Bilateral deafness due to congenital CMV and not rubella reinfection

Two cases of autosomal recessive nephrogenic diabetes insipidus (NDI) were evaluated. Both cases were found to be compound heterozygote for missense mutations in the aquaporin-2 (AQP2) gene. To determine the structural-functional relationship, the mutated AQP2 proteins, T125M, G175R, A190T, and P262L, were expressed in Xenopus oocytes and examined by measurement of water permeability, immunoblot, and immunocytochemistry. Our results suggest that T125M and G175R are nonfunctional water channels, whereas the translocation to the plasma membrane is impaired in A190T and P262L.     

Defective aquaporin-2 trafficking in nephrogenic diabetes insipidus and correction by chemical chaperones

Five single-point aquaporin-2 (AQP2) mutations that cause non-X-linked nephrogenic diabetes insipidus (NDI) were characterized to establish the cellular defect and to develop therapeutic strategies. In Xenopus oocytes expressing AQP2 cRNAs, single-channel water permeabilities of mutants L22V, T126M, and A147T were similar to that of wild-type AQP2, whereas R187C and C181W were nonfunctional. In [35S]methionine pulse-chase experiments in transiently transfected CHO cells, half-times for AQP2 degradation were approximately 4 h for wild-type AQP2 and L22V, and mildly decreased for T126M (2.7 h), C181W (2.4 h), R187C (2.0 h), and A147T (1.8 h). Immunofluorescence showed three distinct AQP2-staining patterns: plasma membrane and endosomal staining (wild-type, L22V), endoplasmic reticulum (ER) staining (T126M > A147T approximately R187C), or a mixed pattern of reticular and perinuclear vesicular staining. Immunoblot of fractionated vesicles confirmed primary ER localization of T126M, R187C, and A147T. To determine if the AQP2-trafficking defect is correctable, cells were incubated with the "chemical chaperone" glycerol for 48 h. Immunoblot showed that glycerol produced a nearly complete redistribution of AQP2 (T126M, A147T, and R187C) from ER to membrane/endosome fractions. Immunofluorescence confirmed the cellular redistribution. Redistribution of AQP2 mutants was also demonstrated in transfected MDCK cells, and using the chaperones TMAO and DMSO in place of glycerol in CHO cells. Water permeability measurements indicated that functional correction was achieved. These results indicate defective mammalian cell processing of mutant AQP2 water channels in NDI, and provide evidence for pharmacological correction of the processing defect by chemical chaperones.     

Mutations in the vasopressin V2 receptor and aquaporin-2 genes in 12 families with congenital nephrogenic diabetes insipidus

Congenital nephrogenic diabetes insipidus (CNDI) is a rare inherited disorder characterized by renal tubular insensitivity to the antidiuretic effect of arginine vasopressin (AVP). In a large majority of the cases, nephrogenic diabetes insipidus is an X-linked recessive disorder caused by mutations in the AVP V2 receptor gene (AVPR2). In the remaining cases, the disease is autosomal recessive or dominant and, for these patients, mutations in the aquaporin 2 gene (AQP2) have been reported. Fourteen probands belonging to 12 families were analyzed by single-strand conformational polymorphism and direct sequencing of the AVPR2 and AQP2 genes. Ten mutations of the AVPR2 gene (six previously reported mutations and four novel mutations: G107E, W193X, L43P, and 15delC) were identified. Three mutations of the AQP2 gene were also identified in two patients: the first patient is homozygous for the R85X mutation and the second is a compound heterozygote for V168 M and S216P mutations. Extrarenal responses to infusion of the strong V2 agonist 1-desamino-8-D-arginine vasopressin allowed AVPR2- and AQP2-associated forms of CNDI to be distinguished in three patients. This test also identified an unexpectedly high urinary osmolality (614 mosmol/kg) in a patient with a P322S mutation of AVPR2 gene and a mild form of CNDI.     

