Aquaporin Family Research Articles

Expression profiles of aquaporins in rat conjunctiva, cornea, lacrimal gland and Meibomian gland

The aim of the study was to elucidate aquaporin (AQP) family member mRNA expression and protein expression/localization in the rat lacrimal functional unit. The mRNA expression of all rat AQPs (AQP0–9, 11–12) in palpebral, fornical, and bulbar conjunctiva, cornea, lacrimal gland, and Meibomian gland was measured by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) and real time RT-PCR. Antibodies against AQP1, 3, 4, 5, 9, and 11 were used in Western blotting and immunohistochemistry to determine protein expression and distribution. Our study demonstrated characteristic AQP expression profiles in rat ocular tissues. AQP1, 3, 4, 5, 8, 9, 11, and 12 mRNA were detected in conjunctiva. AQP0, 1, 2, 3, 4, 5, 6, 11, and 12 mRNA were expressed in cornea. AQP0, 1, 2, 3, 4, 5, 7, 8, and 11 mRNA were detected in lacrimal gland. AQP1, 3, 4, 5, 7, 8, 9, 11, and 12 mRNA were identified in Meibomian gland. By Western blot, AQP1, 3, 5, and 11 were detected in conjunctiva; AQP1, 3, 5, and 11 were identified in cornea; AQP1, 3, 4, 5, and 11 were detected in lacrimal gland; and AQP1, 3, 4, 5, 9, and 11 were present in Meibomian gland. Immunohistochemistry localized AQPs to distinct sites in the various tissues. This study rigorously analyzed AQPs expression and localization in rat conjunctiva, cornea, lacrimal gland, and Meibomian gland tissues. Our findings provide a comprehensive platform for further investigation into the physiological or pathophysiological relevance of AQPs in ocular surface.

Yeast Aquaglyceroporins Use the Transmembrane Core to Restrict Glycerol Transport

Aquaglyceroporins are transmembrane proteins belonging to the family of aquaporins, which facilitate the passage of specific uncharged solutes across membranes of cells. The yeast aquaglyceroporin Fps1 is important for osmoadaptation by regulating intracellular glycerol levels during changes in external osmolarity. Upon high osmolarity conditions, yeast accumulates glycerol by increased production of the osmolyte and by restricting glycerol efflux through Fps1. The extended cytosolic termini of Fps1 contain short domains that are important for regulating glycerol flux through the channel. Here we show that the transmembrane core of the protein plays an equally important role. The evidence is based on results from an intragenic suppressor mutation screen and domain swapping between the regulated variant of Fps1 from Saccharomyces cerevisiae and the hyperactive Fps1 ortholog from Ashbya gossypii. This suggests a novel mechanism for regulation of glycerol flux in yeast, where the termini alone are not sufficient to restrict Fps1 transport. We propose that glycerol flux through the channel is regulated by interplay between the transmembrane helices and the termini. This mechanism enables yeast cells to fine-tune intracellular glycerol levels at a wide range of extracellular osmolarities.

Different Impacts of Aquaporin 4 and MAOA Allele Variation Among Olanzapine, Risperidone, and Paliperidone in Schizophrenia

Apoptosis has been considered to be involved in schizophrenia. Water channels are modulated just before apoptosis. In the aquaporin family, aquaporin 4 (AQP-4) is most highly expressed in the brain and is supposed to play an important role in a neuronal environment. In this clinical study, we investigated the relationship between the AQP-4 polymorphism and drug response in schizophrenia under the control of the MAOA (monoamine oxidase A) promoter gene. We recruited 91 patients with schizophrenia, and they were randomized to receive olanzapine (n = 44), risperidone (n = 23), or paliperidone (n = 24). Genotyping of AQP-4 and MAOA polymorphisms was done in all patients. Patients with the AQP-4 non-C polymorphism needed a higher dosage of olanzapine for treatment (z = 4.163, P = 0.041), and patients with a short form of the MAOA polymorphism needed a higher dosage of risperidone for treatment (z = 5.124, P = 0.024). Patients who smoked cigarettes needed a higher dosage of olanzapine for treatment (z = 4.905, P = 0.027), but cigarette smoking did not affect the dosage of paliperidone. The AQP-4 polymorphism may have an effect in influencing the dosage of olanzapine. However, the roles of AQP-4 polymorphisms in the blood-brain barrier and different neuroprotective effects need further exploration in future studies.

