β-catenin, Pax2, and Pten Panel Identifies Precancers Among Histologically Subdiagnostic Endometrial Lesions

Despite refinements in histologic criteria for the diagnosis of endometrioid precancers, many challenging cases are encountered in daily practice, creating diagnostic uncertainty and suboptimal patient management. Recently, an immunohistochemical 3-marker panel consisting of β-catenin, Pax2, and Pten was identified as a useful diagnostic adjunct. However, previous studies focused either on cancers or diagnostically unambiguous precancers, leaving questions about the applicability and utility of the panel in endometria with architectural features near or below the threshold of accepted histologic criteria for endometrioid precancers. Here, in a retrospective study of 90 patients, we evaluated the performance of the 3-marker panel. Notably, the panel detected a subset of disordered proliferative endometria (8/44, 18%), nonatypical hyperplasias (19/40, 48%), and cases with ambiguous features (3/6, 50%) with aberrancy for ≥1 markers. Marker-aberrant cases were more likely to progress to endometrioid precancer or cancer ( P =0.0002). Patterns of marker aberrancy in the index and progressor cases from individual patients provided evidence for origin in a common precursor, and next-generation sequencing of the progressor cases rationalized marker aberrancy for β-catenin and Pten. The results unequivocally demonstrate that some lesions that do not approach current histologic thresholds are bona fide neoplastic precursors with clinically-relevant driver events that can be detected by the 3-marker panel. The findings provide further validation for the diagnostic utility of the panel in clinical practice and its application in difficult or ambiguous cases.

Different staining patterns of ovarian Brenner tumor and the associated mucinous tumor

The association of ovarian Brenner tumors and adjacent mucinous tumors is well known but not completely understood. In this study, we analyzed immunohistochemical markers on Brenner tumors and their associated mucinous tumor to explore Mullerian as well as Wolffian and germ cell derivation and determine if the mucinous component is independent or related to the Brenner tumor. Of 32 consecutive cases of Brenner tumors, 8 were identified with significant mucinous component, and 7 additional cases included foci of mucinous epithelium within the Brenner transitional nests. All Brenner tumors were diffusely positive for GATA3 and negative for Paired box gene 8, PAX2, and Sal-like protein 4. Interestingly, the areas of mucinous epithelium as well as mucinous tumors, intermixed and adjacent to the Brenner tumor, were negative for all 4 markers; however, occasional basal-like cells retained expression of GATA3. The immunoprofile of mucinous tumors associated with Brenner tumors shares the lack of Mullerian markers PAX2 and Paired box gene 8 with the Brenner tumor but differs in the expression of GATA3 only in the Brenner tumor component.

California sea lion (Zalophus californianus) aerial hearing sensitivity measured using auditory steady-state response and psychophysical methods

Although electrophysiological methods of measuring the hearing sensitivity of pinnipeds are not yet as refined as those for dolphins and porpoises, they appear to be a promising supplement to traditional psychophysical procedures. In order to further standardize electrophysiological methods with pinnipeds, a within-subject comparison of psychophysical and auditory steady-state response (ASSR) measures of aerial hearing sensitivity was conducted with a 1.5-yr-old California sea lion. The psychophysical audiogram was similar to those previously reported for otariids, with a U-shape, and thresholds near 10 dB re 20 μPa at 8 and 16 kHz. ASSR thresholds measured using both single and multiple simultaneous amplitude-modulated tones closely reproduced the psychophysical audiogram, although the mean ASSR thresholds were elevated relative to psychophysical thresholds. Differences between psychophysical and ASSR thresholds were greatest at the low- and high-frequency ends of the audiogram. Thresholds measured using the multiple ASSR method were not different from those measured using the single ASSR method. The multiple ASSR method was more rapid than the single ASSR method, and allowed for threshold measurements at seven frequencies in less than 20 min. The multiple ASSR method may be especially advantageous for hearing sensitivity measurements with otariid subjects that are untrained for psychophysical procedures.

