Comparative role of phosphotyrosine kinase domains of c-ros and c-ret protooncogenes in metanephric development with respect to growth factors and matrix morphogens

Pre-clinical modelling of ROS1+ non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a heterogeneous group of diseases which accounts for 80% of newly diagnosed lung cancers. In the previous decade, a new molecular subset of NSCLC patients (around 2%) harboring rearrangements of the c-ros oncogene 1 was defined. ROS1+ NSCLC is typically diagnosed in young, nonsmoker individuals presenting an adenocarcinoma histology. Patients can benefit from tyrosine kinase inhibitors (TKIs) such as crizotinib and entrectinib, compounds initially approved to treat ALK-, MET- or NTRK- rearranged malignancies respectively. Given the low prevalence of ROS1-rearranged tumors, the use of TKIs was authorized based on pre-clinical evidence using limited experimental models, followed by basket clinical trials. After initiating targeted therapy, disease relapse is reported in approximately 50% of cases as a result of the appearance of resistance mechanisms. The restricted availability of TKIs active against resistance events critically reduces the overall survival. In this review we discuss the pre-clinical ROS1+ NSCLC models developed up to date, highlighting their strengths and limitations with respect to the unmet clinical needs. By combining gene-editing tools and novel cell culture approaches, newly developed pre-clinical models will enhance the development of next-generation tyrosine kinase inhibitors that overcome resistant tumor cell subpopulations.

The Impact of PTPRK and ROS1 Polymorphisms on the Preeclampsia Risk in Han Chinese Women

Objective

Preeclampsia (PE) is a severe complication in pregnancy and a leading cause of maternal and infant mortality. However, the exact underlying etiology of PE remains unknown. Emerging evidence indicates that the cause of PE is associated with genetic factors. Therefore, the aim of this study is to identify susceptibility genes to PE.

Materials and Methods

Human Exome BeadChip assays were conducted using 370 cases and 482 controls and 21 loci were discovered. A further independent set of 958 cases and 1007 controls were recruited for genotyping to determine whether the genes of interest ROS1 and PTPRK are associated with PE. Immunohistochemistry was used for localization. Both qPCR and Western blotting were utilized to investigate the levels of PTPRK in placentas of 20 PE and 20 normal pregnancies.

Results

The allele frequency of PTPRK rs3190930 differed significantly between PE and controls and was particularly significant in severe PE subgroup and early-onset PE subgroup. PTPRK is primarily localized in placental trophoblast cells. The mRNA and protein levels of PTPRK in PE were significantly higher than those in controls.

Conclusion

These results suggest that PTPRK appears to be a previously unrecognized susceptibility gene for PE in Han Chinese women, and its expression is also associated with PE, while ROS1 rs9489124 has no apparent correlation with PE risk.

Cellular heterogeneity in the ureteric progenitor niche and distinct profiles of branching morphogenesis in organ development

Branching morphogenesis creates arborized epithelial networks. In the mammalian kidney, an epithelial progenitor pool at ureteric branch tips (UBTs) creates the urine-transporting collecting system. Using region-specific mouse reporter strains, we performed an RNA-seq screen, identifying tip- and stalk-enriched gene sets in the developing collecting duct system. Detailed in situ hybridization studies of tip-enriched predictions identified UBT-enriched gene sets conserved between the mouse and human kidney. Comparative spatial analysis of their UBT niche expression highlighted distinct patterns of gene expression revealing novel molecular heterogeneity within the UBT progenitor population. To identify kidney-specific and shared programs of branching morphogenesis, comparative expression studies on the developing mouse lung were combined with in silico analysis of the developing mouse salivary gland. These studies highlight a shared gene set with multi-organ tip enrichment and a gene set specific to UBTs. This comprehensive analysis extends our current understanding of the ureteric branch tip niche.

Molecular Markers with Predictive and Prognostic Relevance in Lung Cancer

Lung cancer accounts for the majority of cancer-related deaths worldwide of which non-small-cell lung carcinoma alone takes a toll of around 85%. Platinum-based therapy is the stronghold for lung cancer at present. The discovery of various molecular alterations that underlie lung cancer has contributed to the development of specifically targeted therapies employing specific mutation inhibitors. Targeted chemotherapy based on molecular profiling has shown great promise in lung cancer treatment. Various molecular markers with predictive and prognostic significance in lung cancer have evolved as a result of advanced research. Testing of EGFR and Kras mutations is now a common practice among community oncologists, and more recently, ALK rearrangements have been added to this group. This paper discusses various predictive and prognostic markers that are being investigated and have shown significant relevance which can be exploited for targeted treatment in lung cancer.

ROS receptor tyrosine kinase: a new potential target for anticancer drugs

ROS kinase is one of the last two remaining orphan receptor tyrosine kinases with an as yet unidentified ligand. The normal functions of human ROS kinase in different body tissues have not been fully identified so far. However, the ectopic expression, as well as the production of variable mutant forms of ROS kinase has been reported in a number of cancers, such as glioblastoma multiforme, and non-small cell lung cancer, suggesting a role for ROS kinase in deriving such tumors. It is thought also that c-ROS gene may have a role in some cardiovascular diseases, and the fact that homozygous male mice targeted against c-ROS gene are healthy but infertile, has inspired researchers to think about ROS inhibition as a method for development of new male contraceptives. The recent discovery of new selective and potent inhibitors for ROS kinase, along with the development of new specific diagnostic methods for the detection of ROS fusion proteins, raises the importance of using these selective inhibitors for targeting ROS mutations as a new method for treatment of cancers harboring such genes. This review focuses on the ectopic expression of ROS and its fusion proteins in different cancer types and highlights the importance of targeting these proteins for treatment of substantial cancers. It describes also the recent advances in the field of ROS kinase inhibition, and the potential clinical applications of ROS kinase inhibitors.

Molecular characterization of lung dysplasia induced by c-Raf-1

Background

Lung cancer is a multistage process with poor prognosis and high morbidity. Importantly, the genetics of dysplasia, a facultative cancer, at the edge of malignant transformation is unknown.

Methodology/Principal Findings

We employed laser microdissection to harvest c-Raf1- induced dysplastic as opposed to transgenic but otherwise morphologically unaltered epithelium and compared findings to non-transgenic lung. We then employed microarrays to search genome wide for gene regulatory networks. A total of 120 and 287 genes were significantly regulated, respectively. Dysplasia was exclusive associated with up-regulation of genes coding for cell growth and proliferation, cell-to-cell signalling and interaction, lipid metabolism, development, and cancer. Likewise, when dysplasia was compared with non-transgenic cells up-regulation of cancer associated genes, tight junction proteins, xenobiotic defence and developmental regulators was observed. Further, in a comparison of the data sets of dysplasia vs transgenic and dysplasia vs non-transgenic 114 genes were regulated in common. We additionally confirmed regulation of some genes by immunohistochemistry and therefore demonstrate good concordance between gene regulation and coded protein.

