Kidney-specific cadherin (cdh16) is expressed in embryonic kidney, lung, and sex ducts

TNF- α from the Proximal Nephron Exacerbates Aristolochic Acid Nephropathy

Key Points

Proximal tubular TNF aggravates kidney injury and fibrogenesis in aristolochic acid nephropathy. Tubular TNF disrupts the cell cycle in injured tubular epithelial cells. TNF-mediated toxic renal injury is independent of systemic immune responses.

Background

Aristolochic acid nephropathy (AAN) presents with tubular epithelial cell (TEC) damage and tubulointerstitial inflammation. Although TNF-α regulates cell apoptosis and inflammatory responses, the effects of tubular TNF in the progression of AAN require elucidation.

Methods

Floxed TNF mice on the 129/SvEv background were crossed with PEPCK-Cre mice to generate PEPCK-Cre + TNF flox/flox (TNF PTKO) mice or bred with Ksp-Cre mice to generate KSP-Cre + TNF flox/flox (TNF DNKO) mice. TNF PTKO, TNF DNKO, and wild-type controls (Cre negative littermates) were subjected to acute and chronic AAN.

Results

Deletion of TNF in the proximal but not distal nephron attenuated kidney injury, renal inflammation, and tubulointerstitial fibrosis after acute or chronic aristolochic acid (AA) exposure. The TNF PTKO mice did not have altered numbers of infiltrating myeloid cells in AAN kidneys. Nevertheless, kidneys from AA-treated TNF PTKO mice had reduced levels of proteins involved in regulated cell death, higher proportions of TECs in the G0/G1 phase, and reduced TEC proportions in the G2/M phase. Pifithrin-α , which restores the cell cycle, abrogated differences between the wild-type and PTKO cohorts in G2/M phase arrest of TECs and kidney fibrosis after AA exposure.

Conclusions

TNF from the proximal but not the distal nephron propagates kidney injury and fibrogenesis in AAN in part by inducing G2/M cell cycle arrest of TECs.

Durable alveolar engraftment of PSC-derived lung epithelial cells into immunocompetent mice

Durable reconstitution of the distal lung epithelium with pluripotent stem cell (PSC) derivatives, if realized, would represent a promising therapy for diseases that result from alveolar damage. Here, we differentiate murine PSCs into self-renewing lung epithelial progenitors able to engraft into the injured distal lung epithelium of immunocompetent, syngeneic mouse recipients. After transplantation, these progenitors mature in the distal lung, assuming the molecular phenotypes of alveolar type 2 (AT2) and type 1 (AT1) cells. After months in vivo, donor-derived cells retain their mature phenotypes, as characterized by single-cell RNA sequencing (scRNA-seq), histologic profiling, and functional assessment that demonstrates continued capacity of the engrafted cells to proliferate and differentiate. These results indicate durable reconstitution of the distal lung's facultative progenitor and differentiated epithelial cell compartments with PSC-derived cells, thus establishing a novel model for pulmonary cell therapy that can be utilized to better understand the mechanisms and utility of engraftment.

Epithelial and mesenchymal fate decisions in Wolffian duct development

Wolffian ducts (WDs) are the paired embryonic structures that give rise to internal male reproductive tract organs. WDs are initially formed in both sexes but have sex-specific fates during sexual differentiation. Understanding WD differentiation requires insights into the process of fate decisions of epithelial and mesenchymal cells, which are tightly coordinated by endocrine, paracrine, and autocrine signals. In this review, we discuss current advances in understanding the fate-decision process of WD epithelial and mesenchymal lineages from their initial formation at the embryonic stage to postnatal differentiation. Finally, we discuss aberrant cell differentiation in WD abnormalities and pathologies and identify opportunities for future investigations.