Optic nerve dysplasia and renal insufficiency in a family with a novel PAX2 mutation, Arg115X: further ophthalmologic delineation of the renal-coloboma syndrome

Renal-coloboma syndrome, an autosomal dominant disorder associated with mutations in PAX2, is characterized by colobomatous eye defects, renal hypoplasia, vesicoureteral reflux, high-frequency hearing loss, and rarely central nervous system abnormalities. We identified a three-generation family with optic nerve colobomatous dysplasia and renal disease. We report the identification of a novel mutation in PAX2 in this family with renal-coloboma syndrome, Arg115X. We also report on the ocular and extraocular manifestations of PAX2 mutations for all cases of renal-coloboma syndrome reported to date.

Polyamines are involved in murine kidney development controlling expression of c-ret, E-cadherin, and Pax2/8 genes

Polyamines play an important role in cell growth and differentiation. We studied changes in morphogenesis and the expression of the developmental control genes in the embryonic mouse kidney in response to polyamine depletion, using a kidney organ culture approach and reducing the polyamine pools with alpha-difluoromethylornithine (DFMO), an irreversible suicide inhibitor of ornithine decarboxylase (ODC). We found that inhibition of ODC results in a systematic kidney organogenesis phenotype, in that the DFMO-treated kidney specimens were of smaller size, had less epithelial ureteric bud branches, and their mesenchymal-derived tubule formation was retarded. These dysmorphologies were shown to be associated with changes in cell proliferation. Whole-mount in situ experiments revealed that inhibition of ODC causes increases in epithelial c-ret and E-cadherin and a decrease in mesenchymal Pax-8 expression, whereas levels of epithelial Wnt-11, mesenchymal GDNF, FoxD1, and Pax-2 transcripts remain unchanged. We studied regulation of the Pax-2 gene by analyzing a mouse line in which lacZ was driven by an 8.5 kb Pax-2 enhancer in the epithelial ureteric bud, and found that Pax-2 expression, as indicated by lacZ expression, increased after DFMO treatment. Transient transfection experiments in HEK 293 cells with the minimal Pax-2 promoter showed enhanced transcription upon reduction of the polyamine pools. We propose that ODC and polyamines have an important role in kidney organogenesis, being involved in the regulation of the expression of genes implicated in epithelial-mesenchymal tissue interactions.

Pax2 expression patterns in the developing chick inner ear

The fate specification of the developing vertebrate inner ear could be determined by complex regulatory genetic pathways involving the Pax2/5/8 genes. Pax2 expression has been reported in the otic placode and vesicle of all vertebrates that have been studied. Loss-of-function experiments suggest that the Pax2 gene plays a key role in the development of the cochlear duct and acoustic ganglion. Despite all these data, the role of Pax2 gene in the specification of the otic epithelium is still only poorly defined. In the present work, we report a detailed study of the spatial and temporal Pax2 expression patterns during the development of the chick inner ear. In the period analysed, Pax2 is expressed only in some presumptive sensory patches, but not all, even though all sensory patches show the scattered Pax2 expression pattern later on. We also show that Pax2 is also expressed in several non-sensory structures.

Eya 1 acts as a critical regulator for specifying the metanephric mesenchyme

Although it is well established that the Gdnf-Ret signal transduction pathway initiates metanephric induction, no single regulator has yet been identified to specify the metanephric mesenchyme or blastema within the intermediate mesoderm, the earliest step of metanephric kidney development and the molecular mechanisms controlling Gdnf expression are essentially unknown. Previous studies have shown that a loss of Eya 1 function leads to renal agenesis that is a likely result of failure of metanephric induction. The studies presented here demonstrate that Eya 1 specifies the metanephric blastema within the intermediate mesoderm at the caudal end of the nephrogenic cord. In contrast to its specific roles in metanephric development, Eya 1 appears dispensable for the formation of nephric duct and mesonephric tubules. Using a combination of null and hypomorphic Eya 1 mutants, we now demonstrated that approximately 20% of normal Eya 1 protein level is sufficient for establishing the metanephric blastema and inducing the ureteric bud formation but not for its normal branching. Using Eya 1, Gdnf, Six 1 and Pax 2 mutant mice, we show that Eya 1 probably functions at the top of the genetic hierarchy controlling kidney organogenesis and it acts in combination with Six 1 and Pax 2 to regulate Gdnf expression during UB outgrowth and branching. These findings uncover an essential function for Eya 1 as a critical determination factor in acquiring metanephric fate within the intermediate mesoderm and as a key regulator of Gdnf expression during ureteric induction and branching morphogenesis.