The in vivo balance between B cell clonal expansion and elimination is regulated by CD95 both on B cells and in their micro-environment

In congenital nephrogenic diabetes insipidus, the renal collecting ducts are resistant to the antidiuretic action of arginine vasopressin or to its antidiuretic analog 1-deamino[8-D-arginine] vasopressin (dDAVP). This is a rare, but now well described entity secondary to either mutations in the AVPR2 gene that codes for the vasopressin antidiuretic (V2) receptor or to mutations in the AQP2 gene that codes for the vasopressin-dependent water channel. A majority (> 90%) of congenital nephrogenic diabetes insipidus patients have AVPR2 mutations: Of 115 families with congenital nephrogenic diabetes insipidus, 105 families had AVPR2 mutations, and 10 had AQP2 mutations. When studied in vitro, most AVPR2 mutations lead to receptors that are trapped intracellularly and are unable to reach the plasma membrane. A minority of the mutant receptors reach the cell surface but are unable to bind vasopressin or to trigger an intracellular adenosine 3:5-cyclic phosphate signal properly. Most of the reported mutations are secondary to a complete loss of function of the receptor, and only a few mutations have been associated with a mild phenotype. These advances provide diagnostic tools for physicians caring for these patients because, when the disease causing mutation has been identified, carrier and perinatal testing could be done by mutation analysis.     

Application of mRNA differential display to investigate gene expression in thermotolerant cells of Saccharomyces cerevisiae

In nephrogenic diabetes insipidus, the kidney is unable to concentrate urine despite normal or elevated concentrations of the antidiuretic hormone arginine vasopressin (AVP). In congenital nephrogenic diabetes insipidus (NDI), the obvious clinical manifestations of the disease, that is polyuria and polydipsia, are present at birth and need to be immediately recognized to avoid severe episodes of dehydration. Most (>90%) congenital NDI patients have mutations in the AVPR2 gene, the Xq28 gene coding for the vasopressin V2 (antidiuretic) receptor. In <10% of the families studied, congenital NDI has an autosomal recessive inheritance and mutations of the aquaporin-2 gene (AQP2), ie, the vasopressin-sensitive water channel, have been identified. When studied in vitro, most AVPR2 mutations lead to receptors that are trapped intracellularly and are unable to reach the plasma membrane. A minority of the mutant receptors reach the cell surface but are unable to bind AVP or to trigger an intracellular cyclic adenosine-monophosphate (cAMP) signal. Similarly AQP2 mutant proteins are trapped intracellularly and cannot be expressed at the luminal membrane. The acquired form of NDI is much more common than the congenital form, is almost always less severe, and is associated with downregulation of AQP2. The advances described here are examples of "bedside physiology" and provide diagnostic tools for physicians caring for these patients.     

Comprehensive evaluation of long-term trends in occupational exposure: Part 1. Description of the database

The regulation of water excretion by the kidney is one of the few physiologic processes that are prominent in everyday life. This process predominantly occurs in renal collecting duct cells, where transcellular water reabsorption is induced after binding of the pituitary hormone arginine-vasopressin to its vasopressin type-2 receptor and the subsequent insertion of aquaporin-2 (AQP2) water channels in the apical membrane of these cells. Removal of the hormone triggers endocytosis of AQP2 and restores the water-impermeable state of the collecting duct cells. Nephrogenic diabetes insipidus is characterized by the inability of the kidney to concentrate urine in response to vasopressin; the vasopressin type-2 receptor and the AQP2 water channel have both been shown to be involved in this disease. This article focuses on mutations in the vasopressin V2 receptor and aquaporin-2 water channel identified in nephrogenic diabetes insipidus patients, and on the effects of these mutations on the transport and function of these proteins upon expression in cell systems.     

Aquaporins in Saccharomyces. Genetic and functional distinctions between laboratory and wild-type strains

Aquaporin water channel proteins mediate the transport of water across cell membranes in numerous species. The Saccharomyces genome data base contains an open reading frame (here designated AQY1) that encodes a protein with strong homology to aquaporins. AQY1 from laboratory and wild-type strains of Saccharomyces were expressed in Xenopus oocytes to determine the coefficients of osmotic water permeability (Pf). Oocytes injected with wild-type AQY1 cRNAs exhibit high Pf values, whereas oocytes injected with AQY1 cRNAs from laboratory strains exhibit low Pf values and have reduced levels of Aqy1p due to two amino acid substitutions. When the AQY1 gene was deleted from a wild-type yeast and cells were cultured in vitro with cycled hypo-osmolar or hyper-osmolar stresses, the AQY1 null yeast showed significantly improved viability when compared with the parental wild-type strain. We conclude that Saccharomyces cerevisiae contains at least one aquaporin gene, but it is not functional in laboratory strains due to apparent negative selection pressures resulting from in vitro methods.     