Physiological functions of ferroportin in the regulation of renal iron recycling and ischemic acute kidney injury

Renal iron recycling preserves filtered iron from urinary excretion. However, it remains debated whether ferroportin (FPN), the only known iron exporter, is functionally involved in renal iron recycling and whether renal iron recycling is required for systemic iron homeostasis. We deleted FPN in whole nephrons by use of a Nestin-Cre and in the distal nephrons and collecting ducts, using a Ksp-Cre, and investigated its impacts on renal iron recycling and systemic iron homeostasis. FPN deletion by Nestin-Cre, but not by Ksp-Cre, caused excess iron retention and increased ferritin heavy chain (FTH1) specifically in the proximal tubules and resulted in the reduction of serum and hepatic iron. The systemic iron redistribution was aggravated, resulting in anemia and the marked downregulation of hepatic hepcidin in elderly FPN knockout (KO)/Nestin-Cre mice. Similarly, in iron-deficient FPN KO/Nestin-Cre mice, the renal iron retention worsened anemia with the activation of the erythropoietin-erythroferrone-hepcidin pathway and the downregulation of hepatic hepcidin. Hence, FPN likely located at the basolateral membrane of the proximal tubules to export iron into the circulation and was required for renal iron recycling and systemic iron homeostasis particularly in elderly and iron-deficient mice. Moreover, FPN deletion in the proximal tubules alleviated ischemic acute kidney injury, possibly by upregulating FTH1 to limit catalytic iron and by priming antioxidant mechanisms, indicating that FPN could be deleterious in the pathophysiology of ischemic acute kidney injury (AKI) and thus may be a potential target for the prevention and mitigation of ischemic AKI.

Hypoxia inhibits nephrogenesis through paracrine Vegfa despite the ability to enhance tubulogenesis

Reduced nephron number predisposes to hypertension and kidney disease. Interaction of the branching ureteric bud and surrounding mesenchymal cells determines nephron number. Since oxygen supply may be critical for intrauterine development, we tested whether hypoxia and hypoxia-inducible factor-1α (HIF-1α) influence nephrogenesis. We found that HIF-1α is required for branching of MDCK cells. In addition, culture of metanephric mouse kidneys with ureteric bud cell-specific stabilization or knockout of HIF-1α revealed a positive impact of HIF-1α on nephrogenesis. In contrast, widespread stabilization of HIF-1α in metanephric kidneys through hypoxia or HIF stabilizers impaired nephrogenesis, and pharmacological HIF inhibition enhanced nephrogenesis. Several lines of evidence suggest an inhibitory effect through the hypoxia response of mesenchymal cells. HIF-1α was expressed in mesenchymal cells during nephrogenesis. Expression of the anti-branching factors Bmp4 and Vegfa, secreted by mesenchymal cells, was increased upon HIF stabilization. The conditioned medium from hypoxic metanephric kidneys inhibited MDCK branching, which was partially rescued by Vegfa antibodies. Thus, the effect of HIF-1α on nephrogenesis appears context dependent. While HIF-1α in the ureteric bud is of importance for proper branching morphogenesis, the net effect of hypoxia-induced HIF activation in the embryonic kidney appears to be mesenchymal cell-dependent inhibition of ureter branching.

Rapid and efficient differentiation of human pluripotent stem cells into intermediate mesoderm that forms tubules expressing kidney proximal tubular markers

Human pluripotent stem cells (hPSCs) can generate a diversity of cell types, but few methods have been developed to derive cells of the kidney lineage. Here, we report a highly efficient system for differentiating human embryonic stem cells and induced pluripotent stem cells (referred to collectively as hPSCs) into cells expressing markers of the intermediate mesoderm (IM) that subsequently form tubule-like structures. Treatment of hPSCs with the glycogen synthase kinase-3β inhibitor CHIR99021 induced BRACHYURY(+)MIXL1(+) mesendoderm differentiation with nearly 100% efficiency. In the absence of additional exogenous factors, CHIR99021-induced mesendodermal cells preferentially differentiated into cells expressing markers of lateral plate mesoderm with minimal IM differentiation. However, the sequential treatment of hPSCs with CHIR99021 followed by fibroblast growth factor-2 and retinoic acid generated PAX2(+)LHX1(+) cells with 70%-80% efficiency after 3 days of differentiation. Upon growth factor withdrawal, these PAX2(+)LHX1(+) cells gave rise to apically ciliated tubular structures that coexpressed the proximal tubule markers Lotus tetragonolobus lectin, N-cadherin, and kidney-specific protein and partially integrated into embryonic kidney explant cultures. With the addition of FGF9 and activin, PAX2(+)LHX1(+) cells specifically differentiated into cells expressing SIX2, SALL1, and WT1, markers of cap mesenchyme nephron progenitor cells. Our findings demonstrate the effective role of fibroblast growth factor signaling in inducing IM differentiation in hPSCs and establish the most rapid and efficient system whereby hPSCs can be differentiated into cells with features characteristic of kidney lineage cells.

