Transmembrane carbonic anhydrase isozymes IX and XII in the female mouse reproductive organs

The immunolocalization of HIF-2α, GLUT1 and CAIX in porcine oviduct during the estrous cycle

Oxygen (O₂ ) rates in the oviduct are essential to human and animal reproduction. These rates are regulated by the activity of hypoxia markers such as the hypoxia-inducible factors (HIFs), the glucose transporters (GLUT), and the carbonic anhydrase (CA). In the porcine model, scarce studies have been reported regarding these markers and their effects in reproduction are unknown. The objective was to characterize the immunolocalization of HIF-2α, GLUT1, and CAIX in porcine oviducts throughout the estrous cycle. Oviducts (ampulla and isthmus) of adult sows (n = 45) were collected for histological and immunohistochemical analysis with HIF-2α, GLUT1, and CAIX markers. The percentage of immunopositive area was quantified, and the differences among phases of the estrous cycle were analyzed (folicular, early luteal, and late luteal). The three markers showed epithelial presence mainly. Significantly lower expression of HIF-2α was found in the luteal phases, especially in the isthmus. GLUT1 expression did not change throughout the estrous cycle, but differences were found between the ampulla and isthmus. CAIX expression showed the highest, with a significant downward trend throughout estrous cycle. The ubiquitous expression of hypoxia markers shows the porcine oviduct physiology in relation to O₂ . The differential expression of HIF-2α, GLUT1, and CAIX in different subcompartments of the oviduct throughout the estrous cycle contributes to improve the knowledge of the cell physiology of the oviduct, which can be useful in fertilization studies.

Hydroxysafflor yellow A attenuates oxidative stress injury-induced apoptosis in the nucleus pulposus cell line and regulates extracellular matrix balance via CA XII

Intervertebral disc degeneration (IVDD) is the main cause of lower back pain. Oxidative stress injury and degradation of the extracellular matrix (ECM) are important factors causing IVDD, while hydroxysafflor yellow A (HSYA) has significant anti-oxidative stress and anti-apoptotic effects. The present study aimed to investigate the protective role of HSYA in IVDD using nucleus pulposus (NP) cells. A Cell Counting Kit-8 assay was used to detect cell viability following HSYA and tert-Butyl hydroperoxide (TBHP) treatment. Cellular reactive oxygen species levels and the level of apoptosis were measured using flow cytometry. The concentration of superoxide dismutase (SOD), malondialdehyde (MDA), catalase (CAT) and glutathione peroxidase GSH-Px were detected using ELISA. DAPI staining was performed for nuclear morphology analysis, while western blot analysis was used to detect apoptotic- and ECM-related protein expression levels. Bioinformatics analysis was used to predict the binding site between HSYA and carbonic anhydrase 12 (CA12; CA XII). NP cells were transfected withsmall interference RNA (siRNA) for CA XII downregulation. Following TBHP treatment, the level of ROS increased significantly, and the concentrations of SOD, CAT and GSH-Px were decreased. In addition, the apoptosis level of the NP cell line significantly increased following TBHP treatment. Furthermore, the expression levels of ECM-related proteins, collagen II and aggrecan were significantly decreased, and the protein expression level of MMP-13 was significantly increased. HSYA (10 µM) could effectively alleviate the effects of TBHP on NP cell apoptosis, oxidative stress damage and the expression level of ECM-related proteins. A binding site was found between HSYA and CA XII. In addition, CA XII-siRNA significantly reduced the increase in the expression level of collagen II and aggrecan proteins and decrease in the expression level of MMP-13 induced by HSYA in the NP cell line. In conclusion, HSYA could attenuate oxidative stress injury and apoptosis induced by TBHP in the NP cell line, and could improve the regulation of ECM balance.

