Embryonal hyperplasia of Bowman's capsular epithelium in patients with WT1 mutations

Embryonal hyperplasia of Bowman's capsular epithelium (EHBCE) is a rare condition, observed in patients with end-stage renal disease when treated with long-term dialysis. Immunohistochemical studies have suggested that EHBCE originates from the visceral epithelium of the Bowman's capsule. Here we report two patients with WT1 missense mutations in exon 7, who received continuous ambulatory peritoneal dialysis and developed EHBCE without Wilms tumor. One patient showed manifestations of Denys-Drash syndrome (DDS), while the other patient exhibited rapid progress into end-stage renal disease, but no genitourinary anomaly. Recently, abnormal expression of WT1 and PAX2 was shown in the podocytes in diffuse mesangial sclerosis (DMS) associated with DDS and isolated DMS. We hypothesize that EHBCE is a reversion of Bowman's capsular epithelial cells to an earlier cell differentiation state, which has the characteristics of a progenitor cell of both Bowman's capsular epithelia and podocytes. Immunohistochemical analysis of WT1, PAX2, vimentin, cytokeratin, and epithelial membrane antigen was performed in the kidney specimens obtained at autopsy or surgery. Abnormal expression of WT1 and PAX2 in the EHBCE was observed in both patients, supporting our hypothesis. The nephropathy associated with constitutional WT1 mutations might therefore be associated with EHBCE.

Zinc finger protein sall2 is not essential for embryonic and kidney development

SALL/Sall is a mammalian homolog of the Drosophila region-specific homeotic gene spalt (sal), and heterozygous mutations in SALL1 in humans lead to Townes-Brocks syndrome. We earlier reported that mice deficient in Sall1 die in the perinatal period and that kidney agenesis or severe dysgenesis are present. We have now generated mice lacking Sall2, another Sall family gene. Although Sall2 is expressed mostly in an overlapping fashion versus that of Sall1, Sall2-deficient mice show no apparent abnormal phenotypes. Morphology and gene expression patterns of the mutant kidney were not affected. Mice lacking both Sall1 and Sall2 show kidney phenotypes comparable to those of Sall1 knockout, thereby demonstrating the dispensable roles of Sall2 in embryonic and kidney development.

Region specific gene expressions in the central nervous system of the ascidian embryo

The vertebrate brain is regionalized during development into forebrain, midbrain and hindbrain. Fibroblast growth factor 8 (FGF8) is expressed in the midbrain/hindbrain boundary (MHB) and functions as an organizer molecule. Previous studies demonstrated that the brain of basal chordates or ascidians is also regionalized at least into fore/midbrain and hindbrain. To better understand the ascidian brain regionalization, the expression of the Ciona Fgf8/17/18 gene was compared with the expression of Otx, En and Pax2/5/8 genes. The expression pattern of these genes resembled that of the genes in the vertebrate forebrain, midbrain, MHB and hindbrain, each of those domains being characterized by sole or combined expression of Otx, Pax2/5/8, En and Fgf8/17/18. In addition, the putative forebrain and midbrain expressed Ci-FgfL and Ci-Fgf9/16/20, respectively. Therefore, the regionalization of the ascidian larval central nervous system was also marked by the expression of Fgf genes.

Involvement of Pax-2 in the action of activin A on tubular cell regeneration

It has been recently shown that in ischemic rat kidneys activin A is induced in tubular cells and inhibits their regeneration. The present study was conducted to further investigate the action of activin A in tubular cells during regeneration. Among genes thought to be critical for kidney development, Pax-2 was upregulated in tubular cells during regeneration after renal ischemia. Pax-2 protein was localized in nuclei of tubular and interstitial cells, some of which co-expressed a mesenchymal cell marker, vimentin, suggesting that a population of Pax-2-positive cells have properties of immature progenitor-like tubular cells. The Pax-2-expressing cells co-expressed a cell proliferation marker, BrdU, activin A, and the type II activin receptor. Activin A modulated growth of BrdU/Pax-2 double-positive cells since an administration of follistatin increased; conversely, exogenous activin A decreased the number of BrdU/Pax-2 double-positive cells after renal ischemia. Activin A also reduced the expression of Pax-2 in cultured metanephroi. A proximal tubular cell line, LLC-PK(1) cells, was used to further study the mode of action of activin A. The expression of Pax-2 was not detected in quiescent LLC-PK(1) cells, but it was markedly increased when growth was stimulated. Under this condition, activin A significantly inhibited DNA synthesis and reduced the expression of Pax-2 in LLC-PK(1) cells. In contrast, blockade of the activin signaling by overexpressing dominantly negative mutant receptor enhanced the expression level of Pax-2 in LLC-PK(1) cells and induced an immature phenotype. These results suggest that activin A regulates tubular cell growth and differentiation by modulating the expression of Pax-2 during regeneration.