A distinct preisthmic histogenetic domain is defined by overlap of Otx2 and Pax2 gene expression in the avian caudal midbrain

Correlative in situ hybridization of Otx2, Pax2, Gbx2, and Fgf8 mRNA probes in adjacent serial sections through the chicken midbrain and isthmus at early to intermediate stages of development served to map in detail the area of overlap of Otx2 and Pax2 transcripts in the caudal midbrain. The neuronal populations developing within this preisthmic domain made up a caudal part of the midbrain reticular formation, the interfascicular nucleus, and the magnocellular (pre)isthmic nucleus, plus the corresponding part of the periaqueductal gray. The torus semicircularis-the inferior colliculus homolog-expressed Otx2 in its ventricular lining exclusively, but it never expressed Pax2. The parvicellular isthmic nucleus, although placed inside the midbrain lobe, never expressed Otx2, and its cells rapidly down-regulated an early transient Pax2 signal; this pattern is consistent with its reported isthmic origin and forward tangential translocation. This analysis reveals the existence of four distinct midbrain histogenetic domains along the longitudinal axis, at least for the alar plate. These presumably result from step-like isthmic organizer effects on Otx2-expressing midbrain neuroepithelium at different distances from a caudal FGF8 morphogen source (isthmic Fgf8-positive domain). The final phenotypes of these domains are histologically diverse and make up the griseum tectale (rostrally), the optic tectum, the torus semicircularis, and the presently characterized preisthmic domain (lying closest to the isthmic organizer). Available comparative data for reptiles and mammals suggest the general validity of this scheme.

Interaction of the LMX1B and PAX2 gene products suggests possible molecular basis of differential phenotypes in Nail-Patella syndrome

The LMX1B gene, encoding a protein involved in limb, kidney and eye development, is mutated in patients affected by Nail-Patella syndrome. Inter- and intrafamilial variability is common in this disorder for skeletal abnormalities, presence and severity of nephropathy and ocular anomalies. Phenotypic variability might depend on interactions of the LMX1B causative gene with other genes during development of both kidney and eye, which might act as modifier genes. Results are presented on the interaction between LMX1B and PAX2 proteins, obtained by both direct yeast two-hybrid assay and coimmunoprecipitation. Such interaction provides support to further studies on pathways underlying important developmental processes.

The lens has a specific influence on optic nerve and tectum development in the blind cavefish Astyanax

We used the teleost Astyanaxmexicanus to examine the role of the lens in optic nerve and tectum development. This speciesis unusually suited for studies of nervous system development and evolution because of its two extant forms: an eyed surface dwelling (surface fish) and several blind cave dwelling (cavefish) forms. Cavefish embryos initially form eye primordia, but the lens eventually dies by apoptosis, then the retina ceases to grow, and finally the degenerating eyes sink into the orbits. Transplantation of an embryonic surface fish lens into a cavefish optic cup restores eye development. We show here that retinal nerve fibers are formed and project to the optic tectum in cavefish embryos. In adult cavefish that have completed lens degeneration, however, the number of retinal axons in the optic nerve is substantially reduced compared to surface fish. The presumptive brain domains of embryonic cavefish are not altered relative to surface fish based on expression of the regional marker genes Pax6, Pax2.1, and engrailed2. In contrast, the adult cavefish brain is elongated, the optic tectum is diminished in volume, and the number of tectal neurons is reduced relative to surface fish. Unilateral transplantation of an embryonic surface fish lens into a cavefish optic cup increases the size of the optic nerve, the number of retinotectal projections from the restored eye, and the volume and neuronal content of the contralateral optic tectum. The results suggest that the lens has a specific influence on optic nerve and tectum development during eye growth in Astyanax.

