment. It appears that microdissection of nephron tubules combined with reverse transcription-polymerase chain reaction defines the molecular identity of the amplified gene product and its segmental distribution in the nephron. We propose that altered gene expression may be the mechanism underlying enhanced Na(+) pump activity along the nephron in diabetic rats.

Structure, promoter analysis, and chromosomal localization of the murine H(+)/K(+)-ATPase alpha 2 subunit gene

The H(+)/K(+)-ATPase alpha2 subunit (HK alpha 2) of distal colon and renal collecting ducts plays a critical role in potassium and acid-base homeostasis. The isolation and complete sequence of the murine HK alpha 2 gene are reported. The HK alpha 2 gene contains 23 exons and spans 23.5 kb of genomic DNA. The exon/intron organization is comparable to that of the human ATP1AL1 gene. Primer extension and 5'-rapid amplification of cDNA ends of distal colon RNA were used to map the transcription initiation site. Fluorescence in situ hybridization analysis localized the HK alpha 2 gene to murine chromosome 14C3. Sequence analysis of 7.2 kb of the 5'-flanking region revealed numerous consensus sites for transcription factors, including two potential glucocorticoid response elements. Transient transfection of promoter-luciferase constructs demonstrated strong basal HK alpha 2 promoter activity in renal collecting duct cells but not in fibroblasts or in a medullary thick ascending limb of Henle's loop cell line. Deletion analysis revealed that the proximal 0.2 kb of the promoter was sufficient to confer activity in collecting duct cells. These data should prove important in elucidation of the mechanisms controlling the differential, tissue-specific expression of the HK alpha 2 gene.

Human skeletal muscle fibres: molecular and functional diversity

Contractile and energetic properties of human skeletal muscle have been studied for many years in vivo in the body. It has been, however, difficult to identify the specific role of muscle fibres in modulating muscle performance. Recently it has become possible to dissect short segments of single human muscle fibres from biopsy samples and make them work in nearly physiologic conditions in vitro. At the same time, the development of molecular biology has provided a wealth of information on muscle proteins and their genes and new techniques have allowed analysis of the protein isoform composition of the same fibre segments used for functional studies. In this way the histological identification of three main human muscle fibre types (I, IIA and IIX, previously called IIB) has been followed by a precise description of molecular composition and functional and biochemical properties. It has become apparent that the expression of different protein isoforms and therefore the existence of distinct muscle fibre phenotypes is one of the main determinants of the muscle performance in vivo. The present review will first describe the mechanisms through which molecular diversity is generated and how fibre types can be identified on the basis of structural and functional characteristics. Then the molecular and functional diversity will be examined with regard to (1) the myofibrillar apparatus; (2) the sarcolemma and the sarcoplasmic reticulum; and (3) the metabolic systems devoted to producing ATP. The last section of the review will discuss the advantage that fibre diversity can offer in optimizing muscle contractile performance.

The molecular basis of hypertension

More than 50 million Americans display blood pressures outside the safe physiological range. Unfortunately for most individuals, the molecular basis of hypertension is unknown, in part because pathological elevations of blood pressure are the result of abnormal expression of multiple genes. This review identifies a number of important blood pressure regulatory genes including their loci in the human, mouse, and rat genome. Phenotypes of gene deletions and overexpression in mice are summarized. More detailed discussion of selected gene products follows, beginning with proteins involved in ion transport, specifically the epithelial sodium channel and sodium proton exchangers. Next, proteins involved in vasodilation/natriuresis are discussed with emphasis on natriuretic peptides, guanylin/uroguanylin, and nitric oxide. The renin angiotensin aldosterone system has an important role antagonizing the vasodilatory cyclic GMP system.

