Effect of hyperosmotic stimulation on aquaporins gene expression in chick kidney

Bird aquaporins: Molecular machinery for urine concentration

Water conservation is one of the most challenging processes for terrestrial vertebrates and is necessary for their survival. Birds are the only vertebrate animals other than mammals that have the ability to concentrate their urine. Previously, we identified and characterized aquaporins (AQP)1-4 responsible for urine concentration in Japanese quail kidneys. Today, a total of 13 orthologs for these genes have been reported in birds. Bird AQPs can be classified into four subfamilies: 1) Classical AQPs (AQP0-5 and novel member, AQP4-like) that conserve the selectivity filter; 2) aquaglyceroporins (AQP3, 7, 9 and 10) that retain an aspartic acid residue in the second NPA box and expand the pore to accept larger molecules; 3) unorthodox AQPs (AQP11-12) which structurally resemble their mammalian counterparts; 4) AQP8-type, a subfamily that differs from mammalian AQP8. Interestingly, over the course of time, birds lost their mammalian counterpart AQP6 but obtained a novel AQP4-like aquaporin member. In quail and/or chicken kidneys, at least six AQPs are expressed. Quail AQP1 (qAQP1) is expressed in both cortical and medullary proximal tubules but is absent in the descending limb (DL) and the thick ascending limb (TAL), supporting our previous finding that the DL and TAL are water impermeable. AQP2, an arginine vasotocin (AVT)-sensitive water channel, is exclusively expressed in the principal cells of the collecting duct (CD). AQP4 is unlikely to participate in free water resorption from the collecting duct (CD), and only AQP3 may represent an exit pathway for water reabsorbed apically via AQP2. While AQP9 is not expressed in mammalian kidneys, AQP9 was recently found in chicken kidneys. This review summarizes the current knowledge of the structure, function and expression of bird AQPs.

Effects of Betaine Supplementation on Live Performance, Selected Blood Parameters, and Expression of Water Channel and Stress-Related mRNA Transcripts of Delayed Placement Broiler Chicks

This study examined the effect of supplemental betaine on live performance, selected blood parameters, and gene expression of water channel proteins (Aquaporins, AQP) of broiler chicks delayed in placement for 48 h post-hatch. In total, 540 newly-hatched male broiler chicks were obtained from a local hatchery and were randomly allotted to one of five treatments with nine replicates per treatment (12 chicks per replicate). Chicks were either placed immediately, control; held for 48 h post-hatch with no access to feed or water, Holdnull; held for 48 h with free access to drinking water only, HoldW; held for 48 h with free access to drinking water supplemented with 1 ml per L of betaine solution (40% betaine), HoldB1; or held for 48 h with free access to drinking water supplemented with 2 ml per L of betaine solution (40% betaine), HoldB2 group. The results showed that post-hatch holding for 48 h depressed feed intake and body weight gain during the entire 15 d study period with no beneficial effect of supplemental betaine. Chicks in the HoldB2 group had elevated serum glucose, triglycerides, and aspartate aminotransferase 48 h post-hatch. Early water deprivation directly affected the brain proopiomelanocortin (POMC) and hepatic glucocorticoid receptors (GR) expression and induced significant changes in various aquaporins (AQP1, AQP2, AQP4, and AQP9). In conclusion, betaine supplementation to chicks held for 48 h post-hatch resulted in some changes in blood biochemical indices with no effects on performance during the first 15 days of life. The results suggest that betaine supplementation could ameliorate the stressful effects of water deprivation on POMC and GR expression and maintain cellular osmosis through interactions with variable aquaporins expression, particularly the AQP1 and AQP2. Further investigations are required to investigate the molecular mechanisms underlying the selective regulatory expression of different aquaporins in relation to betaine supplementation.

Strong phenotypic divergence in spite of low genetic structure in the endemic Mangrove Warbler subspecies (Setophaga petechia xanthotera) of Costa Rica