Nephric lineage specification by Pax2 and Pax8

The mammalian kidney develops in three successive steps from the initial pronephros via the mesonephros to the adult metanephros. Although the nephric lineage is specified during pronephros induction, no single regulator, including the transcription factor Pax2 or Pax8, has yet been identified to control this initial phase of kidney development. In this paper, we demonstrate that mouse embryos lacking both Pax2 and Pax8 are unable to form the pronephros or any later nephric structures. In these double-mutant embryos, the intermediate mesoderm does not undergo the mesenchymal-epithelial transitions required for nephric duct formation, fails to initiate the kidney-specific expression of Lim1 and c-Ret, and is lost by apoptosis 1 d after failed pronephric induction. Conversely, retroviral misexpression of Pax2 was sufficient to induce ectopic nephric structures in the intermediate mesoderm and genital ridge of chick embryos. Together, these data identify Pax2 and Pax8 as critical regulators that specify the nephric lineage.

[Renal-coloboma syndrome]

CASE REPORT

We describe a woman with optic disc pit and bilateral renal hypoplasia as a papillorenal syndrome. DNA analysis for PAX2 mutations revealed a heterozygous mutation (nucleotide 619 in exon 9). A first uncle and a cousin had the same PAX2 mutation.

DISCUSSION

The association of optic nerve colobomas and renal anomalies comprises a autosomal dominant syndrome for mutations in the PAX2 gene. Ophthalmic and renal diseases are highly variable; the ophthalmologist must check for a renal problem when a coloboma is detected.

Pax 2 expression in mesodermal segmentation and its relationship with EphA4 and Lunatic-fringe during chicken somitogenesis

In the Pax gene family, which encodes DNA-binding proteins, Pax 2 has been known to play important roles in the formation of the midbrain/hindbrain boundary, eye, inner ear and kidney in vertebrates (Bioessays 19 (1997) 755). In this article, we report a segmentally regulated pattern of Pax 2 expression during chicken somitogenesis. Pax 2 mRNA is localized in the rostral end of the unsegmented presomitic mesoderm (PSM), abutting anteriorly on a prospective segmentation border. This pattern repeats every segmentation cycle (90 min) observed in ovo and also in the half embryo culture assay in which one half of PSM along the midline is fixed immediately while the other half is cultured for a given period. We also determined the sequence of changes in Pax 2 expression during a segmentation cycle by comparing the pattern of Pax 2 with that of Lunatic-fringe (L-fringe), known to cycle periodically in posterior PSM. A systematic comparison of the expression patterns between Pax 2, L-fringe and EphA4 further highlighted a close relationship between EphA4 and Pax 2 during a segmentation cycle. Lastly, Pax 2 is not segmentally expressed in mouse PSM, suggestive of species (avian)-specific mechanisms underlying somitic segmentation.

Motoneuron-derived neurotrophin-3 is a survival factor for PAX2-expressing spinal interneurons

Rat spinal cord interneurons undergo programmed cell death shortly after birth. We investigated here whether cell death of interneurons could be regulated by trophic factors produced by motoneurons, one of their main targets. To test this hypothesis, we studied the effect of the selective destruction of motoneurons on the survival of interneurons in organotypic cultures of embryonic rat spinal cords. Motoneurons were eliminated by an anti-p75(NTR)-specific immunotoxin (192 IgG-saporin). We then observed a decrease of 28% in the number of ventral spinal interneurons immunoreactive (IR) for the homeoprotein PAX2. This was correlated with an increase in the number of apoptotic nuclei in the same area. Because neurotrophin-3 (NT-3) is specifically produced by motoneurons and because interneurons express the NT-3 high-affinity receptor trkC, we examined the role of NT-3 in the survival of PAX2-IR interneurons. Addition of NT-3 to 192 IgG-saporin-treated explants rescued ventral PAX2-IR interneurons. Depletion of secreted NT-3 by anti-NT-3 antibodies induced 66% loss of ventral PAX2-IR interneurons. We conclude that motoneuron-derived NT-3 is a trophic factor for ventral PAX2-IR interneurons.