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS): high-resolution physical and transcript map of the candidate region in chromosome region 13q11

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS or SACS) is a neurodegenerative disease frequent in northeastern Québec. In a previous study, we localized the disease gene to chromosome region 13q11 by identifying excess sharing of a marker allele in patients followed by linkage analysis and haplotyping. To create a detailed physical map of this region, we screened CEPH mega-YACs with 41 chromosome 13 sequence-tagged-sites (STSs) known to map to 13q11-q12. The YAC contig, composed of 27 clones, extends on the genetic map from D13S175 to D13S221, an estimated distance of at least 19.3 cM. A high-resolution BAC and PAC map that includes the ARSACS critical region flanked by D13S1275 and D13S292 was constructed. These YAC and BAC/PAC maps allowed the accurate placement of 29 genes and ESTs previously mapped to the proximal region of chromosome 13q. We confirmed the position of two candidate genes within the critical region and mapped the other 27 genes and ESTs to nearby intervals. Six BAC/PAC clones form a contig between D13S232 and D13S787 for sequencing within the ARSACS critical region.

Mapping of the Na+, K(+)-ATPase subunit alpha 2 (ATP1A2) and muscle phosphofructokinase (PFKM) genes in pig by somatic cell hybrid analysis

Two expressed sequence tags were isolated from a porcine skeletal muscle cDNA library and identified as the putative partial cDNAs of the porcine Na+, K(+)-ATPase subunit alpha 2 (ATP1A2) and muscle phosphofructokinase (PFKM) genes after sequencing and homology search. Results of analysis of a pig-rodent somatic cell hybrid panel by PCR allowed the assignments of ATP1A2 to porcine chromosome (chr) 4 and of PFKM to porcine chr 5. These assignments support previously observed conservation of syntenic relationships between human chr 1 and porcine chr 4 and between human chr 12 and porcine chr 5.

Evidence for an allelic association between bipolar disorder and a Na+, K+ adenosine triphosphatase alpha subunit gene (ATP1A3)

BACKGROUND

Disturbances in central nervous system Na+, K+ adenosine triphosphatase (ATPase) activity have previously been proposed as being involved in the pathophysiology of bipolar mood disorder.

METHODS

We have examined one particular alpha subunit of this enzyme for allelic association in a sample of 85 Irish bipolar patients and 85 matched controls.

RESULTS

There was evidence for an overall allelic association between the disease and a dinucleotide polymorphism within the ATP1A3 gene (p = .022). Subjects were then analyzed on the basis of a number of criteria, and the significance of the association increased when cases were divided based on the nature of the first episode. Patients who presented with a depressive episode first showed a significant association (p = .001) with this polymorphism.

CONCLUSIONS

The results presented here provide preliminary evidence of an association between bipolar disorder and an alpha subunit of Na+, K+ ATPase, the expression of which predominates in the brain.

Structural organization and chromosomal localization of the human Na,K-ATPase beta 3 subunit gene and pseudogene

We have cloned and characterized the Na,K-ATPase beta 3 subunit gene (ATP1B3), and a beta 3 subunit pseudogene (ATP1B3P1), from a human PAC genomic library. The beta 3 subunit gene is > 50 kb in size and is split into 7 exons. The exon/intron organization of the beta 3 subunit gene is identical to that of the Na,K-ATPase beta 3 subunit gene, indicating that these two genes evolved from a common evolutionary ancestor. Comparison of the promoter region of the human and mouse beta 3 subunit gene reveals a high degree of homology within a 300-bp segment located immediately upstream of the translation start site, suggesting that control elements that serve to regulate the cell-specific expression of the beta 3 subunit gene are likely to be located within this conserved region. Dot blot analysis of beta 3 subunit transcripts revealed expression within virtually all human tissues, while in situ hybridization showed expression of beta 3 mRNA in both neurons and glia of rat brain. Fluorescence in situ hybridization with PAC DNA clones localized ATP1B3 to the q22-->23 region of Chromosome (Chr) 3, and the beta 3 pseudogene to the p13-->15 region of Chr 2.

