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International audience; Congenital abnormalities of the kidney and the urinary tract (CAKUT) belong to the most common birth defectsin human, but the molecular basis for the majority of CAKUT patients remains unknown. Here we show thatthe transcription factor SOX11 is a crucial regulator of kidney development. SOX11 is expressed in bothmesenchymal and epithelial components of the early kidney anlagen. Deletion of Sox11 in mice causes anextension of the domain expressing Gdnf within rostral regions of the nephrogenic cord and results in duplexkidney formation. On the molecular level SOX11 directly binds and regulates a locus control region of theprotocadherin B cluster. At later stages of kidney development, SOX11 becomes restricted to the intermediatesegment of the developing nephron where it is required for the elongation of Henle’s loop. Finally, mutationanalysis in a cohort of patients suffering from CAKUT identified a series of rare SOX11 variants, one of whichinterferes with the transactivation capacity of the SOX11 protein. Taken together these data demonstrate akey role for SOX11 in normal kidney development and may suggest that variants in this gene predispose toCAKUT in humans

Background: Specification of the metanephric mesenchyme is a central step of kidney development as this mesenchyme promotes nephric duct induction to form a ureteric bud near its caudal end. Before ureteric bud formation, the caudal nephric duct swells to form a pseudostratified epithelial domain that later emerges as the tip of the bud. However, the signals that promote the formation of the transient epithelial domain remain unclear. Here, we investigated the early roles of the mesenchymal factor Six family and its cofactor Eya on the initial induction of nephric duct development. Results: The nephrogenic progenitor population is initially present but significantly reduced in mice lacking both Six1 and Six4 and undertakes an abnormal cell death pathway to be completely eliminated by ∼E10.5–E11.0, similar to that observed in Eya1-/- embryos. Consequently, the nephric duct fails to be induced to undergo normal proliferation to pseudostratify and form the ureteric bud in Six1-/-;Six4-/- or Eya1-/- embryos. Conclusions: Our data support a model where Eya-Six may form a complex to regulate nephron progenitor cell development before metanephric specification and are critical mesenchymal factors for inducing nephric duct development. Developmental Dynamics 244:866–873, 2015. © 2015 Wiley Periodicals, Inc.

ROBO2 plays a key role in regulating ureteric bud (UB) formation in the embryo, with mutations in humans and mice leading to supernumerary kidneys. Previous studies have established that the number and position of UB outgrowths is determined by the domain of metanephric mesenchymal Gdnf expression, which is expanded anteriorly in Robo2 mouse mutants. To clarify how this phenotype arises, we used high-resolution 3D imaging to reveal an increase in the number of nephrogenic cord cells, leading to extension of the metanephric mesenchyme field in Robo2-null mouse embryos. Ex vivo experiments suggested a dependence of this effect on proliferative signals from the Wolffian duct. Loss of Robo2 resulted in a failure of the normal separation of the mesenchyme from the Wolffian duct/ureteric epithelium, suggesting that aberrant juxtaposition of these two compartments in Robo2-null mice exposes the mesenchyme to abnormally high levels of proliferative stimuli. Our data suggest a new model in which SLIT-ROBO signalling acts not by attenuating Gdnf expression or activity, but instead by limiting epithelial/mesenchymal interactions in the nascent metanephros and restricting the extent of the nephrogenic field. These insights illuminate the aetiology of multiplex kidney formation in human individuals with ROBO2 mutations.