Interleukin-1 stimulates hypothalamic inhibitory amino acid neurotransmitter release

In order to get a better insight into the function of amino acid residues located in the second transmembrane domain of the cystic fibrosis transmembrane conductance regulator (CFTR) protein, all exon 18 mutations found in cystic fibrosis (CF) patients were characterized at the protein and at the electrophysiological level. Of the different mutations present in transmembrane helix 12 (M1137V, M1137R, I11139V and deltaM1140), and the intracytoplasmic loop connecting TM12 and NBD2 (D1152H and D1154G), only M1137R interfered with the proper maturation of the protein. Permeability studies performed after injection of the different wild-type and mutant cRNAs in Xenopus laevis oocytes indicated that the mutations did not alter the permeability sequence of the CFTR channels. The whole cell cAMP activated chloride currents, however, were significantly reduced for M1137V, I1139V, D1152H and D1154G and close to zero for deltaM1140, indicating that these mutations interfere with the proper gating of the chloride channels.     

Characterization of 19 disease-associated missense mutations in the regulatory domain of the cystic fibrosis transmembrane conductance regulator

In order to gain a better insight into the structure and function of the regulatory domain (RD) of the cystic fibrosis transmembrane conductance regulator (CFTR) protein, 19 RD missense mutations that had been identified in patients were functionally characterized. Nine of these (I601F, L610S, A613T, D614G, I618T, L619S, H620P, G628R and L633P) resulted in aberrant processing. No or a very small number of functional CFTR proteins will therefore appear at the cell membrane in cells expressing these mutants. These mutations were clustered in the N-terminal part of the RD, suggesting that this subdomain has a folding pattern that is very sensitive to amino acid changes. Mutations that caused no aberrant processing were further characterized at the electrophysiological level. First, they were studied at the whole cell level in Xenopus laevis oocytes. Mutants that induced a whole cell current that was significantly different from wild-type CFTR were subsequently analysed at the single channel level in COS1 cells transiently expressing the different mutant and wild-type proteins. Three mutant chloride channels, G622D, R792G and E822K CFTR, were characterized by significantly lower intrinsic chloride channel activities compared with wild-type CFTR. Two mutations, H620Q and A800G, resulted in increased intrinsic chloride transport activities. Finally, T665S and E826K CFTR had single channel properties not significantly different from wild-type CFTR.     

Detection of K-ras mutations in lung carcinomas: relationship to prognosis

The K-ras mutation is one of the most common genetic alterations found in human lung cancer. To evaluate the prognostic value of ras gene alterations in lung cancer in a U.S. population, we have screened 173 human lung tumors, which included 127 adenocarcinomas, 37 squamous carcinomas, and 9 adenosquamous carcinomas, for mutations in the K-ras gene using the combination of the PCR and denaturing gradient gel electrophoresis. Forty-three tumors contained K-ras mutations. Of these, 41 were identified among the adenocarcinomas (32%), 1 among the squamous carcinomas (2.7%), and 1 among the adenosquamous carcinomas (11%). Forty of these mutations were found in codon 12 and consisted of 24 G to T transversions, 12 G to A transitions, 2 G to C transversions, and 1 double GG to TT mutation. Two other G to T transversions were found in codon 13, and 1 A to C transversion was found in codon 61. The data showed that gender did not seem to affect the incidence and the types of the K-ras mutations or amino acid changes. Examination of the mutations in adenocarcinomas in relation to overall survival showed no difference in adenocarcinomas with K-ras mutations compared with K-ras-negative adenocarcinomas. However, the substitution of the wild-type GGT (glycine) at codon 12 with a GTT (valine) or a CGT (arginine) showed a strong trend (P = 0.07) toward a poorer prognosis compared with wild-type or other amino acid substitutions. Substitution of the wild-type glycine for aspartate (GAT) showed a strong trend (P = 0.06) for a better outcome than the valine or arginine substitution. Although these trends will require larger patient populations for verification, these data suggest that the prognostic significance of K-ras mutations may depend on the amino acid substitution in the p21(ras) protein.     

mRNA from frog corneal epithelium increases water permeability in Xenopus oocytes