Characterization and quantification of full-length and truncated Na,K-ATPase alpha 1 and beta 1 RNA transcripts expressed in human retinal pigment epithelium

We have characterized cDNA clones encoding the alpha 1 and beta 1 subunits of Na,K-ATPase produced in the human retinal pigment epithelium (hRPE). In addition to isolating clones corresponding to known sequences of Na,K-ATPase subunits, we report hitherto unknown forms of Na,K-ATPase with unique deduced amino acid (aa) sequences in their C-termini. Truncated cDNA sequences were found for both the beta 1 and alpha 1 subunits. While the beta 1 sequence is truncated by two aa residues at the C terminus, in the alpha 1 sequence 342 aa have been replaced by a unique sequence containing only 44 aa. Interestingly, this new C-terminal polypeptide shows sequence similarities to the Ca(2+)-ATPase and contains consensus sequence elements for phosphorylation and cell adhesion, suggesting expression of Na,K-ATPase subunits with unique functions. Using reverse transcription-polymerase chain reaction, RNA sequences for alpha 1, beta 1 and their corresponding truncated isoforms were quantified. 4.0 x 10(5) alpha 1 and 2.3 x 10(5) beta 1 molecules were found per ng of mRNA from hRPE. Much lower levels were detected for truncated alpha 1 and beta 1 (3.6 x 10(3) and 2.7 x 10(3) molecules/ng, respectively). These data corroborate the expression of truncated transcripts coding for unique aa sequences in hRPE, and suggest that factors other than alpha 1 and beta 1 mRNA levels regulate the equimolar accumulation of alpha and beta subunits in the plasma membrane.

Cloning and characterization of the entire cDNA encoded by ATP1AL1--a member of the human Na,K/H,K-ATPase gene family

The cDNA for ATP1AL1--the fifth member of the human Na,K-/H,K-ATPase gene family--was cloned and sequenced. The deduced primary ATP1AL1 translation product is 1,039 amino acids in length and has Mr of 114,543. The encoded protein has all of the structural features common to known catalytic subunits of P-type membrane ion-transporting ATPases and is equally distant (63-64% of identity) from the Na,K-ATPase isoforms and the gastric H,K-ATPase. The ATP1AL1 encoded protein was proposed to represent a new separate group within the family of human potassium-dependent ion pumps.

Distribution of alpha 1 subunit isoform of (Na,K)-ATPase in the rat spinal cord

Three isoforms of the alpha subunit of (Na,K)-ATPase have been identified in the rat central nervous system. Using a probe specific for the alpha 1 isoform, mRNA levels were measured from five sections of the rat spinal cord using slot blot techniques. Assigning a value of 1 to the slope obtained from the cervical section, the upper thoracic section was 2.6 times higher; the midthoracic section was 4.5 times higher; the lower thoracic section was 2.6 times higher; and the lumbar section was 1.7 times higher. The results suggest that alpha 1 isoform mRNA levels are not uniform throughout the spinal cord. In situ hybridization techniques showed that alpha 1 isoform mRNA was diffusely abundant in glial and central canal ependymal cells, while labeled neurons were localized exclusively in laterally located anterior horn neurons in cervical, thoracic, and lumbar segments and in ventromedial neurons in mid-thoracic spinal cord. Also, dorsal root ganglia neurons were extensively labeled at all segments.

Genes encoding the H,K-ATPase alpha and Na,K-ATPase alpha 3 subunits are linked on mouse chromosome 7 and human chromosome 19

We have used linkage analysis and fluorescence in situ hybridization to determine the chromosomal organization and location of the mouse (Atp4a) and human (ATP4A) genes encoding the H,K-ATPase alpha subunit. Linkage analysis in recombinant inbred (BXD) strains of mice localized Atp4a to mouse Chromosome (Chr) 7. Segregation of restriction fragment length polymorphisms in backcross progeny of Mus musculus x Mus spretus mating confirmed this assignment and indicates that Atp4a and Atp1a3 (gene encoding the murine Na,K-ATPase alpha 3 subunit) are linked and separated by a distance of approximately 2 cM. Analysis of the segregation of simple sequence repeats suggested the gene order centromere-D7Mit21-D7Mit57/Atp1a3-D7Mit72/Atp 4a. A human Chr 19-enriched cosmid library was screened with both H,K-ATPase alpha and Na,K-ATPase alpha 3 subunit cDNA probes to isolate the corresponding human genes (ATP4A and ATP1A3, respectively). Fluorescence in situ hybridization with gene-specific cosmid clones localized ATP4A to the q13.1 region, and proximal to ATP1A3, which maps to the q13.2 region, of Chr 19. These results indicate that ATP4A and ATP1A3 are linked in both the mouse and human genomes.

