Allele-specific Expression of the Murine Ren-1 Genes

Protein Kinase G Is Involved in Acute but Not in Long-Term Regulation of Renin Secretion

Pharmacological inhibition of the renin–angiotensin–aldosterone system (RAAS) is, in combination with diuretics, the first-choice treatment for hypertension, although 10–20% of patients do not respond adequately. Next to the RAAS, the nitric oxide/cGMP/protein kinase G (PKG) system is the second fundamental blood pressure regulator. Whether both systems influence each other is not well-studied. It has been shown that nitric oxide (NO) supports renin recruitment via activation of soluble guanylate cyclase (sGC) and subsequent generation of cGMP. Whether this leads to an ensuing activation of PKGs in this context is not known. PKGIα, as well as PKGII, is expressed in renin-producing cells. Hence, we analyzed whether these enzymes play a role regarding renin synthesis, secretion, or recruitment. We generated renin-cell-specific PKGI-knockout mice and either stimulated or inhibited the renin system in these mice by salt diets. To exclude the possibility that one kinase isoform can compensate the lack of the other, we also studied double-knockout animals with a conditional knockout of PKGI in juxtaglomerular cells (JG cells) and a ubiquitous knockout of PKGII. We analyzed blood pressure, renin mRNA and renal renin protein content as well as plasma renin concentration. Furthermore, we stimulated the cGMP system in these mice using BAY 41-8543, an sGC stimulator, and examined renin regulation either after acute administration or after 7 days (application once daily). We did not reveal any striking differences regarding long-term renin regulation in the studied mouse models. Yet, when we studied the acute effect of BAY 41-8543 on renin secretion in isolated perfused kidneys as well as in living animals, we found that the administration of the substance led to a significant increase in plasma renin concentration in control animals. This effect was completely abolished in double-knockout animals. However, after 7 days of once daily application, we did not detect a persistent increase in renin mRNA or protein in any studied genotype. Therefore, we conclude that in mice, cGMP and PKG are involved in the acute regulation of renin release but have no influence on long-term renin adjustment.

Cells of renin lineage are progenitors of podocytes and parietal epithelial cells in experimental glomerular disease

Glomerular injury leads to podocyte loss, a process directly underlying progressive glomerular scarring and decline of kidney function. The inherent repair process is limited by the inability of podocytes to regenerate. Cells of renin lineage residing alongside glomerular capillaries are reported to have progenitor capacity. We investigated whether cells of renin lineage can repopulate the glomerulus after podocyte injury and serve as glomerular epithelial cell progenitors. Kidney cells expressing renin were genetically fate-mapped in adult Ren1cCreER×Rs-tdTomato-R, Ren1cCre×Rs-ZsGreen-R, and Ren1dCre×Z/EG reporter mice. Podocyte depletion was induced in all three cell-specific reporter mice by cytotoxic anti-podocyte antibodies. After a decrease in podocyte number, a significant increase in the number of labeled cells of renin lineage was observed in glomeruli in a focal distribution along Bowman's capsule, within the glomerular tuft, or in both locations. A subset of cells lining Bowman's capsule activated expression of the glomerular parietal epithelial cell markers paired box protein PAX2 and claudin-1. A subset of labeled cells within the glomerular tuft expressed the podocyte markers Wilms tumor protein 1, nephrin, podocin, and synaptopodin. Neither renin mRNA nor renin protein was detected de novo in diseased glomeruli. These findings provide initial evidence that cells of renin lineage may enhance glomerular regeneration by serving as progenitors for glomerular epithelial cells in glomerular disease characterized by podocyte depletion.

Regulation of renin enhancer activity by nuclear factor I and Sp1/Sp3

Transcription of the mouse Ren-1(c) gene in kidney tumor-derived As4.1 cells, which express high levels of renin mRNA, is dependent on a proximal promoter element and a 242-bp enhancer region located 2.6 kb upstream of the transcription start site. We showed previously that the enhancer contains a cAMP responsive element (CRE) and an E-box. Mutation of either element resulted in almost complete loss of the Ren-1(c) expression. In this report we show that there are additional transcription factor-binding sites within the Ren-1(c) enhancer contributing to the enhancer activity. Electrophoretic mobility shift and supershift assays have identified four nuclear factor I (NFI)-binding sites, an Sp1/Sp3 site and an unidentified transcription factor-binding site (Ei) located upstream of the CRE and E-box. Mutation of the Sp1/Sp3 site or Ei reduced Ren-1(c) expression by 40% or 30%, respectively, while mutations of four NFI-binding sites resulted in an 89% decrease in expression. Thus, these protein-DNA interaction sites are essential for transcription of mouse renin genes. There are four homologous NFI genes (NFI-A, -B, -C and -X) in vertebrates and multiple alternatively spliced isoforms from each gene. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assays have demonstrated that NFI-X is the predominant NFI mRNA expressed in As4.1 cells. Direct study of involvement of NFI-X in regulation of renin genes is underway.