Conclusion

Our study identified transcriptional networks at successive stages of tumor-development, i.e. from histological unaltered but transgenic lungs to nuclear atypia. Our SP-C/c-raf transgenic mouse model revealed interesting and novel candidate genes and pathways that provide clues on the mechanism forcing respiratory epithelium into dysplasia and subsequently cancer, some of which might also be useful in the molecular imaging and flagging of early stages of disease.

New insights into epididymal biology and function

BACKGROUND

The epididymis performs an important role in the maturation of spermatozoa including their acquisition of progressive motility and fertilizing ability. However, the molecular mechanisms that govern these maturational events are still poorly defined. This review focuses on recent progress in our understanding of epididymal function including its development, role of the luminal microenvironment in sperm maturation, regulation and novel mechanisms the epididymis utilizes to carry out some of its functions.

METHODS

A systematic search of Pubmed was carried out using the search term 'epididymis'. Articles that were published in the English language until the end of August 2008 and that focused on the specific topics described above were included. Additional papers cited in the primary reference were also included.

RESULTS

While the majority of these findings were the result of studies in animal models, recent studies in the human epididymis are also presented including gene profiling studies to examine regionalized expression in normal epididymides as well as in those from vasectomized patients.

CONCLUSIONS

Significant progress has been made in our understanding of epididymal function providing new insights that ultimately could improve human health. The data also indicate that the human epididymis plays an important role in sperm maturation but has unique properties compared with animal models.

The multifaceted roles of the receptor tyrosine kinase ROS in development and cancer

The proto-oncogene receptor tyrosine kinase ROS was originally discovered through the identification of oncogenic variants isolated from tumors. These discoveries spearheaded a body of work aimed at elucidating the function of this evolutionarily conserved receptor in development and cancer. Through genetic and biochemical approaches, progress in the characterization of ROS points to distinctive roles in the program of epithelial cell differentiation during the development of a variety of organs. Although substantial, these advances remain hampered by the absence of an identified ligand, making ROS one of the last two remaining orphan receptor tyrosine kinases. Recent studies on the oncogenic activation of ROS as a result of different chromosomal rearrangements found in brain and lung cancers have shed light on the molecular mechanisms underlying ROS transforming activities. ROS and its oncogenic variants therefore constitute clinically relevant targets for cancer therapeutic intervention. This review highlights the various roles that this receptor plays in multiple system networks in normalcy and disease and points to future directions towards the elucidation of ROS function in the context of ligand identification, signaling pathways and clinical applications.

The use of Endo-Porter to deliver morpholinos in kidney organ culture

Cellular interactions in development of the kidney are used as a model of reciprocal inductive events between epithelium and mesenchyme. Time- and labor-intensive methods have been developed to study this phenomenon. For example, in mice, the targeted disruption of genes in vivo has been used to modify the genetic program directing kidney development. However, gene targeting is a resource-intensive approach and alternative strategies for gene and protein modification in the kidney need to be developed. Herein, we have developed an efficient system for the delivery of antisense morpholino to alter normal protein expression. We describe the use of Endo-Porter to effectively deliver morpholinos to all parts and regions of the kidney explant. Also, we definitively show via confocal microscopy and Western blot analysis that the use of Endo-Porter in delivering antisense morpholinos is robust throughout the entire kidney explant, providing efficient suppression of protein expression. This method saves time and cost when compared with targeted disruption and is an improvement upon previous kidney organ culture methods.

Expression and potential role of dentin phosphophoryn (DPP) in mouse embryonic tissues involved in epithelial-mesenchymal interactions and branching morphogenesis

Dentin sialophosphoprotein (DSPP) is synthesized in both mesenchyme and epithelium at varying stages of tooth development. At the tooth cap stage, corresponding to embryonic day (E) 13.5 of mouse embryonic life, the phosphophoryn (DPP) portion of DSPP was immunohistochemically localized to the enamel organ with intense staining of oral ectoderm but no expression in dental follicle mesenchyme. Surprisingly, DPP was also expressed in ureteric bud branches of embryonic metanephric kidney and alveolar epithelial buds of developing lung. Reverse transcriptase-polymerase chain reaction analysis verified the presence of DSPP mRNA with identical sequences in the tooth, lung, and kidney. The DSPP(-/-) mouse with ablated DPP expression in the teeth, also exhibited aberrant organogenesis in kidney and lung. In the kidney, malformed metanephric S-shaped bodies and increased mesenchymal apoptosis were observed. Inclusion of anti-DPP antibodies in organ culture of metanephroi, harvested from E13.5 wild-type mice, likewise resulted in altered ureteric bud morphogenesis, suggesting a role for DPP in epithelial-mesenchymal interactions in meristic tissues during embryonic development.

LGR4 regulates the postnatal development and integrity of male reproductive tracts in mice

The roles of the leucine-rich repeat domain containing G protein-coupled receptor (GPCR) 4 (Lgr4), which is one of the orphan GPCRs, were analyzed with the Lgr4 hypomorphic mutant mouse line (Lgr4(Gt)). This homozygous mutant had only one-tenth the normal transcription level; furthermore, 60% of them survived to adulthood. The homozygous male was infertile, showing morphologic abnormalities in both the testes and the epididymides. In the testes, luminal swelling, loss of germinal epithelium in the seminiferous tubules, and rete testis dilation were observed. Cauda epididymidis sperm were immotile. Rete testis dilation was due to a water reabsorption failure caused by a decreased expression of an estrogen receptor (ESR1) and SLC9A3 in the efferent ducts. Although we found differential regulation of ESR1 expression in the efferent ducts and the epididymis, the role of ESR1 in the epididymis remains unclear. The epididymis contained short and dilated tubules and completely lacked its initial segment. In the caput region, we observed multilamination and distortion of the basement membranes (BMs) with an accumulation of laminin. Rupture of swollen epididymal ducts was observed, leading to an invasion of macrophages into the lumen. Male infertility was probably due to the combination of a developmental defect of the epididymis and the rupture of the epithelium resulting in the immotile spermatozoa. These results indicate that Lgr4 has pivotal roles to play in the regulation of ESR1 expression, the control of duct elongation through BM remodeling, and the regional differentiation of the caput epididymidis.

ROS fusion tyrosine kinase activates a SH2 domain-containing phosphatase-2/phosphatidylinositol 3-kinase/mammalian target of rapamycin signaling axis to form glioblastoma in mice

Glioblastoma multiforme is the most common and lethal form of primary brain cancer. Diagnosis of this advanced glioma has a poor prognosis due to the ineffectiveness of current therapies. Aberrant expression of receptor tyrosine kinases (RTK) in glioblastoma multiformes is suggestive of their role in initiation and maintenance of these tumors of the central nervous system. In fact, ectopic expression of the orphan RTK ROS is a frequent event in human brain cancers, yet the pathologic significance of this expression remains undetermined. Here, we show that a glioblastoma-associated, ligand-independent rearrangement product of ROS (FIG-ROS) cooperates with loss of the tumor suppressor gene locus Ink4a;Arf to produce glioblastomas in the mouse. We show that this FIG-ROS-mediated tumor formation in vivo parallels the activation of the tyrosine phosphatase SH2 domain-containing phosphatase-2 (SHP-2) and a phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin signaling axis in tumors and tumor-derived cell lines. We have established a fully penetrant preclinical model for adult onset of glioblastoma multiforme in keeping with major genetic events observed in the human disease. These findings provide novel and important insights into the role of ROS and SHP-2 function in solid tumor biology and set the stage for preclinical testing of targeted therapeutic approaches.

