Aquaporins are water channels that are usually found in tissues where water movements are abundant and/or
physiologically important. High water permeability has been reported in mammalian sperm. To elucidate the molecular
basis for the high water permeability of vertebrate sperm, Ishibashi et al. (1997) screened a rat testis library for
additional members of the aquaporin gene family. They isolated a cDNA encoding AQP7, a predicted 269-amino acid
protein. AQP7 contains the 6 transmembrane domains and intracellular N and C termini characteristic of aquaporins.
General function
Channel/transport protein
Comment
Cellular localization
Plasma membrane
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Ovarian function
Oogenesis, Early embryo development
Comment
Expression of Aquaporins in Human Embryos and Potential Role of AQP3 and AQP7 in Preimplantation Mouse Embryo Development. Xiong Y et al. Background/Aims: Water channels, also named aquaporins (AQPs), play crucial roles in cellular water homeostasis. Methods: RT-PCR indicated the mRNA expression of AQPs 1-5, 7, 9, and 11-12, but not AQPs 0, 6, 8, and 10 in the 2~8-cell stage human embryos. AQP3 and AQP7 were further analyzed for their mRNA expression and protein expression in the oocyte, zygote, 2-cell embryo, 4-cell embryo, 8-cell embryo, morula, and blastocyst from both human and mouse using RT-PCR and immunofluorescence, respectively. Results: AQP3 and AQP7 were detected in all these stages. Knockdown of either AQP3 or AQP7 by targeted siRNA injection into 2-cell mouse embryos significantly inhibited preimplantation embryo development. However, knockdown of AQP3 in JAr spheroid did not affect its attachment to Ishikawa cells. Conclusion: These data demonstrate that multiple aquaporins are expressed in the early stage human embryos and that AQP3 and AQP7 may play a role in preimplantation mouse embryo development.
Aquaglyceroporin-7 Overexpression in Women with the Polycystic Ovary Syndrome. Seow KM et al. Background: Aquaglyceroporin-7 (AQP7) is an adipose glycerol channel protein that has been suggested to be involved in whole-body glucose homeostasis and insulin sensitivity. The aim of this study was to investigate the expression of AQP7 in visceral adipose tissues from women with the polycystic ovary syndrome (PCOS). Methods: AQP7 mRNA and protein levels were measured in omental adipose tissue from 5 women with the PCOS and 4 healthy controls matched for body mass index and age; this was done by the real-time polymerase chain reaction (PCR) and Western blotting. Results: The women with the PCOS had significantly higher homeostasis model insulin resistance indices (HOMA(IR)) and their quantitative insulin sensitivity check indices were significantly lower compared to the controls (p < 0.05). No significant difference was noted between the two groups for the plasma glycerol concentration. AQP7 mRNA expression and protein levels in omental adipose tissue from women with the PCOS were significantly higher than those of the controls (p = 0.007). AQP7 expression showed a positive correlation with fasting insulin levels, insulin levels at 2 h after glucose loading and HOMA(IR) in women with the PCOS. Conclusion: AQP7 overexpression may be related to insulin sensitivity and glucose homeostasis in women with the PCOS.
Expression regulated by
Comment
Ovarian localization
Oocyte
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Edashige K, et al 2000 reported the expression of mRNAs of the aquaporin family in mouse oocytes and embryos.
The total RNA of mouse oocytes at metaphase II and
embryos at the 4-cell, morula, and blastocyst stages was isolated,
reverse-transcribed, and subjected to nested PCR amplification. Aquaporins
were expressed in both oocytes and embryos, but the types were different among
the developmental stages: aquaporins 3 and 7 were expressed in oocytes and
embryos at all stages examined, but aquaporins 8 and 9 were expressed only in
blastocysts. On the other hand, aquaporins 1, 2, 4, 5, and 6 were not detected
in any of the stages examined. The present study shows that
aquaporins are expressed in mammalian oocytes and embryos. These aquaporins
may play a role in water transport and conceivably also in cryoprotectant
transport across the plasma membrane in these cells.
Follicle stages
Preovulatory
Comment
Ford P, et al 2000 studied the mechanisms involved in water movements during oocyte
maturation. Volume changes, induced by an osmotic gradient, were
followed by video microscopy in rat oocytes, The water osmotic permeability
(P-osm) of immature oocytes (proestrus) was sensitive to HgCl2 and phloretin.
In contrast, mature oocytes (estrus) had a reduced P-osm that was not
sensitive to these compounds. When proestrus oocytes were incubated in vitro
at 37 degrees C they spontaneously arrived at maturity and its P-osm decreased
between four and six hours of incubation. RT-PCR experiments were performed
using specific primers for all rat aquaporins that had been cloned. It was found
that aquaporin-9 transcript (AQP9) is present in proestrus oocytes but not in
estrus oocytes. Nisha A McConnell,et al 2002 believe water permeability of an antral follicle occurs primarily through a transcellular mechanism, which may be mediated by the functional presence of aquaporins-7, -8, and -9 in rat granulosa cells.