Critical roles of a cyclic AMP responsive element and an E-box in regulation of mouse renin gene expression

Mouse As4.1 cells, obtained after transgene-targeted oncogenesis to induce neoplasia in renal renin expressing cells, express high levels of renin mRNA from their endogenous Ren-1(c) gene. We have previously identified a 242-base pair enhancer (coordinates -2866 to -2625 relative to the CAP site) upstream of the mouse Ren-1(c) gene. This enhancer, in combination with the proximal promoter (-117 to +6), activates transcription nearly 2 orders of magnitude in an orientation independent fashion. To further delimit sequences necessary for transcriptional activation, renin promoter-luciferase reporter gene constructs containing selected regions of the Ren-1(c) enhancer were analyzed after transfection into As4.1 cells. These results demonstrate that several regions are required for full enhancer activity. Sequences from -2699 to -2672, which are critical for the enhancer activity, contain a cyclic AMP responsive element (CRE) and an E-box. Electrophoretic mobility shift assays demonstrated that transcription factors CREB/CREM and USF1/USF2 in As4.1 cell nuclear extracts bind to oligonucleotides containing the Ren-1(c) CRE and E-box, respectively. These two elements are capable of synergistically activating transcription from the Ren-1(c) promoter. Moreover, mutation of either the CRE or E-box results in almost complete loss of enhancer activity, suggesting the critical roles these two elements play in regulating mouse Ren-1(c) gene expression. Although the Ren-1(c) gene contains a CRE, its expression is not induced by cAMP in As4.1 cells. This appears to reflect constitutive activation of protein kinase A in As4.1 cells since treatment with the protein kinase A inhibitor, H-89, caused a significant reduction in Ren-1(c) gene expression and this reduction is mediated through the CRE at -2699 to -2688.

An Abd-B class HOX.PBX recognition sequence is required for expression from the mouse Ren-1c gene

Expression from the mouse Ren-1(c) gene in As4.1 cells is dependent on a proximal promoter element (PPE) located at approximately -60 and a 241-base pair enhancer region located at -2625 relative to the transcription start site. The PPE (TAATAAATCAA) is identical to a consensus HOX.PBX binding sequence. Further, PBX1b has been shown to be a component of a PPE-specific binding complex present in nuclear extracts from As4.1 cells. The binding affinities of different paralog HOX members to the PPE were examined in the absence or presence of PBX1b. HOXB6, -B7, and -C8 failed to bind the PPE alone but showed weak affinity in the presence of PBX1b. In contrast, HOXD10 and to a lesser degree HOXB9 bound the PPE with high affinities regardless of whether PBX1b was present. Abd-B HOX members, including HOXD10, -A10, -A9, -B9, and -C9, are expressed in As4.1 cells. The ability of HOX and PBX1b to form a ternary complex with PREP1 on the PPE is also demonstrated both in vivo and in vitro. Point mutations in either the HOX or PBX half-site of the PPE disrupted the formation of the HOX.PBX complex and dramatically decreased transcriptional activity of the Ren-1(c) gene demonstrating that both the HOX and PBX half-sites are critical for mouse renin gene expression. These results strongly implicate Abd-B class Hox genes and their cofactors as major determinants of the sites of renin expression.

Granulation rescue and developmental marking of juxtaglomerular cells using "piggy-BAC" recombination of the mouse ren locus