Na(+)-K(+)-ATPase alpha 1- and beta 1-subunit degradation: evidence for multiple subunit specific rates

Na(+)-K(+)-ATPase is a heterodimeric plasma membrane protein consisting of an alpha-catalytic and a beta-glycoprotein subunit. Because these two subunits are derived from two separate genes, they may not be synthesized with stoichiometric equivalence. The aim of this study was to estimate relative rates of synthesis and degradation of nascent and mature Na(+)-K(+)-ATPase alpha- and beta-subunits to determine whether either of the nascent subunits accumulates in excess and, if so, the fate of the excess subunits. We studied a pig kidney cell line (LLC-PK1/Cl4) that expresses only alpha 1- and beta 1-subunits. Relative synthesis and degradation rates of nascent subunits were first estimated by pulsing cells for 10 min with [35S]methionine followed by chase periods of up to 120 min and by immunoprecipitation. We found that directly after labeling, beta-subunits were present in threefold excess over alpha-subunits and that nearly 50% of this beta-subunit pool was degraded by 60 min. Nascent alpha-subunits were not degraded during the chase period. In a second strategy to examine relative rates of nascent alpha- vs. beta-subunit accumulation, cells were pulsed for 5-60 min and immunoprecipitated directly (without chase). The rate of accumulation of labeled alpha was greater than that of beta between 5 and 60 min, consistent with the results of the pulse-chase strategy, demonstrating a significant component of degradation of beta during this period. Despite the very different degradation rates of newly synthesized alpha- vs. beta-subunits, the degradation rates of alpha- and beta-subunits beyond 4 h after synthesis were indistinguishable (t0.5 = 10-12 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Human genes containing polymorphic trinucleotide repeats

Expansions of trinucleotide repeats within gene transcripts are responsible for fragile X syndrome, myotonic dystrophy and spinal and bulbar muscular atrophy. To identify other human genes with similar features as candidates for triplet repeat expansion mutations, we screened human cDNA libraries with repeat probes and searched databases for transcribed genes with repeats. From both strategies, 40 genes were identified and 14 characterized. Five were found to contain repeats which are highly polymorphic including the N-cadherin, BCR, glutathione-S-transferase and Na+/K+ ATPase (beta-subunit) genes. These data demonstrate the occurrence of other human loci which may undergo this novel mechanism of mutagenesis giving rise to genetic disease.

The human cationic amino acid transporter (ATRC1): Physical and genetic mapping to 13q12–q14

The product of the mouse Rec-1 locus is an integral membrane protein that determines susceptibility to infection by murine ecotropic retroviruses. Recently it has been determined that its role in normal cell metabolism is transport of the cationic amino acids, arginine, lysine, and ornithine across the plasma membrane. Southern blot analysis of genomic DNA from a panel of 48 mouse-human somatic cell hybrids assigned the human version of this gene, ATRC1, to chromosome 13. Chromosomal in situ hybridization localized the gene to 13q12-q14. A restriction fragment length polymorphism (RFLP) was detected with TaqI. There were two alleles with frequencies of 0.29 and 0.71. Pairwise linkage analysis established linkage between ATRC1 and ATP1AL1, D13S1, D13S6, D13S10, D13S11, D13S21, D13S22, D13S33, D13S36, and D13S37. Multilocus linkage analysis of five of the loci indicated that the most likely order of loci in this region was D13S11-ATP1AL1-ATRC1-D13S6-D13S33.