Carbonic Anhydrase IX-Mouse versus Human

In contrast to human carbonic anhydrase IX (hCA IX) that has been extensively studied with respect to its molecular and functional properties as well as regulation and expression, the mouse ortholog has been investigated primarily in relation to tissue distribution and characterization of CA IX-deficient mice. Thus, no data describing transcriptional regulation and functional properties of the mouse CA IX (mCA IX) have been published so far, despite its evident potential as a biomarker/target in pre-clinical animal models of tumor hypoxia. Here, we investigated for the first time, the transcriptional regulation of the Car9 gene with a detailed description of its promoter. Moreover, we performed a functional analysis of the mCA IX protein focused on pH regulation, cell-cell adhesion, and migration. Finally, we revealed an absence of a soluble extracellular form of mCA IX and provided the first experimental evidence of mCA IX presence in exosomes. In conclusion, though the protein characteristics of hCA IX and mCA IX are highly similar, and the transcription of both genes is predominantly governed by hypoxia, some attributes of transcriptional regulation are specific for either human or mouse and as such, could result in different tissue expression and data interpretation.

RNA-seq Transcriptome Analysis in Ovarian Tissue of Pelibuey Breed to Explore the Regulation of Prolificacy

The Pelibuey sheep (Ovis aries) is an indigenous breed distributed in the tropical regions of Mexico. The prolificacy of this sheep is on average from 1 to 1.5 lambs, being an important breeding characteristic that owners seek to increase with the purpose of economic improvements. New-generation RNA sequencing technology has been used to identify the genes that are expressed in the ovarian tissue of sheep that have two or more lambs per parturition, as well as to elucidate the metabolic pathways that are affected by the expression of these genes, with the purpose of better understanding the prolificacy in the sheep. In the present study, the transcriptional expression of multiparous and uniparous sheep was compared using RNA sequencing. Multiparous (M group) and uniparous (U group) sheep that had a genealogical record for three generations (M, n = 5 and U, n = 5) were selected. RNA was extracted from ovarian tissue and subsequently used to prepare the libraries that were sequenced using the Illumina NextSeq500 platform. A total of 31,575 genes were detected from the transcriptomic analysis of which 4908 were significantly expressed (p-value ≤ 0.001) in the ovary of sheep. Subsequently, a second filter was carried out to evaluate the false discovery rate (FDR) and select those genes with p-values ≤ 0.05 and values of expression ≥ 1 (log2), obtaining 354 differential expressed genes (DEG): 120 genes up-regulated and 234 genes down-regulated in the group M with respect to the group U. Through Gene Ontology (GO) and metabolic analysis, we obtained information on the function of differentially expressed genes, and its importance in the reproduction of multiparous sheep. This result suggest that genes identified in the present study participate in the development of the final stages of follicles.

Effects of Marantodes pumilum (Kacip Fatimah) on vaginal pH and expression of vacoular ATPase and carbonic anhydrase in the vagina of sex-steroid deficient female rats

BACKGROUND

In sex-steroid deficiency, increased in the pH of vaginal fluid is due to low estrogen levels.

HYPOTHESIS

Consumption of Marantodes pumilum leaves helps to ameliorate increased in vaginal fluid pH in sex-steroid deficient condition.

PURPOSE

To investigate changes in vaginal fluid pH and expression of proteins that participate in pH changes i.e vacoular (V)-ATPases and carbonic anhydrases (CA) in the vagina following M. pumilum leaves consumption.

METHODS

Ovariectomized adult female rats were treated orally with M. pumilum leaves extract (MPE) at 100, 250 and 500 mg/kg.b.w and estradiol at 0.2 µg/kg/b.w for 28 days. At the end of the treatment, vaginal fluid pH was measured in anesthetised rats by using micropH probe. Following sacrificed, levels of V-ATPase and CA proteins and mRNAs in the vagina were identified by Western blotting and real-time PCR, respectively. Protein distribution was visualized by immunohistochemistry.

RESULTS

Administration of MPE causes the pH of vaginal fluid to decrease and expression and distribution of vaginal V-ATPase A & B and CA II, III, IX, XII and XIII to increase.

CONCLUSIONS

The decrease in vaginal fluid pH following MPE treatment suggested that this herb has potential to be used to ameliorate vaginal fluid pH changes in sex-steroid deficient condition.