The role of Ret receptor tyrosine kinase in dopaminergic neuron development

Glial cell line-derived neurotrophic factor (GDNF) is one of the most potent trophic factors identified for promoting survival and function of dopaminergic (DA) neurons in the midbrain. Ret, a member of the receptor tyrosine kinase (RTK) superfamily transduces GDNF signaling. The role of Ret in the development of DA neurons is not clear however. Here we demonstrate the involvement of Ret in the DA neuron development both in vitro and in vivo. The dopamine transporter (DAT) gene was clearly induced in rat embryonic neural precursors that had been transfected with Ret. Temporary blockade of Ret expression in embryos using Ret antisense oligonucleotides (Ret-AS-ODN) in vivo led to reduced striatal DA content and a decrease of tyrosine hydroxylase (TH) positive fibers in the striatum. Additionally, some DA neurons in the substantia nigra (SN) underwent apoptotic cell death following the Ret-AS-ODN treatment. Taken together, the data suggest that normal function of Ret is required in vivo for the maturation of DA neurons, in particular for cell survival and fiber innervation. We further demonstrated Ret-induced expression of DAT in vitro.

Integrins as a distinct subtype of dependence receptors

In the absence of their cognate ligand, dependence receptors trigger programmed cell death. This function is the defining feature of dependence receptors, which include members of several different protein families. The integrins are a family of heterodimeric receptors for extracellular matrix (ECM) proteins, mediating cell anchorage and migration. Integrins share characteristics with dependence receptors, and integrin binding to substrate ECM ligands is essential for cell survival. Although integrins do not conform in all characteristics to the established definitions of dependence receptors, alterations in the expression of integrins and their ligands during physiological and pathological events, such as wound healing, angiogenesis and tumorigenesis, do regulate cell fate in a ligand-dependent manner. This biosensory function of integrins fits well with our current concept of dependence receptor action, and thus integrins may rightly be considered to comprise a distinct subclass of dependence receptor.

Alterations in fetal kidney development and elevations in arterial blood pressure in young adult sheep after clinical doses of antenatal glucocorticoids

Epidemiologic studies have yielded controversial information regarding an association between antenatal steroid administration and elevations in arterial blood pressure (BP). The aim of the study was to determine whether antenatal administration of a clinically relevant dose of steroids at a time when fetal nephrogenesis is at its highest results in abnormal kidney development and adult hypertension. Pregnant sheep were treated with either vehicle or betamethasone. Maternal injections were given 24 h apart at 80 d of gestational age (dGA; 0.55 of gestation). Animals were studied either as fetuses or as immature adults. Fetuses were delivered by cesarean section at 135 dGA. Adults were studied at 6 mo of age. Betamethasone administration did not induce premature labor or intrauterine growth restriction. In the betamethasone-exposed group, we found at 135 dGA a 25.5% decrease in the number of glomeruli with no differences in fetal kidney weight. In adults, mean, systolic, and diastolic arterial BPs were significantly higher, whereas there were no significant differences in heart rate over the same study period. The major finding of this study is that a single course of antenatal steroids alters renal development and is associated with elevations in arterial BP in lambs at 6 mo of age. We conclude that antenatal glucocorticoid administration under the National Institutes of Health consensus guidelines may alter human fetal renal development.

Spatiotemporal regulation of morphogenetic molecules during in vitro branching of the isolated ureteric bud: toward a model of branching through budding in the developing kidney

In search of guiding principles involved in the branching of epithelial tubes in the developing kidney, we analyzed branching of the ureteric bud (UB) in whole kidney culture as well as in isolated UB culture independent of mesenchyme but in the presence of mesenchymally derived soluble factors. Microinjection of the UB lumen (both in the isolated UB and in the whole kidney) with fluorescently labeled dextran sulfate demonstrated that branching occurred via smooth tubular epithelial outpouches with a lumen continuous with that of the original structure. Epithelial cells within these outpouches cells were wedge-shaped with actin, myosin-2 and ezrin localized to the luminal side, raising the possibility of a "purse-string" mechanism. Electron microscopy and decoration of heparan sulfates with biotinylated FGF2 revealed that the basolateral surface of the cells remained intact, without the type of cytoplasmic extensions (invadopodia) that are seen in three-dimensional MDCK, mIMCD, and UB cell culture models of branching tubulogenesis. Several growth factor receptors (i.e., FGFR1, FGFR2, c-Ret) and metalloproteases (i.e., MT1-MMP) were localized toward branching UB tips. A large survey of markers revealed the ER chaperone BiP to be highly expressed at UB tips, which, by electron microscopy, are enriched in rough endoplasmic reticulum and Golgi, supporting high activity in the synthesis of transmembrane and secretory proteins at UB tips. After early diffuse proliferation, proliferating and mitotic cells were mostly found within the branching ampullae, whereas apoptotic cells were mostly found in stalks. Gene array experiments, together with protein expression analysis by immunoblotting, revealed a differential spatiotemporal distribution of several proteins associated with epithelial maturation and polarization, including intercellular junctional proteins (e.g., ZO-1, claudin-3, E-cadherin) and the subapical cytoskeletal/microvillar protein ezrin. In addition, Ksp-cadherin was found at UB ampullary cells next to developing outpouches, suggesting a role in epithelial-mesenchymal interactions. These data from the isolated UB culture system support a model where UB branching occurs through outpouching possibly mediated by wedge-shaped cells created through an apical cytoskeletal purse-string mechanism. Additional potential mechanisms include (1) differential localization of growth factor receptors and metalloproteases at tips relative to stalks; (2) creation of a secretory epithelium, in part manifested by increased expression of the ER chaperone BiP, at tips relative to stalks; (3) after initial diffuse proliferation, coexistence of a balance of proliferation vs. apoptosis favoring tip growth with a very different balance in elongating stalks; and (4) differential maturation of the tight and adherens junctions as the structures develop. Because, without mesenchyme, both lateral and bifid branching occurs (including the ureter), the mesenchyme probably restricts lateral branching and provides guidance cues in vivo for directional branching and elongation as well as functioning to modulate tubular caliber and induce differentiation. Selective cadherin, claudin, and microvillar protein expression as the UB matures likely enables the formation of a tight, polarized differentiated epithelium. Although, in vivo, metanephric mesenchyme development occurs simultaneously with UB branching, these studies shed light on how (mesenchymally derived) soluble factors alone regulate spatial and temporal expression of morphogenetic molecules and processes (proliferation, apoptosis, etc.) postulated to be essential to the UB branching program as it forms an arborized structure with a continuous lumen.