A contiguous linkage map of chromosome 13q with 39 distinct loci separated on average by 5.1 centimorgans

A fine-structure linkage map of chromosome 13q is presented. This map contains 39 continuously linked loci defined by genotypes generated from the CEPH family DNAs with 56 probe and enzyme combinations. An alpha-satellite probe for sequences on chromosome 13 was included, resulting in a complete map of 13q with 39 distinct loci. The map spans 1.715 M in males and 2.099 M in females and the mean genetic distance between adjacent loci is 5.1 cM. Although there was generally a several-fold excess of female recombination in the interstitial portion of 13q, an excess of recombination in males was observed at both ends of this chromosomal arm. This map should be useful for the localization of any additional marker, gene, or disease locus of interest on chromosome 13q.

Chromosome 1 Charcot-Marie-Tooth disease (CMT1B) locus in the Fc gamma receptor gene region

The Charcot-Marie-Tooth disease (hereditary motor and sensory neuropathy) loci have been reported to be on at least three chromosomes: 1 (CMT1B, HMSN1B), 17 (CMT1A), and X (CMTX). In this study multipoint linkage analysis of two Duffy-linked families given a combined LOD score of 8.65 to establish that the Duffy-linked CMT1B gene exists in the 18 centimorgan region between the antithrombin III gene and the Duffy/sodium-potassium ATPase loci. The simultaneous segregation of polymorphisms near the CMT1A locus on chromosome 17 excludes linkage to this chromosome region in both families. Polymorphic sites that flank the CMT1B gene have been subchromosomally localized to the proximal chromosome-1 long arm (1q21.2----1q25) by spot blot analysis of sorted chromosomes, polymorphic deletion analysis, in situ hybridization, and multipoint linkage analysis.

Differential distribution of (Na,K)-ATPase alpha isoform mRNAs in the peripheral nervous system

mRNA transcripts for 3 isoforms of the alpha subunit of (Na,K)-ATPase have been previously identified in the nervous system (designated alpha 1, alpha 2, and alpha 3). In order to study the localization and expression of the different alpha isoforms in the peripheral nervous system, we prepared probes from the unique 3' untranslated region of alpha 1 cDNA, and from the translated region of alpha 3 cDNA. These probes were used in dot blot and in situ hybridization assays of rat spinal cord, dorsal root ganglia (DRG), and sciatic nerve. Within the ventral horn of lumbar spinal cord, alpha 1 mRNA was found in a discrete set of laterally placed motor neurons, while alpha 3 was found in all the identified neurons of the spinal cord, including those motor neurons containing alpha 1. In the lumbar DRG, alpha 3 was uniformly distributed in DRG neurons, while alpha 1 was abundant in some neurons but little or none was found in other neurons. Satellite cells contained neither isoform. Schwann cells in sciatic nerve were labeled with the alpha 1 probe in a perinuclear distribution, but contained no detectable alpha 3. Dot blot analysis showed alpha 1 and alpha 3 in spinal cord and DRG, but only alpha 1 in peripheral nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of two genes encoding plasma membrane Ca2(+)-transporting ATPases to human chromosomes 1q25-32 and 12q21-23

Human plasma membrane Ca2(+)-ATPase (PMCA) isoforms are encoded by at least four separate genes and the diversity of these enzymes is further increased by alternative splicing of transcripts. Cloned cDNAs for two of these isoforms have been used as probes to localize chromosomally the human PMCA1 (ATP2B1) gene to 12q21-q23 and PMCA4 (ATP2B2) to 1q25-q32. These results were obtained by three independent methods, including Southern analysis of human-rodent somatic cell hybrids, in situ hybridization of human metaphase spreads, and genetic linkage analysis in the CEPH pedigrees. High-frequency RFLPs detected at each locus were used in these linkage analyses. No evidence was obtained for multiple copies of the gene at either locus. A cross-hybridizing sequence was detected with PMCA4 probes on Xq13-qter at low stringency. Further studies are required to determine whether this X-chromosomal sequence represents a third member of the PMCA gene family.