Organogenesis requires the differentiation and integration of distinct populations of cells to form a functional organ. In the kidney, reciprocal interactions between the ureter and the nephrogenic mesenchyme are required for organ formation. Additionally, the differentiation and integration of stromal cells are also necessary for the proper development of this organ. Much remains to be understood regarding the origin of cortical stromal cells and the pathways involved in their formation and function. By generating triple mutants in the Hox10 paralogous group genes, we demonstrate that Hox10 genes play a critical role in the developing kidney. Careful examination of control kidneys show that Foxd1-expressing stromal precursor cells are first observed in a cap-like pattern anterior to the metanephric mesenchyme and these cells subsequently integrate posteriorly into the kidney periphery as development proceeds. While the initial cap-like pattern of Foxd1-expressing cortical stromal cells is unaffected in Hox10 mutants, these cells fail to become properly integrated into the kidney, and do not differentiate to form the kidney capsule. Consistent with loss of cortical stromal cell function, Hox10 mutant kidneys display reduced and aberrant ureter branching, decreased nephrogenesis. These data therefore provide critical novel insights into the cellular and genetic mechanisms governing cortical cell development during kidney organogenesis. These results, combined with previous evidence demonstrating that Hox11 genes are necessary for patterning the metanephric mesenchyme, support a model whereby distinct populations in the nephrogenic cord are regulated by unique Hox codes, and that differential Hox function along the AP axis of the nephrogenic cord is critical for the differentiation and integration of these cell types during kidney organogenesis.

During the third week of pregnancy, the process of gastrulation results in the formation of trilaminar embryo in humans. This is the beginning of morphogenesis (development of body form). Three germ layers, ectoderm, mesoderm, and endoderm, are present. A specific part of mesoderm, the intermediate mesoderm, gives rise to urogenital system gradually. It starts to develop from nephrogenic cord, which divides in nephrotomes. They give rise to pronephroi and subsequently mesonephroi, the transitory kidneys. Finally, metanephroi appear as the permanent organs, from two different structures: the metanephrogenic blastema (mesenchimal component) that leads to nephrons, and ureteric bud (epithelial component) that gives rise to collecting tubules, calices, renal pelvis, and ureter. Following developmental steps depend on inductive signaling between metanephrogenic blastema and ureteric bud. Many genes, regulating proteins and pathways are involved in the physiological organogenesis. Cell proliferation and apoptosis keep the balance of the growth. Defects in these molecular and morphogenetic mechanisms may cause various congenital abnormalities of the kidney and urinary tract (CAKUT), which represent a family of diseases with a diverse anatomical spectrum.

Publisher Summary This chapter focuses on various molecules involved in the regulation of metanephrogenesis. The chapter assigns specific cellular roles to molecules based on their null or misexpression phenotypes. Lim1 encodes a LIM domain containing homeobox protein that is expressed in the early lateral plate and intermediate mesoderm of most vertebrates. Although the expression pattern suggests that Lim1 may be involved in ureteric bud formation and tubulogenesis, at the moment, it can only be implicated in differentiation of the intermediate mesoderm. Eya1 is a member of a growing family of genes that are homologous to the Drosophila eyes absent (eya) gene. Eya1 plays an essential but limited role in the regulation of mesenchymal gene activity in response to MM determinants. Pax-2 encodes a paired box-containing transcription factor expressed in multiple embryonic tissues and is expressed in the nephrogenic cord at E8.5 and maintained in the mesonephric duct and tubules. Pax-2 is also expressed in the ureter, as it invades the metanephric anlage. In addition to its role in early nephrogenesis, antisense, and misexpression, Pax-2 may play a more general role in epithelialization.

The morphological changes produced in the mesonephric tubule during ontogenesis, not previously reported in amphibians, are described in Rana ridibunda tadpoles using light and electron microscopic methods. The rudimentary nephron units do not develop synchronously along the subperitoneal nephrogenic ridged cord. The first signs of morphogenesis are the presence of round euchromatinic nuclei and mitotic figures. The subsequent developmental stages are characterized by detachment of the rudimentary nephrons from the nephrogenic cord. Renal corpuscle formation is characterized by glomerular expansion, differentiation of large fenestrated capillaries and the presence of a discrete mesangium and a small capsular space. Interstitial capillaries next to the renal corpuscle rudiments appear to induce invagination and differentiation of the capsular epithelium. Developing podocytes were cuboidal undifferentiated epithelial cells with scarce primary processes and with an extensive part of the cell surface lying flat on the glomerular basement membrane. These features reflect low or no glomerular filtration during nephron development. The ciliated neck segment and peritoneal funnels show similar structural features. The latter were not physically connected with the nephrons, but opened into renal blood vessels. Involutive peritoneal funnels were observed.