Treatment with Myf5-morpholino results in somite patterning and brain formation defects in zebrafish

Myf-5 is a stage-dependent transcription factor associated with somitogenesis. To study its biological functions in zebrafish, we injected the Myf5-morpholinos ZMF-MO (antisense nucleotides 28 to 52) and ZMF-OTHER (antisense nucleotides 3 to 27) into zebrafish embryos to establish a myf-5 gene knockdown. No phenotypic abnormalities were observed following injection with 0.2 ng of ZMF-MO, but defects were displayed in 2 of 118 (1.7%) surviving embryos injected with 1 ng ZMF-MO. Morphological defects became more severe with increased dosages: 105 of 270 (38.9%) surviving embryos injected with 4.5 ng of ZMF-MO displayed such abnormalities as the absence of eyes or brains in addition to the following low-dosage defects in 24 hpf embryos: longitudinal yolk sacs, incomplete epiboly coverage, abnormal and suspended tail buds, diffused somite boundaries, and head shrinkage. Similar results were observed in the 4.5 ng ZMF-OTHER injection group. However, when fish were co-injected with 4.5 ng ZMF-MO and 4.5 ng myf-5 mRNA, abnormality rates decreased from 49.6% to 5.5%. Our results show that the brain krox20 gene was down-regulated at rhombomere 3; the pax2.1 gene was completely down-regulated; myoD was expressed normally; myogenin was substantially down-regulated in whole somites; and desmin was partly inhibited in newly forming somites. Our conclusion is that zebrafish Myf-5 may play important roles in brain formation and in the convergence and extension of shield epiblasts and tail buds during early embryogenesis, in addition to its well-understood role as a muscle regulatory factor in somites.

An in ovo chicken model to study the systemic and localized teratogenic effects of valproic acid

BACKGROUND

The antiepileptic valproic acid (VPA) is a teratogen whose embryopathic mechanism(s) remain uncertain. Elucidating potential cellular and molecular effects of VPA is complicated by systemic application paradigms. We developed an in ovo model to reproduce the teratogenic effects of VPA and a localized VPA application procedure to determine whether VPA can selectively effect abnormal development in one region of the embryo.

METHODS

VPA was applied topically to chicken embryos in ovo at different embryonic stages. Embryos were later evaluated for gross and skeletal anomalies. Pax-2 and Pax-6 protein expression in the developing eye was also evaluated because VPA-induced eye anomalies are similar to those seen by the disruption of Pax-2 and Pax-6. For localized application, a thin sheet of the synthetic polymer Elvax was impregnated with VPA. A small piece of the VPA-impregnated polymer was applied directly to the presumptive wing bud region in Stage 10-17 embryos. Embryos were examined for gross and skeletal anomalies. Sham controls were employed for all experiments.

RESULTS

Chicken embryos exposed to VPA in ovo demonstrated increased mortality, growth delay and anomalies similar to ones previously seen in humans: neural tube, cardiovascular, craniofacial, limb and skeletal. Pax-2 and Pax-6 protein expression was qualitatively diminished in the eye. Localized wing bud VPA exposure caused structural abnormalities in the developing wing in the absence of other anomalies in the embryos. These wing defects were similar to those observed after topical whole-embryo VPA application.

CONCLUSIONS

These results indicate that at least one mechanism for the teratogenicity of VPA involves a direct effect on developing tissue. The nature of the abnormalities observed implies that this effect may be mediated by disruption of genes that regulate pattern formation.

Pax-2 activates the proglucagon gene promoter but is not essential for proglucagon gene expression or development of proglucagon-producing cell lineages in the murine pancreas or intestine