Update of extracellular matrix, its receptors, and cell adhesion molecules in mammalian nephrogenesis

One of the hallmarks of mammalian nephrogenesis includes a mesenchymal-epithelial transition that is accomplished by intercalation of the ureteric bud, an epithelium-lined tubelike structure, into an undifferentiated mesenchyme, and the latter then undergoes an inductive transformation and differentiates into an epithelial phenotype. At the same time, the differentiating mesenchyme reciprocates by inducing branching morphogenesis of the ureteric bud, which forms a treelike structure with dichotomous iterations. These reciprocal inductive interactions lead to the development of a functioning nephron unit made up of a glomerulus and proximal and distal tubules. The inductive interactions and differentiation events are modulated by a number of transcription factors, protooncogenes, and growth factors and their receptors, which regulate the expression of target morphogenetic modulators including the ECM, integrin receptors, and cell adhesion molecules. These target macromolecules exhibit spatiotemporal and stage-specific developmental regulation in the metanephros. The ECM molecules expressed at the epithelial-mesenchymal interface are perhaps the most relevant and conducive to the paracrine-juxtacrine interactions in a scenario where the ligand is expressed in the mesenchyme while the receptor is located in the ureteric bud epithelium or vice versa. In addition, expression of the target ECM macromolecules is regulated by matrix metalloproteinases and their inhibitors to generate a concentration gradient at the interface to further propel epithelial-mesenchymal interactions so that nephrogenesis can proceed seamlessly. In this review, we discuss and update our current understanding of the role of the ECM and related macromolecules with respect to metanephric development.

Gene and protein expression in the epididymis of infertile c-ros receptor tyrosine kinase-deficient mice

Transgenic male mice bearing inactive mutations of the receptor tyrosine kinase c-ros lack the initial segment of the epididymis and are infertile. Several techniques were applied to determine differences in gene expression in the epididymal caput of heterozygous fertile (HET) and infertile homozygous knockout (KO) males that may explain the infertility. Complementary DNA arrays, gene chips, Northern and Western blots, and immunohistochemistry indicated that some proteins were downregulated, including the initial segment/proximal caput-specific genes c-ros, cystatin-related epididymal-spermatogenic (CRES), and lipocalin mouse epididymal protein 17 (MEP17), whereas other caput-enriched genes (glutathione peroxidase 5, a disintegrin and metalloproteinase [ADAM7], bone morphogenetic proteins 7 and 8a, A-raf, CCAAT/enhancer binding protein beta, PEA3) were unchanged. Genes normally absent from the initial segment (gamma-glutamyltranspeptidase, prostaglandin D2 synthetase, alkaline phosphatase) were expressed in the undifferentiated proximal caput of the KO. More distally, lipocalin 2 (24p3), CRISP1 (formerly MEP7), PEBP (MEP9), and mE-RABP (MEP10) were unchanged in expression. Immunohistochemistry and Western blots confirmed the absence of CRES in epididymal tissue and fluid and the continued presence of CRES in spermatozoa of the KO mouse. The glutamate transporters EAAC1 (EAAT3) and EAAT5 were downregulated and upregulated, respectively. The genes of over 70 transporters, channels, and pores were detected in the caput epididymidis, but in the KO, only three were downregulated and six upregulated. The changes in these genes could affect sperm function by modifying the composition of epididymal fluid and explain the infertility of the KO males. These genes may be targets for a posttesticular contraceptive.

Renal development in high-glucose ambience and diabetic embryopathy

Maternal diabetes has an adverse influence on the intrauterine growth of the fetus, which is attributable to the exposure of the mammalian embryo to an abnormal metabolic environment. A sustained exposure of the fetus to such an environment (ie, elevated concentration of glucose), during the first 6 to 8 weeks of gestation in humans may result in diabetic embryopathy, which is characterized by a multitude of congenital birth defects, including those of the nervous, cardiovascular, skeletal, and urogenital systems. The urogenital abnormalities may be associated with caudal regression syndrome or may occur alone in the form of partial or total renal agenesis. Similarly, an increase in the incidence of morphogenetic defects is observed in offsprings of streptozotocin-induced diabetic rats and mice and also in nonobese diabetic mice. In certain instances, failure in the growth of lower part of embryos or newborn mice has been observed in animals with a severe diabetic state. For further delineation of the mechanisms involved in the pathogenesis of diabetic embryopathy, the investigators used whole-embryo culture systems, and found that glucose can induce defects mainly confined to the lower part of the body involving the genitourinary system. Similarly, dysmorphogenesis of the embryonic metanephros is observed when it is subjected to high concentrations of D-glucose and its epimer D-mannose. This article discusses certain aspects of diabetic embryopathy with an emphasis on changes that occur in the fetal metanephros in high-glucose ambience.

Oncogenic targeting of an activated tyrosine kinase to the Golgi apparatus in a glioblastoma

Activating oncogenic mutations of receptor tyrosine kinases (RTKs) have been reported in several types of cancers. In many cases, genomic rearrangements lead to the fusion of unrelated genes to the DNA coding for the kinase domain of RTKs. All RTK-derived fusion proteins reported so far display oligomerization sequences within the 5' fusion partners that are responsible for oncogenic activation. Here, we report a mechanism by which an altered RTK gains oncogenic potential in a glioblastoma cell line. A microdeletion on 6q21 results in the fusion of FIG, a gene coding for a Golgi apparatus-associated protein, to the kinase domain of the protooncogene c-ROS. The fused protein product FIG-ROS is a potent oncogene, and its transforming potential resides in its ability to interact with and become localized to the Golgi apparatus. Thus we have found a RTK fusion protein whose subcellular location leads to constitutive kinase activation and results in oncogenic transformation.

Morphogenesis during mouse embryonic kidney explant culture

BACKGROUND

Renal organogenesis is routinely studied using cultured murine embryonic kidneys, but the application of this model has not yet been subjected to rigorous standards.

METHODS

We measured ex vivo growth and morphogenesis of day 13 murine kidneys and evaluated the importance of culture conditions and biological variables.

RESULTS

Kidney size was measured in two dimensions as planar surface area and was shown to correlate highly with volume (R2 = 0.60, P < 0.005). The final surface area of kidneys was directly dependent on the initial starting size (R2 = 0.61, P < 0.05), suggesting that the final surface area is not a valid outcome measurement unless starting size is equal among treatments. Relative growth rate, defined as (final surface area - initial surface area)/initial surface area, was a good measure of growth and independent of size and anatomical position (P> 0.05). Significant differences in size and growth rates were observed among litters (P < 0.05), implying that kidneys from a given litter must be randomized to avoid confounding results. Planar surface area of each explant increased in proportion to ureteric bud branching (R2 = 0.6854, P < 0.05). In a comparison of a variety of base media and supplements, kidney explants were observed to grow best in Dulbecco's modified Eagle's medium (DMEM)/F12 with 5% fetal bovine serum and to sustain growth for up to 96 hours, despite decreased proliferation and increased apoptosis at this time point.

CONCLUSIONS

These results represent an important step in establishing standardized procedures for the use of cultured embryonic kidneys and will improve our ability to apply the model to better understand kidney morphogenesis.