Despite the enormous advances in genetics, links between phenotypes and genotypes have been made for only a few nonmodel organisms. However, such links can be essential to understand mechanisms of ecological speciation. The Costa Rican endemic Mangrove Warbler subspecies provides an excellent subject to study differentiation with gene flow, as it is distributed along a strong precipitation gradient on the Pacific coast with no strong geographic barriers to isolate populations. Mangrove Warbler populations could be subject to divergent selection driven by precipitation, which influences soil salinity levels, which in turn influences forest structure and food resources. We used single nucleotide polymorphisms (SNPs) and morphological traits to examine the balance between neutral genetic and phenotypic divergence to determine whether selection has acted on traits and genes with functions related to specific environmental variables. We present evidence showing: (a) associations between environmental variables and SNPs, identifying candidate genes related to bill morphology (BMP) and osmoregulation, (b) absence of population genetic structure in neutrally evolving markers, (c) divergence in bill size across the precipitation gradient, and (d) strong phenotypic differentiation (P ST) which largely exceeds neutral genetic differentiation (F ST) in bill size. Our results indicate an important role for salinity, forest structure, and resource availability in maintaining phenotypic divergence of Mangrove Warblers through natural selection. Our findings add to the growing body of literature identifying the processes involved in phenotypic differentiation along environmental gradients in the face of gene flow.

Expression of aquaporin 4 in the chicken oviduct following tamoxifen treatment

This study was designed to examine whether aquaporin 4 (AQP4) is present in the chicken oviduct, and if so, whether its expression changes during pause in laying induced by tamoxifen (TMX; oestrogen receptor modulator) treatment. The control chickens were injected with a vehicle (ethanol) and the experimental ones with TMX at a dose of 6 mg/kg of body weight. Birds were treated daily until complete cessation of egg laying. The oviductal parts, that is the infundibulum, magnum, isthmus, shell gland and vagina were isolated from hens on day 8 of the experiment, and subsequently, the gene and protein expressions of AQP4 in tissues were examined by real-time PCR and Western blot, respectively. Immunohistochemical localization of AQP4 in the wall of the chicken oviduct was also investigated. Both mRNA and protein of AQP4 were found in all segments of the chicken oviduct. The relative expression [RQ] of AQP4 was the highest in the infundibulum and the vagina and the lowest, less detectable, in the magnum and isthmus. The pattern of AQP4 protein expression was similar to that of mRNA. Treatment of hens with TMX decreased the mRNA and protein levels of AQP4 in the oviduct. Immunohistochemistry demonstrated tissue and cell-dependent localization of AQP4 protein in the oviductal wall. The intensity of the immunopositive reaction was as follows: the infundibulum > vagina > shell gland ≥ isthmus >˃ magnum. In the control chickens, the immunoreactivity for AQP4 in all oviductal segments was stronger compared with the TMX-treated hens. The results obtained indicate that AQP4 takes part in the regulation of water transport required for the formation of egg in the chicken oviduct. Moreover, a relationship between oestrogen action and AQP4 gene and protein expression is suggested.

The muscular dystrophic chicken is hypernatremic

1. The E3 ubiquitin protein ligase 1 (WWP1) gene, the mutation of which causes muscular dystrophy in chickens, is expressed not only in the pectoral muscle, but also in a number of tissues such as the kidney. Therefore, this study examined some parameters related to kidney function in muscular dystrophic (MD) chickens. 2. Plasma osmolality, Na⁺ and K⁺ concentrations, aldosterone levels, and the expression of aquaporin (AQP) 2, AQP3, and α subunits of the amiloride-sensitive epithelial sodium channel (αENaC) were analysed in the kidneys of 5-week-old MD chickens and White Leghorn (WL) chickens under physiological conditions or after one day of water deprivation. 3. Plasma osmolality, Na⁺ concentrations, and plasma aldosterone levels were significantly higher in MD chickens than in WL chickens. αENaC mRNA expression levels were lower in MD chickens than in WL chickens. AQP2 and AQP3 mRNA expression levels were similar in the two strains of chickens. 4. Plasma osmolality correlated with aldosterone levels and AQP2 and αENaC mRNA levels in WL chickens. In MD chickens, plasma osmolality correlated with AQP2 mRNA levels, but not with plasma aldosterone or αENaC mRNA levels. 5. These results suggest that neither water reabsorption nor the expression of AQP2 and AQP3 is impaired in MD chickens and that a WWP1 gene mutation may or may not directly induce an abnormality in Na⁺-reabsorption in the kidneys of MD chickens, potentially through αENaC.