PURPOSE: To investigate the existence of a water channel in the frog corneal epithelium by studying the osmotic water permeability (Pf) of Xenopus oocytes expressing the mRNA message from frog corneal epithelium. METHODS: Total RNA was obtained from corneal epithelium by a single-step phase separation method, and poly A+ RNA was isolated using oligo-dT columns. This mRNA was injected into the oocytes. After a 48-hour incubation, oocyte volume changes elicited by a hypoosmotic solution were measured with a computerized video system. RESULTS: Oocytes injected with 50 nl mRNA (1 microgram/microliter) showed a significant increase in Pf compared to water-injected controls (8.4 +/- 1.5 to 17.5 +/- 1.9 cm.sec-1 x 10(-4), P < 0.005). mRNA-injected oocytes exposed to a higher external [Cl-] showed a heightened permeability. Furthermore, Pf of oocytes exposed to a solution containing the recognized water-channel blocker HgCl2 was significantly lower than the Pf of mRNA-injected oocytes not exposed to HgCl2. CONCLUSIONS: Evidence was found for a water channel in the frog corneal epithelium because oocytes injected with the epithelial mRNA manifested increased water permeability. The increase in water permeability was larger in the presence of external Cl- and was inhibited by HgCl2. This finding correlates with measurements of Pf in the intact epithelium in which apical Cl- induced an increase in transepithelial water permeability prevented by HgCl2.     

Relativistic density-dependent Hartree-Fock approach for finite nuclei

Two precore predominant mutations of human hepatitis B virus (HBV) at either nucleotide (nt) 1896 or nt 1899 often occur in combination. At nt 1896, a G to A mutation creates a TAG stop codon at codon 28 of precore protein. At nt 1899, a G to A mutation changes glycine at codon 29 to aspartic acid. To assess the effect of each individual mutation as well as any interaction between these two mutations, HBV derivatives bearing one or both precore predominant mutations have been constructed. HBV e-Ag-negative mutants bearing a TAG stop codon mutation at codon 28 uniformly replicate at least 20-fold better than mutants bearing a TGA stop codon at the same amino acid position, irrespective of the sequence context at nt 1899. A single mutation at nt 1899, changing the wild-type G to a pyrimidine (T or C) is deleterious to viral RNA encapsidation and DNA replication. Our results explain in part why only a purine (G or A) at nt 1899, never a pyrimidine, is observed in natural HBV genomes. The effects caused by these two closely linked mutations on viral replication are not independent of each other. The stringent selection for a highly efficient RNA encapsidation element may play a crucial role in the natural occurrence of these two closely linked precore mutations. The putative 27-amino-acid peptide resulting from the truncation of precore by the nt 1896 mutation has no apparent effect on viral replication. The preferential occurrence of the G to A mutation at nt 1896 and 1899, instead of at other nonpredominant positions, is likely to be a combined consequence of both selection and higher intrinsic mutation frequency at these positions.     

Observations on the California mortality studies

Since the discovery of aquaporin water channels, insight into the molecular mechanism by which rapid osmotic water occurs across cell membranes has greatly improved. Aquaporin-2 is the vasopressin-responsive water channel in the collecting duct, and vasopressin control of water permeability in the collecting duct occurs in two ways: a short-term regulation and a long-term adaptation. In congenital nephrogenic diabetes insipidus, the kidney does not respond to vasopressin. Ninety percent of these patients carry a mutation in the gene coding for the vasopressin V2 receptor located on the X chromosome. Autosomal recessive and dominant forms of nephrogenic diabetes insipidus that are caused by mutations in the aquaporin-2 gene have now been described. This review focuses on recent insight in the molecular and cellular defect in autosomal nephrogenic diabetes insipidus.     

Combined effects of insulin treatment and adipose tissue-specific agouti expression on the development of obesity

BACKGROUND & AIMS: Infantile and childhood liver tumors have been found in 0.42% of individuals with a germline mutation in the adenomatous polyposis coli (APC) gene. This study analyzed a hepatocellular adenoma of a 2-year-old child at risk for familial adenomatous polyposis to identify genetic alterations in hepatic tumors initiated by APC germline mutations. METHODS: Mutation screening was performed for the APC gene (protein truncation test and DNA sequence analysis), p53 gene (complementary DNA cloning and sequencing), and members of the Ras gene family (complementary DNA sequence analysis). RESULTS: Both the mother and child had a germinal CGA-->TGA transition at codon 1451 leading to an Arg1451Ter stop mutation in the APC gene. Loss of the wild-type APC allele as a second hit revealed hemizygosity of the inherited mutation in the tumor. Furthermore, a CGC-->CAC transition in the p53 gene of the adenoma resulted in an Arg-->His missense mutation in codon 175. No loss of heterozygosity was detected at the p53 locus. Ras gene mutations were not found. CONCLUSIONS: Biallelic inactivation of APC gene and p53 mutation are early events in hepatocellular tumorigenesis. Additional reports will confirm whether inherited APC gene mutations between codon 1444 and 1578 increase the risk for hepatic tumors.     