Zebrafish Lmx1b.1 and Lmx1b.2 are required for maintenance of the isthmic organizer

The mesencephalic and metencephalic region (MMR) of the vertebrate central nervous system develops in response to signals produced by the isthmic organizer (IsO). We have previously reported that the LIM homeobox transcription factor Lmx1b is expressed within the chick IsO, where it is sufficient to maintain expression of the secreted factor wnt1. In this paper, we show that zebrafish express two Lmx1b orthologs, lmx1b.1 and lmx1b.2, in the rostral IsO, and demonstrate that these genes are necessary for key aspects of MMR development. Simultaneous knockdown of Lmx1b.1 and Lmx1b.2 using morpholino antisense oligos results in a loss of wnt1, wnt3a, wnt10b, pax8 and fgf8 expression at the IsO, leading ultimately to programmed cell death and the loss of the isthmic constriction and cerebellum. Single morpholino knockdown of either Lmx1b.1 or Lmx1b.2 has no discernible effect on MMR development. Maintenance of lmx1b.1 and lmx1b.2 expression at the isthmus requires the function of no isthmus/pax2.1, as well as Fgf signaling. Transient misexpression of Lmx1b.1 or Lmx1b.2 during early MMR development induces ectopic wnt1 and fgf8 expression in the MMR, as well as throughout much of the embryo. We propose that Lmx1b.1- and Lmx1b.2-mediated regulation of wnt1, wnt3a, wnt10b, pax8 and fgf8 maintains cell survival in the isthmocerebellar region.

Phenotypic analyses of mouse embryos with ubiquitous expression of Oct4: effects on mid-hindbrain patterning and gene expression

Oct4 is a transcription factor that has been associated with pluripotency and fate determination in the initial cell lineages of mammals. On the other hand, Pou2, the ortholog of Oct4 in zebrafish, serves additional later functions during brain development acting as a differentiation switch. In mice, Oct4 is expressed throughout the neural plate of embryos until embryonic day (E) 8.0. In this study, we produced transgenic mouse embryos that ubiquitously express Oct4 and analyzed the consequences during development. We show that, at E8.0, a higher dosage of Oct4 in the neuroectoderm is sufficient to transiently alter mid-hindbrain patterning and produced a strong up-regulation of Pax2, indicating that Oct4 can regulate this gene in vivo. After E9.5, ectopic Oct4 in this region produced cell death and affected the development of the forebrain, suggesting that, at these later stages, Oct4 down-regulation is necessary for normal development to proceed. The phenotype of the transgenic embryos was also accompanied with an increase of Fgf8 expression in several of its endogenous domains, suggesting the possibility that Oct4 can participate in the regulation of expression of this ligand. Our observations support the hypothesis that Oct4, like zebrafish Pou2, has a conserved function during early brain patterning in mouse.

A bipotent neural progenitor cell line cloned from a cerebellum of an adultp53-deficient mouse generates both neurons and oligodendrocytes

Here we report developmental characteristics of a clonal cell line 2Y-3t established from a multifocal neoplasm that arose in a cerebellum of an adult p53-deficient mouse. The tumorigenicity of the line was not observed in soft agar assay or in nude mouse assay. In serum-containing medium, 2Y-3t cells were epithelial-like in morphology and were mitotic. When they were cultured in serum-free medium, the expressions of neural stem and/or progenitor cell markers were decreased. Concomitantly, the expressions of neuronal and oligodendrocyte markers were increased in concert with morphological differentiation, and DNA synthesis ceased. None of astrocyte markers were detected under these culture conditions. Double-labelling studies revealed that two cell populations coexisted, expressing neuronal or oligodendrocyte markers. Triiodothyronine (T3) increased the oligodendrocyte population when 2Y-3t cells were cultured in serum-free medium. Recloning of the line gave rise to three types of subclones. Sixteen subclones were capable of generating both neurons and oligodendrocytes, four subclones were capable of generating only neurons and one subclone was capable of generating only oligodendrocytes. Thus, 2Y-3t cells have characteristics of bipotent neural progenitor cells capable of generating both neurons and oligodendrocytes. In addition, the line expressed mRNA for Pax-2 and had GAD67-positive cells when cultured in serum-free medium. However, none of the mRNAs for Zic-1, Math1, zebrin or Calbindin-D28k were detected, suggesting that the 2Y-3t line might generate the GABAergic interneuron lineage of the mouse cerebellum.