SBA-positive fibers between the CD ampulla, mesenchyme, and renal capsule

During kidney development, the CD shows two peculiarities. First, the tip of the CD ampulla is always found at a specific distance from the organ capsule. Second, the CD growth occurs as a perfectly straight elongation. It is unknown whether the CD-specific growth is dependent on hormonal action or on structural elements. Histochemical experiments on neonatal rabbit kidney yielded new insight into the interface of the CD ampulla and the surrounding nephrogenic mesenchyme. Incubation of tissue sections with soybean lectin (SBA) showed the existence of fibers extending in a radial course from the ampullar tip through the mesenchyme toward the organ capsule. SBA labeling did not colocalize with collagen type I, III, IV, V, and VI, laminin, fibronectin, and tenascin. It is assumed that while the kidney increases in volume the structural fixation of the ampullar tip by the SBA-positive fibers causes CD ampullae to maintain a constant distance from the organ capsule. The connection would explain the linear extension of the CD in relation to the organ capsule. In addition, the presented data suggest that the SBA-positive fibers between ampullar tip and organ capsule create a structural microcompartmentation of the nephrogenic zone.

Developmental expression and biochemical characterization of Emu family members

Kidney development has often served as a model for epithelial-mesenchymal cell interaction where the branching epithelium of the ureteric bud induces the metanephrogenic mesenchyme to form epithelial nephrons. In a screen for genes differentially expressed during kidney development, we have identified a novel gene that is dynamically expressed in the branching ureter and the developing nephrons. It was designated Emu1 since it shares an N-terminal cysteine-rich domain with Emilin1/2 and Multimerin. This highly conserved EMI domain is also found in another novel protein (Emu2) of similar protein structure: an N-terminal signal peptide followed by the EMI domain, an interrupted collagen stretch, and a conserved C-terminal domain of unknown function. We identified two further secreted EMI domain proteins, prompting us to compare their gene and protein structures, the EMI domain phylogeny, as well as the embryonic expression pattern of known (Emilin1/2, Multimerin) and novel (Emu1/2, Emilin3, Multimerin2) Emu gene family members. Emu1 and Emu2 not only show a similar structural organization, but furthermore a striking complementary expression in organs developing through epithelial-mesenchymal interactions. In these tissues, Emu1 is restricted to epithelial and Emu2 to mesenchymal cells. Preliminary biochemical analysis of Emu1/2 confirmed that they are secreted glycoproteins which are attached to the extracellular matrix and capable of forming homo- and heteromers via disulfide bonding. The widespread, but individually distinct expression patterns of all Emu gene family members suggest multiple functions during mouse embryogenesis. Their multidomain protein structure may indicate that Emu proteins interact with several different extracellular matrix components and serve to connect and integrate the function of multiple partner molecules.

Erk MAP kinase regulates branching morphogenesis in the developing mouse kidney

Branching morphogenesis of epithelium is a common and important feature of organogenesis; it is, for example, responsible for development of renal collecting ducts, lung airways, milk ducts of mammary glands and seminal ducts of the prostate. In each case, epithelial development is controlled by a variety of mesenchyme-derived molecules, both soluble (e.g. growth factors) and insoluble (e.g. extracellular matrix). Little is known about how these varied influences are integrated to produce a coherent morphogenetic response, but integration is likely to be achieved at least partly by cytoplasmic signal transduction networks. Work in other systems (Drosophila tracheae, MDCK models) suggests that the mitogen-activated protein (MAP) kinase pathway might be important to epithelial branching. We have investigated the role of the MAP kinase pathway in one of the best characterised mammalian examples of branching morphogenesis, the ureteric bud of the metanephric kidney. We find that Erk MAP kinase is normally active in ureteric bud, and that inhibiting Erk activation with the MAP kinase kinase inhibitor, PD98059, reversibly inhibits branching in a dose-dependent manner, while allowing tubule elongation to continue. When Erk activation is inhibited, ureteric bud tips show less cell proliferation than controls and they also produce fewer laminin-rich processes penetrating the mesenchyme and fail to show the strong concentration of apical actin filaments typical of controls; apoptosis and expression of Ret and Ros, are, however, normal. The activity of the Erk MAP kinase pathway is dependent on at least two known regulators of ureteric bud branching; the GDNF-Ret signalling system and sulphated glycosaminoglycans. MAP kinase is therefore essential for normal branching morphogenesis of the ureteric bud, and lies downstream of significant extracellular regulators of ureteric bud development.

Role of membrane-type matrix metalloproteinase 1 (MT-1-MMP), MMP-2, and its inhibitor in nephrogenesis

Extracellular matrix (ECM) proteins, their integrin receptors, and matrix metalloproteinases (MMPs), the ECM-degrading enzymes, are believed to be involved in various biological processes, including embryogenesis. In the present study, we investigated the role of membrane type MMP, MT-1-MMP, an activator pro-MMP-2, in metanephric development. Also, its relationship with MMP-2 and its inhibitor, TIMP-2, was studied. Since mRNAs of MT-1-MMP and MMP-2 are respectively expressed in the ureteric bud epithelia and mesenchyme, they are ideally suited for juxtacrine/paracrine interactions during renal development. Northern blot analyses revealed a single approximately 4.5-kb mRNA transcript of MT-1-MMP, and its expression was developmentally regulated. Inclusion of MT-1-MMP antisense oligodeoxynucleotide (ODN) in the culture media induced dysmorphogenetic changes in the embryonic metanephros. MMP-2 antisense ODN also induced similar changes, but they were relatively less; on the other hand TIMP-2 antisense ODN induced a mild increase in the size of explants. Concomitant exposure of MT-1-MMP and MMP-2 antisense ODNs induced profound alterations in the metanephroi. Treatment of TIMP-2 antisense ODN to metanephroi exposed to MT-1-MMP/MMP-2 antisense notably restored the morphology of the explants. Specificity of the MT-1-MMP antisense ODN was reflected in the selective decrease in its mRNA and protein expression. The MT-1-MMP antisense ODN also resulted in a failure in the activation of pro-MMP-2 to MMP-2. These findings suggest that the trimacromolecular complex of MT-1-MMP:MMP-2:TIMP-2 modulates the organogenesis of the metanephros, conceivably by mediating paracrine/juxtacrine epithelial:mesenchymal interactions.

Embryonic renal epithelia: induction, nephrogenesis, and cell differentiation

Embryonic metanephroi, differentiating into the adult kidney, have come to be a generally accepted model system for organogenesis. Nephrogenesis implies a highly controlled series of morphogenetic and differentiation events that starts with reciprocal inductive interactions between two different primordial tissues and leads, in one of two mainstream processes, to the formation of mesenchymal condensations and aggregates. These go through the intricate process of mesenchyme-to-epithelium transition by which epithelial cell polarization is initiated, and they continue to differentiate into the highly specialized epithelial cell populations of the nephron. Each step along the developmental metanephrogenic pathway is initiated and organized by signaling molecules that are locally secreted polypeptides encoded by different gene families and regulated by transcription factors. Nephrogenesis proceeds from the deep to the outer cortex, and it is directed by a second, entirely different developmental process, the ductal branching of the ureteric bud-derived collecting tubule. Both systems, the nephrogenic (mesenchymal) and the ductogenic (ureteric), undergo a repeat series of inductive signaling that serves to organize the architecture and differentiated cell functions in a cascade of developmental gene programs. The aim of this review is to present a coherent picture of principles and mechanisms in embryonic renal epithelia.