CDH16/Ksp-cadherin is expressed in the developing thyroid gland and is strongly down-regulated in thyroid carcinomas

Cadherin (CDH)16/kidney-specific-cadherin was first described as a kidney-specific adhesion molecule and thereafter found expressed also in the thyroid gland. We show here that CDH16 fully colocalizes with CDH1/E-cadherin on the basolateral plasma membrane of mouse and human thyrocytes. In thyrocyte cultures, the expression of CDH16 is dependent upon TSH, as other thyroid differentiation markers. In the developing mouse thyroid, CDH16 is expressed at embryonic day 10.5, 1-2 d after the main thyroid-specific transcription factors involved in thyroid cell differentiation. In human thyroid carcinomas, as determined by quantitative RT-PCR, CDH16 expression decreases in papillary, follicular, and anaplastic thyroid carcinomas, and the decrease is more pronounced than that of CDH1. Moreover, by immunofluorescence and confocal microscopy, it appears that although CDH16-negative tumor cells may still be positive for CDH1, CDH1-negative cells are also negative for CDH16, indicating a more extensive loss of the latter and suggesting that CDH16 loss might precede that of CDH1. Loss of CDH16 appears to be a marker of epithelial-mesenchymal transition as indicated by its decrease in cultured thyroid cells after TGF-β treatment. Finally, the decrease in CDH16 is paralleled in part by the decrease in α B-crystallin, which was proposed to mediate the interaction of CDH16 cytosolic tail with the cell cytoskeleton. In conclusion, CDH16 is a thyroid-selective and hormone-dependent adhesion protein that might play a role during thyroid development and that may be a useful marker to monitor thyroid carcinomas.

Identification of anchor genes during kidney development defines ontological relationships, molecular subcompartments and regulatory pathways

The development of the mammalian kidney is well conserved from mouse to man. Despite considerable temporal and spatial data on gene expression in mammalian kidney development, primarily in rodent species, there is a paucity of genes whose expression is absolutely specific to a given anatomical compartment and/or developmental stage, defined here as ‘anchor’ genes. We previously generated an atlas of gene expression in the developing mouse kidney using microarray analysis of anatomical compartments collected via laser capture microdissection. Here, this data is further analysed to identify anchor genes via stringent bioinformatic filtering followed by high resolution section in situ hybridisation performed on 200 transcripts selected as specific to one of 11 anatomical compartments within the midgestation mouse kidney. A total of 37 anchor genes were identified across 6 compartments with the early proximal tubule being the compartment richest in anchor genes. Analysis of minimal and evolutionarily conserved promoter regions of this set of 25 anchor genes identified enrichment of transcription factor binding sites for Hnf4a and Hnf1b, RbpJ (Notch signalling), PPARγ:RxRA and COUP-TF family transcription factors. This was reinforced by GO analyses which also identified these anchor genes as targets in processes including epithelial proliferation and proximal tubular function. As well as defining anchor genes, this large scale validation of gene expression identified a further 92 compartment-enriched genes able to subcompartmentalise key processes during murine renal organogenesis spatially or ontologically. This included a cohort of 13 ureteric epithelial genes revealing previously unappreciated compartmentalisation of the collecting duct system and a series of early tubule genes suggesting that segmentation into proximal tubule, loop of Henle and distal tubule does not occur until the onset of glomerular vascularisation. Overall, this study serves to illuminate previously ill-defined stages of patterning and will enable further refinement of the lineage relationships within mammalian kidney development.

Subfractionation of differentiating human embryonic stem cell populations allows the isolation of a mesodermal population enriched for intermediate mesoderm and putative renal progenitors