Expression of aquaporin 4 in the chicken ovary in relation to follicle development

In the mammalian ovary, aquaporins (AQPs) are thought to be involved in the regulation of fluid transport within the follicular wall and antrum formation. Data concerning the AQPs in the avian ovary is very limited. Therefore, the present study was designed to examine whether the AQP4 is present in the chicken ovary, and if so, what is its distribution in the ovarian compartment of the laying hen. Localization of AQP4 in the ovarian follicles at different stage of development was also investigated. After decapitation of hens the stroma with primordial follicles and white (1-4 mm), yellowish (4-8 mm), small yellow and the three largest yellow pre-ovulatory follicles F3-F1 (F3 < F2 < F1; 20-36 mm) were isolated from the ovary. The granulosa and theca layers were separated from the pre-ovulatory follicles. The AQP4 mRNA and protein were detected in all examined ovarian compartments by the real-time PCR and Western blot analyses, respectively. The relative expression of AQP4 was depended on follicular size and the layer of follicular wall. It was the lowest in the granulosa layer of pre-ovulatory follicles and the highest in the ovarian stroma as well as white and yellowish follicles. Along with approaching of the largest follicle to ovulation the gradual decrease in AQP4 protein level in the granulosa layer was observed. Immunoreactivity for AQP4 was present in the granulosa and theca cells (theca interna ≥ theca externa > granulosa). The obtained results suggest that AQP4 may take part in the regulation of water transport required for follicle development in the chicken ovary.

Molecular Cloning of cDNA Encoding an Aquaglyceroporin, AQP-h9, in the Japanese Tree Frog, Hyla japonica: Possible Roles of AQP-h9 in Freeze Tolerance

In order to study the freeze-tolerance mechanism in the Japanese tree frog, Hyla japonica, wecloned a eDNA encoding aquaporin (AQP) 9 from its liver. The predicted amino acid sequence ofH. japonica AQP9 (AQP-h9) contained six putative transmembrane domains and two conservedAsn-Pro-Aia motifs, which are characteristic of AQPs. A swelling assay using Xenopus laevisoocytes injected with AQP-h9 cRNA showed that AQP-h9 facilitated water and glycerol permeation,confirming its property as an aquaglyceroporin. Subsequently, glycerol concentrations in serumand tissue extracts were compared among tree frogs that were hibernating, frozen, or thawed afterfreezing. Serum glycerol concentration of thawed frogs was significantly higher than that of hibernatingfrogs. Glycerol content in the liver did not change in the freezing experiment, whereas thatin the skeletal muscle was elevated in thawed frogs as compared with hibernating or frozen frogs. Histological examination of the liver showed that erythrocytes aggregated in the sinusoids during hibernation and freezing, and immunoreactive AQP-h9 protein was detected over the erythrocytes. The AQP-h9 labeling was more intense in frozen frogs than in hibernating frogs, but nearly undetectable in thawed frogs. For the skeletal muscle, weak labels for AQP-h9 were observed in the cytoplasm of myocytes of hibernating frogs. AQP-h9 labeling was markedly enhanced by freezing and was decreased by thawing. These results indicate that glycerol may act as a c;:ryoprotectant in H. japonica and that during hibernation, particularly during freezing, AQP-h9 may be involved in glycerol uptake in erythrocytes in the liver and in intracellular glycerol transport in the skeletal muscle cells.

Epigenetic profiles of pre-diabetes transitioning to type 2 diabetes and nephropathy

AIM: To examine DNA methylation profiles in a longitudinal comparison of pre-diabetes mellitus (Pre-DM) subjects who transitioned to type 2 diabetes mellitus (T2DM).

METHODS: We performed DNA methylation study in bisulphite converted DNA from Pre-DM (n = 11) at baseline and at their transition to T2DM using Illumina Infinium HumanMethylation27 BeadChip, that enables the query of 27578 individual cytosines at CpG loci throughout the genome, which are focused on the promoter regions of 14495 genes.

RESULTS: There were 694 CpG sites hypomethylated and 174 CpG sites hypermethylated in progression from Pre-DM to T2DM, representing putative genes involved in glucose and fructose metabolism, inflammation, oxidative and mitochondrial stress, and fatty acid metabolism. These results suggest that this high throughput platform is able to identify hundreds of prospective CpG sites associated with diverse genes that may reflect differences in Pre-DM compared with T2DM. In addition, there were CpG hypomethylation changes associated with a number of genes that may be associated with development of complications of diabetes, such as nephropathy. These hypomethylation changes were observed in all of the subjects.

CONCLUSION: These data suggest that some epigenomic changes that may be involved in the progression of diabetes and/or the development of complications may be apparent at the Pre-DM state or during the transition to diabetes. Hypomethylation of a number of genes related to kidney function may be an early marker for developing diabetic nephropathy.