Mice lacking a functional Ren-1(d) gene exhibit a complete lack of renal juxtaglomerular cell granulation and atypical macula densa morphology. Transgenic mice carrying a 145-kilobase BAC clone encompassing the Ren-1(d) and Ren-2 loci were generated, characterized, and backcrossed with Ren-1(d-/-) mice. Homozygous Ren-1(d)-null mice expressing the BAC clone exhibited complete restoration of normal renal structure. Homologous recombination in Escherichia coli was used to generate a modified version of the BAC clone, in which an IRESbeta-geo cassette was inserted specifically into the Ren-1(d) gene. When introduced into the germline, the modified clone provided a marker for juxtaglomerular cell differentiation and beta-geo was expressed appropriately in juxtaglomerular cells throughout development. Parallel backcross experiments onto the Ren-1(d)-null background demonstrated that the juxtaglomerular cells expressed the modified Ren-1(d) locus in the absence of regranulation. These data demonstrate that the nongranulated cells constitute bona fide juxtaglomerular cells despite their altered morphology, that overexpression of renin-2 cannot compensate for the loss of renin-1(d), and that primary structural differences between the two isoforms are responsible for the differences in granulation. The use of BAC modification as part of functional complementation studies illustrates the potential for in vivo molecular dissection of key physiological mechanisms.

Comparative study of renin-containing cells. Histological approaches

The juxtaglomerular apparatus is known to be the functional unit of renin control. In the present review, the author will describe the comparative characteristics of renin-containing (RC) cells as well as extrarenal distribution, paying special attention to developmental and topographical approaches. The characteristic locality of RC cells suggests that the secretion of renin is performed at a site beside the adventitia or via the glomerular capillaries. Ontogenetical and phylogenetical investigations of RC cells have provided interesting findings on their morphogenesis. Analysis of the endocrine kidney after unilateral obstruction of the ureter provides some findings about the origin of RC cells and the processing of renin granules. Observation of developing adrenal renin suggests that there is important involvement of angiotensin II produced by renin synthesis in the morphogenesis of the adrenal gland in the fetal stage. Coagulating gland (CG) renin is characterized by testosterone-regulated and exocrine mechanisms. Recently, all or some of the components of the renin-angiotensin system (RAS) have been reported to be synthesized and secreted outside of classical organs or tissues. In the future, the real function of local RAS will be clarified by using gene targeting in mice.

Homeostasis in mice with genetically decreased angiotensinogen is primarily by an increased number of renin-producing cells

Here we investigate the biochemical, molecular, and cellular changes directed toward blood pressure homeostasis that occur in the endocrine branch of the renin-angiotensin system of mice having one angiotensinogen gene inactivated. No compensatory up-regulation of the remaining normal allele occurs in the liver, the main tissue of angiotensinogen synthesis. No significant changes occur in expression of the genes coding for the angiotensin converting enzyme or the major pressor-mediating receptor for angiotensin, but plasma renin concentration in the mice having only one copy of the angiotensinogen gene is greater than twice wild-type. This increase is mediated primarily by a modest increase in the proportion of renal glomeruli producing renin in their juxtaglomerular apparatus and by four times wild-type numbers of renin-producing cells along afferent arterioles of the glomeruli rather than by up-regulating renin production in cells already committed to its synthesis.

Characterization of adrenocortical cell lines produced by genetically targeted tumorigenesis in transgenic mice

Using transgenic mice, we targeted SV40 T antigen and the bacterial neomycin resistance gene to steroidogenic tissues using a human P450 cholesterol side-chain cleavage promoter. Expression of SV40 T antigen resulted in adrenocortical tumors. Adrenocortical cell lines from one of these tumors (ST5R) was previously characterized. We have now obtained clonal lines from the second more differentiated tumor. After dispersion of the left adrenal tumor, ST5L parental cells were selected with G418 and subcloned. The resulting adrenocortical subcloned cell lines are more highly differentiated than those cell lines resulting from the right adrenal tumor (ST5R). ST5L cell lines secrete progesterone and corticosterone to varying degrees, whereas ST5R cells secrete only progesterone. One of the clonal cell lines, ST5Lc16, expresses both P450c11 beta and P450c11AS mRNAs, which normally are regionally distributed in different zones of the adrenal cortex. Thus, ST5Lc16 cells may be progenitor cells for both glomerulosa and fasciculata cells and may provide clues to the cellular and molecular events leading to the differentiation of the glomerulosa and the fasciculata-reticularis. Other ST5Lc cell lines are more representative of the fasciculata-reticularis, because they express P450c11 beta mRNA and secrete corticosterone, and they neither express P450c11AS mRNA nor do they secrete aldosterone. All cell lines also have 21-hydroxylase activity, but none express P450c21, indicating that some other, as yet unidentified, enzyme has this activity. In all cell lines, steroid secretion is regulable by cAMP stimulation but not by ACTH stimulation. All ST5L cell lines also express mouse renin-1 mRNA. In addition to their utility in studies of adrenal steroidogenesis, these cell lines may also be useful in studying the etiology of adrenocortical tumors.