The CEPH consortium linkage map of human chromosome 1

This paper describes the Centre d'Etude du Polymorphisme Humain (CEPH) consortium linkage map of human chromosome 1. The map contains 101 loci defined by genotypes generated from CEPH family DNAs with 146 different contributions from 11 laboratories. A total of 58 loci are uniquely placed on the map with likelihood support of at least 1000:1. The map extends from loci in the terminal bands of both chromosome arms (locus D1Z2 in 1p36.3 and D1S68 in 1q44) and is anchored at the centromere by the D1Z5 alpha-satellite polymorphism. With the exception of a single locus, the remaining loci are arrayed on the fixed map in short intervals and their possible locations are indicated. Multipoint linkage analyses provided estimates that the male, female, and sex-averaged maps extend for 308, 478, and 390 cM, respectively. The sex-averaged map contains only four intervals greater than 15 cM, and the mean genetic distance between the 58 uniquely placed loci is 6.7 cM.

Differential distribution of (Na, K)-ATPase alpha isoforms in the central nervous system

1. mRNA transcripts for three isoforms of the alpha subunit of (Na,K)-ATPase have been previously identified in the rat nervous system and designated alpha 1, alpha 2 and alpha 3. 2. In order to study the localization and expression of the different alpha isoform mRNAs on a regional and cellular level in the brain, we prepared probes from the unique 3' untranslated region of rat alpha 1 cDNA and from a segment containing a portion of the translated region of rat alpha 3 cDNA. These probes were used in dot blot and in situ hybridization assays of rat brain. 3. alpha 1 mRNA was found predominantly in cerebral cortex, dentate gyrus of hippocampus, and specific isolated brain-stem nuclei such as locus ceruleus and motor nuclei V and VII. In contrast alpha 3 mRNA was found predominantly in pyramidal neurons in the deep layers of cerebral cortex, in both pyramidal and dentate gyrus neurons of the hippocampus, and in neurons of most subcortical structures of the thalamus, basal ganglia, and brain-stem nuclei. 4. In the cerebellum, Purkinje cells showed predominantly alpha 3, as did stellate and basket cells. The granule cells contained predominantly alpha 1. 5. These experiments show that mRNAs for both alpha 1 and alpha 3 isoforms of (Na,K)-ATPase are found in neurons of the CNS. The isoforms have unique cellular and regional distributions, which in some cases overlap.

Apical polarity of Na,K-ATPase in retinal pigment epithelium is linked to a reversal of the ankyrin-fodrin submembrane cytoskeleton

In striking contrast to most other transporting epithelia (e.g., urinary or digestive systems), where Na,K-ATPase is expressed basolaterally, the retinal pigment epithelium (RPE) cells display Na,K-ATPase pumps on the apical membrane. We report here studies aimed to identify the mechanisms underlying this polarity "reversal" of the RPE Na,K-ATPase. By immunofluorescence on thin frozen sections, both alpha and beta subunits were localized on the apical surface of both freshly isolated rat RPE monolayers and RPE monolayers grown in culture. The polarity of the RPE cell is not completely reversed, however, since aminopeptidase, an apically located protein in kidney epithelia, was also found on the apical surface of RPE cells. We used subunit- and isoform-specific cDNA probes to determine that RPE Na,K-ATPase has the same isoform (alpha 1) as the one found in kidney. Ankyrin and fodrin, proteins of the basolateral membrane cytoskeleton of kidney epithelial cells known to be associated with the Na,K-ATPase (Nelson, W. J., and R. W. Hammerton. 1989. J. Cell Biol. 110:349-357) also displayed a reversed apical localization in RPE and were intimately associated to Na,K-ATPase, as revealed by cross-linking experiments. These results indicate that an entire membrane-cytoskeleton complex is assembled with opposite polarity in RPE cells. We discuss our observations in the context of current knowledge on protein sorting mechanisms in epithelial cells.