Human embryonic stem (ES) cells are pluripotent and are believed to be able to generate all cell types in the body. As such, they have potential applications in regenerative therapy for kidney disease. However, before this can be achieved, a protocol to differentiate human ES cells to mesodermal renal progenitor lineages is required. Reduction of serum concentration and feeder layer density reduction cultures were used to differentiate human ES cells for 14 days. Differentiated ES cells were then fractionated by flow cytometry based on expression of the markers CD24, podocalyxin, and GCTM2 to isolate putative renal cells. These cells up-regulated the expression of the renal transcription factors PAX2, LHX1, and WT1 when compared with unfractionated human ES cells. Immunohistochemical assays confirmed that a subset of cells within this fraction co-expressed nuclear WT1 and PAX2 proteins. Transcriptome profiling also showed that the most differentially up-regulated genes in this fraction preferentially associated with kidney development in comparison with any other lineage. When compared with a transcriptome profile database of urogenital development (GUDMAP), the top 200 differentially up-regulated genes in this fraction strongly clustered into a group of genes associated with the metanephric mesenchyme at E11.5 and the corticonephrogenic interstitium at E15.5 of murine kidney development. Hence, this approach confirms an ability to direct human ES cells toward a renal progenitor state.

Truncated P-cadherin is produced in oral squamous cell carcinoma

Cadherins belong to a family of homophilic cell-cell adhesion proteins that are responsible for the establishment of a precise cell architecture and tissue integrity. Moreover, experimental data suggest that loss of intercellular adhesion is inversely correlated with cellular differentiation. Furthermore, dedifferentiation is closely linked to tumor progression. Recently, we have shown that a secreted 50 kDa N-terminal fragment of P-cadherin plays a role in the progression of malignant melanoma. In this study, we have detected both the full-length and the truncated versions of P-cadherin in cell lysates of differentiated head and neck oral squamous cell carcinoma cell lines, whereas in cell lysates of dedifferentiated cell lines, we detected only the truncated 50 kDa version of P-cadherin. Treatment of the cell lines with a recombinantly expressed biotinylated, soluble 50 kDa form of the N-terminal part of P-cadherin revealed a major effect on cell aggregation and migration of oral squamous cell carcinoma cells. However, the 50 kDa N-terminal fragment of P-cadherin did not show any influence on cell proliferation in 2D and 3D cell culture. These results suggest that generation of truncated P-cadherin during the progression of oral squamous carcinoma attenuates tissue integrity, facilitates cellular separation, and leads to the acquisition of a more migratory phenotype.

Gene Expression Profiling and Its Relevance to the Blood-Epididymal Barrier in the Human Epididymis1

The luminal environment along the epididymal duct is important for spermatozoal maturation. This environment is unique and created by the blood-epididymal barrier, which is formed by tight and adhering junctions. For the human epididymis, little information exists on the proteins that comprise these junctions. Our objectives were to assess the gene expression profiles in the different segments of the human epididymis and to identify the proteins that make up the blood-epididymal barrier. Using microarrays, we identified 2980 genes that were differentially expressed by at least 2-fold between the various segments. Of the many genes involved in diverse functions, were those that encoded adhesion proteins (cadherins and catenins) and tight junctional proteins (claudins [CLDN] and others). PCR analyses confirmed the microarray data. Immunolocalization of CLDNs 1, 3, 4, 8, and 10 revealed that the localization of CLDNs differed along the epididymis. In all three segments, CLDNs 1, 3, and 4 were localized to tight junctions, along the lateral margins of adjacent principal cells, and at the interface between basal and principal cells. CLDN8 was localized to tight junctions in all three segments, in addition to being localized in the caput along the lateral margins of principal cells, and in the corpus, at the interface between principal and basal cells. CLDN10, tight junction protein 1, and occludin were localized exclusively to tight junctions in all three epididymal segments. These data indicate that the epididymis displays a complex pattern of gene expression, which includes genes that are implicated in the formation of the blood-epididymal barrier, which suggests complex regulation of this barrier.

Snail activation disrupts tissue homeostasis and induces fibrosis in the adult kidney

During embryonic development, the kidney epithelium originates from cells that undergo a mesenchymal to epithelial transition (MET). The reverse process, epithelium to mesenchyme transition (EMT), has been implicated in epithelial tumor progression and in the fibrosis that leads to end-stage kidney failure. Snail transcription factors induce both natural and pathological EMT, but their implication in renal development and disease is still unclear. We show that Snail genes are downregulated during the MET that occurs during renal development and that this is correlated with Cadherin-16 expression. Snail suppresses Cadherin-16 via the direct repression of the kidney differentiation factor HNF-1beta, a novel route by which Snail disrupts epithelial homeostasis. Indeed, Snail activation is sufficient to induce EMT and kidney fibrosis in adult transgenic mice. Significantly, Snail is also activated in patients with renal fibrosis. Thus, Snail expression is suppressed during renal development and it must remain silent in the mature kidney where its aberrant activation leads to fibrosis.