Detection of coagulating gland renin by hybridohistochemistry

To obtain evidence of renin-synthesizing cells in the murine coagulating gland (CG), CG renin mRNA was detected by hybridohistochemistry, as well as in vitro reverse transcriptase-polymerase chain reaction (RT-PCR) in intact, castrated and testosterone-treated C57BL/6 mice. Hybridohistochemistry using paraffin sections of the kidneys and the CGs for the detection of renin mRNA was performed with digoxigenin-labelled probes. Some paraffin sections were immunohistochemically stained for renin by the peroxidase-anti-peroxidase method. Total RNA was extracted, incubated by reverse transcriptase, and amplified by PCR. In the kidneys, the immunoreactivity and the positive signals of hybridohistochemistry using an antisense probe were restricted to the same juxtaglomerular cells. In the control and at 7 days after testosterone administration to castrated mice, both renin-immunoreactivity and -hybridoreactivity were expressed by the epithelial cells in the CGs, while, in the CGs of the castrated mice and 3 days after testosterone injection of castrated animals, neither renin-immunoreactivity nor -hybridoreactivity was detected in the epithelial cells. Using RT-PCR, renin mRNA from the mice in the control and 7 days after testosterone injection of castrated was amplified, whereas, in the castrated and the 3 days after testosterone injection of castrated groups, it was not detected. The data presented here provide additional evidence that CG renin is regulated by testosterone.

Role of proximal promoter elements in regulation of renin gene transcription

Mouse As4.1 cells, obtained after transgene-targeted oncogenesis to induce neoplasia in renal renin-expressing cells, express high levels of renin mRNA from the endogenous Ren-1(c) gene. We have used these cells to characterize the role of the Ren-1(c) proximal promoter (+6 to -117) in the regulation of renin gene transcription. It was found that 4.1 kilobases (kb) of Ren-1(c) 5'-flanking sequence, in combination with the proximal promoter, are required for strong activation (approximately 2 orders of magnitude over the basal level of the promoter alone) of the chloramphenicol acetyltransferase reporter in transfection assays. Within the 4.1-kb fragment, a 241-base pair region was identified that retains full activity in an orientation-independent manner in combination with the promoter. The resulting transcripts initiate at the normal renin start site. Electrophoretic mobility shift assays identified a sequence at approximately position -60 in the promoter region that binds nuclear proteins specific for renin-expressing As4.1 cells. Mutations in this sequence, which disrupt binding of nuclear protein(s), completely abolish activation of transcription by the 4. 1-kb fragment. Activation of transcription by the 241-base pair enhancer was still observed, although it was diminished in magnitude (60-fold over the mutated promoter alone). We present a model derived from the current data that suggests that regulation of renin expression is achieved through cooperation of transcription factors binding at the proximal promoter element and a distal enhancer element to abrogate or override the effects of an intervening negative regulatory region.

Some physiological outcomes of renin gene studies

1. The cloning of the renin gene has permitted studies of its physiological regulation, extrarenal expression and role in disease. 2. Marked modulation of renin mRNA concentration is seen in adrenal, heart and hypothalamus in response to sodium depletion and inhibition of AII formation, as well as in models of renal and genetic hypertension in the rat. 3. One important outcome of studies of the promoter has been the discovery of a cyclic AMP-responsive sequence. 4. Sequence variations have been detected in or near the renin gene and have been used as markers in studies of its role in cardiovascular disease aetiology. 5. In conclusion, molecular biology has, in the past decade, made a significant contribution to the understanding of renin physiology and pathophysiology.

Transgenic animals in the study of blood pressure regulation and hypertension

It is generally accepted that the etiology of essential hypertension is due to a complex interplay of genetic and environmental factors. A great deal of research effort over the past ten years has been focused on the identification of genes the variants of which predispose individuals to high blood pressure. Consequently, transgenic and knockout animals have become important research tools, providing experimental systems in which defined genetic manipulations can be introduced on uniform genetic backgrounds while minimizing environmental variation. These animal models have provided the means by which candidate genes thought to be involved in blood pressure regulation have been studied. Furthermore, these models can be used to test the significance of genes and gene variants identified via genome-wide searches as potential causes of hypertension. The purpose of this review is to provide a brief discussion of transgenic and knockout methodology and its application to study the genetic basis of hypertension.