Identification of Pax2-regulated genes by expression profiling of the mid-hindbrain organizer region

The paired domain transcription factor Pax2 is required for the formation of the isthmic organizer (IsO) at the midbrain-hindbrain boundary, where it initiates expression of the IsO signal Fgf8. To gain further insight into the role of Pax2 in mid-hindbrain patterning, we searched for novel Pax2-regulated genes by cDNA microarray analysis of FACS-sorted GFP+ mid-hindbrain cells from wild-type and Pax2-/- embryos carrying a Pax2(GFP) BAC transgene. Here, we report the identification of five genes that depend on Pax2 function for their expression in the mid-hindbrain boundary region. These genes code for the transcription factors En2 and Brn1 (Pou3f3), the intracellular signaling modifiers Sef and Tapp1, and the non-coding RNA Ncrms. The Brn1 gene was further identified as a direct target of Pax2, as two functional Pax2-binding sites in the promoter and in an upstream regulatory element of Brn1 were essential for lacZ transgene expression at the mid-hindbrain boundary. Moreover, ectopic expression of a dominant-negative Brn1 protein in chick embryos implicated Brn1 in Fgf8 gene regulation. Together, these data defined novel functions of Pax2 in the establishment of distinct transcriptional programs and in the control of intracellular signaling during mid-hindbrain development.

Angiotensin II stimulates Pax-2 in rat kidney proximal tubular cells: impact on proliferation and apoptosis

BACKGROUND

The intrarenal renin-angiotensin system (RAS) is intimately involved in the tubular cell proliferation, apoptosis and regeneration that occur following renal injury. Though tubular angiotensin II (Ang II) type 2 receptors (AT2R) decrease greatly after birth, their number increases after injury. Notably, during recovery from injury, renal tubular cells display a relatively immature phenotype expressing genes that are involved in nephron development, for example, the paired homeobox-2 gene (Pax-2). The present investigation hypothesized that AT2R activation would stimulate Pax-2 gene expression in immortalized rat renal proximal tubular cells (IRPTC), as we have found in fetal cells.

METHODS

Pax-2 gene expression in IRPTC was evaluated by immunofluorescence, Western blot, reverse transcription-polymerase chain reaction (RT-PCR) with or without Ang II treatment; apoptosis and proliferation were analyzed by terminal transferase-mediated deoxyuridine triphosphate (dUTP) nick end-labeling (TUNEL) assay and bromodeoxyuridine (BrdU) incorporation in stable IRPTC transformants with Pax-2 sense and antisense orientation, respectively.

RESULTS

Ang II up-regulated Pax-2 gene expression via AT2R in IRPTC. The stimulatory effect of both Ang II on Pax-2 gene expression was blocked by PD123319 (AT2R inhibitor), AG 490 (specific Janus kinase 2 (JAK2) inhibitor) and genistein (tyrosine kinase inhibitor), but not by losartan (AT1R inhibitor). Stable transfection of sense Pax-2 cDNA increased, whereas antisense Pax-2 cDNA down-regulated Pax-2 expression.

CONCLUSION

Our studies suggest that Ang II stimulates Pax-2 gene expression in IRPTC via AT2R and the JAK2/signal transducers and activators of transcription (STAT) signaling transduction pathway, which may be important in renal repair following injury. Cells lacking Pax-2 gene expression appear to be prone toward apoptosis rather than proliferation.

De novo insG619 mutation in PAX2 gene in a Japanese patient with papillorenal syndrome

PURPOSE

To describe a Japanese patient with papillorenal syndrome (PRS) and to identify the genetic defect responsible for the disease.

DESIGN

Interventional case report.

METHODS

Complete ophthalmologic and systemic examinations were performed, and direct genomic sequencing of the PAX2 gene.

RESULTS

Fundus examination of a 3-year-old Japanese girl showed atypical coloboma bilaterally. At 6 years of age, she presented with proteinuria, and renal ultrasonography showed hypoplastic kidneys bilaterally. Molecular genetic analysis of the PAX2 gene revealed a de novo heterozygous insertion of a G at position 619.