Rapid Aquaporin Translocation Regulates Cellular Water Flow

The control of cellular water flow is mediated by the aquaporin (AQP) family of membrane proteins. The structural features of the family and the mechanism of selective water passage through the AQP pore are established, but there remains a gap in our knowledge of how water transport is regulated. Two broad possibilities exist. One is controlling the passage of water through the AQP pore, but this only has been observed as a phenomenon in some plant and microbial AQPs. An alternative is controlling the number of AQPs in the cell membrane. Here, we describe a novel pathway in mammalian cells whereby a hypotonic stimulus directly induces intracellular calcium elevations through transient receptor potential channels, which trigger AQP1 translocation. This translocation, which has a direct role in cell volume regulation, occurs within 30 s and is dependent on calmodulin activation and phosphorylation of AQP1 at two threonine residues by protein kinase C. This direct mechanism provides a rationale for the changes in water transport that are required in response to constantly changing local cellular water availability. Moreover, because calcium is a pluripotent and ubiquitous second messenger in biological systems, the discovery of its role in the regulation of AQP translocation has ramifications for diverse physiological and pathophysiological processes, as well as providing an explanation for the rapid regulation of water flow that is necessary for cell homeostasis.

Functional Characterization of a Novel Aquaporin from Dictyostelium discoideum Amoebae Implies a Unique Gating Mechanism

The social amoeba Dictyostelium discoideum is a widely used model organism for studying basic functions of protozoan and metazoan cells, such as osmoregulation and cell motility. There is evidence from other species that cellular water channels, aquaporins (AQP), are central to both processes. Yet, data on D. discoideum AQPs is almost absent. Despite cloning of two putative D. discoideum AQPs, WacA, and AqpA, water permeability has not been shown. Further, WacA and AqpA are expressed at the late multicellular stage and in spores but not in amoebae. We cloned a novel AQP, AqpB, from amoeboidal D. discoideum cells. Wild-type AqpB was impermeable to water, glycerol, and urea when expressed in Xenopus laevis oocytes. Neither stepwise truncation of the N terminus nor selected point mutations activated the water channel. However, mutational truncation by 12 amino acids of an extraordinary long intracellular loop induced water permeability of AqpB, hinting at a novel gating mechanism. This AqpB mutant was inhibited by mercuric chloride, confirming the presence of a cysteine residue in the selectivity filter as predicted by our structure model. We detected AqpB by Western blot analysis in a glycosylated and a non-glycosylated form throughout all developmental stages. When expressed in D. discoideum amoebae, AqpB-GFP fusion constructs localized to vacuolar structures, to the plasma membrane, and to lamellipodia-like membrane protrusions. We conclude that the localization pattern in conjunction with channel gating may be indicative of AqpB functions in osmoregulation as well as cell motility of D. discoideum.

Ontogeny of Aquaporins in Human Fetal Membranes1

It has been proposed that four members of the aquaporin family (AQPs 1, 3, 8, and 9) are involved in the control of amniotic fluid (AF) homeostasis, as illustrated by their differential expression patterns in normal and pathological human term fetal membranes. However, there are no data available to date on their ontogeny throughout pregnancy. Our objective was to determine spatiotemporal expression profiles of the mRNA and proteins of all 13 members of this transmembrane channel family. For this purpose, we used healthy fetal membranes from the first, second, and third trimesters of pregnancy. Total mRNA and proteins were extracted from total membranes and from separated amnion and chorion. Quantitative PCR, Western blot, and immunohistochemistry experiments were carried out to determine the presence of AQPs and to quantify their spatiotemporal expression patterns throughout pregnancy. The WISH cell line was tested to propose a cellular model for the role of AQPs in the amnion compartment. AQP11 expression was established in amniotic membranes at term. Aquaporins 1, 3, 8, 9, and 11 mRNA and proteins were present in amnion and chorion throughout human gestation. Each AQP has a time-specific expression pattern, with AQP1 presenting the highest variation in terms of mRNA and protein levels. The WISH cell line also expressed the same five AQPs. Taken together, these results indicate that AQPs are expressed and potentially involved in the regulation of AF homeostasis throughout pregnancy. This also clearly supports the hypothesis that abnormal expression could occur at any time during pregnancy, ultimately leading to obstetrical pathologies such as polyhydramnios or oligohydramnios.