Carbonic anhydrase XII functions in health and disease

Human CAXII was initially identified as a cancer marker in different cancers and tumors. Expression of CAXII is regulated by hypoxia and estrogen receptors. CAXII expression has been also detected in several tissues, whereas in cancer and tumor tissues its expression is several fold higher. In brain tumors, an alternatively spliced form of CAXII is expressed. Higher expression of CAXII in breast cancer is indicative of lower grade disease. CAXII plays a key role in several physiological functions. Mutation in the CAXII gene causes cystic fibrosis-like syndrome and salt wasting disease. CAXII is also seen in nuclear pulposus cells of the vertebrae. Aging dependent stiffness or degeneration of backbone correlates with CAXII expression level. This finding suggests a possible implication of CAXII as a biomarker for chronic back pain and a pharmacological target for possible treatment of chronic back pain.

Role of Proton Pumps in Tumorigenesis

One of the differences between normal and cancer cells is lower pH of the extracellular space in tumors. Low pH in the extracellular space activates proteases and stimulates tumor invasion and metastasis. Tumor cells display higher level of the HIF1α transcription factor that promotes cell switch from mitochondrial respiration to glycolysis. The terminal product of glycolysis is lactate. Lactate formation from pyruvate is catalyzed by the specific HIF1α-dependent isoform of lactate dehydrogenase A. Because lactate accumulation is deleterious for the cell, it is actively exported by monocarboxylate transporters. Lactate is cotransported with proton, which acidifies the extracellular space. Another protein that contributes to proton concentration increase in the extracellular space is tumor-specific HIF1α-dependent carbonic anhydrase IX, which generates a proton in the reaction between carbon dioxide and water. The activity of Na+/H+ exchanger (another protein pump) is stimulated by stress factors (e.g. osmotic shock) and proliferation stimuli. This review describes the mechanisms of proton pump activation and reviews results of studies on effects of various proton pump inhibitors on tumor functioning and growth in cell culture and in vivo. The prospects of combined application of proton pump inhibitors and cytostatics in cancer therapy are discussed.

Estrogen and progesterone differentially regulate carbonic anhydrase II, III, IX, XII, and XIII in ovariectomized rat uteri

Changes in the uterus expression of carbonic anhydrase (CA) II, III, IX, XII, and XIII were investigated under the influence of sex-steroids in order to elucidate mechanisms underlying differential effects of these hormones on uterine pH. Uteri of ovariectomised rats receiving over three days either vehicle, estrogen, or progesterone or three days estrogen followed by three days either vehicle or progesterone were harvested. Messenger RNA (mRNA) and protein levels were quantified by real-time PCR and Western blotting, respectively. The distribution of CA isoenzymes proteins were examined by immunohistochemistry. The levels of CAII, III, XII, and XIII mRNAs and proteins were elevated while levels of CAIX mRNA and protein were reduced following progesterone-only and estrogen plus progesterone treatment, compared to the control and estrogen plus vehicle, respectively. Following estrogen treatment, expression of CAII, IX, XII, and CAXIII mRNAs and proteins were reduced, but remained at a level higher than control, except for CAIX, where its level was higher than the control and following progesterone treatment. Under progesterone-only and estrogen plus progesterone influences, high levels of CAII, III, XII, and XIII were observed in uterine lumenal and glandular epithelia and myometrium. However, a high level of CAIX was observed only under the influence of estrogen at the similar locations. In conclusion, high expression of CAII, III, XII, and XIII under the influence of progesterone and estrogen plus progesterone could result in the reduction of uterine tissue and fluid pH; however, the significance of high levels of CAIX expression under the influence of estrogen remains unclear.