Tissue-specific proglucagon gene transcription is achieved through combinations of transcription factors expressed in pancreatic A cells and enteroendocrine L cells of the small and large intestine. Cell transfection and electrophoretic mobility shift assay experiments previously identified Pax-2 as a regulator of islet proglucagon gene expression. We examined whether Pax-2 regulates gut proglucagon gene expression using enteroendocrine cell lines and Pax2(1NEU) mutant mice. Immunoreactive Pax-2 was detected in STC-1 enteroendocrine cells, and Pax-2 activated proglucagon promoter activity in transfected baby hamster kidney and GLUTag cells. Pax-2 antisera diminished the formation of a Pax-2-G3 complex in electrophoretic mobility shift assay studies using nuclear extracts from islet and enteroendocrine cell lines. Surprisingly, Pax-2 mRNA transcripts were not detected by RT-PCR in RNA isolated from adult rat pancreas, rat islets, embryonic d 19 or adult murine pancreas and gastrointestinal tract. Furthermore, embryonic d 19 or neonatal d 1 Pax2(1NEU) mice exhibited normal islet A cells and gut endocrine L cells, and no decrement in pancreatic or intestinal glucagon gene expression. These findings demonstrate that Pax-2 is not essential for the developmental formation of islet A or gut L cells and does not play a role in the physiological control of proglucagon gene expression in vivo.

Extensive cell movements accompany formation of the otic placode

During development, the vertebrate inner ear arises from the otic placode, a thickened portion of the ectoderm next to the hindbrain. Here, the first detailed fate maps of this region in the chick embryo are presented. At head process stages, placode precursors are scattered throughout a large region of the embryonic ectoderm, where they intermingle with future neural, neural crest, epidermal, and other placode cells. Within the next few hours, dramatic cell movements shift the future otic placode cells toward the midline and ultimately result in convergence to their final position next to rhombomeres 5-6. Individual cells and small cell groups undergo constant cell rearrangements and appear to sort out from nonotic cells. While the major portion of the otic placode is derived from the nonneural ectoderm, the neural folds also contribute cells to the placode at least until the four-somite stage. Comparison of these fate maps with gene expression patterns at equivalent stages reveals molecular heterogeneity of otic precursor cells in terms of their expression of dlx5, msx1, Six4, and ERNI. Although Pax2 expression coincides with the region where otic precursors are found from stage 8, not all Pax2-positive cells will ultimately contribute to the otic placode.

Specification of the mammalian cochlea is dependent on Sonic hedgehog

Organization of the inner ear into auditory and vestibular components is dependent on localized patterns of gene expression within the otic vesicle. Surrounding tissues are known to influence compartmentalization of the otic vesicle, yet the participating signals remain unclear. This study identifies Sonic hedgehog (Shh) secreted by the notochord and/or floor plate as a primary regulator of auditory cell fates within the mouse inner ear. Whereas otic induction proceeds normally in Shh(-/-) embryos, morphogenesis of the inner ear is greatly perturbed by midgestation. Ventral otic derivatives including the cochlear duct and cochleovestibular ganglia failed to develop in the absence of Shh. The origin of the inner ear defects in Shh(-/-) embryos could be traced back to alterations in the expression of a number of genes involved in cell fate specification including Pax2, Otx1, Otx2, Tbx1, and Ngn1. We further show that several of these genes are targets of Shh signaling given their ectopic activation in transgenic mice that misexpress Shh in the inner ear. Taken together, our data support a model whereby auditory cell fates in the otic vesicle are established by the direct action of Shh.

Bone morphogenetic proteins are involved in fetal kidney tissue transplantation-induced neuroprotection in stroke rats

Both bone morphogenetic proteins (BMPs) and glial cell line-derived neurotrophic factor (GDNF) reduce ischemia-induced cerebral injury in rats. Intracerebral transplantation of fetal kidney tissue, which normally expresses BMPs and GDNF during development, reduces ischemic injury in cerebral cortex. In this study, we tested the hypothesis that BMP is involved in this neuroprotective response. Fetal kidney tissue was cut into small pieces and transplanted into cortical areas adjacent to the right middle cerebral artery (MCA) in adult rats. In situ hybridization of brain indicated that these fetal kidney transplants contained high levels of BMP-7 mRNA three days after grafting. Immunohistochemical analysis of grafted brain showed co-localization of BMP-7 and PAX-2 immunoreactivity in the graft, suggesting that these transplants contained BMP protein. Some animals were grafted with fetal kidney tissue after intraventricular administration (ICV) of the BMP antagonist noggin (1 micro g) or after vehicle, followed by MCA ligation for 60 min. Animals receiving fetal kidney tissue transplantation developed significantly less body asymmetry, as compared to stroke animals that either did not receive transplantation or received fetal kidney grafts and noggin pretreatment. Analysis of these brains after triphenyltetrazolium chloride staining showed that fetal kidney tissue transplantation reduced the volume of infarction in the cerebral cortex. Noggin pretreatment reduced the protection induced by fetal kidney grafting, although noggin itself did not cause increase in cerebral infarction. Eight hours after ischemia, brain homogenates were obtained from grafted and control animals to assay caspase-3 enzymatic activity. This analysis demonstrated that fetal kidney grafts significantly reduced ischemia-induced caspase-3 activity. Reduction of caspase-3 activity could also be antagonized by noggin pretreatment. In conclusion, our data suggest that fetal kidney transplantation reduces ischemia/reperfusion-induced cortical infarction and behavioral deficits in adult rats, which are, at least partially, mediated through the effect of BMPs from the transplants.