Urogenital system development in mammals requires the coordinated differentiation of two distinct tissues, the ductal epithelium and the nephrogenic mesenchyme, both derived from the intermediate mesoderm of the early embryo. The former give rise to the genital tracts, ureters and kidney collecting duct system, whereas mesenchymal components undergo epithelial transformation to form nephrons in both the mesonephric (embryonic) and metanephric (definitive) kidney. Pax-2 is a transcriptional regulator of the paired-box family and is widely expressed during the development of both ductal and mesenchymal components of the urogenital system. We report here that Pax-2 homozygous mutant newborn mice lack kidneys, ureters and genital tracts. We attribute these defects to dysgenesis of both ductal and mesenchymal components of the developing urogenital system. The Wolffian and Müllerian ducts, precursors of male and female genital tracts, respectively, develop only partially and degenerate during embryogenesis. The ureters, inducers of the metanephros are absent and therefore kidney development does not take place. Mesenchyme of the nephrogenic cord fails to undergo epithelial transformation and is not able to form tubules in the mesonephros. In addition, we show that the expression of specific markers for each of these components is de-regulated in Pax-2 mutants. These data show that Pax-2 is required for multiple steps during the differentiation of intermediate mesoderm. In addition, Pax-2 mouse mutants provide an animal model for human hereditary kidney diseases.

The definitive opisthonephros of the adult lamprey, Petromyzon marinus L., develops during metamorphosis from the nephrogenic cord confined within a nephric fold and extending from the posterior tip of the larval opisthonephros to the cloaca. This development is initiated prior to the first signs of external metamorphosis and begins with the simultaneous appearance of clusters of cells scattered along the entire length of the cord. Proliferation of these cell clusters and their elongation to connect to the closely associated archinephric duct results in the formation of rudimentary nephron units. Subsequent development involves the formation of tubular lumina, branching of the tubules, and the participation of the proximal ends of the newly formed tubules in the formation of the single renal corpuscle. Growth in size of the kidney is the result of lengthening of the existing tubules through cell proliferation rather than through the addition of new nephrons. This growth appears to be at the expense of adipose tissue within the nephric fold. During later stages of metamorphosis, cell proliferation is more prevalent in the ventral part of the nephric fold where a parallel system of tubules develops. The development of the definitive opisthonephros during metamorphosis of lamprey may prove to be a useful model for further studies of tissue differentiation and interaction during kidney development in vertebrates.

Summary. The development and degeneration of the mesonephros of the sheep is described with particular reference to the curious glomerular structure occupying the cranial one-third of the organ and here referred to as the giant glomerulus. The giant glomerulus and in particular the cranial two tubules draining it on either side provide useful landmarks whereby corresponding regions may be compared at different ages. An attempt is made to analyse the factors which determine the form and relations of the definitive glomeruli and tubules. These factors include the early relations of the somitic stalks and nephrogenic cord, the precocity of growth and vascularization of the preglomerular tissue and the degree of overcrowding and overlapping of the tubule primordia. The cellular activities of the mesonephric tubules are described and discussed and the view is upheld that these are of a peculiar secretory nature. The processes occurring in degeneration are outlined and the absence of the massive cranial degeneration described by Felix in man is commented upon.

Embryonic mouse kidney mesenchymes of various ages were tested for their abilities to initiate and supportureteric bud morphogenesis in vitro. Nephrogenic cord mesenchyme taken from animals before metanephros initiation (10 days) was combined with ureteric buds. The buds showed no morphogenesis. This was true for presumptive metanephric mesenchyme and for mesenchymes (pronephric and mesonephric) already undergoing nephrogenesis. These results indicate basic physiological differences between pronephric, mesonephric and metanephric regions of the cord. When entire nephric systems were cultured alone no metanephros developed. This, and the fact that presumptive metanephric mesenchyme had no influence on ureteric buds, indicates that metanephros initiation (both bud and mesenchyme) results from some activity originating outside the nephrogenic cord. When combined with metanephric mesenchyme at various stages of tubulogenesis (loose, condensed, or tubular), ureteric buds branched only in the presence of the loose mesenchyme. Branching occurred in loose mesenchyme taken from 11 to 15 day kidneys. Apparently once a given group of cells begins tubulogenesis they lose their ability to induce ureteric bud morphogenesis. As tubulogenesis proceeds, the amount of loose mesenchymes per kidney decreases sharply. Ultimate size of the metanephros may be established by depletion of loose mesenchyme resulting in its ureteric bud-inducing potential falling below some critical level.

