Corin mRNA Research Articles

Novel Antihypertension Mechanism of β-Glucan by Corin and ANP-Mediated Natriuresis in Mice

Many of the β-glucans are known to have antihypertensive activities, but, except for angiotensin-converting enzyme II inhibition, the underlying mechanisms remain unclear. Corin is an atrial natriuretic peptide (ANP)-converting enzyme. Activated corin cleaves pro-ANP to ANP, which regulates water–sodium balance and lowers blood pressure. Here, we reported a novel antihypertensive mechanism of β-glucans, involved with corin and ANP in mice. We showed that multiple oral administrations of β-glucan induced the expression of corin and ANP, and also increased natriuresis in mice. Microarray analysis showed that corin gene expression was only upregulated in mice liver by multiple, not single, oral administrations of the β-glucan fraction of Phellinus baumii (BGF). Corin was induced in liver and kidney tissues by the β-glucans from zymosan and barley, as well as by BGF. In addition to P. baumii, β-glucans from two other mushrooms, Phellinus linteus and Ganoderma lucidum, also induced corin mRNA expression in mouse liver. ELISA immunoassays showed that ANP production was increased in liver tissue by all the β-glucans tested, but not in the heart and kidney. Urinary sodium excretion was significantly increased by treatment with β-glucans in the order of BGF, zymosan, and barley, both in 1% normal and 10% high-sodium diets. In conclusion, we found that the oral administration of β-glucans could induce corin expression, ANP production, and sodium excretion in mice. Our findings will be helpful for investigations of β-glucans in corin and ANP-related fields, including blood pressure, salt–water balance, and circulation.

Abstract P309: Aberrant Corin and PCSK6 in the Placenta of Hyperinsulinemic Dams

Introduction: Corin, a serine protease converts pro-atrial natriuretic peptide (pro-ANP) and pro-brain natriuretic peptide (pro-BNP) to the mature respective peptides. There is evidence that the pregnant uterus produces ANP, where it promotes spiral artery remodelling, essential for adequate blood supply to the developing conceptus. Aim: Here we examine corin and PCSK6, a key enzyme in the conversion of pro-corin to corin, in the placenta of hyperinsulinemic dams (HD) in comparison to normal pregnant dams (NPD). Materials and Methods: Female Wistar rats were rendered hyperinsulinemic by subcutaneous insulin pellet, mated and followed to day 21 of pregnancy. Both groups were then sacrificed and their placentas were dissected together with the implantation site designated mesometrial triangle (MT). Placentas and MT were sectioned from the maternal through the fetal surface to the base of the MT. For western blot (WB) the placentas and MT were separated, snap frozen in liquid nitrogen and stored at –80°C. RNA expression of corin was carried out by in-situ hybridization in 5 NPD and 6 HD with corin probe (RNAscope® Assay 2.5 Detection Reagent, Cat No. 507231) and image analysis was performed. Results: As previously described, HD (n=20) developed hypertension as compared with in NPD (n=16). Moreover, HD exhibited lower placental and foetal weights. Corin and PCSK6 mRNA and immunoreactive peptide were detected in the mesometrial tissues. Corin abundance as determined by western blot was significantly decreased in the placenta/ mesometrial triangle by ~40% (P<0.02), as was PCSK6 immunoreactivity. Corin and PCSK6 mRNAs displayed similar pattern of alterations as protein abundance, where in-situ hybridization for corin mRNA revealed a 50% (P<0.001) expression reduction. Corin mRNA was specifically expressed by cytotrophoblasts in the labyrinth. Concomitant with the downregulation of corin/PCSK6, ANP levels decreased in the MT of HD. Summary and Conclusion: Corin, PCSK6 and ANP are all expressed in the placenta of NPD but declined in dams with chronic hyperinsulinemia, suggesting a role of corin/PCSK6 pathway in the prevention of pregnancy-induced hypertension and intrauterine growth restriction, in this setting.

Natriuretic peptides system in the pulmonary tissue of rats with heart failure: potential involvement in lung edema and inflammation.