Pax-2 interacts with RB and reverses its repression on the promoter of Rig-1, a Robo member

RB plays dual roles in the regulation of cell proliferation and differentiation. The nervous tissue-specific gene Rig-1, a member of the roundabout (Robo) guidance receptor family, was identified as an RB-regulated gene in the mouse embryo. Herein, we report that a 2.3kb genomic DNA fragment, which contains the first 129 bases of the 5'-untranslated region and 2.2kb of the 5'-flanking region of Rig-1, has a cell type-specific promoter activity. Rig-1 promoter activity is downregulated by RB and upregulated by Pax-2. Furthermore, Rig-1 and Pax-2 mRNAs are coexpressed in the hindbrain and spinal cord of the E11.5 mouse embryo, suggesting that Pax-2 may regulate Rig-1 expression during the embryonic stage. Pax-2 interacts with RB and reverses its transcriptional suppression on the Rig-1 promoter. In summary, the ubiquitous tumor suppressor RB and the neuron-enriched transcription factor Pax-2 may play a role in the regulation of Rig-1 expression during embryogenesis.

Development of dorsal-ventral polarity in the optic vesicle and its presumptive role in eye morphogenesis as shown by embryonic transplantation and in ovo explant culturing

Dorsal and ventral specification in the early optic vesicle appears to play a crucial role in the proper development of the eye. In the present study, we performed embryonic transplantation and organ culturing of the chick optic vesicle in order to investigate how the dorsal-ventral (D-V) polarity is established in the optic vesicle and what role this polarity plays in proper eye development. The left optic vesicle was cut and transplanted inversely in the right eye cavity of host chick embryos. This method ensured that the D-V polarity was reversed while the anteroposterior axis remained normal. The results showed that the location of the choroid fissure was altered from the normal (ventral) to ectopic positions as the embryonic stage of transplantation progressed from 6 to 18 somites. At the same time, the shape of the optic vesicle and the expression patterns of Pax2 and Tbx5, marker genes for ventral and dorsal regions of the optic vesicle, respectively, changed concomitantly in a similar way. The crucial period was between the 8- and 14-somite stages, and during this period the polarity seemed to be gradually determined. In ovo explant culturing of the optic vesicle showed that the D-V polarity and choroid fissure formation were already specified by the 10-somite stage. These results indicate that the D-V polarity of the optic vesicle is established gradually between 8- and 14-somite stages under the influence of signals derived from the midline portion of the forebrain. The presumptive signal(s) appeared to be transmitted from proximal to distal regions within the optic vesicle. A severe anomaly was observed in the development of optic vesicles reversely transplanted around the 10-somite stage: the optic cup formation was disturbed and subsequently the neural retina and pigment epithelium did not develop normally. We concluded that establishment of the D-V polarity in the optic vesicle plays an essential role in the patterning and differentiation of the neural retina and pigment epithelium.

Expression of nuclear transcription factor PAX2 in renal biopsies of juvenile nephronophthisis