The Aquaporin Family: A Novel Player in the Progression of Adenocarcinoma of the Lung

目的．細胞膜水輸送チャネルとして発見されたアクアポリンaquaporin（AQP）にがんの発生や進展に関わる新規機能の存在が近年提唱された．本稿では多様な肺腺癌亜型におけるAQPの発現と進展への関与に関する知見を紹介する．結果．肺癌ではAQP1，3，4，5が腺癌細胞に発現する．その発現は，1）細胞分化に相当する極性を有するAQP1，3の発現，2）極性は保たれるが正常肺では認められないAQP5の異所性発現，3）極性を喪失したAQP1，5の過剰発現に区分される．1）は細気管支肺胞上皮癌に高頻度で，進展に伴い減少する．2）は肺胞上皮癌のみならず異型腺腫様過形成でも見られ，腫瘍発生に関係していると考えられる．3）は微小浸潤部から観察され始め，進展とともに頻度を増し，生命予後と有意な関連を示す．AQP1は浸潤先進部での発現亢進と浸潤部lamellipodia細胞膜での発現を介した，AQP5は細胞増殖や上皮間質移行関連分子の活性化を介した肺腺癌の浸潤・転移能亢進への関与が示唆されている．AQP5の発現と粘液産生性肺癌の進展，AQP1の過剰発現と微小乳頭状成分の侵襲性との関連性も認められる．また，AQP4は肺腺癌で発現レベルが高く，生命予後良好因子となる．結論．AQP1，5は肺腺癌の進展に関わる重要分子の一つと考えられ，新たな進展阻止法の確立のための標的分子となる可能性が示唆される．

Expression and Localization of Aquaporins in Benign Prostate Hyperplasia and Prostate Cancer

The aquaporin (AQP) families of water channels are intrinsic membrane proteins that facilitate selective water and small solute movement across the plasma membrane. The purposes of this study were to determine the expression and localization of AQPs in benign prostatic hyperplasia and prostate cancer. Prostatic tissue was collected from patients with benign prostatic hyperplasia or prostate cancer by transurethral resection of the prostate. The expression and cellular localization of the AQPs were determined in the human prostate by Western blot and immunohistochemistry. AQP1, 3, and 9 were expressed in the human prostate. Western blot analysis revealed bands at 28-36 kDa for the AQP1, 3, and 9 proteins. Of these proteins, AQP3 and 9 were expressed in the epithelium. Immunolabeling showed that AQP1 was mainly expressed in the capillaries and venules of the prostate, AQP9 was expressed in the cytoplasm of the epithelium, and AQP3 was mainly associated with the plasma membrane of the prostatic epithelium. Only AQP3 expression was localized in the cell membrane, and expressed AQP3 was translocated to the cytoplasm in prostate cancer. The epithelium in the human prostate expresses AQP3 and 9 proteins, and the capillaries and venules of the prostate express AQP1. Characterizing or modifying the expression of AQP3 may lead to an understanding of the role of the AQPs in human prostatic disease.

Aquaporins in human breast cancer: Identification and involvement in carcinogenesis of breast cancer

Aquaporins (AQPs) play important roles in water and glycerol transport. Recently, the role of AQPs in human carcinogenesis has become an area of great interest. However, little is known about the function of AQPs in human breast cancer. The aim of this study was to investigate the expression profile of AQPs in human breast cancer and its significance. In this study, we screened the expression profile of AQP0-12 in breast cancer tissues and corresponding normal tissues by RT-PCR, Western blotting and immunohistochemistry. AQP1, 3-5, and 10-12 were expressed in human breast cancer and/or normal breast tissues, and AQP1 and 3-5 exhibited differential expression. AQP1 was expressed in cell membranes and its expression was higher in cancer than that in normal tissues. AQP4 was expressed in the cell membrane and cytoplasm and was detected markedly stronger in normal than in cancer tissues. AQP5 was expressed mainly in cell membranes in carcinoma tissues, but was almost absent in normal breast tissues. Expression of AQP5 was associated with cellular differentiation, lymph node invasion, and clinicopathological staging. These observations suggested that several subtypes of the AQP family play a role in human breast carcinogenesis.

Alternative angiogenic pathways in melanoma: the role of AQP1

AQP1 belongs to aquaporins family, water-specific, membrane-channel proteins expressed preferentially by microvessels, favoring angiogenesis and increasing permeability. Recently, we have demonstrated that AQP1 has a role as bio-mechanic sensor modulating and stabilizing the organization of cytoskeleton. In the present paper, we have studied the expression of AQP1 and VEGF pathways in vitro and in tumors xenografts obtained injecting murine (B16-BL6) or human (WM115) melanoma cells in syngeneic or NOD-SCID mice, respectively. Alltogether, our data show the presence of alternative angiogenic pathways in melanoma tumor xenografts and show, for the first time, a connection between AQP1 and VEGF pathway to facilitate vacuolisation and tube formation.