The family of human Na,K-ATPase genes. ATP1AL1 gene is transcriptionally competent and probably encodes the related ion transport ATPase

The multigene family of human Na,K-ATPase is composed of 5 alpha-subunit genes, 3 of which were shown to encode the functionally active alpha 1, alpha 2 and alpha 3 isoforms of the catalytic subunits. This report describes the isolation, mapping and partial sequencing of the fourth gene (ATP1AL1) that was demonstrated here to be functionally active and expressed in human brain and kidney. Limited DNA sequencing of the ATP1AL1 exons allowed one to suggest that the gene probably encodes a new ion transport ATPase rather than an isoform of the Na,K-ATPase or the closely related H,K-ATPase.

Assignment of Amog (adhesion molecule on glia) gene to mouse chromosome 11 near Zfp-3 and Asgr-1,2 and to human chromosome 17

AMOG, identified as an adhesion molecule that mediates neuron-astrocyte interaction, has structural similarity to the beta-subunit of Na,K ATPase. We have mapped the AMOG gene to human chromosome 17 and mouse chromosome 11 by somatic cell hybrid analysis. Recombinant inbred strain mapping has placed the Amog locus close to genes for zinc finger protein-3 and the asialoglycoprotein receptor in a region of mouse chromosome 11 that is homologous to human 17p.

Structure, expression, and genetic linkage of the mouse BCM1 (OX45 or Blast-1) antigen. Evidence for genetic duplication giving rise to the BCM1 region on mouse chromosome 1 and the CD2/LFA3 region on mouse chromosome 3

The mouse BCM1 (OX45, Blast-1) antigen has been cDNA cloned and sequenced to provide data supporting the view that BCM1, LFA3, and CD2 constitute a subgroup within the Ig superfamily. Mouse BCM1 is widely expressed on leukocytes and is likely to be anchored to the cell surface by a glycosyl-phosphatidylinositol anchor, as is the case for rat and human BCM1 antigen. Genetic linkage studies by recombination and pulse field analysis showed the BCM1 locus (Bcm-1) to be on distal mouse chromosome 1 and to be linked within 1,600 kb to the locus for an ATPase alpha chain gene (Atpa-3). A similar relationship was established between the human BCM1 locus (BCM1) and ATP1A2, and other markers on chromosome 1q. Conservation of genomic organization within a segment of human chromosome 1q and mouse chromosome 1 was demonstrated. A similar situation is seen in the region of the CD2 and LFA3 genes between mouse chromosome 3 and human chromosome 1p. Furthermore, the CD2/LFA3 genes are linked within 580 kb to Atpa-1/ATP1A1 genes to provide a parallel situation to the linkage between Bcm-1/BCM1 and Atpa-3/ATP1A2 on chromosomes 1 (mouse) and 1q (human). Taken together, the data suggest duplication of a chromosome region including the precursors of the genes for BCM1, CD2, and LFA3, and the ATPase genes to give rise to the linkage groups now observed. The duplicated regions may have stayed together on chromosome 1 in the human (with the insertion of a centromere), while in the mouse, the genetic regions are proposed to have become dispersed in the formation of chromosomes 1 and 3. CD2 and LFA3 are more dissimilar in sequence than BCM1 and LFA3, and if the precursors of the CD2 and LFA3 loci formed before the proposed chromosome segment duplication, then a gene encoding a recognizer molecule for BCM1 may exist in linkage with Bcm-1/BCM1 on chromosome 1 (mouse) and 1q (human).