PAX2, a homeotic gene of 'paired box family', is a nuclear transcription factor expressed in mesenchymal/epithelial conversion during the early stages of nephrogenesis; however, its repression is necessary for terminal differentiation of mature tubular cells. Transgenic overexpression in animal model causes epithelial hyperproliferation and microcyst formation. In humans, PAX2 expression has been observed in cystic and dysplasic tubular epithelia in kidney malformation and in kidney disease. We have investigated PAX2 expression and its colocalization with cytokeratin and/or vimentin in 17 biopsies of juvenile nephronophthisis (NPH), an autosomal-recessive renal disease characterized by diffuse renal fibrosis and occasional cysts. Fourteen cases were analyzed for deletion and mutation in the NPH1 gene locus and 33% resulted to be deleted or mutated; for the remaining cases the diagnosis was based on clinical and pathological criteria. The control group included 4 congenital dysplastic kidneys, and 10 biopsies of nephropathies with secondary chronic tubulointerstitial damage. In all cases of renal dysplasia a strong nuclear positivity was observed in immature tubules surrounded by alphaSMA-positive mesenchymal cells. In NI biopsies the tubular epithelia were almost PAX2 negative, although tubulointerstitial damage was severe. In 14/17 NPH1 moderate-to-strong nuclear PAX2 positivity of tubular cells was observed, particularly in cystic distal tubules located at the corticomedullary junction, but also in proximal tubular sections. The PAX2 signal co-localized more with cytokeratin staining than with vimentin. Our results confirm the observation of PAX2 expression in immature dysplastic tubules and its repression in mature renal tubular cells, also in the presence of severe secondary interstitial fibrosis. PAX2 seems to be overexpressed in NPH. The genetic defect of NPH, a disease probably due to a primary defect along the cascade of mesenchymal epithelial differentiation, could generate a functionally abnormal protein involved in focal adhesion signaling and cell/matrix interaction. The failure of PAX2 repression or its reactivation in NPH could be a marker of hyperproliferation and incomplete maturation of epithelial tubular cells, probably due to a defect cell/matrix cross-talk, and involved in interstitial fibrosis and cysts formation.

pax2.1is required for the development of thyroid follicles in zebrafish

The thyroid gland is an organ primarily composed of endoderm-derived follicular cells. Although disturbed embryonic development of the thyroid gland leads to congenital hypothyroidism in humans and mammals, the underlying principles of thyroid organogenesis are largely unknown. In this study, we introduce zebrafish as a model to investigate the molecular and genetic mechanisms that control thyroid development. Marker gene expression suggests that the molecular pathways of early thyroid development are essentially conserved between fish and mammals. However during larval stages, we find both conserved and divergent features of development compared with mammals. A major difference is that in fish, we find evidence for hormone production not only in thyroid follicular cells, but also in an anterior non-follicular group of cells.

We show that pax2.1 and pax8, members of the zebrafish pax2/5/8 paralogue group, are expressed in the thyroid primordium. Whereas in mice, only Pax8 has a function during thyroid development, analysis of the zebrafish pax2.1 mutant no isthmus (noi–/–) demonstrates that pax2.1 has a role comparable with mouse Pax8 in differentiation of the thyroid follicular cells. Early steps of thyroid development are normal in noi–/–, but later expression of molecular markers is lost and the formation of follicles fails. Interestingly, the anterior non-follicular site of thyroid hormone production is not affected in noi–/–. Thus, in zebrafish, some remaining thyroid hormone synthesis takes place independent of the pathway leading to thyroid follicle formation. We suggest that the noi–/– mutant serves as a new zebrafish model for hypothyroidism.

The Dlx5 homeobox gene is essential for vestibular morphogenesis in the mouse embryo through a BMP4-mediated pathway

In the mouse embryo, Dlx5 is expressed in the otic placode and vesicle, and later in the semicircular canals of the inner ear. In mice homozygous for a null Dlx5/LacZ allele, a severe dysmorphogenesis of the vestibular region is observed, characterized by the absence of semicircular canals and the shortening of the endolymphatic duct. Minor defects are observed in the cochlea, although Dlx5 is not expressed in this region. Cristae formation is severely impaired; however, sensory epithelial cells, recognized by calretinin immunostaining, are present in the vestibular epithelium of Dlx5(-/-) mice. The maculae of utricle and saccule are present but cells appear sparse and misplaced. The abnormal morphogenesis of the semicircular canals is accompanied by an altered distribution of proliferating and apoptotic cells. In the Dlx5(-/-) embryos, no changes in expression of Nkx5.1(Hmx3), Pax2, and Lfng have been seen, while expression of bone morphogenetic protein-4 (Bmp4) was drastically reduced. Notably, BMP4 has been shown to play a fundamental role in vestibular morphogenesis of the chick embryo. We propose that development of the semicircular canals and the vestibular inner ear requires the independent control of several homeobox genes, which appear to exert their function via tight regulation of BPM4 expression and the regional organization of cell differentiation, proliferation, and apoptosis.

Activin A: an autocrine regulator of cell growth and differentiation in renal proximal tubular cells

BACKGROUND

Activin A is involved in tubular regeneration after ischemia/reperfusion injury. The present study was conducted to examine the role of activin A in cell growth, apoptosis and differentiation of tubular cells.

