Metanephric rat-mouse chimeras to study cell lineage of the nephron

Tubular control of renin synthesis and secretion

The intratubular composition of fluid at the tubulovascular contact site of the juxtaglomerular apparatus serves as regulatory input for secretion and synthesis of renin. Experimental evidence, mostly from in vitro perfused preparations, indicates an inverse relation between luminal NaCl concentration and renin secretion. The cellular transduction mechanism is initiated by concentration-dependent NaCl uptake through the Na-K-2Cl cotransporter (NKCC2) with activation of NKCC2 causing inhibition and deactivation of NKCC2 causing stimulation of renin release. Changes in NKCC2 activity are coupled to alterations in the generation of paracrine factors that interact with granular cells. Among these factors, generation of PGE2 in a COX-2-dependent fashion appears to play a dominant role in the stimulatory arm of tubular control of renin release. [NaCl] is a determinant of local PG release over an appropriate concentration range, and blockade of COX-2 activity interferes with the NaCl dependency of renin secretion. The complex array of local paracrine controls also includes nNOS-mediated synthesis of nitric oxide, with NO playing the role of a modifier of the intracellular signaling pathway. A role of adenosine may be particularly important when [NaCl] is increased, and at least some of the available evidence is consistent with an important suppressive effect of adenosine at higher salt concentrations.

Kidney tissue reconstruction by fetal kidney cell transplantation: effect of gestation stage of fetal kidney cells

Dialysis and kidney transplantation, current therapies for kidney failure, have limitations such as severe complications, donor shortage, and immune-related problems. The development of an alternative treatment for kidney failure is demanded. The present study shows that the transplantation of fetal kidney cells reconstitutes functional kidney tissue, and that the gestation stage of kidney cells influences the kidney reconstitution. Fetal kidney cells were isolated from metanephroi of rat fetuses at various gestation stages and transplanted into the omentum or kidney of immunodeficient mice. Immunophenotype analysis of fetal kidney cells showed apparent expression of stem cell markers. Three weeks after transplantation, histological analyses of retrieved grafts revealed the formation of kidney structures, including fluorescently labeled transplanted cells, suggesting the potential of fetal kidney cells to reconstitute kidney tissues. The grafts retrieved from omentum contained cystic fluids with concentrated solutes. However, transplanted early fetal kidney cells had also differentiated into nonrenal tissues such as bone and cartilage. In addition, transplantation of fetal kidney cells from a later gestation stage resulted in poor kidney structure formation. Kidney-specific genes were strongly expressed in the earlier cell transplants. The cells at an earlier gestation stage had higher colony forming ability than the cells at a later stage. This study demonstrates the reconstitution of kidney tissue by transplanting fetal kidney cells and the presence of an optimal time window in which fetal kidney cells regenerate kidney tissues. Disclosure of potential conflicts of interest is found at the end of this article.

A method for cold storage and transport of viable embryonic kidney rudiments

Organ culture of mouse embryonic kidneys is a powerful system for studying normal renal development and for researching the developmental effects of experimental perturbations (drugs, antibodies, interfering RNA, and so on). In standard protocols, embryonic kidneys are isolated by delicate micro-dissection and placed in organ culture as soon as possible after the death of the donor mouse, before there is time to genotype them or to transport them elsewhere. This report demonstrates that fully viable embryonic kidneys can be isolated and cultured from crudely dissected caudal portions of embryos that have been stored on ice or at 4 degrees C for several days. This very simple technique can save considerable resources in laboratories that culture kidneys of transgenic mice: (i) cold storage allows embryos to be genotyped before their kidneys are cultured, and (ii) cold transport allows kidney research laboratories to study kidneys of transgenic mice raised elsewhere without the need for expensive importing of the mouse line itself. It will therefore substantially augment the ability of kidney research labs to perform pilot experiments on large numbers of different transgenic animals and to collaborate in new ways.