Expression of renin in coagulating glands is regulated by testosterone

BACKGROUND

The presence of extrarenal or local renin-angiotensin system (RAS) has been noted in several tissues, although its functions have not yet been clarified. Renin from the coagulating gland (CG) is the most recently discovered local RAS and is a significant subject for investigation because large amounts of both mRNA and proteins are detected in this organ. Recently, it has been reported that testosterone influences renin synthesis in several extrarenal tissues, although it has no effect on intrarenal renin. Therefore, it is possible that CG renin is also regulated by testosterone.

METHODS

Forty-four male C57BL/6 mice, aged 3 wk to 6 mo, were used in studies on the ontogeny and androgen regulation of the RAS in the CG. The tissues were fixed with Bouin's solution and paraffin sections were stained with immunohistochemical methods using antirenin antiserum. In each immunostained section, the relative number of renin-containing cells in terminal portions of the CG were counted.

RESULTS

Immunoreactivity for renin was first detected at 6 wk after birth. After that time, the number of renin-containing cells gradually increased throughout the experiment. In adults, several patterns of renin immunoreactivity were demonstrated in almost all epithelial cells of CGs, specifically; (1) basolateral granular reaction, (2) diffuse immunoreactivity throughout the cytoplasm, and (3) restricted nuclear reaction. Excretory products of some terminal lumina were also found to be positive for renin. At 10 days after castration, renin-containing cells in ductal termini were decreased and remained at low levels until at 4 wk after castration. After testosterone injection, numerical values of renin-containing cells were high at 1 wk and then decreased at 2-3 wk.

CONCLUSION

It is suggested that CG renin of the mouse is expressed together with sexual maturation during development and that it depends on the testis, possibly the male sex hormone.

Expression of the human renin gene in transgenic mice throughout ontogeny

Expression of a human renin genomic DNA clone extending 900 base pairs upstream and 400 base pairs downstream of the gene has been previously examined in adult transgenic mice. In adults, expression of human renin was evident in kidney, reproductive tissues, adrenal gland and lung. Previous studies of mouse and rat renin have demonstrated that kidney renin becomes evident at approximately 15 days of gestation and that expression is localized first to smooth muscle cells of the developing renal arterial tree and becomes progressively restricted to juxtaglomerular cells. As a prelude to performing cell specificity studies to elucidate the pattern of human renin gene expression in the developing kidney, 15.5 and 17.5 days of gestation fetuses and newborns were obtained for expression analysis. Tissues were pooled and expression was examined in kidney, liver, gastrointestinal (GI) tract, lung, heart and brain. The number of transgenic fetuses in each pool was determined by human renin-specific polymerase chain reaction of DNA purified from placenta or tail biopsies. Renal human renin expression was abundant at all three time points. Expression was also evident in the GI tract at 15.5 and 17.5 days of gestation. Interestingly, although no human renin mRNA was evident in lung at 15.5 or 17.5 days of gestation, extremely high levels of human renin mRNA were detected in the newborn lung. Expression of the human renin gene in these tissues was further confirmed by differential primer extension analysis which is capable of differentiating the closely related human and mouse renin messages.(ABSTRACT TRUNCATED AT 250 WORDS)

Transgenic animal models of cardiovascular disease

Transgenic experimentation has become a crucial part of hypertension and atherosclerosis research, and is growing more important in several other areas of cardiovascular disease. It has recently made a particular contribution to understanding the role of the renin-angiotensin system in controlling hypertension. The study of blood pressure regulation, cardiac hypertrophy, atherogenesis and thrombosis are also benefiting from the transgenic approach.

Regulated tissue- and cell-specific expression of the human renin gene in transgenic mice

Transgenic mice containing the human renin gene were constructed with the aim of examining the tissue- and cell-specific expression of human renin. The human renin transgene used consisted of a genomic sequence extending approximately 900 bp upstream and 400 bp downstream of the coding region and included all exon and intron sequences. Two assays were developed to differentiate human renin transcripts from endogenous mouse renin transcripts at the whole-tissue level. High level human renin expression was evident in the kidney, adrenal gland, ovary, testis, lung, and adipose tissue of all four transgenic lines examined. Human renin mRNA could also be detected at lower levels in the submandibular gland and heart of two different individual lines. No expression was evident in the liver or brain of any line tested. In situ hybridization revealed the human renin mRNA to be localized and exquisitely restricted to renal juxtaglomerular cells. Treatment of transgenic mice with captopril resulted in an increase in the accumulation of renal renin mRNAs derived from both the mouse and human renin genes. Plasma renin activity assays using synthetic human renin substrate clearly demonstrated the elaboration of active human renin into the systemic circulation of transgenic mice. These data strongly suggest that the human renin transgene exhibits both tissue- and cell-specific expression in transgenic mice. Its expression is entrained to the same regulatory signals as the endogenous renin gene in kidney, and active human renin is released into the plasma of the transgenic mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Strategies towards a transgenic model of essential hypertension