Congestive heart failure (CHF) often leads to progressive cardiac hypertrophy and salt/water retention as evident by peripheral and lung edema. Although the pathogenesis of CHF remains largely unclarified, it is widely accepted that neurohormonal changes and inflammatory processes are profoundly involved in structural and functional deterioration of vital organs including, heart, kidney and lungs. Corin, a cardiac serine protease, is responsible for converting pro-ANP and pro-BNP to biologically active natriuretic peptides (NPs). Although the involvement of corin in cardiac hypertrophy and heart failure was extensively studied, the alterations in corin and PCSK6, a key enzyme in the conversion of procorin to corin, have not been studied in the pulmonary tissue. Thus, this study aims at examining the status of PCSK6/Corin in the lung of rats with CHF induced by the creation of aorto-caval fistula (ACF) between the abdominal aorta and vena cava in SD rats. Rats with ACF were divided into 2 subgroups based on the pattern of their daily sodium excretion, compensated and decompensated CHF. Placement of ACF led to cardiac hypertrophy, pulmonary congestion, and renal dysfunction, which were more severe in the decompensated subgroup, despite remarkable elevation of circulatory ANP and BNP levels. Corin mRNA and immunoreactive peptide were detected in pulmonary tissue of all experimental groups. However, the expression and abundance of pulmonary corin significantly increased in the decompensated animals, but not in the compensated ones. Noteworthy, the expression of PCSK6 and ANP/BNP in the pulmonary tissue followed a similar pattern as corin. The upregulation of pulmonary Corin/PCSK6 and NPs were accompanied by local activation of cathepsin L and certain cytokines including IL-6. In light of the anti-inflammatory role of NPs, we postulate that the obtained upregulation of pulmonary PCSK6/Corin along NPs in rats with decompensated CHF may represent a counterbalance response to the inflammatory milieu characterizing CHF especially in severe cases.

Increased levels of soluble corin in pre-eclampsia and fetal growth restriction

Atrial natriuretic peptide is biologically activated by the atrial natriuretic peptide-converting enzyme, corin, and has an important role in regulating blood pressure. We detected elevated serum corin levels in women with pre-eclampsia. Interestingly, the serum corin levels were also found to be elevated in pregnancies with a related disorder, unexplained fetal growth restriction (FGR) without hypertension, suggesting that this phenomenon is not simply a response to maternal hypertension. CORIN mRNA levels were not elevated in placentas from pre-eclampsia or unexplained FGR cases. Likewise, similar signal intensities were found for corin in placental syncytiotrophoblast cells by immunostaining. In contrast, corin signals were higher in maternal decidua cells from pre-eclampsia and unexplained FGR cases. These data suggest that corin may be upregulated in maternal decidua in response to an etiologic pathway that is common to pre-eclampsia and FGR.

Reduced urinary corin levels in patients with chronic kidney disease

Corin is a cardiac protease that regulates BP (blood pressure) by activating natriuretic peptides. Recent animal studies identified corin expression in the kidney where it may regulate renal function. In the present study, we tested the hypothesis that corin may be present in human urine and that urinary corin levels may be altered in patients with kidney disease. We obtained urine and kidney tissue samples from normal individuals and CKD (chronic kidney disease) patients. Using ELISA, we detected corin protein in human urine. In normal individuals, urinary corin levels did not correlate with that of plasma, indicating that urinary corin is probably of kidney origin. Compared with normal controls, CKD patients had markedly reduced urinary corin levels and this reduction correlated with disease severity. By immunostaining, human corin protein was identified on the epithelial cell surface in renal tubules. The renal corin mRNA and protein levels were significantly lower in CKD patients than non-CKD controls. The results indicate that renal tubular corin may be shed into urine and that urinary and renal corin levels were reduced in CKD patients. These data suggest that reduced corin levels in the kidney may reflect the underlying pathology in CKD.

Corin, an enzyme with a putative role in spiral artery remodeling, is up-regulated in late secretory endometrium and first trimester decidua