Enhanced expression of sodium hydrogen exchanger (NHE)-1, 2 and 4 in the uteri of rat model for post-menopause under phytoestrogen genistein influence

Maintaining near normal uterine fluid pH is important for restoring uterine function after menopause. We hypothesized that genistein could restore uterine fluid pH via its effect on NHE expression. This study therefore investigated changes in uterine NHE-1, 2 and 4 expression under genistein influence. Ovariectomized female rats received genistein (25, 50 or 100mg/kg/day) for seven consecutive days. Uteri were harvested and NHE-1, 2 and 4 mRNA expression were analyzed by Real-time PCR while distribution of these transporters' protein was observed by immunohistochemistry. Expression of NHE-1, 2 and 4 mRNA increased with increasing doses of genistein which was antagonized by ICI 182780. Under genistein influence, NHE-1, 2 and 4 proteins were found to be distributed at apical membrane of endometrial luminal epithelia. Enhanced expression of NHE-1, 2 and 4 in ovariectomised rat uteri by genistein might help to restore pH of uterine fluid which could be useful for women after menopause.

Genistein disrupts glucocorticoid receptor signaling in human uterine endometrial Ishikawa cells

BACKGROUND

The link between environmental estrogen exposure and defects in the female reproductive tract is well established. The phytoestrogen genistein is able to modulate uterine estrogen receptor (ER) activity, and dietary exposure is associated with uterine pathologies. Regulation of stress and immune functions by the glucocorticoid receptor (GR) is also an integral part of maintaining reproductive tract function; disruption of GR signaling by genistein may also have a role in the adverse effects of genistein.

OBJECTIVE

We evaluated the transcriptional response to genistein in Ishikawa cells and investigated the effects of genistein on GR-mediated target genes.

METHODS

We used Ishikawa cells as a model system to identify novel targets of genistein and the synthetic glucocorticoid dexamethasone through whole genome microarray analysis. Common gene targets were defined and response patterns verified by quantitative real-time reverse-transcription polymerase chain reaction. The mechanism of transcriptional antagonism was determined for select genes.

RESULTS

Genistein regulated numerous genes in Ishikawa cells independently of estradiol, and the response to coadministration of genistein and dexamethasone was unique compared with the response to either estradiol or dexamethasone alone. Furthermore, genistein altered glucocorticoid regulation of GR target genes. In a select set of genes, co-regulation by dexamethasone and genistein was found to require both GR and ERα signaling, respectively.

CONCLUSIONS

Using Ishikawa cells, we observed that exposure to genistein resulted in distinct changes in gene expression and unique differences in the GR transcriptome.

Expression pattern of carbonic anhydrase IX in Medullary thyroid carcinoma supports a role for RET-mediated activation of the HIF pathway

Medullary thyroid carcinoma is a relatively rare tumor with poor prognosis and therapy response. Its phenotype is determined by both genetic alterations (activating RET oncoprotein) and physiological stresses, namely hypoxia [activating hypoxia-inducible factor (HIF)]. Here, we investigated the cooperation between these two mechanisms. The idea emerged from the immunohistochemical analysis of carbonic anhydrases (CA) IX and XII expression in thyroid cancer. Although CAXII was present in all types of thyroid carcinomas, CAIX, a direct HIF target implicated in tumor progression, was associated with aggressive medullary and anaplastic carcinomas, and its expression pattern in medullary thyroid carcinomas suggested contribution of both hypoxic and oncogenic signaling. Therefore, we analyzed the CA9 promoter activity in transfected tumor cells expressing RET and/or the HIF-α subunit. We showed that overexpression of both wild-type and mutant RET can increase the CA9 promoter activity induced by HIF-1 (but not HIF-2) in hypoxia. Similar results were obtained with another HIF-1-regulated promoter derived from the lactate dehydrogenase A gene. Moreover, inhibition of the major kinase pathways, which transmit signals from RET and regulate HIF-1, abrogated their cooperative effect on the CA9 promoter. Thus, we brought the first experimental evidence for the crosstalk between RET and HIF-1 that can explain the increased expression of CAIX in medullary thyroid carcinoma and provide a rationale for therapy simultaneously targeting both pathways.