Elucidating the function of primary cilia by conditional gene inactivation

PURPOSE OF REVIEW

This review discusses recent experimental approaches to determine the function of primary cilia by conditional inactivation of genes crucial for cilia formation.

RECENT FINDINGS

A functional role in the sensing of fluid flow was recently assigned to the primary cilia. This discovery shed light onto how cells sense dynamic fluid movements. Conditional inactivation of primary cilia formation in later ontogenic stages demonstrated the crucial role renal primary cilia play in the control of cell proliferation.

SUMMARY

Primary cilia can act as flow sensors, transmitting signals by means of calcium influx into the cells. Structures based on primary cilia are also crucial for the function of photoreceptor cells and it can be expected that additional functions of these organelles will be determined in the future. An important experimental approach to elucidate the involvement of primary cilia in other physiological processes is to specifically inactivate genes crucial for formation of primary cilia. Morphological and physiological changes induced by the loss of primary cilia will help determine additional roles primary cilia play in physiology and organ development.

Identification of FGF10 Targets in the Embryonic Lung Epithelium during Bud Morphogenesis

Genetic studies implicate Fgf10-Fgfr2 signaling as a critical regulator of bud morphogenesis in the embryo. However, little is known about the transcriptional targets of Fgf10 during this process. Here we identified global changes in gene expression in lung epithelial explants undergoing FGF10-mediated budding in the absence of other growth factors and mesenchyme. Targets were confirmed by their localization at sites where endogenous Fgf10 signaling is active in embryonic lungs and by demonstrating their induction in intact lungs in response to local application of FGF10 protein. We show that the initial stages of budding are characterized by marked up-regulation of genes associated with cell rearrangement and cell migration, inflammatory process, and lipid metabolism but not cell proliferation. We also found that some genes implicated in tumor invasion and metastatic behavior are epithelial targets of Fgf10 in the lung and other developing organs that depend on Fgf10-Fgfr2 signaling to properly form. Our approach identifies Fgf10 targets that are common to multiple biological processes and provides insights into potential mechanisms by which Fgf signaling regulates epithelial cell behavior.

Loss of N-cadherin and alpha-catenin in the proximal tubules of aging male Fischer 344 rats

Aging is associated with a loss of renal reserve, and increased sensitivity to either xenobiotic or physiologic insult. Given the critical role of the cadherin/catenin complex in establishing and maintaining the integrity and polarity of tubular epithelial cells, it was hypothesized that aging was associated with alterations in renal cadherin/catenin complexes. Histological assessment of aged (24 months) kidneys harvested from male Fischer 344 rats demonstrates mild degeneration of proximal tubules, multifocal chronic lymphocytic infiltration, moderate development of protein casts inside tubules, and tubular dilatation or degeneration. Western blot analysis revealed that N-cadherin protein expression is not constant over 24 months. N-cadherin expression increased from 4 to 9 months, with peak levels at 9 and 13 months. A decrease in expression was seen at 19 months and an almost complete loss of expression was seen at 24 months. In contrast, the expression of E- and Ksp-cadherin was constant over 24 months. A loss of alpha-catenin at was seen at 19 and 24 months in the absence of changes in beta-, gamma-, and p120-catenin. This pattern of N-cadherin expression (increase followed by decrease) was confirmed by real-time PCR analysis, which demonstrated a similar pattern as the Western blot, suggesting that the loss of N-cadherin protein was due to decreased gene expression. The loss of N-cadherin was specific for the kidney, as no changes in N-cadherin expression in the liver, brain, or testes were seen during aging. The conclusion that loss of N-cadherin expression is a critical component of the renal dysfunction associated with aging is supported by the finding that caloric restriction attenuates the loss of N-cadherin, as well as the finding that a significant loss of N-cadherin is seen in the kidneys of ZDF x SHHF rats, a genetic model of end-stage renal disease. Cadherin and catenin expression was further analyzed by immunofluorescence. A significant loss of staining of both N-cadherin and alpha-catenin was seen in the proximal tubules of rats at 24 months. Interestingly, this corresponded with delocalization of the alpha-1 subunit of the Na+K+-ATPase, i.e. aberrant staining on cell-cell borders and some indication of apical staining in proximal tubules. Taken together, these data suggest that aging is associated with decreased expression of N-cadherin and alpha-catenin and is associated with a loss of cell polarity.