The generation of genetically modified animals by transgenic technology has proven to be a surprisingly versatile resource for researchers, providing an increasing number of new tools for biological investigation. As well as permitting the analysis of gene function and regulation in vivo, modifications of the techniques are being used to suppress or abolish the expression of specific genes, and further refinements have permitted the ablation of specific cell-types and the development of differentiated cell lines from tissue-specific tumours. In hypertension research, where many important questions have been frustratingly difficult to address by previously available methods, the advances afforded by transgenic studies have already been significant and are likely to be even more profound in the future. With the further development of these techniques, it may be possible to produce new and more representative models of essential hypertension.

Molecular genetics of hypertension

During the last decades the evidence that a genetic component contributes to the development of primary hypertension has been accumulating. The identification of the genes involved in blood pressure regulation, however, is only starting to emerge. The recent advances in recombinant DNA technology provide new molecular genetic strategies in cardiovascular research. In this review we will discuss the testing of candidate genes in vivo by transgenic techniques. Furthermore, we will describe the possibilities to identify the genes implicated in primary hypertension by genetic linkage analysis using polymorphic DNA markers.

DNA insertions distinguish the duplicated renin genes of DBA/2 and M. hortulanus mice

In a survey of inbred and wild mouse DNAs for genetic variation at the duplicate renin loci, Ren-1 and Ren-2, a variant Not I hybridization pattern was observed in the wild mouse M. hortulanus. To determine the basis for this variation, the structure of the M. hortulanus renin loci has been examined in detail and compared to that of the inbred strain DBA/2. Overall, the gross features of structure in this chromosomal region are conserved in both Mus species. In particular, the sequence at the recombination site between the linked Ren-1 and Ren-2 loci was found to be identical in both DBA/2 and M. hortulanus, indicating that the renin gene duplication occurred prior to the divergence of ancestors of these mice. Renin flanking sequences in M. hortulanus, however, were found to lack four DNA insertions totaling approximately 10.5 kb which reside near the DBA/2 loci. The postduplication evolution of the mouse renin genes is thus characterized by a number of insertion and/or deletion events within nearby flanking sequences. Analysis of renin expression showed little or no difference between these mice in steady state renin RNA levels in most tissues examined, suggesting that these insertions do not influence expression at those sites. A notable exception is the adrenal gland, in which DBA/2 and M. hortulanus mice exhibit different patterns of developmentally regulated renin expression.

Differential expression of the murine and rat renin genes in peripheral subcutaneous tissue

We have previously identified peripheral subcutaneous tissue as a bonafide site of primary renin expression in the mouse fetus by virtue of oncogene mediated tumorigenesis in transgenic mice. In this report we demonstrate that the murine renin genes are differentially expressed in this tissue. Through selective breeding and differential primer extension we demonstrate that Ren-1d and Ren-1c transcripts were several fold more abundant than Ren-2. Renin transcripts were also identified in fetal subcutaneous tissues of Spontaneously Hypertensive (SHR) and Wistar Kyoto (WKY) rats. We conclude from these studies that expression of renin during fetal development may be widespread in rodents with its temporal and spatial localization consistent with a role in fetal development.

Tissue and cell specific expression of a renin promoter-reporter gene construct in transgenic mice

The tissue specific expression of a fusion transgene consisting of 4.6 kb of Ren-2 5' flanking sequence and the SV40 T antigen viral oncogene was analyzed by northern hybridization and immunocytochemistry. Among the 10 tissues examined, endogenous renin transcripts were identified in and restricted to kidney, submandibular gland, testes and ovary consistent with the expression pattern of the Ren-1c gene. In addition to these tissues, significant levels of transgene mRNA were detectable in the brain. Expression of the transgene was restricted to juxtaglomerular cells in the kidney and the granular convoluted tubule cells of submandibular gland. These results suggest that 4.6 Kb of Ren-2 5' flanking sequence is sufficient to confer tissue and cell specific expression upon an exogenous reporter gene.