In-vivo functional study on the involvement of CFTR, SLC26A6, NHE-1 and CA isoenzymes II and XII in uterine fluid pH, volume and electrolyte regulation in rats under different sex-steroid influence

Precise control of uterine fluid pH, volume and electrolytes is important for the reproductive processes. In this study, we examined the functional involvement of multiple proteins including Cystic Fibrosis Transmembrane Regulator (CFTR), Cl(-)/HCO3 (-) exchanger (SLC26A6), sodium-hydrogen exchanger-1 (NHE-1) and carbonic anhydrase (CA) in the regulation of these uterine fluid parameters.

METHODS

Adult female WKY rats were divided into intact, non-ovariectomised at different oestrous cycle phases and ovariectomised treated with sex-steroids. Following oestrous phase identification or sex-steroid treatment, in-vivo uterine perfusion was performed with and without the presence of these inhibitors: glibenclamide, DIDS, ACTZ and EIPA. The pH, volume, Cl(-), HCO3 (-) and Na(+) concentrations of the perfusate from different groups were then analyzed. Meanwhile, the expression of CFTR, SLC26A6, NHE-1, CAII and CAXII was visualized by immunohistochemistry (IHC).

RESULTS

Parallel increase in the pH, volume, Cl(-), HCO3 (-) and Na(+) concentrations was observed at estrus (Es), proestrus (Ps) and following 17β-oestradiol (E) treatment, which was inhibited by glibenclamide, DIDS and ACTZ while parallel reduction in these parameters was observed at diestrus (Ds) and following progesterone (P) treatment which was inhibited by ACTZ and EIPA. CFTR and SLC26A6 expression were up-regulated under E dominance, while NHE-1 expression was up-regulated under P dominance. Meanwhile, CA isoenzymes were expressed under both E and P influence.

CONCLUSION

CFTR, SLC26A6 and CA were involved in mediating parallel increase in the uterine fluid volume, pH and electrolyte concentration under E while NHE and CA were involved in mediating the reduction of these parameters under P.

Carbonic anhydrase isozymes II, IX, and XII in uterine tumors

Histopathological diagnostics of gynecological malignancies continues to be challenging despite the well established criteria. For example, the morphological distinction of uterine leiomyosarcoma from certain variants of benign leiomyoma can be difficult. Herein, we investigated the expression of Carbonic anhydrase (CA) II, IX, and XII in the normal endometrium, leiomyomas, uterine sarcomas, and endometrial adenocarcinomas using immunohistochemistry. These isozymes are considered promising diagnostic markers and therapeutic targets. The normal endometrium showed high CA XII expression, whereas the signals were lower in endometrial adenocarcinoma (p < 0.004). Only sporadic CA IX staining was found in the normal endometrium, whereas the enzyme was overexpressed in most cases of endometrial adenocarcinoma (p < 0.005). CA II expression was slightly weaker in the normal endometrium than that in the adenocarcinomas (p < 0.008). Positive immunostaining reactions for CAs were observed in the uterine sarcomas, whereas all leiomyomas were negative for CA II and XII. A comparison between leiomyomas and sarcomas showed statistically significant differences for all studied isozymes (p < 0.001). Our study shows that CA isozymes could together serve as histopathological biomarkers for differential diagnosis between uterine leiomyosarcoma and leiomyoma. In addition to being found in leiomyosarcomas, CA II and IX were overexpressed in endometrial adenocarcinoma, where they might regulate the pH of the tumor microenvironment.

Immunohistochemical assessment of intrinsic and extrinsic markers of hypoxia in reproductive tissue: differential expression of HIF1α and HIF2α in rat oviduct and endometrium