What is the nature of cellular Corin expression in human gestational tissues? CORIN is expressed in non-pregnant late secretory phase endometrium, first trimester human implantation sites and is up-regulated with decidualization ex vivo. Adequate trophoblast invasion and spiral artery remodeling/transformation is critical for successful implantation. CORIN, best known for its role in activating atrial natruietic peptide (ANP) to regulate blood pressure, has recently been proposed to be centrally involved in trophoblast invasion and spiral artery remodeling. It is postulated that ANP, activated by CORIN, promotes trophoblast invasion and that a deficiency causes pre-eclampsia. Mice deficient in either Corin or ANP displayed poor trophoblast invasion, impaired spiral artery remodeling and phenocopied human pre-eclampsia. However, the precise cellular localization of CORIN within human gestational tissues has not been well characterized. We measured CORIN protein localization in a number of human gestational tissues relevant to early embryo/placental implantation: non-pregnant (NP) endometrial biopsies (n = 5 per phase of the menstrual cycle), first trimester placental bed biopsies (n = 12) and pre-term control (n = 10) and severe early onset preeclamptic placentas (n = 15). Endometrial stromal cells were isolated from human endometrial biopsies (n = 5) and induced to decidualize ex vivo. Finally, CORIN concentrations were measured in serum obtained from pregnant women during the first trimester of whom, 56 subsequently ended up with a healthy term delivery (controls), 18 developed fetal growth restriction (FGR) and 21 had a miscarriage. We performed immunohistochemistry to assess CORIN localization. Changes in Corin mRNA expression in human endometrial stromal cells decidualized ex vivo were measured by quantitative RT-PCR, and levels of CORIN within human sera were measured by ELISA. CORIN was expressed in both NP late secretory phase endometrium and first trimester decidua within placental bed biopsies. Importantly, decidualization of primary human endometrial cells ex vivo significantly increased Corin expression (P < 0.05). CORIN was also detected within the villous cytotrophoblast, but there was no change in mRNA levels in placentas complicated by severe preterm pre-eclampsia when compared with pre-term controls. Although CORIN was detected in first trimester serum, levels did not change across gestation, nor could they predict miscarriage or FGR (other disorders of impaired placental invasion). Owing to the fact that we utilized early pregnancy human specimens, this is mainly a descriptive study with a limited amount of functional experiments. This is the first study to thoroughly characterize Corin mRNA and protein expression in human gestational tissue. Our findings support recent data from murine studies collectively suggesting that CORIN plays a critical role in trophoblast migration and spiral artery remodeling during early pregnancy in humans. Therefore, further studies of CORIN biology in early pregnancy may identify new therapeutic targets to improve implantation quality in early pregnancy and potentially reduce the rates of pregnancy complications caused by inadequate implantation (pre-eclampsia, FGR and miscarriage). This study was supported by The National Health and Medical Research Council of Australia (Salary support #490970, #490995). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. The authors declare that no competing interests exist.

Differential expression of the pro-natriuretic peptide convertases corin and furin in experimental heart failure and atrial fibrosis.

In heart failure (HF), the cardiac hormone natriuretic peptides (NPs) atrial (ANP), B-type (BNP), and C-type (CNP) play a key role to protect cardiac remodeling. The proprotein convertases corin and furin process their respective pro-NPs into active NPs. Here we define in a canine model of HF furin and corin gene and protein expression in normal and failing left atrium (LA) or ventricle (LV) testing the hypothesis that the NP proproteins convertases production is altered in experimental HF. Experimental canine HF was produced by rapid right ventricular pacing for 10 days. NPs, furin, and corin mRNA expression were determined by quantitative RT-PCR. Protein concentration or expression was determined by immunostaining, radioimmunoassay, or Western blot. Furin and corin proteins were present in normal canine LA and LV myocardium and vasculature and in smooth muscle cells. In normal canines, expression of NPs was dominant in the atrium compared with the ventricle. In experimental early stage HF characterized with marked atrial fibrosis, ANP, BNP, and CNP mRNA, and protein concentrations were higher in HF LA but not HF LV compared with normals. In LA, corin mRNA and protein expressions in HF were lower, whereas furin mRNA and protein expressions were higher than normals. NPs and furin expressions were augmented in the atrium in experimental early stage HF and, conversely, corin mRNA and protein expressions were decreased with atrial remodeling. Selective changes of these NP convertases may have significance in the regulation of pro-NP processing and atrial remodeling in early stage HF.

Decreased renal corin expression contributes to sodium retention in proteinuric kidney diseases

Patients with proteinuric kidney diseases often have symptoms of salt and water retention. It has been hypothesized that dysregulated sodium absorption is due to increased proteolytic cleavage of epithelial sodium channels (ENaCs) and increased Na,K-ATPase expression. Microarray analysis identified a reduction in kidney corin mRNA expression in rat models of puromycin aminonucleoside-induced nephrotic syndrome and acute anti-Thy1 glomerulonephritis (GN). As atrial natriuretic peptide (ANP) resistance is a mechanism accounting for volume retention, we analyzed the renal expression and function of corin; a type II transmembrane serine protease that converts pro-ANP to active ANP. Immunohistochemical analysis found that corin colocalized with ANP. The nephrotic and glomerulonephritic models exhibited concomitant increased pro-ANP and decreased ANP protein levels in the kidney consistent with low amounts of corin. Importantly, kidneys from corin knockout mice had increased amounts of renal β-ENaC and its activators, phosphodiesterase (PDE) 5 and protein kinase G II, when compared to wild-type mice. A similar expression profile was also found in cell culture suggesting the increase in PDE5 and kinase G II could account for the increase in β-ENaC seen in nephrotic syndrome and GN. Thus, we suggest that corin might be involved in the salt retention seen in glomerular diseases.