Quantitative analysis of ascorbic acid permeability of aquaporin 0 in the lens

Aquaporin 0 (AQP0) is a lens-specific protein comprising more than 30% of lens membrane protein content and is a member of the aquaporin family. Water permeates through AQP0 much more slowly than other aquaporin family members, and other compounds, such as glycerol, also permeate AQP0. In the lens, ascorbic acid (AA) is found at high concentrations, protecting the lens from photochemical events such as photo-oxidation. The aim of the present study was to clarify the function of AQP0. Mouse fibroblast L-cells stably expressing AQP0 were established and incubated in medium containing AA, and intracellular AA levels were measured by high-performance liquid chromatography (HPLC) and 2,6-dichlorophenol-indophenol (DCPIP) analysis. Intracellular AA levels in AQP0-expressing cells quickly rose and reached saturation 10min after incubation in medium containing 1000μM AA. In contrast, AA levels in cells slowly decreased when AA was washed out from the medium. Cells overexpressing AQP0 increased the cellular uptake of AA in a time- and concentration-dependent manner. These data suggest that AA as well as water permeates AQP0.AQP0 expression on Xenopus oocyte membranes was achieved by the injection of AQP0 cRNA into oocytes that were incubated in medium containing AA. Intracellular AA levels were then measured by HPLC. AA uptake was demonstrated in the AQP0-expressing oocytes and was shown to quickly reach saturation. Intracellular AA concentration in oocytes increased in a time- and concentration-dependent manner.The data in the present study show that AA permeates AQP0, reveal the role of AQP0 in AA permeability ex vivo, and also indicate that there is a difference between the import and export of AA via AQP0. These findings suggest that AQP0 plays an important role in controlling lens AA content.

Identification and functional characterization of an ovarian aquaporin from the cockroachBlattella germanicaL. (Dictyoptera, Blattellidae)

Aquaporins (AQPs) are membrane proteins that form water channels, allowing rapid movement of water across cell membranes. AQPs have been reported in species of all life kingdoms and in almost all tissues, but little is known about them in insects. Our purpose was to explore the occurrence of AQPs in the ovary of the phylogenetically basal insect Blattella germanica (L.) and to study their possible role in fluid homeostasis during oogenesis. We isolated an ovarian AQP from B. germanica (BgAQP) that has a deduced amino acid sequence showing six potential transmembrane domains, two NPA motifs and an ar/R constriction region, which are typical features of the AQP family. Phylogenetic analyses indicated that BgAQP belongs to the PRIP group of insect AQPs, previously suggested to be water specific. However, ectopic expression of BgAQP in Xenopus laevis oocytes demonstrated that this AQP transports water and modest amounts of urea, but not glycerol, which suggests that the PRIP group of insect AQPs may have heterogeneous solute preferences. BgAQP was shown to be highly expressed in the ovary, followed by the fat body and muscle tissues, but water stress did not significantly modify the ovarian expression levels. RNA interference (RNAi) reduced BgAQP mRNA levels in the ovary but the oocytes developed normally. The absence of an apparent ovarian phenotype after BgAQP RNAi suggests that other functionally redundant AQPs that were not silenced in our experiments might exist in the ovary of B. germanica.

Characterization of Leishmania donovani Aquaporins Shows Presence of Subcellular Aquaporins Similar to Tonoplast Intrinsic Proteins of Plants