Tubulointerstitial nephritis antigen: an extracellular matrix protein that selectively regulates tubulogenesis vs. glomerulogenesis during mammalian renal development

Tubulointerstitial nephritis antigen (TIN-ag) is an extracellular matrix protein and is expressed in the renal tubular basement membranes. Its role in metanephric development was investigated. TIN-ag cDNA, isolated from the newborn mouse library, had an ORF of 1,425 nucleotides, a putative signal sequence, and an ATP/GTP-binding site. The translated sequence had approximately 80% identity with rabbit TIN-ag. Among various tissues, TIN-ag mRNA was primarily expressed in the newborn kidney. In the embryonic metanephros, TIN-ag expression was confined to the distal convolution or pole of the S-shaped body, the segment of the nascent nephron that is the progenitor of renal tubules. Treatment with TIN-ag antisense oligodeoxynucleotide induced dysmorphogenesis of the embryonic metanephroi, malformation of the S-shaped body, and a decrease in the tubular population, whereas the glomeruli were unaffected. Treatment also led to a decrease of TIN-Ag mRNA, de novo synthesis of TIN-ag protein, and its antibody reactivity. The mRNA expression of glomerular epithelial protein 1 (a marker for renal podocytes), anti-heparan-sulfate-proteoglycan antibody reactivity, and wheat germ agglutinin lectin staining of the metanephros were unaffected. The anti-TIN-ag antibody treatment also caused deformation of the S-shaped body and a reduction in the tubular population, whereas the glomeruli were unchanged. The data suggest that the TIN-ag, unlike other basement membrane proteins, selectively regulates tubulogenesis, whereas glomerulogenesis is largely unaffected.

Cloning of rat fibrillin-2 cDNA and its role in branching morphogenesis of embryonic lung

Fibrillin-2 is an extracellular matrix protein. It is associated with elastic fibers in several tissues and is believed to serve as a ligand for alphavbeta3 integrin, the latter being a known morphogen. In this study, the role of fibrillin-2 in lung development was investigated. Also, rat fibrillin-2 cDNA was isolated and sequenced and its spatiotemporal expression determined. It had approximately 88% homology with human fibrillin-2 and had Ca(2+) binding epidermal growth factor-like domains, transforming growth factor-beta binding protein motifs, and two RGD binding sites. Northern blot analysis revealed an approximately 10-kb transcript, and fibrillin-2 expression was developmentally regulated, and it paralleled that of tropoelastin. At day 13 of gestation, fibrillin-2 was expressed in the mesenchyme and at the epithelial:mesenchymal interface. From day 13 to 19 of gestation, its expression intensified and was confined around the tracheobronchial airways, while it lessened during the postnatal period. Immunoprecipitation revealed an approximately 350-kDa band by SDS-PAGE. Treatment with fibrillin-2 antisense oligodeoxynucleotide induced dysmorphogenesis of the lung explants. They were smaller and had rudimentary lung bud branches, collapsed conducting airways, and loose expanded mesenchyme. Concomitantly, fibrillin-2 mRNA, antibody reactivity in the explants, and fibrillin-2-specific radioincorporation were reduced. Anti-alphav and -laminin antibody reactivity and their respective incorporated specific radioactivities were unaltered. These data indicate that fibrillin-2 modulates organogenesis of the lung in the context of epithelial:mesenchymal interactions. Conceivably, the collapse of the conducting airways may also be related to the perturbed biology of the fibrillin-2 interacting protein, i.e., elastin, the latter being critical for the normal biophysiology of the lungs.

Branching morphogenesis independent of mesenchymal-epithelial contact in the developing kidney

Whether mesenchymal-epithelial interactions leading to branching morphogenesis in developing epithelial tissues such as the kidney require direct cell-cell contact or are due to soluble mediators elaborated by the inducing tissue has been the subject of much debate. Here we demonstrate that ureteric bud (UB) epithelium, from which the kidney collecting system and upper urinary tract are derived, can undergo impressive three-dimensional branching morphogenesis when cultured in the appropriate extracellular matrix context in the absence of direct contact with mesenchymal tissue, indicating that the program for branching morphogenesis is inherent to the UB. Both a soluble factor in BSN cell-conditioned medium (BSN-CM) derived from an immortalized cell line thought to originate in the early metanephric mesenchyme and glial cell line-derived neurotrophic factor (GDNF) were required for early and later events in branching morphogenesis. In the absence of BSN-CM, the isolated UB did not survive; a similar result was obtained in the presence of neutralizing antibodies against glial cell line-derived neurotrophic factor. Preliminary analysis of key activity present in BSN-CM indicates that it is a heat-sensitive, heparin-binding factor with a probable molecular mass greater than 100 kDa. When the in vitro cultured UB was recombined with freshly isolated metanephric mesenchyme, nephric units were induced in the mesenchyme, and the UB branches underwent elongation. Our data suggest that, although UB branching morphogenesis per se does not require direct mesenchymal contact, such contact may play a key role in regulating branch elongation and establishing the pattern of branching. The results also suggest an approach to in vitro engineering of nephron.

Hirschsprung disease and other enteric dysganglionoses

Hirschsprung disease has become a paradigm for multigene disorders because the same basic phenotype is associated with mutations in at least seven distinct genes. As such, the condition poses distinct challenges for clinicians, patients, diagnostic pathologists, and basic scientists, who must cope with the implications of this genetic complexity to comprehend the pathogenesis of the disorder and effectively manage patients. This review focuses on the anatomic pathology, genetics, and pathogenesis of Hirschsprung disease and related conditions. The nature and functions of "Hirschsprung disease genes" are examined in detail and emphasis is placed on the importance of animal models to this field. Where possible, potential uses and limitations of new data concerning molecular genetics and pathogenesis are discussed as they relate to contemporary medical practices.

Caspase activity is required for nephrogenesis in the developing mouse metanephros

Programmed cell death is a mechanism through which organisms get rid of unwanted cells and is thought to be an important process in organogenesis. Although large-scale cell death is observed in the developing kidney, the precise roles of cell death in kidney organogenesis remain to be elucidated. To address this question, we prevented cell death in metanephric explants by applying caspase inhibitors. Administration of caspase inhibitors (Z-D-CH2DCB and Ac-DEVD-CHO) effectively prevented the cell death that is normally observed in nondifferentiating mesenchymal cells. Both ureteric bud branching and nephrogenesis were prevented by caspase inhibition. Our results suggest that caspases are crucial in kidney organogenesis and cell death in the nondifferentiating mesenchyme.