Scar myofibroblasts of the infarcted rat heart express natriuretic peptides

The present study examined whether natriuretic peptide expression in the scar of post-myocardial infarcted (MI) rats was derived at least in part by residing myofibroblasts. ANP and BNP mRNA levels were significantly increased in the non-infarcted left ventricle and scar of 1-week post-MI male rats, as compared to the left ventricle of normal rats. The infarct region contained myofibroblasts and contracted cardiac myocytes residing predominantly in the epicardial border zone. In primary passage scar-derived myofibroblasts, alpha-myosin heavy chain mRNA was undetectable, whereas ANP, BNP, as well as adrenomedullin and corin mRNA expression persisted. In 1-3 day cultured primary passage myofibroblasts, prepro-ANP, mature ANP, and BNP staining was observed in the cytoplasm/perinuclear region co-incident with unorganized alpha-smooth muscle actin. Following 4-7 days in culture, myofibroblasts expressed organized alpha-smooth muscle actin filaments. However, natriuretic peptides were predominantly detected in the nucleus and cytoplasm, and thin filaments occupying the perinuclear region were positive for prepro-ANP and BNP. Isoproterenol treatment of first passage scar myofibroblasts increased protein synthesis and induced BNP mRNA expression, whereas ANP mRNA levels remained unchanged. By contrast, neither ANP nor BNP mRNAs were induced following exposure to AII despite increased protein synthesis. These data highlight the novel observation that scar myofibroblasts synthesized ANP, BNP, adrenomedullin, and expressed the pro-convertase corin. Constitutive and sympathetic-driven natriuretic peptide synthesis by myofibroblasts may in part influence reparative fibrosis.

Changes in production and metabolism of brain natriuretic peptide in rats with myocardial necrosis

In this study, we employed rat model of acute myocardial necrosis induced by isoproterenol (ISO) to study the possible roles of corin, the protease uniquely distributing in myocardium to convert pro-brain natriuretic peptide (proBNP) to BNP, and neutral endopeptidase (NEP), the major enzyme to degrade BNP, in changing the levels of BNP. In rats with isoproterenol alone, the myocardium necrosis occurred and the cardiac function was inhibited; the BNP contents in plasma and myocardium were upregulated, so did the myocardial corin mRNA level; the NEP activity in plasma and myocardium were downregulated. Omapatrilat (OMA) treatment relieved myocardial lesions and improved cardiac function. In the plasma and myocardium, omapatrilat treatment increased BNP contents, reduced NEP activity; in myocardium, mRNA level of proBNP and corin decreased, but NEP mRNA expression increased. Our study confirmed that omapatrilat treated myocardial necrosis effectively and suggested that increased BNP in rats with myocardial necrosis could depend on increased production and conversion as well as decreased degradation.

Upregulation of corin gene expression in hypertrophic cardiomyocytes and failing myocardium.

High levels of plasma atrial natriuretic peptides (ANP) are associated with pathological conditions such as congestive heart failure (CHF). Recently, we have identified a cardiac serine protease, corin, that is the pro-ANP convertase. In this study, we examined the regulation of corin gene expression in cultured hypertrophic cardiomyocytes and in the left ventricular (LV) myocardium of a rat model of heart failure. Quantitative RT-PCR analysis showed that both corin and ANP mRNA levels were significantly increased in phenylephrine (PE)-stimulated rat neonatal cardiomyocytes in culture. The increase in corin mRNA correlated closely with the increase in cell size and ANP mRNA expression in the PE-treated cells (r = 0.95, P < 0.01; r = 0.92, P < 0.01, respectively). The PE-treated cardiomyocytes had an increased activity in converting recombinant human pro-ANP to biologically active ANP, as determined by a pro-ANP processing assay and a cell-based cGMP assay. In a rat model of heart failure induced by ligation of the left coronary artery, corin mRNA expression in the noninfarcted LV myocardium was significantly higher than that of control heart tissues from sham-operated animals, when examined by Northern blot analysis and RT-PCR at 8 wk. These results indicate that the corin gene is upregulated in hypertrophic cardiomyocytes and failing myocardium. Increased corin expression may contribute to elevation of ANP in the setting of cardiac hypertrophy and heart failure.