Developmental genetics of the female reproductive tract in mammals

The female reproductive tract receives the oocytes for fertilization, supports the development of the fetus and provides the passage for birth. Although abnormalities of this organ system can result in infertility and even death, until recently relatively little was known about the genetic processes that underlie its development. By drawing primarily on mouse mutagenesis studies and the analysis of human mutations we review the emerging genetic pathways that regulate female reproductive-tract formation in mammals and that are implicated in congenital abnormalities of this organ system. We also show that these pathways might be conserved between invertebrates and mammals.

Following the expression of a kidney-specific gene from early development to adulthood

Ksp-cadherin (Cadherin 16) is a unique, tissue-specific member of the cadherin family of cell adhesion proteins that is expressed exclusively in tubular epithelial cells in the adult kidney and developing genitourinary (GU) tract. Since its original identification in 1995, Ksp-cadherin has proven to be a useful experimental model for studies of kidney-specific and developmental gene regulation. These investigations have led to the creation of new strains of transgenic mice that will be useful for studies of renal cell lineage and tissue-specific gene targeting. Recent studies have also identified Ksp-cadherin as the first kidney-specific promoter that it is regulated by HNF-1beta (hepatocyte nuclear factor-1beta), a transcription factor that has been implicated in human renal cystic disease.

Regulation of kidney-specific Ksp-cadherin gene promoter by hepatocyte nuclear factor-1beta

Kidney-specific cadherin (Ksp-cadherin) is a tissue-specific member of the cadherin family that is expressed exclusively in the kidney and developing genitourinary tract. Recent studies have shown that the proximal 250 bp of the Ksp-cadherin gene promoter are sufficient to direct tissue-specific gene expression in vivo and in vitro. The proximal 120 bp of the promoter are evolutionarily conserved between mouse and human and contain a DNase I hypersensitive site that is kidney cell specific. At position -55, the promoter contains a consensus recognition site for hepatocyte nuclear factor-1 (HNF-1). Mutations of the consensus HNF-1 site and downstream GC-boxes inhibit promoter activity in transfected cells. HNF-1alpha and HNF-1beta bind specifically to the -55 site, and both proteins transactivate the promoter directly. Expression of Ksp-cadherin is not altered in the kidneys of HNF-1alpha-deficient mice. However, expression of a gain-of-function HNF-1beta mutant stimulates Ksp-cadherin promoter activity in transfected cells, whereas expression of a dominant-negative mutant inhibits activity. These studies identify Ksp-cadherin as the first kidney-specific promoter that has been shown to be regulated by HNF-1beta. Mutations of HNF-1beta, as occur in humans with inherited renal cysts and diabetes, may cause dysregulated Ksp-cadherin promoter activity.

A minimal Ksp-cadherin promoter linked to a green fluorescent protein reporter gene exhibits tissue-specific expression in the developing kidney and genitourinary tract

Ksp-cadherin is a unique, tissue-specific member of the cadherin family of cell adhesion molecules that is expressed exclusively in tubular epithelial cells in the kidney and developing genitourinary (GU) tract. Transgenic mice carrying 3425 bp of the Ksp-cadherin 5' flanking region linked to a lacZ reporter gene express beta-galactosidase exclusively in the kidney, although the expression pattern is incomplete (Am J Physiol 277: F599-F610, 1999). To further define the region that mediates tissue-specific expression, transgenic mice carrying 1341 bp or 324 bp of the 5' flanking region linked to a green fluorescent protein (GFP) reporter gene were produced. Transgenic mice carrying 1341 bp of the 5' flanking region expressed GFP in all embryonic tissues that endogenously express Ksp-cadherin, including the ureteric bud, Wolffian duct, Müllerian duct, and developing tubules in the mesonephros and metanephros. In the adult kidney, GFP was highly expressed in thick ascending limbs of Henle's loops and collecting ducts and weakly expressed in proximal tubules and Bowman's capsules. Transgenic mice carrying 324 bp of the 5' flanking region exhibited expression exclusively in tubular epithelial cells in the developing kidney and GU tract. Immunoblot analysis showed that the expression of GFP was restricted to the kidney in adult mice. Taken together, these results demonstrate that 324 bp of the Ksp-cadherin 5' flanking region is sufficient to direct epithelial-specific expression in the developing kidney and GU tract. Transgenic mice that express GFP in the mesonephros, metanephros, ureteric bud, and sex ducts may be useful for cell lineage studies.