Renal responses to salinity change in snakes with and without salt glands

To understand renal responses to salinity change in aquatic reptiles, we examined the structure and function of the kidney in three species of snake: a marine species with a salt gland (Laticauda semifasciata), a marine species without a salt gland (Nerodia clarkii clarkii) and a freshwater species without a salt gland (Nerodia fasciata). Both marine species maintained relatively constant plasma ions, even after acclimation to saltwater. By contrast, both plasma Cl(-) and mortality increased with salinity in the freshwater species. To investigate putative renal ion regulatory mechanisms, we examined the distribution and abundance of Na(+)/K(+)-ATPase (NKA) and the Na(+)/K(+)/2Cl(-) cotransporter (NKCC2). In all species, NKA localized to the basolateral membranes of the distal tubule and the connecting segments and collecting ducts only; there was no effect of salinity on the distribution of NKA or on the abundance of NKA mRNA in any species. NKCC2 protein was undetectable in the kidney of any of the species and there was no effect of salinity on NKCC2 mRNA abundance. We also examined the distribution and abundance of aquaporin 3 (AQP3) in the kidney of these species; although putative AQP3 localized to the basolateral membranes of the connecting segments and collecting ducts of all three species, there was no effect of salinity on the localization of the protein or the abundance of the transcript. Interestingly, we found very few differences across species, suggesting that the snake kidney may play a trivial role in limiting habitat use.

TonEBP regulates hyperosmolality-induced arginine vasotocin gene expression in the chick (Gallus domesticus)

Arginine vasotocin (AVT) is expressed mainly in the paraventircular and supraoptic nuclei of the hypothalamus in chicken. This peptide is known to act as an antidiuretic hormone and its gene expression is stimulated by hyperosmolality. However, the transcription factors that regulate the AVT gene expression induced by hyperosmolality are still unknown. In this study, we examined the role of hyper-tonicity enhancer binding protein (TonEBP) in the transcriptional regulation of AVT gene in chicken. TonEBP mRNA expression levels increased at 1h after salt-loading treatment in the hypothalamus. This increase preceded that in AVT and c-fos mRNA expression. Intracerebroventricular injections of TonEBP antisense oligonucleotides, before the salt-loading treatment, prevented the increase in AVT gene expression. These results, all together, suggest that the transcription factor TonEBP may be involved in the regulation of AVT genes expression in response to a hyperosmotic environment in chicken.

Integrative sequence and tissue expression profiling of chicken and mammalian aquaporins

BACKGROUND

Proteins that selectively transport water across the membranes of cells are recognized as important in the normal functioning of the body systems of vertebrates. There are 13 known mammalian aquaporins (AQP0 to AQP12), some of which have been shown to have unexpected cellular roles beyond transmembrane water transport. The availability of non-mammalian vertebrate animal models has the potential to provide insight into the emergence of diverse function in the aquaporins. The domesticated chicken (Gallus gallus) is the premier avian model for biological research; however, only a limited number of studies have compared chicken and mammalian aquaporins. The identification of aquaporins that share functional motifs or are expressed in the same tissues in human and chicken could allow the further functional analyses of homologous aquaporins in both species. We hypothesize that integrative analyses of protein sequences and body site expression of human, mouse, rat and chicken aquaporins has the potential to yield novel biological hypotheses about the unexpected cellular roles of aquaporins beyond transmembrane water transport.

RESULTS

A total of 76 aquaporin transcript models derived from 47 aquaporin genes were obtained for human, mouse, rat and chicken. Eleven body sites (brain, connective tissue, head, heart, liver, muscle, ovary, pancreas, small intestine, spleen and testis) were identified in which there is suggested expression of at least one mammalian and one chicken aquaporin. This study demonstrates that modern on-line analysis tools, a novel matrix integration technique, and the availability of the chicken genome for comparative genomics and expression analysis enables hypothesis generation in several important areas including: (i) alternative transcription and speciation effects on the conservation of functional motifs in vertebrate aquaporins; (ii) the emergence of basolateral targeting in mammalian species; (iii) the potential of the cysteine-rich AQP11 as a possible target in the pathophysiology of neurodegenerative disorders such as autism that involve Purkinje cells; and (iv) possible impairment of function of pancreas-expressed AQP12 during pancreatotropic necrosis in avian influenza virus infection.

CONCLUSION

The investigation of aquaporin function in chicken and mammalian species has the potential to accelerate the discovery of novel knowledge of aquaporins in both avian and mammalian species.