Leishmania donovani, a protozoan parasite, resides in the macrophages of the mammalian host. The aquaporin family of proteins form important components of the parasite-host interface. The parasite-host interface could be a potential target for chemotherapy. Analysis of L. major and L. infantum genomes showed the presence of five aquaporins (AQPs) annotated as AQP9 (230aa), AQP putative (294aa), AQP-like protein (279aa), AQP1 (314aa) and AQP-like protein (596aa). We report here the structural modeling, localization and functional characterization of the AQPs from L. donovani. LdAQP1, LdAQP9, LdAQP2860 and LdAQP2870 have the canonical NPA-NPA motifs, whereas LdAQP putative has a non-canonical NPM-NPA motif. In the carboxyl terminal to the second NPA box of all AQPs except AQP1, a valine/alanine residue was found instead of the arginine. In that respect these four AQPs are similar to tonoplast intrinsic proteins in plants, which are localized to intracellular organelles. Confocal microscopy of L. donovani expressing GFP-tagged AQPs showed an intracellular localization of LdAQP9 and LdAQP2870. Real-time PCR assays showed expression of all aquaporins except LdAQP2860, whose level was undetectable. Three-dimensional homology modeling of the AQPs showed that LdAQP1 structure bears greater topological similarity to the aquaglyceroporin than to aquaporin of E. coli. The pore of LdAQP1 was very different from the rest in shape and size. The cavity of LdAQP2860 was highly irregular and undefined in geometry. For functional characterization, four AQP proteins were heterologously expressed in yeast. In the fps1Δ yeast cells, which lacked the key aquaglyceroporin, LdAQP1 alone displayed an osmosensitive phenotype indicating glycerol transport activity. However, expression of LdAQP1 and LdAQP putative in a yeast gpd1Δ strain, deleted for glycerol production, conferred osmosensitive phenotype indicating water transport activity or aquaporin function. Our analysis for the first time shows the presence of subcellular aquaporins and provides structural and functional characterization of aquaporins in Leishmania donovani.

Evaluation of circulating acylated-ghrelin, leptin, growth hormone, IGF-1, IGFBP-1, IGFBP-3 and their correlation with healthy pregnant subjects

In this review, we have tried to summarize most available data dealing with the aquaporin (AQP) family of water channels in the CNS. Two aquaporins have been identified so far in the CNS, AQP1 and AQP4. AQP1 is restricted to the choroid plexus of the lateral ventricles, which raises a role for this aquaporin in cerebrospinal fluid formation. AQP4 is the predominant water channel in the brain and it is more widely distributed than originally believed, with a marked prevalence over periventricular areas. In the first part of this review, we examine the complete distribution pattern of AQP4 in the CNS including its rostro-caudal localization to end with its subcellular location. After discussing scarce data dealing with regulation of aquaporins in the CNS, we focus in potential roles for aquaporins. Novel recent data highlights very important roles for this aquaporin in the normal and pathological brain including, among others, role in potassium buffering, body fluid homeostasis, central osmoreception and development and restoration of brain edema.

A calorimetric study on the concentration dependent of hemoglobin tetramer assembly

In this review, we have tried to summarize most available data dealing with the aquaporin (AQP) family of water channels in the CNS. Two aquaporins have been identified so far in the CNS, AQP1 and AQP4. AQP1 is restricted to the choroid plexus of the lateral ventricles, which raises a role for this aquaporin in cerebrospinal fluid formation. AQP4 is the predominant water channel in the brain and it is more widely distributed than originally believed, with a marked prevalence over periventricular areas. In the first part of this review, we examine the complete distribution pattern of AQP4 in the CNS including its rostro-caudal localization to end with its subcellular location. After discussing scarce data dealing with regulation of aquaporins in the CNS, we focus in potential roles for aquaporins. Novel recent data highlights very important roles for this aquaporin in the normal and pathological brain including, among others, role in potassium buffering, body fluid homeostasis, central osmoreception and development and restoration of brain edema.

Developmental pattern of aquaporin expression in barley (Hordeum vulgare L.) leaves.

Aquaporins are multifunctional membrane channels which belong to the family of major intrinsic proteins (MIPs) and are best known for their ability to facilitate the movement of water. In the present study, earlier results from microarray experiments were followed up. These experiments had suggested that, in barley (Hordeum vulgare L.), aquaporin family members are expressed in distinct patterns during leaf development. Real-time PCR and in situ hybridization were used to analyse the level and tissue-distribution of expression of candidate aquaporins, focusing on plasma membrane and tonoplast intrinsic proteins (PIPs, TIPs). Water channel function of seven aquaporins, whose transcripts were the most abundant and the most variable, was tested through expression in yeast and, in part, through expression in oocytes. All PIP1 and PIP2 subfamily members changed in expression during leaf development, with expression being much higher or lower in growing compared with mature tissue. The same applied to those TIPs which were expressed at detectable levels. Specific roles during leaf development are proposed for particular aquaporins.