Hypoxia is thought to be critical in regulating physiological processes within the female reproductive system, including ovulation, composition of the fluid in the oviductal/uterine lumens and ovarian follicle development. This study examined the localisation of exogenous (pimonidazole) and endogenous [hypoxia inducible factor 1α and 2α (HIF1α, -2α), glucose transporter type 1 (GLUT1) and carbonic anhydrase 9 (CAIX)] hypoxia-related antigens within the oviduct and uterus of the rat reproductive tract. The extent to which each endogenous antigen co-compartmentalised with pimonidazole was also assessed. Female Wistar Furth rats (n = 10) were injected intraperitoneally with pimonidazole (60 mg/kg) 1 h prior to death. Reproductive tissues were removed immediately following death and fixed in 4% paraformaldehyde before being embedded in paraffin. Serial sections were cut (6-7 μm thick) and antigens of interest identified using standard immunohistochemical procedures. The mucosal epithelia of the ampulla, isthmus and uterus were immunopositive for pimonidazole in most sections. Co-compartmentalisation of pimonidazole with HIF1α was only expressed in the mucosa of the uterus whilst co-compartmentalisation with HIF2α was observed in the mucosa of the ampulla, isthmus and uterus. Both GLUT1 and CAIX were co-compartmentalised with pimonidazole in mucosa of the isthmus and uterus. This study confirms that mucosal regions of the rat oviduct and uterus frequently experience severe hypoxia and there are compartment specific variations in expression of endogenous hypoxia-related antigens, including the HIF isoforms. The latter observation may relate to target gene specificity of HIF isoforms or perhaps HIF2α's responsiveness to non-hypoxic stimuli such as hypoglycaemia independently of HIF1α.

Autosomal recessive hyponatremia due to isolated salt wasting in sweat associated with a mutation in the active site of Carbonic Anhydrase 12

Genetic disorders of excessive salt loss from sweat glands have been observed in pseudohypoaldosteronism type I (PHA) and cystic fibrosis that result from mutations in genes encoding epithelial Na+ channel (ENaC) subunits and the transmembrane conductance regulator (CFTR), respectively. We identified a novel autosomal recessive form of isolated salt wasting in sweat, which leads to severe infantile hyponatremic dehydration. Three affected individuals from a small Bedouin clan presented with failure to thrive, hyponatremic dehydration and hyperkalemia with isolated sweat salt wasting. Using positional cloning, we identified the association of a Glu143Lys mutation in carbonic anhydrase 12 (CA12) with the disease. Carbonic anhydrase is a zinc metalloenzyme that catalyzes the reversible hydration of carbon dioxide to form a bicarbonate anion and a proton. Glu143 in CA12 is essential for zinc coordination in this metalloenzyme and lowering of the protein-metal affinity reduces its catalytic activity. This is the first presentation of an isolated loss of salt from sweat gland mimicking PHA, associated with a mutation in the CA12 gene not previously implicated in human disorders. Our data demonstrate the importance of bicarbonate anion and proton production on salt concentration in sweat and its significance for sodium homeostasis.

Tumour hypoxia induces a metabolic shift causing acidosis: a common feature in cancer

Maintenance of cellular pH homeostasis is fundamental to life. A number of key intracellular pH (pHi) regulating systems including the Na⁺/H⁺ exchangers, the proton pump, the monocarboxylate transporters, the HCO₃⁻ transporters and exchangers and the membrane-associated and cytosolic carbonic anhydrases cooperate in maintaining a pHi that is permissive for cell survival. A common feature of tumours is acidosis caused by hypoxia (low oxygen tension). In addition to oncogene activation and transformation, hypoxia is responsible for inducing acidosis through a shift in cellular metabolism that generates a high acid load in the tumour microenvironment. However, hypoxia and oncogene activation also allow cells to adapt to the potentially toxic effects of an excess in acidosis. Hypoxia does so by inducing the activity of a transcription factor the hypoxia-inducible factor (HIF), and particularly HIF-1, that in turn enhances the expression of a number of pHi-regulating systems that cope with acidosis. In this review, we will focus on the characterization and function of some of the hypoxia-inducible pH-regulating systems and their induction by hypoxic stress. It is essential to understand the fundamentals of pH regulation to meet the challenge consisting in targeting tumour metabolism and acidosis as an anti-tumour approach. We will summarize strategies that take advantage of intracellular and extracellular pH regulation to target the primary tumour and metastatic growth, and to turn around resistance to chemotherapy and radiotherapy.