Molecular biological studies on patients with nephrogenic diabetes insipidus]

Nephrogenic diabetes insipidus is a rare, mostly X-linked recessive disorder characterised by renal tubular resistance to the antidiuretic effect of arginine vasopressin. The gene responsible for the X-linked nephrogenic diabetes insipidus, the G-protein-coupled vasopressin V2-receptor, has been localised on the Xq28 region. In this study four patients were investigated with molecular genetic methods. Diagnosis was based on clinical symptoms and lack of increase of urinary osmolality after administration of the arginine vasopressin, or the synthetic vasopressin analogue DDAVP. Three different mutations (C112R, N317K, W323S) were found in three patients, while no mutation was detected in the fourth patient. Since earlier histiocytosis X has been diagnosed in this patient, this patient has probably central diabetes insipidus. Although the main symptoms of the disease can be found in all patients, there are significant differences in the seriousness of the symptoms as well as in some other symptoms. The explanations might be the different mutations in the V2-receptor gene and the various other genetic and environmental factors; these findings provide further evidence that X-linked nephrogen diabetes insipidus results from defects in the V2-receptor gene.     

Functional analysis of nodulin 26, an aquaporin in soybean root nodule symbiosomes

Upon infection of soybean roots, nitrogen-fixing bacteria become enclosed in a specific organelle known as the symbiosome. The symbiosome membrane (SM) is a selectively permeable barrier that controls metabolite flux between the plant cytosol and the symbiotic bacterium inside. Nodulin 26 (NOD 26), a member of the aquaporin (AQP) water channel family, is a major protein component of the SM. Expression of NOD 26 in Xenopus oocytes gave a mercury-sensitive increase in osmotic water permeability (Pf). To define the biophysical properties of NOD 26 water channels in their native membranes, symbiosomes were isolated from soybean root nodules and the SM separated as vesicles from the bacteria. Permeabilities were measured using stopped-flow fluorimetry in SM vesicles with entrapped carboxyfluorescein. Osmotic water permeability (Pf) of SM was high, with a value of 0.05 +/- 0.003 cm/s observed at 20 degrees C (mean +/- S.E.; n = 15). Water flow exhibited a low activation energy, was inhibited by HgCl2 (0.1 mM), and exhibited a unit conductance of 3.2 +/- 1.3 x 10(-15) cm3/s, a value 30-fold lower than that of AQP 1, the red blood cell water channel. Diffusive water permeability (Pd) was 0.0024 +/- 0.0002 cm/s, and the resulting Pf to Pd ratio was 18.3, indicating that water crosses the SM in single file fashion via the NOD 26 water channel. In addition to high water permeability, SM vesicles also show high mercury-sensitive permeability to glycerol and formamide, but not urea, suggesting that NOD 26 also fluxes these solutes. Overall, we conclude that NOD 26 acts as a water channel with a single channel conductance that is 30-fold lower than AQP 1. Because the solutes that permeate NOD 26 are far larger than water, and water appears to cross the channel via a single file pathway, solute flux across NOD 26 appears to occur by a pathway that is distinct from that for water.     

How enzymes control the reactivity of adenosylcobalamin: effect on coenzyme binding and catalysis of mutations in the conserved histidine-aspartate pair of glutamate mutase

Glutamate mutase is one of a group of adenosylcobalamin-dependent enzymes that catalyze unusual isomerizations that proceed through the formation of radical intermediates. It shares a structurally similar cobalamin-binding domain with methylcobalamin-dependent methionine synthase. In particular, both proteins contain the "DXHXXG" cobalamin-binding motif, in which the histidine provides the axial ligand to cobalt. The effects of mutating the conserved histidine and aspartate residues in methionine synthase have recently been described [Jarrett, J. T., Amaratunga, M., Drennan, C. L., Scholten, J. D., Sands, R. H., Ludwig, M. L., & Matthews, R. G. (1996) Biochemistry 35, 2464-2475]. Here, we describe how similar mutations in the "DXHXXG" motif of glutamate mutase affect coenzyme binding and catalysis in an adenosylcobalamin-dependent reaction. The mutations made in the MutS subunit of glutamate mutase were His16Gly, His16Gln, Asp14Asn, Asp14Glu, and Asp14Ala. All the mutations affect, in varying degrees, the rate of catalysis, the affinity of the protein for the coenzyme, and the coordination of cobalt. Mutations of either Asp14 or His16 decrease k(cat) by 1000-fold, and whereas cob(II)alamin accumulates as an intermediate in the wild-type enzyme, it does not accumulate in the mutants, suggesting the rate-determining step is altered. The apparent Kd for adenosylcobalamin is raised by about 50-fold when His16 is mutated and by 5-10-fold when Asp16 is mutated. There are extensive differences between the UV-visible spectra of wild-type and mutant holoenzymes, indicating that the mutant enzymes coordinate cobalt less well. Overall, the properties of these mutants differ quite markedly from those observed when similar mutations were introduced into methionine synthase.     