Development of a Novel Ligand, [11C]TGN-020, for Aquaporin 4 Positron Emission Tomography Imaging

Aquaporin 4 (AQP4), the most abundant isozyme of the water specific membrane transporter aquaporin family, has now been implicated to play a significant role in the pathogenesis of various disease processes of the nervous system from epilepsy to Alzheimer’s disease. Considering its clinical relevance, it is highly desirable to develop a noninvasive method for the quantitative analysis of AQP distribution in humans under clinical settings. Currently, the method of choice for such diagnostic examinations continues to be positron emission tomography (PET). Here, we report the successful development of a PET ligand for AQP4 imaging based on TGN-020, a potent AQP4 inhibitor developed previously in our laboratory. Utilizing [11C]-TGN-020, PET images were successfully generated in wild type and AQP4 null mice, providing a basis for future evaluation regarding its suitability for clinical studies.

Expression and function of aquaporins in peripheral nervous system

The expression and role of the aquaporin (AQP) family water channels in the peripheral nervous system was less investigated. Since 2004, however, significant progress has been made in the immunolocalization, regulation and function of AQPs in the peripheral nervous system. These studies showed selective localization of three AQPs (AQP1, AQP2, and AQP4) in dorsal root ganglion neurons, enteric neurons and glial cells, periodontal Ruffini endings, trigeminal ganglion neurons and vomeronasal sensory neurons. Functional characterization in transgenic knockout mouse model revealed important role of AQP1 in pain perception. This review will summarize the progress in this field and discuss possible involvement of AQPs in peripheral neuropathies and their potential as novel drug targets.

The aromatic/arginine selectivity filter of NIP aquaporins plays a critical role in substrate selectivity for silicon, boron, and arsenic

Nodulin-26-like intrinsic proteins (NIPs) of the aquaporin family are involved in the transport of diverse solutes, but the mechanisms controlling the selectivity of transport substrates are poorly understood. The purpose of this study was to investigate how the aromatic/arginine (ar/R) selectivity filter influences the substrate selectivity of two NIP aquaporins; the silicic acid (Si) transporter OsLsi1 (OsNIP2;1) from rice and the boric acid (B) transporter AtNIP5;1 from Arabidopsis; both proteins are also permeable to arsenite. Native and site-directed mutagenized variants of the two genes were expressed in Xenopus oocytes and the transport activities for Si, B, arsenite, and water were assayed. Substitution of the amino acid at the ar/R second helix (H2) position of OsLsi1 did not affect the transport activities for Si, B, and arsenite, but that at the H5 position resulted in a total loss of Si and B transport activities and a partial loss of arsenite transport activity. Conversely, changes of the AtNIP5;1 ar/R selectivity filter and the NPA motifs to the OsLsi1 type did not result in a gain of Si transport activity. B transport activity was partially lost in the H5 mutant but unaffected in the H2 mutant of AtNIP5;1. In contrast, both the single and double mutations at the H2 and/or H5 positions of AtNIP5;1 did not affect arsenite transport activity. The results reveal that the residue at the H5 position of the ar/R filter of both OsLsi1 and AtNIP5;1 plays a key role in the permeability to Si and B, but there is a relatively low selectivity for arsenite.

Aquaporins: for more than water at the plant–fungus interface?

Aquaporins are abundant membrane proteins that channel water, but also small uncharged molecules, across the membranes of plants, animals and microbes (Maurel et al., 2008). In this issue of New Phytologist, Dietz et al. (pp. 927–940) report on a thorough molecular and functional analysis of the whole aquaporin family of an ectomycorrhizal (ECM) fungus, the basidiomycete Laccaria bicolor. This study is novel as it describes, from an evolutionary perspective, the diversity of aquaporins in a fungus, which, with the exception of the yeast Saccharomyces cerevisiae, had not been extensively studied at a genome scale in these organisms. This study is also of special importance as it addresses the role of aquaporins in both nutrient and water exchanges during symbiosis between plants and fungi, with a potentially great impact on water and nutrient economy in forest ecosystems. In brief, Dietz et al. screened the full genomic sequence of Laccaria bicolor to identify seven open reading frames (ORFs) encoding aquaporin homologues. They used heterologous expression in yeast and Xenopus oocytes to characterize the ability of these homologues to transport water but also various solutes such as glycerol, urea andammonium (NH4+)/ammonia (NH3). It is of note that nitrogen (N) compounds, some of which are putative aquaporin substrates, are, besides water, crucial during ECM symbiosis. Similar to observations of aquaporins in other organisms, various selectivity profiles were identified for the L. bicolor aquaporins; some isoforms specifically transported water whereas others were also permeable to urea, glycerol and/or NH3.