Cadherin-17 is required to maintain pronephric duct integrity during zebrafish development

We have isolated a zebrafish cadherin that is orthologous to human LI-cadherin (CDH17). Zebrafish cdh17 is expressed exclusively in the pronephric ducts during embryogenesis, and in the mesonephros during larval development and adulthood. Like its mammalian ortholog, cdh17 is also expressed in liver and intestine in adult zebrafish. We show that cdh17-positive mesodermal cells do not contribute to the hematopoietic system. Consistent with a cell adhesion role for Cdh17, depletion of Cdh17 function using antisense morpholino oligonucleotides compromised cell cohesion during pronephric duct formation. Our results indicate that Cdh17 is necessary for maintaining the integrity of the pronephric ducts during zebrafish embryogenesis. This finding contrasts with the role of mammalian CDH17, which does not appear to be involved in nephric development.

Epithelial-specific Cre/lox recombination in the developing kidney and genitourinary tract

Ksp-cadherin is a unique, tissue-specific member of the cadherin family of cell adhesion molecules that is expressed in tubular epithelial cells in the kidney and developing genitourinary (GU) tract. It has recently been shown that a 1341-bp fragment of the 5' flanking region containing the Ksp-cadherin gene promoter can recapitulate the complete expression pattern of the gene in the developing kidney and GU tract. Similar to the endogenous Ksp-cadherin gene, transgenes containing 1341 bp of the 5' flanking region are expressed in developing nephrons, ureteric bud, mesonephric tubules, Wolffian duct, and Müllerian duct. In adult mice, the expression is restricted to renal tubules. In the current study, Ksp1.3/Cre transgenic mice carrying 1329 bp of the Ksp-cadherin 5' flanking region linked to the Cre recombinase gene were produced. Adult transgenic mice expressed Cre recombinase in renal tubules, especially collecting ducts and thick ascending limbs of Henle's loops. Transgenic embryos expressed Cre recombinase in the branching ureteric bud, developing renal tubules, and sex ducts. Ksp1.3/Cre transgenic mice were crossed with mice carrying a lacZ reporter gene that is activated by Cre/lox-mediated genetic recombination. Bitransgenic progeny expressed lacZ exclusively in renal tubules, mesonephric tubules, ureteric bud, developing ureter, and Wolffian duct. These results demonstrate that Ksp1.3/Cre transgenic mice express Cre recombinase exclusively in the kidney and developing GU tract and can mediate epithelial-specific Cre/lox recombination in these tissues. Ksp1.3/Cre transgenic mice should be useful for cell lineage studies and kidney-specific gene targeting.

Large-scale screen for genes involved in gonad development

The vertebrate gonad develops from the intermediate mesoderm as an initially bipotential organ anlage, the genital ridge. In mammals, Sry acts as a genetic switch towards testis development. Sox9 has been shown to act downstream of Sry in testis development, while Dax1 appears to counteract Sry. Few more genes have been implicated in early gonad development. However, the genetic networks controlling early differentiation events in testis and ovary are still far from being understood. In order to provide a broader basis for the molecular analysis of gonad development, high-throughput gene expression analysis was utilized to identify genes specifically expressed in the gonad. In total, among 138 genes isolated which showed tissue specific expression in the embryo, 79 were detected in the developing gonad or sex ducts. Twenty-seven have not been functionally described before, while 40 represent known genes and 12 are putative mouse orthologues. Forty-five of the latter two groups (86%) have not been described previously in the fetal gonad. In addition, 21 of the gonad specific genes showed sex-dimorphic expression suggesting a role in sex determination and/or gonad differentiation. Eighteen of the latter (86%) have not been described previously in the fetal gonad. In total we provide new data on 72 genes which may play a role in gonad or sex duct development and/or sex determination. Thus we have generated a large gene resource for the investigation of these processes, and demonstrate the suitability of high-throughput gene expression screening for the genetic analysis of organogenesis.