Molecular regulation of nephron endowment

Recent data suggests that the number of nephrons in normal adult human kidneys ranges from approximately 300,000 to more than 1 million. There is increasing evidence that reduced nephron number, either inherited or acquired, is associated with the development of essential hypertension, chronic renal failure, renal disease in transitional indigenous populations, and possibly the long-term success of renal allografts. Three processes ultimately govern the number of nephrons formed during the development of the permanent kidney (metanephros): branching of the ureteric duct in the metanephric mesenchyme; condensation of mesenchymal cells at the tips of the ureteric branches; and conversion of the mesenchymal condensates into epithelium. This epithelium then grows and differentiates to form nephrons. In recent years, we have learned a great deal about the molecular regulation of these three central processes and hence the molecular regulation of nephron endowment. Data has come from studies on cell lines, isolated ureteric duct epithelial cells, isolated metanephric mesenchyme, and whole metanephric organ culture, as well as from studies of heterozygous and homozygous null mutant mice. With accurate and precise methods now available for estimating the total number of nephrons in kidneys, more advances in our understanding of the molecular regulation of nephron endowment can be expected in the near future.

Ganglioneuromas and renal anomalies are induced by activated RET(MEN2B) in transgenic mice

Multiple endocrine neoplasia type 2B (MEN2B) is an autosomal dominant syndrome characterized by the development of medullary thyroid carcinoma, pheochromocytomas, musculoskeletal anomalies and mucosal ganglioneuromas. MEN2B is caused by a specific mutation (Met918-->Thr) in the RET receptor tyrosine kinase. Different mutations of RET lead to other conditions including MEN2A, familial medullary thyroid carcinoma and intestinal aganglionosis (Hirschsprung disease). Transgenic mice were created using the dopamine beta-hydroxylase promoter to direct expression of RET(MEN2B) in the developing sympathetic and enteric nervous systems and the adrenal medulla. DbetaH-RET(MEN2B) transgenic mice developed benign neuroglial tumors, histologically identical to human ganglioneuromas, in their sympathetic nervous systems and adrenal glands. The enteric nervous system was not affected. The neoplasms in DbetaH-RET(MEN2B) mice were similar to benign neuroglial tumors induced in transgenic mice by activated Ras expression under control of the same promoter. Levels of phosphorylated MAP kinase were not increased in the RET(MEN2B)-induced neurolglial proliferations, suggesting that alternative pathways may play a role in the pathogenesis of these lesions. Transgenic mice with the highest levels of DbetaH-RET(MEN2B) expression, unexpectedly developed renal malformations analogous to those reported with loss of function mutations in the Ret gene.

Relevance of extracellular matrix, its receptors, and cell adhesion molecules in mammalian nephrogenesis

Mammalian nephrogenesis begins by the reciprocal interaction of the ureteric bud with the undifferentiated mesenchyme. The mesenchyme differentiates into an epithelial phenotype with the development of the glomerulus and proximal and distal tubules. At the same time, the mesenchyme stimulates the branching morphogenesis of the ureteric bud that differentiates into the collecting ducts. These inductive interactions and differentiation events are modulated by a number of macromolecules, including the extracellular matrix (ECM), integrin receptors, and cell adhesion molecules. Many of these macromolecules exhibit spatiotemporal developmental regulation in the metanephros. Some are expressed in the mesenchyme, whereas others appear in the ureteric bud epithelia. The molecules expressed in the mesenchyme or at the epithelial:mesenchymal interface may serve as ligands while those in the epithelia serve as the receptors. In such a scenario the ligand and the receptor would be ideally suited for epithelial:mesenchymal paracrine/juxtacrine interactions that are also influenced by RGD sequences and Ca2+ binding domains of the ECM proteins and their receptors. This review addresses the role of such interactions in metanephric development.

Growth factors in metanephric development

During embryonic life, renal morphogenesis is characterized by a defined period of intense cellular activity, inductive-transformation of undifferentiated cells to polarized epithelia, in-growth of capillaries into an intricate parenchymal epithelial-mesenchymal mass, and finally the maturation into an organ with diverse structural and biological functions. It should be emphasized that the interactions between various growth factors and their receptors, FCM glycoproteins and proto-oncogenes are required for proper epithelial: mesenchymal interactions essential to the process of nephrogenesis. A balance between the activities of these macromolecules, whether essential or redundant, is needed to orchestrate the proper cell signals and responses to assure the progression of normal organogenesis. Finally, in spite of the enormous wealth of data in the literature, the process of renal development is so complex that a clear picture has yet to emerge of the precise coordinated and sequential events that result in the formation of a mature functioning kidney.

The tip-top branching ureter

Organ rudiments with their epithelial bud and adjacent mesenchyme look much the same at their initial stage of differentiation. The subsequent branching of the epithelial anlagen determines the final pattern of the organs, but the mesenchyme provides essential signals for epithelial differentiation. Glial cell line derived neurotrophic factor (GDNF) has recently been shown to regulate ureteric branching morphogenesis and is thereby the first defined signalling molecule in the embryonic metanephric kidney. GDNF is expressed by the mesenchyme, binds to the tip of the ureteric bud and functions in both bud induction and bud orientation. The active receptor complex for GDNF includes the receptor tyrosine kinase Ret and a novel class of glycosylphosphatidylinositol-linked receptors, called GDNF family receptor alpha s.

Glial-cell-line-derived neurotrophic factor is required for bud initiation from ureteric epithelium

The shapes of different organs can be explained largely by two fundamental characteristics of their epithelial rudiments - the pattern of branching and the rate of proliferation. Glial-cell-line-derived neurotrophic factor (GDNF) has recently been implicated in the development of metanephric ureteric epithelium (Pichel, J. G., Shen, L., Sheng, H. Z., Granholm, A.-C., Drago, J., Grinberg, A., Lee, E. J., Huang, S. P., Saarma, M., Hoffer, B.J., Sariola, H. and Westphal, H. (1996). Nature 382, 73–76; Sanchez, M.P., Silos-Santiago, I., Frisen, J., He, B., Lira, S.A. and Barbacid, M. (1996). Nature 382, 70–73; Vega, Q.C., Worby, C.A., Lechner, M.S., Dixon, J.E. and Dressler, G.R. (1996). Proc. Nat. Acad. Sci. USA 93, 10657–10661). We have analysed the target cells of GDNF and the manner in which it controls ureteric development, and have compared it with other growth factors that have been associated with the regulation of branching morphogenesis, namely hepatocyte growth factor (HGF) and transforming growth factor-beta1 (TGFbeta1). We show that GDNF binds directly to the tips of ureteric bud branches, and that it has the ability to promote primary ureteric buds from various segments of Wolffian duct and to attract ureteric branches towards the source of GDNF. It increases cell adhesion, but is not obviously mitogenic for ureteric cells. The data indicate that GDNF is required primarily for bud initiation. Comparison of GDNF, HGF and TGFbeta1 suggests that the latter act later than GDNF, and may represent a partially redundant set of mesenchyme-derived growth factors that control ureteric development. Thus, GDNF is the first defined inducer in the embryonic metanephric kidney.