METHODS

We performed cell proliferation assays (MTT assay, [3H]-thymidine incorporation) and apoptosis detection assays (nuclear staining, DNA ladder formation, TUNEL staining) using LLC-PK1 cells. Expression of activin and activin receptor in LLC-PK1 cells also were examined by real-time polymerase chain reaction (PCR) and immunostaining. Stable cell lines expressing the truncated type II activin receptor were generated and the phenotype of these cells was analyzed.

RESULTS

Activin A inhibited DNA synthesis and cell growth in a dose-dependent manner and induced apoptosis in LLC-PK1 cells. The expression level of mRNA for the activin betaA subunit was markedly increased when the growth was stimulated. The expression of the type II activin receptor was observed in LLC-PK1 cells. The growth rate of cells expressing dominantly negative activin receptor was significantly faster than that of non-transfected cells. The expression level and pattern of cytokeratin and vimentin in these cells were quite different compared to non-transfected cells. When cultured in collagen gel, these cells formed multiple processes, which was not observed in non-transfected cells. Finally, the expression of Pax-2 was markedly elevated in these cells.

CONCLUSIONS

Activin A acts as an autocrine inhibitor of cell growth, an inducer of apoptosis, and an important modulator of differentiation in cultured proximal tubular cells.

Pax genes and eye organogenesis

Pax6 is a highly conserved gene that controls eye development in all species where it has been tested. In spite of this common 'master control regulator', the eyes of different animals are morphologically very different and it is believed that they have evolved independently multiple times through evolution. Recent works looking at eye development in 'primitive' species offer some explanation as to the surprising amount of conservation in genetic and morphogenetic pathways involved in eye development. These studies not only implicate the Pax genes but also the So/Six gene family in playing a crucial ancestral role in visual system development.

Non-allelic heterogeneity in familial unilateral renal adysplasia

We report three families with dominant unilateral renal adysplasia without vesico-ureteral reflux. No dysmorphia or anomalies were evident in the reproductive system. Ophthalmological examination excluded the presence of optic nerve coloboma or other ocular anomalies. No mutations were detected in the EMX(2) and in PAX(2) genes of affected members. Other homeobox genes could be responsible for this anomaly in these three families.

Dysregulation of podocyte phenotype in idiopathic collapsing glomerulopathy and HIV-associated nephropathy

BACKGROUND

Idiopathic collapsing glomerulopathy (ICG) and HIV-associated nephropathy (HIV-AN) are characterized by severe nephrotic syndrome, collapse and sclerosis of the glomerular tuft with prominent podocyte alterations and extensive tubulointerstitial lesions. We previously showed phenotypic changes in podocytes from patients with diffuse mesangial sclerosis, a severe glomerulopathy sharing several morphological features with collapsing glomerulopathy. The aim of this study was to analyze the podocyte phenotype in ICG and HIV-AN.

METHODS

Using immunohistochemical techniques, we studied the podocyte expression of the transcription factor WT1 and its target PAX2, GLEPP1, synaptopodin and vimentin as markers of podocyte maturity and of proliferating cell nuclear antigen (PCNA) as a marker of proliferation. Apoptosis was analyzed by the TUNEL method. Results from renal biopsies of ICG and HIV-AN were compared with those obtained from normal kidney, minimal change nephrotic syndrome (MCNS), focal and segmental glomerulosclerosis (FSGS) and membranous glomerulonephritis (MGN).

RESULTS

Abnormal distribution of WT1 and PAX2 and extensive loss of podocyte markers were observed in ICG and HIV-AN; this dysregulation was associated with podocyte proliferation without detectable apoptosis. In contrast, no podocyte changes were detected in MCNS or MGN. In FSGS, phenotypic changes, without proliferation, were restricted to podocytes surrounding focal and segmental glomerular lesions. Increased PCNA expression and apoptosis were observed in ICG and HIV-AN tubular cells.

CONCLUSION

Dysregulation of podocyte phenotype and proliferation are present in both ICG and HIV-AN. This suggests that, whatever their etiology, both types of collapsing glomerulopathy share a common pathogenic pathway. Upregulation of cell proliferation and apoptosis observed in tubular epithelial cells is probably involved in the occurrence of severe tubulointerstitial lesions in collapsing glomerulonephritis.