CONCLUSIONS

Our findings suggest that an abnormal development of the optic stalk led to the optic disk dysplasia in PAX2-associated PRS. This indicates that we should consider renal abnormalities when an atypical round coloboma is present. Molecular genetic analysis of the PAX2 gene in combination with renal ultrasonography can help in making an earlier diagnosis of the disease.

Expression of aquaporins and PAX-2 compared to CD10 and cytokeratin 7 in renal neoplasms: a tissue microarray study

Diagnostic use of antibodies against aquaporin water channel proteins and PAX-2, a nuclear transcription factor in renal development, was tested in 202 renal neoplasms, using tissue microarray technique. Immunohistochemistry for aquaporin-1, aquaporin-2, PAX-2, CD10, and cytokeratin 7 was performed on 102 clear cell renal cell carcinomas, 44 papillary renal cell carcinomas (among them 34 type 1 and 10 type 2), 24 chromophobe renal cell carcinomas, three collecting duct carcinomas (carcinomas of the collecting ducts of Bellini), and 29 oncocytomas. Aquaporin-1 expression was found in clear cell renal cell carcinomas and papillary renal cell carcinomas of both types (78 and 73%, respectively), but not in chromophobe renal cell carcinomas, collecting duct carcinomas, and oncocytomas. Aquaporin-2 expression was not seen in any of the tested tumors. PAX-2 and CD10 was found in the majority of clear cell renal cell carcinomas (88 and 85%, respectively) but only in few papillary renal cell carcinomas, chromophobe renal cell carcinomas and oncocytomas. Decrease or loss of aquaporin-1 and PAX-2 was shown in higher grades compared to lower grades of clear cell renal cell carcinomas (P<0.0001 and <0.0245, respectively). Cytokeratin 7 was rarely seen in clear cell renal cell carcinomas, type 2 papillary renal cell carcinomas, and oncocytomas, but was found in the majority of type 1 papillary renal cell carcinomas (97.1%) and chromophobe renal cell carcinomas (88%). Aquaporin-1 and PAX-2 expression was found to correlate with nuclear grading for clear cell renal cell carcinomas but not for papillary renal cell carcinomas. No correlation of tumor stage and aquaporin-1 and PAX-2 expression was seen. Aquaporin-1 and PAX-2 are reliable markers for clear cell renal cell carcinomas of lower grades but not for higher grades. CD10 expression remains stable, independent of nuclear grading.

Isolation of renal progenitor cells from adult human kidney

We describe here isolation and characterization of CD133+ cells derived from normal adult human kidney. These cells lacked the expression of hematopoietic markers and expressed PAX-2, an embryonic renal marker, suggesting their renal origin. Renal tissue-derived CD133+ cells and clones of individual cells were capable of expansion and limited self-renewal and differentiated in vitro into epithelial or endothelial cells. On subcutaneous implantation in SCID mice, the undifferentiated cells formed tubular structures expressing renal epithelial markers. At variance, when differentiated in endothelial cells, these cells formed functional vessels. On intravenous injection in SCID mice with glycerol-induced tubulonecrosis, the in vitro expanded renal-derived CD133+ cells homed into the injured kidney and integrated in tubules. We propose that CD133+ cells from kidney represent a multipotent adult resident stem cell population that may contribute to the repair of renal injury.

Generation of Pax2-Cre mice by modification of a Pax2 bacterial artificial chromosome

The Pax2 gene is expressed in the developing otocyst, kidney, and midbrain-hindbrain boundary. We generated Pax2-Cre transgenic lines by modification of a Pax2 bacterial artificial chromosome (BAC). In one Pax2-Cre line, Cre mRNA starts to be expressed in the otic placode at the late presomite stage. R26R reporter mouse analysis revealed that the Cre expression is sufficient to delete the loxP-flanked sequences in most of the cells in the inner ear. Reporter-positive cells are also detected in other Pax2-expressing tissues such as midbrain, cerebellum, olfactory bulb, and kidney, suggesting that these cells are the descendants of Pax2-expressing cells in these tissues and that Pax2-Cre transgenic mice can delete genes efficiently in these tissues.