Rat corin gene: molecular cloning and reduced expression in experimental heart failure

Stored cardiac pro-atrial natriuretic peptide (pro-ANP) is converted to ANP and released upon stretch from the atria into the circulation. Corin is a serin protease with pro-ANP-converting properties and may be the rate-limiting enzyme in ANP release. This study was aimed to clone and sequence corin in the rat and to analyze corin mRNA expression in heart failure when ANP release upon stretch is blunted. Full-length cDNA of rat corin was obtained from atrial RNA by RT-PCR and sequenced. Tissue distribution as well as regulation of corin mRNA expression in the atria were determined by RT-PCR and RNase protection assay. Heart failure was induced by an infrarenal aortocaval shunt. Stretch was applied to the left atrium in a working heart modus, and ANP was measured in the perfusates. The sequence of rat corin cDNA was found to be 93.6% homologous to mouse corin cDNA. Corin mRNA was expressed almost exclusively in the heart with highest concentrations in both atria. The aortocaval shunt led to cardiac hypertrophy and heart failure. Stretch-induced ANP release was blunted in shunt animals (control 1,195 +/- 197 fmol.min(-1).g(-1); shunt: 639 +/- 99 fmol.min(-1).g(-1), P < 0.05). Corin mRNA expression was decreased in both atria in shunt animals [right atrium: control 0.638 +/- 0.004 arbitrary units (AU), shunt 0.566 +/- 0.014 AU, P < 0.001; left atrium: control 0.564 +/- 0.009 AU, shunt 0.464 +/- 0.009 AU, P < 0.001]. Downregulation of atrial corin mRNA expression may be a novel mechanism for the blunted ANP release in heart failure.

Processing of Pro-atrial Natriuretic Peptide by Corin in Cardiac Myocytes

Corin is a type II transmembrane serine protease abundantly expressed in the heart. In a previous study using transfected 293 cells, we showed that corin converted pro-atrial natriuretic peptide (pro-ANP) to atrial natriuretic peptide (ANP), suggesting that corin is likely the pro-ANP convertase. Because other serine proteases such as thrombin and kallikrein had previously also been shown to cleave pro-ANP in vitro, it remained to demonstrate that corin is indeed the endogenous pro-ANP convertase in cardiomyocytes. In this study, we examined pro-ANP processing in a murine cardiac muscle cell line, HL-5. Northern analysis showed that corin mRNA was present in HL-5 cells. In HL-5 cells transfected with a plasmid expressing pro-ANP, recombinant pro-ANP was converted to mature ANP as determined by Western analysis, indicating the presence of the endogenous pro-ANP convertase in these cells. The processed recombinant ANP was shown to be active in an enzyme-linked immunosorbent assay-based cGMP assay in baby hamster kidney cells. The processing of recombinant pro-ANP in HL-5 cells was highly sequence-specific, because mutation R98A, but not mutations R101A and R102A, in pro-ANP prevented the conversion of pro-ANP to ANP. Expression of recombinant wild-type corin enhanced the processing of pro-ANP in HL-5 cells. In contrast, overexpression of active site mutant corin S985A or transfection of oligonucleotide small interfering RNA duplexes directed against the mouse corin gene completely inhibited the processing of recombinant pro-ANP in HL-5 cells. These results indicate that corin is the physiological pro-ANP convertase in cardiac myocytes.

Corin, a Transmembrane Cardiac Serine Protease, as a Pro-Atrial Natriuretic Peptide Convertase