Developmental regulation and partial-length cloning of tubulointerstitial nephritis antigen of murine metanephros

Tubulointerstitial nephritis antigen (TIN-ag) is an extracellular matrix (ECM) glycoprotein that has been recently isolated and cloned from the rabbit kidney. It is an integral component of the basal lamina, and unlike other basement membrane proteins it is exclusively expressed in the tubular basement membranes (TBMs). Since other ECM glycoproteins have been shown to regulate development of various organ systems, studies were initiated to ascertain its developmental regulation in renal tubulogenesis and glomerulogenesis. Embryonic (day-13 and -17 of gestation), newborn and one-week-old mice kidneys were harvested for expression of TIN-ag as well as cDNA cloning studies. Immunostaining with polyclonal anti-TIN-ag antibody revealed its localization to the basal lamina of ureteric bud branches and epithelial elements of developing nephrons in day-13 embryonic kidneys. Interestingly, it was heavily expressed at the tips of the ureteric bud branches, and was not expressed in the distal convolutions of the S-shaped body stage of the nephrons, the region which forms the future glomerulus. At day-17, TIN-ag expression was less, and the immuno-reactivity was mainly localized to the cortex. In the newborn and one-week-old mice kidneys, the cortical expression of TIN-ag increased progressively, but was absent in the glomeruli. The TIN-ag expression was confined to the cortical TBMs, while absent in the medullary tubules, the latter included segments of the collecting ducts and loop of Henle. Immunoprecipitation studies on [35S]methionine-labeled metanephroi revealed a single band of approximately 58 kDa at day-13, and the incorporated radioactivity decreased at day-17. No high molecular weight isoforms were observed. A partial-length mouse TIN-ag cDNA of approximately 530 bp PCR product was generated, and it had approximately 88% and approximately 93% nucleotide and amino acid sequence homolgy, respectively, with rabbit TIN-ag. Utilizing this cDNA, Northern blot analyses revealed a single transcript of approximately 2 Kb in fetal and postnatal mice kidneys. mRNA expression initially decreased at day-17, and then progressively increased by one week. Utilizing a mouse TIN-ag riboprobe, in situ hybridization studies revealed a generalized diffuse expression of TIN-ag in the epithelial clements of developing nephrons and ureteric bud branches at day-13. Gene expression decreased by day-17, and became confined to the renal cortex, and then progressively increased during the neo- and post-natal periods, but remained absent in the renal medulla and glomeruli. These data indicate that TIN-ag is expressed in the metanephros early in embryonic life in the absence of any detectable isoforms, and it exhibits spatio-temporal characteristics during metanephric development. Being concentrated at the tips of the ureteric bud branches, it is conceivably involved in epithelial:mesenchymal interactions which are highly prevalent during renal organogenesis, and its role in tubulogenesis diverges from glomerulogenesis at the S-shaped body stage of the nephron.

Receptor protein tyrosine kinases in perinatal developing rat kidney

We have identified receptor protein tyrosine kinases (PTKs) that are expressed and/or activated during kidney development. mRNA from fetal rat kidneys in late gestation (embryonic day 21), was used to prepare a cDNA template for polymerase chain reaction amplification with primers based on conserved regions of PTKs, and products were subcloned and sequenced. Among 346 clones, we identified epidermal growth factor receptor (EGF-R), Tie-2, platelet-derived growth factor receptor (PDGF-R)-alpha, PDGF-R beta, Flk-1, Flt-4, fibroblast growth factor receptor (FGF-R)-1, FGF-R3, FGF-R4, Met, and RYK/Nbtk-1. PTK expression was studied by immunoprecipitation and immunoblotting of kidney membrane proteins with specific antibodies. EGF-R, PDGF-R alpha, FGF-R1, FGF-R3, Met, and in some cases Tie-2 protein expression was greater in fetal kidneys, as compared with kidneys from 12-week-old adult rats (controls). Flk-1, PDGF-R beta, and FGF-R4 proteins were expressed comparably, however, Flt-4 was not detected. As a reflection of receptor PTK activity, we assessed endogenous tyrosine phosphorylation, and in vitro autophosphorylation. EGF-R and PDGF-R alpha displayed activity in fetal, but not adult kidneys. FGF-R3 and Flk-1 were active in some fetal kidneys, and the other PTKs were not active. Thus, in late gestational rat kidney, there are distinct patterns of receptor PTK expression and activity. EGF-R, PDGF-R alpha, FGF-R3 and Flk-1 are among the PTKs that are activated, and they may mediate perinatal development of renal epithelial, interstitial, or vascular structures.

Developmental regulation and the role of insulin and insulin receptor in metanephrogenesis

The insulin family of peptides and their receptors influence cellular growth in very early preimplantation embryos. In this study their expression and role in renal organogenesis was investigated. By immunofluorescence microscopy and in situ hybridization, insulin receptor (IR) expression was seen in the ureteric bud branches and early nephron precursors in mouse metanephroi harvested at day 13 of gestation. The expression gradually decreased in successive stages of gestation, and it was confined mainly to renal tubules in 1-week-old mice. Similar developmental regulation of the IR and insulin was observed by reverse transcriptase-polymerase chain reaction (RT-PCR) analyses. Addition of insulin into the culture medium at low concentrations, ranging from 40 to 400 ng/ml, induced trophic changes and increased [3H]thymidine incorporation in the embryonic renal explants, and inclusion of IR beta-subunit-specific antisense oligodeoxynucleotide caused marked dysmorphogenesis and growth retardation of the metanephroi. Specificity of the antisense effect was reflected by immunoprecipitation experiments in which translational blockade of the beta subunit of the IR was observed. RT-PCR analyses revealed that the alpha subunit of the IR was unaffected by the antisense treatment of metanephric explants. Concomitantly, de novo synthesis of morphogenetic regulatory extracellular matrix proteins, especially the proteoglycans, was decreased. Gel-shift analyses indicated a failure in the activation of c-fos promoter region binding protein(s) by insulin in the antisense oligodeoxynucleotide-treated explants. These studies suggest that insulin and its putative receptor are developmentally regulated in the murine embryonic metanephros, and they play a role in renal organogenesis, possibly by affecting other modulators of morphogenesis-i.e., extracellular matrix proteins and protooncogenes.

Integrin alpha8beta1 is critically important for epithelial-mesenchymal interactions during kidney morphogenesis

We present genetic evidence that integrins regulate epithelial-mesenchymal interactions during organogenesis. Mice with a mutation in the alpha8 gene do not express the integrin alpha8 beta1 and exhibit profound deficits in kidney morphogenesis. In wild-type animals, inductive interactions between the ureteric epithelium and metanephric mesenchyme are essential for kidney morphogenesis. In alpha8 mutant homozygotes, growth and branching of the ureteric bud and recruitment of mesenchymal cells into epithelial structures are defective. Consistent with these phenotypes, alpha8 expression is induced in mesenchymal cells upon contact with the ureter. Since none of its previously identified ligands appears likely to mediate the essential functions of alpha8 beta1 in kidney morphogenesis, we have used an alpha8 beta1-alkaline phosphatase chimera to localize novel ligand(s) in the growing ureter. The distribution of these ligand(s) makes them strong candidates for regulators of kidney morphogenesis.