Long-range restriction site mapping of a syntenic segment conserved between human chromosome 1 and mouse chromosome 3

A linkage map determined from segregation analysis of 338 meiotic events in an interspecific mouse cross was utilized to help investigate genomic organization of a linkage group conserved between human chromosome 1p and mouse chromosome 3. Using pulsed-field gel electrophoresis, the genes encoding the lymphocyte adhesion molecule human CD2/murine Ly-37, the alpha 1-subunit of Na, K-ATPase, the beta-subunit of thyrotropin, the beta-subunit of nerve growth factor, and muscle adenylate deaminase were similarly positioned on long-range restriction maps in both species. These studies indicate that the development of detailed genetic maps using interspecific Mus crosses facilitates rapid analysis of murine genomic organization and may enable physical mapping of syntenic regions within the human genome. Moreover, the data suggest profound conservation of genomic organization during mammalian evolution.

The human Na, K-ATPase alpha 1 gene: characterization of the 5'-flanking region and identification of a restriction fragment length polymorphism

We have determined the sequence of the 5'-flanking region and first three exons of the human Na,K-ATPase alpha 1 gene, ATP1A1. Primer extension and S1 nuclease protection analyses of RNA from human kidney, brain, and skeletal muscle indicate that transcription initiates 273 nucleotides upstream of the translation start site. The promoter region contains a potential TATA box at position -27 relative to the transcription initiation site; however, no CCAAT sequence is observed. The 5'-untranslated and 5'-flanking regions are G + C rich. Five sequence elements exhibiting similarity to binding sites for the transcription factor Sp1 are located within the 5'-flanking region. This region also contains potential binding sites for the transcription factors AP-1, AP-2, AP-3, and NF-1, as well as a site which exhibits perfect identity to an 8-bp sequence element important for calcium induction. A comparison of the 5'-flanking region of the alpha 1 and alpha 2 genes reveals differences in potential transcription factor and hormone receptor binding sites which may be important in mediating the tissue- and developmental stage-specific expression of these genes. We have also identified an intragenic DNA probe which detects a restriction fragment length polymorphism at the alpha 1 locus. This marker should facilitate genetic linkage studies designed to evaluate the role of the sodium pump in human disease.

MspI and PvuII polymorphisms in the Na,K-ATPase beta subunit gene ATP1B1

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MspI and PvuII polymorphisms in the Na,K-ATPase alpha subunit related gene ATP1AL1

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Molecular genetics of Na,K-ATPase

Researchers in the past few years have successfully used molecular-genetic approaches to determine the primary structures of several P-type ATPases. The amino-acid sequences of distinct members of this class of ion-transport ATPases (Na,K-, H,K-, and Ca-ATPases) have been deduced by cDNA cloning and sequencing. The Na,K-ATPase belongs to a multiple gene family, the principal diversity apparently resulting from distinct catalytic alpha isoforms. Computer analyses of the hydrophobicity and potential secondary structure of the alpha subunits and primary sequence comparisons with homologs from various species as well as other P-type ATPases have identified common structural features. This has provided the molecular foundation for the design of models and hypotheses aimed at understanding the relationship between structure and function. Development of a hypothetical transmembrane organization for the alpha subunit and application of site-specific mutagenesis techniques have allowed significant progress to be made toward identifying amino acids involved in cardiac glycoside resistance and possibly binding. However, the complex structural and functional features of this protein indicate that extensive research is necessary before a clear understanding of the molecular basis of active cation transport is achieved. This is complicated further by the paucity of information regarding the structural and functional contributions of the beta subunit. Until such information is obtained, the proposed model and functional hypotheses should be considered judiciously. Considerable progress also has been made in characterizing the regulatory complexity involved in expression of multiple alpha-isoform and beta-subunit genes in various tissues and cells during development and in response to hormones and cations. The regulatory mechanisms appear to function at several molecular levels, involving transcriptional, posttranscriptional, translational, and posttranslational processes in a tissue- or cell-specific manner. However, much research is needed to precisely define the contributions of each of these mechanisms. Recent isolation of the genes for these subunits provides the framework for future advances in this area. Continued application of biochemical, biophysical, and molecular genetic techniques is required to provide a detailed understanding of the mechanisms involved in cation transport of this biologically and pharmacologically important enzyme.