P92 Atrial natriuretic peptide (ANP) is a cardiac hormone that reduces high blood pressure by promoting salt excretion, decreasing blood volume and relaxing vessel tension. It is implicated in major cardiovascular diseases such as hypertension and congestive heart failure. In cardiomyocytes, ANP is synthesized as a precursor, pro-ANP, that is converted to biologically active ANP by an unknown membrane-associated serine protease. Recently, we cloned a novel cardiac serine protease, corin, that has the predicted structure of a type II transmembrane protein. Northern and in situ hybridization detected corin mRNA in the heart where its expression was most abundant in cardiomyocytes of the atrium. Corin mRNA was also detected in developing kidney and bones. The overall expression pattern of corin mRNA was very similar to that of ANP, leading to our hypothesis that corin is the pro-ANP convertase. To test this hypothesis, we constructed expression vectors for both human corin and pro-ANP. Recombinant corin and pro-ANP were expressed in human 293 cells. Effects of corin on pro-ANP processing was examined by western analysis. The results showed that human corin, but not control proteases prothrombin and hepsin, converted pro-ANP to ANP in the cell-based experiments. To determine sequence specificity of corin-mediated cleavage in pro-ANP, we constructed a mutant pro-ANP R98G in which the predicted cleave site residue Arg98 was replaced with a Gly. In co-transfection experiments, corin processed wild-type pro-ANP but not mutant pro-ANP R98G, indicating that corin-mediated cleavage in pro-ANP is highly sequence specific. We also examined effects of protease inhibitors on processing of pro-ANP by corin. Our results showed that the activity of corin was inhibited by aprotinin, benzamidine and leupeptin but not soybean trypsin inhibitor. Similar effects of these proteases on pro-ANP processing were reported previously. Thus, corin matches all known characteristics of the long-sought pro-ANP convertase. Identification of corin as the pro-ANP convertase suggests a new regulatory mechanism for the ANP-mediated pathway that is important for controlling blood pressure.

Corin, a Transmembrane Cardiac Serine Protease, as a Pro-Atrial Natriuretic Peptide Convertase

P92 Atrial natriuretic peptide (ANP) is a cardiac hormone that reduces high blood pressure by promoting salt excretion, decreasing blood volume and relaxing vessel tension. It is implicated in major cardiovascular diseases such as hypertension and congestive heart failure. In cardiomyocytes, ANP is synthesized as a precursor, pro-ANP, that is converted to biologically active ANP by an unknown membrane-associated serine protease. Recently, we cloned a novel cardiac serine protease, corin, that has the predicted structure of a type II transmembrane protein. Northern and in situ hybridization detected corin mRNA in the heart where its expression was most abundant in cardiomyocytes of the atrium. Corin mRNA was also detected in developing kidney and bones. The overall expression pattern of corin mRNA was very similar to that of ANP, leading to our hypothesis that corin is the pro-ANP convertase. To test this hypothesis, we constructed expression vectors for both human corin and pro-ANP. Recombinant corin and pro-ANP were expressed in human 293 cells. Effects of corin on pro-ANP processing was examined by western analysis. The results showed that human corin, but not control proteases prothrombin and hepsin, converted pro-ANP to ANP in the cell-based experiments. To determine sequence specificity of corin-mediated cleavage in pro-ANP, we constructed a mutant pro-ANP R98G in which the predicted cleave site residue Arg98 was replaced with a Gly. In co-transfection experiments, corin processed wild-type pro-ANP but not mutant pro-ANP R98G, indicating that corin-mediated cleavage in pro-ANP is highly sequence specific. We also examined effects of protease inhibitors on processing of pro-ANP by corin. Our results showed that the activity of corin was inhibited by aprotinin, benzamidine and leupeptin but not soybean trypsin inhibitor. Similar effects of these proteases on pro-ANP processing were reported previously. Thus, corin matches all known characteristics of the long-sought pro-ANP convertase. Identification of corin as the pro-ANP convertase suggests a new regulatory mechanism for the ANP-mediated pathway that is important for controlling blood pressure.

Corin, a Mosaic Transmembrane Serine Protease Encoded by a Novel cDNA from Human Heart

A novel cDNA has been identified from human heart that encodes an unusual mosaic serine protease, designated corin. Corin has a predicted structure of a type II transmembrane protein and contains two frizzled-like cysteine-rich motifs, seven low density lipoprotein receptor repeats, a macrophage scavenger receptor-like domain, and a trypsin-like protease domain in the extracellular region. Northern analysis showed that corin mRNA was highly expressed in the human heart. In mice, corin mRNA was detected by in situ hybridization in the cardiac myocytes of the embryonic heart as early as embryonic day (E) 9.5. By E11.5-13.5, corin mRNA was most abundant in the primary atrial septum and the trabecular ventricular compartment. Expression in the heart was maintained through the adult. In addition, mouse corin mRNA was also detected in the prehypertrophic chrondrocytes in developing bones. By fluorescent in situ hybridization analysis, the human corin gene was mapped to 4p12-13 where a congenital heart disease locus, total anomalous pulmonary venous return, had been previously localized. The unique domain structure and specific embryonic expression pattern suggest that corin may have a function in cell differentiation during development. The chromosomal localization of the human corin gene makes it an attractive candidate gene for total anomalous pulmonary venous return.