Tumor-associated carbonic anhydrases and their clinical significance

Carbonic anhydrases (CAs) are physiologically important enzymes that catalyze a reversible conversion of carbon dioxide to bicarbonate and participate in ion transport and pH control. Two human isoenzymes, CA IX and CA XII, are overexpressed in cancer and contribute to tumor physiology. Particularly CA IX is confined to only few normal tissues but is ectopically induced in many tumor types mainly due to its strong transcriptional activation by hypoxia accomplished via HIF-1 transcription factor. Therefore, CA IX can serve as a surrogate marker of hypoxia and a prognostic indicator. CA IX appears implicated in cell adhesion and in balance of pH disturbances caused by tumor metabolism. Both tumor-related expression pattern and functional involvement in tumor progression make it a suitable target for anticancer treatment. Here we summarize a current knowledge on CA IX and CA XII, and discuss possibilities of their exploitation for cancer detection, diagnostics, and therapy.

Expression of transmembrane carbonic anhydrases IX and XII in ovarian tumours

AIMS

Carbonic anhydrase (CA) isozymes IX and XII have been suggested to play a role in oncogenic processes. The aim of the present study was to investigate CA IX and XII expression in patients with ovarian tumours.

METHODS AND RESULTS

A series of ovarian tumours was immunostained for CA IX and XII and the results were correlated with histopathological and clinical parameters. Most cases of borderline mucinous cystadenomas, mucinous cystadenocarcinomas and serous cystadenocarcinomas were moderately or strongly positive for CA IX. In malignant tumours, the staining was most prominent in hypoxic regions. Expression of CA XII was detected in all tumour categories, although the mean staining intensity was weaker than for CA IX in all groups except for clear cell carcinomas.

CONCLUSIONS

The wide expression of CA IX and XII in ovarian tumours suggests that these isozymes could represent potential targets in ovarian cancer therapy. The expression pattern of CA IX suggests that it could also serve as a useful histopathological marker protein for hypoxia in malignant ovarian tumours.

Conditional gene expression in the mouse using a Sleeping Beauty gene-trap transposon

Background

Insertional mutagenesis techniques with transposable elements have been popular among geneticists studying model organisms from E. coli to Drosophila and, more recently, the mouse. One such element is the Sleeping Beauty (SB) transposon that has been shown in several studies to be an effective insertional mutagen in the mouse germline. SB transposon vector studies have employed different functional elements and reporter molecules to disrupt and report the expression of endogenous mouse genes. We sought to generate a transposon system that would be capable of reporting the expression pattern of a mouse gene while allowing for conditional expression of a gene of interest in a tissue- or temporal-specific pattern.

Results

Here we report the systematic development and testing of a transposon-based gene-trap system incorporating the doxycycline-repressible Tet-Off (tTA) system that is capable of activating the expression of genes under control of a Tet response element (TRE) promoter. We demonstrate that the gene trap system is fully functional in vitro by introducing the "gene-trap tTA" vector into human cells by transposition and identifying clones that activate expression of a TRE-luciferase transgene in a doxycycline-dependent manner. In transgenic mice, we mobilize gene-trap tTA vectors, discover parameters that can affect germline mobilization rates, and identify candidate gene insertions to demonstrate the in vivo functionality of the vector system. We further demonstrate that the gene-trap can act as a reporter of endogenous gene expression and it can be coupled with bioluminescent imaging to identify genes with tissue-specific expression patterns.

Conclusion

Akin to the GAL4/UAS system used in the fly, we have made progress developing a tool for mutating and revealing the expression of mouse genes by generating the tTA transactivator in the presence of a secondary TRE-regulated reporter molecule. A vector like the gene-trap tTA could provide a means for both annotating mouse genes and creating a resource of mice that express a regulable transcription factor in temporally- and tissue-specific patterns for conditional gene expression studies. These mice would be a valuable resource to the mouse genetics community for purpose of dissecting mammalian gene function.