Mutations in different functional domains of the human muscle acetylcholine receptor alpha subunit in patients with the slow-channel congenital myasthenic syndrome

Congenital myasthenic syndromes are a group of rare genetic disorders that compromise neuromuscular transmission. A subset of these disorders, the slow-channel congenital myasthenic syndrome (SCCMS), is dominantly inherited and has been shown to involve mutations within the muscle acetylcholine receptor (AChR). We have identified three new SCCMS mutations and a further familial case of the alpha G153S mutation. Single channel recordings from wild-type and mutant human AChR expressed in Xenopus oocytes demonstrate that each mutation prolongs channel activation episodes. The novel mutations alpha V156M, alpha T254I and alpha S269I are in different functional domains of the AChR alpha subunit. Whereas alpha T254I is in the pore-lining region, like five of six previously reported SCCMS mutations, alpha S269I and alpha V156M are in extracellular domains. alpha S269I lies within the short extracellular sequence between M2 and M3, and identifies a new region of muscle AChR involved in ACh binding/channel gating. alpha V156M, although located close to alpha G153S which has been shown to increase ACh binding affinity, appears to alter channel function through a different molecular mechanism. Our results demonstrate heterogeneity in the SCCMS, indicate new regions of the AChR involved in ACh binding/channel gating and highlight the potential role of mutations outside the pore-lining regions in altering channel function in other ion channel disorders.     

Expression of rat liver cell membrane transporters for thyroid hormone in Xenopus laevis oocytes

The present study was conducted to explore the possible use of Xenopus laevis oocytes for the expression cloning of cell membrane transporters for iodothyronines. Injection of stage V-VI X. laevis oocytes with 23 ng Wistar rat liver polyadenylated RNA (mRNA) resulted after 3-4 days in a highly significant increase in [125I]T3 (5 nM) uptake from 6.4 +/- 0.8 fmol/oocyte x h in water-injected oocytes to 9.2 +/- 0.65 fmol/oocyte x h (mean +/- SEM; n = 19). In contrast, [125I]T4 (4 nM) uptake was not significantly stimulated by injection of total liver mRNA. T3 uptake induced by liver mRNA was significantly inhibited by replacement of Na+ in the incubation medium by choline+ or by simultaneous incubation with 1 microM unlabeled T3. In contrast, T3 uptake by water-injected oocytes was not Na+ dependent. Fractionation of liver mRNA on a 6-20% sucrose gradient showed that maximal stimulation of T3 uptake was obtained with mRNA of 0.8-2.1 kilobases (kb). In contrast to unfractionated mRNA, the 0.7- to 2.1-kb fraction also significantly stimulated transport of T4, and it was found to induce uptake of T3 sulfate (T3S). Because T3S is a good substrate for type I deiodinase (D1), 2.3 ng rat D1 complementary RNA (cRNA) were injected either alone or together with 23 ng of the 0.8- to 2.1-kb fraction of rat liver mRNA. Compared with water-injected oocytes, injection of D1 cRNA alone did not stimulate uptake of [125I]T3S (1.25 nM). T3S uptake in liver mRNA and D1 cRNA-injected oocytes was similar to that in oocytes injected with mRNA alone, showing that transport of T3S is independent of the metabolic capacity of the oocyte. Furthermore, coinjection of liver mRNA and D1 cRNA strongly increased the production of 125I-, showing that the T3S taken up by the oocyte is indeed transported to the cell interior. In conclusion, injection of rat liver mRNA into X. laevis oocytes resulted in a stimulation of saturable, Na+-dependent T4, T3 and T3S transport, indicating that rat liver contains mRNA(s) coding for plasma membrane transporters for these iodothyronine derivatives.