Characterization of Pax-2 regulatory sequences that direct transgene expression in the Wolffian duct and its derivatives

The Pax family of transcription factors plays important roles in vertebrate organogenesis. Pax-2 is a critical factor in the development of the mammalian urogenital system. Pax-2 is expressed in the epithelia of the ureter, the Müllerian duct, and the Wolffian duct and in the nephrogenic mesenchyme. Gene targeting in the mouse as well as natural mutations in mouse and man have demonstrated the requirement of Pax-2 in the development of these structures. Little is known about the molecular mechanisms regulating Pax-2 expression in the developing urogenital system. As a first step to reveal these mechanisms and to search for the elements and factors controlling Pax-2 expression we have characterized regulatory sequences of the Pax-2 gene in an in vivo reporter assay in the mouse. An 8.5-kb genomic region upstream of the Pax-2 transcription start site directed reporter gene activity in the epithelium of the pronephric duct at 8.25 days postcoitum (dpc) and in the Wolffian duct starting from 9.0 dpc. Expression in the Wolffian duct and its derivatives, the ureter, the collecting duct system, the seminal vesicles, the vas deferens, and the epididymis, was maintained at least until 18.5 dpc. Hence, an element(s) in the 8.5-kb upstream region is sufficient to initiate and maintain Pax-2 expression in the Wolffian duct and its derivatives. In order to more precisely map the Wolffian duct regulatory sequences, a deletion analysis of the 8.5-kb upstream region was performed in a transient in vivo reporter assay. A 0.4-kb subfragment was required for marker gene expression in the Wolffian duct. Misexpression of fgf8 under the control of the 8.5-kb upstream region resulted in polycystic kidneys, demonstrating the general usefulness of Pax-2 regulatory sequences in misexpression of foreign genes in the ureter and collecting duct system of the kidney in transgenic approaches in mice.

Novel expression and regulation of the renin-angiotensin system in metanephric organ culture

To evaluate the presence and regulation of the renin-angiotensin system (RAS) in metanephric organ culture, embryonic day 14 (E14) rat metanephroi were cultured for 6 days. mRNAs for renin and both ANG II receptors (AT(1) and AT(2)) are expressed at E14, and all three genes continue to be expressed in culture. Renin mRNA is localized to developing tubules and ureteral branches in the cultured explants. At E14, renin immunostaining is found in isolated cells scattered within the mesenchyme. As differentiation progresses, renin localizes to the ureteric epithelium, developing tubules and glomeruli. E14 metanephroi contain ANG II, and peptide production persists in culture. Renin activity is present at E14 (6.13 +/- 0.61 pg ANG I. kidney(-1). h(-1)) and in cultured explants (28.84 +/- 1. 13 pg ANG I. kidney(-1). h(-1)). Renin activity in explants is increased by ANG II treatment (70.1 +/- 6.36 vs. 40.97 +/- 1.94 pg ANG I. kidney(-1). h(-1) in control). This increase is prevented by AT(1) blockade, whereas AT(2) antagonism has no effect. These studies document an operational local RAS and a previously undescribed positive-feedback mechanism for renin generation in avascular, cultured developing metanephroi. This novel expression pattern and regulatory mechanism highlight the unique ability of developing renal cells to express an active RAS.

Kidney development branches out

For more than 40 years now, the developing kidney has served as a model paradigm for epithelial-mesenchymal interactions. The principles of inductive signaling, epithelial cell differentiation, and pattern formation are now being addressed with modern genetic and biochemical tools. In addition to the mammalian kidney organ culture model, both zebrafish and Xenopus laevis demonstrate great potential for investigating the molecular mechanisms of kidney organogenesis within a whole organism. In this review, the papers presented in this special issue are discussed with respect to recent progress in the renal development field. Coincidentally, it has become increasingly clear that progress made in renal development can impact our understanding of the genetic basis of disease.

Advances in renal development

Branching morphogenesis, mesenchymal cell condensation and mesenchymal-to-epithelial conversion are key steps in kidney development and morphogenesis of several other organs. Review articles describing our current knowledge of the genetic and molecular regulation of these processes have been published. Therefore, this review focuses on the important question of cell lineage specification during kidney development. We describe how new insights are being made into the specification of kidney cells in the intermediate mesoderm, as well as specification of cells that will form the renal mesenchyme, ureteric duct, nephron tubule epithelium and renal vasculature.