The development of the gonadal primitive medulla in embryonic chick gonads was studied with the light microscope, using serial longitudinal sections from 72 h to 108 h of incubation. The sex of embryos was established from karyotypes. At 72 h, the germinal epithelium in the genital ridges was thickened. The nephrogenic cord was not differentiated into nephrons underneath, although the surrounding mesonephros displayed renal corpuscles and tubules. Clusters and trabeculae of mobilized mesonephric cells piled up under the germinal epithelium, forming the rudiment of the primitive medulla. From 78 h onwards, nephrotome-like structures existed in the mesenchyme underlying the germinal epithelium. Mesonephric cells became detached from their ventral walls and incorporated into the rudiment of the medulla. Finally, at 90 h, when the gonads were constituted, the primitive medulla was definitively formed without any contribution of the germinal epithelium. Adrenal cortical cells, also originating from the mesonephric blastema, showed tight relationships with the gonadal medullarian structures. Our observations support the concept of the mesonephric origin of the gonadal components having male potentialities in birds.

Although transient vestigial excretory organs (the pro- and mesonephros) are recognizable in the human embryo, the definitive kidney is the meta- nephros. This is formed in two parts: the nephrons from the nephrogenic cord and the excretory ducts (collecting tubules, calyces, pelvis and ureter) from the ureteric bud which grows as a branch from the caudal portion of the mesonephric (Wolffian) duct. During early development the ureteric bud grows cranially and impinges on the caudal end of the nephrogenic cord (called the metanephric blastema) where it begins a process of rapid dichotomous branching. The first few generations of branches coalesce to form the renal pelvis and calyces. As further branching occurs, condensations of meta-nephric blastema, from which the nephrons develop, become related to the dilated tip, or ampulla, of each branch of the ureteric bud (Figure 2.1). As the nephrons form they become attached to the ampullae which in turn develop into collecting ducts. Attachment to the growing tip of the ureteric bud branches ensures that the nephrons are carried outwards as they develop.

The supernumerary kidney is an accessory organ with its own blood supply and collecting system. It is a very rare type of congenital renal anomaly with fewer than 100 cases reported since firstly described at 1656 (1). Embryological basis of supernumerary kidney is connected to the ab-normal division of the nephrogenic cord into two metanephric blastemas which will form two kid-neys (2). It may be either completely separate or only loosely attached to the major kidney on the ipsilateral side. This anomaly is usually asymp-tomatic but may rarely become symptomatic in early adulthood (3). The mean age at diagnosis is 36 years. The most common presenting symptoms are pain, fever and a palpable abdominal mass. Ultrasonography, CT and MR urography may be needed to identify the anomaly.We aimed to present a rare case of super-numerary fused and malrotated kidney. Thirty--seven year-old woman was admitted to our clinic with left flank pain. CT scan demonstrated multi-ple calculi in the left kidney and supernumerary fused kidney (Figures 1 and 2). The third kidney was below the right kidney, malrotated and had its own blood supply (Figure-3).Grieshammer and colleagues showed that mutant mice lacking either SLIT2 or its receptor ROBO2 develop supernumerary ureteric buds that are correlated with abnormal maintenance of Gdnf expression in anterior metanephric mesenchyme (4). The SLIT2/ROBO2 intercellular signaling sys-tem restricts, directly or indirectly, in extent of the Gdnf expression and plays a critical role in