Pax2 expression occurs in renal medullary epithelial cells in vivo and in cell culture, is osmoregulated, and promotes osmotic tolerance

Pax2 is a transcription factor that is crucial for kidney development, and it is also expressed in the normal adult kidney, where its physiological function is unknown. In the present study, we find by cDNA microarray analysis that Pax2 expression in second-passage mouse inner-medullary epithelial cells is increased by a high NaCl concentration, which is significant because NaCl levels are normally high in the inner medulla in vivo, and varies with urinary concentration. Furthermore, a high NaCl concentration increases Pax2 mRNA and protein expression in mouse inner medullary collecting duct (mIMCD3) cells, and its transcriptional activity. Pax2 mRNA and protein expression is high in normal adult mouse renal inner medulla but much lower in renal cortex. Pax2 protein is present in collecting duct cells in both renal medulla and cortex and in thin descending limbs of Henle's loop in inner medulla. Treating Brattleboro rats with desamino-Cys-1,d-Arg-8 vasopressin, which increases inner-medullary NaCl concentration, causes a 4-fold increase in inner-medullary Pax2 protein. Treatment with furosemide, which decreases inner-medullary NaCl, reduces inner-medullary Pax2 mRNA and protein. Pax2-specific short interfering RNA increases high NaCl concentration-induced activation of caspase-3 and apoptotic bodies in mIMCD3 cells. We thus conclude that (i) Pax2 is expressed in normal renal medulla, (ii) its expression is regulated there by the normally high and variable NaCl concentration, and (iii) it protects renal medullary cells from high NaCl concentration-induced apoptosis.

Macular abnormalities and optic disk anomaly associated with a new PAX2 missense mutation

PURPOSE

To report a family with macular abnormalities accompanied by anomalies of the optic disk and kidney associated with a new PAX2 missense mutation.

DESIGN

Observational case report.

METHODS

A 34-year-old female presented with horizontal nystagmus, poor visual acuity, and chronic renal failure. She had bilateral colobomatous disk anomaly and foveal hypoplasia. Her mother also had renal dysfunction and bilaterally impaired vision. Besides the optic disk dysplasia, the fovea was hypoplastic in the right eye, whereas pigmented macular atrophy was observed in the left eye. The entire coding regions of PAX2 and PAX6 were screened for mutations.

RESULTS

A heterozygous mutation G755C in exon 2 of PAX2 that results in a missense mutation, R71T, was identified in the proband and her mother. No mutations were detected in PAX6.

CONCLUSIONS

A new PAX2 missense mutation, R71T, may cause macular abnormalities in addition to anomalies of the optic disk and the kidney.

Pax8 and Pax2a function synergistically in otic specification, downstream of the Foxi1 and Dlx3b transcription factors

The vertebrate inner ear arises from an ectodermal thickening, the otic placode, that forms adjacent to the presumptive hindbrain. Previous studies have suggested that competent ectodermal cells respond to Fgf signals from adjacent tissues and express two highly related paired box transcription factors Pax2a and Pax8 in the developing placode. We show that compromising the functions of both Pax2a and Pax8 together blocks zebrafish ear development, leaving only a few residual otic cells. This suggests that Pax2a and Pax8 are the main effectors downstream of Fgf signals. Our results further provide evidence that pax8 expression and pax2a expression are regulated by two independent factors, Foxi1 and Dlx3b, respectively. Combined loss of both factors eliminates all indications of otic specification. We suggest that the Foxi1-Pax8 pathway provides an early 'jumpstart' of otic specification that is maintained by the Dlx3b-Pax2a pathway.

Zebrafish pax8 is required for otic placode induction and plays a redundant role with Pax2 genes in the maintenance of the otic placode

Vertebrate Pax2 and Pax8 proteins are closely related transcription factors hypothesized to regulate early aspects of inner ear development. In zebrafish and mouse, Pax8 expression is the earliest known marker of otic induction, and Pax2 homologs are expressed at slightly later stages of placodal development. Analysis of compound mutants has not been reported. To facilitate analysis of zebrafish pax8, we completed sequencing of the entire gene, including the 5' and 3' UTRs. pax8 transcripts undergo complex alternative splicing to generate at least ten distinct isoforms. Two different subclasses of pax8 splice isoforms encode different translation initiation sites. Antisense morpholinos (MOs) were designed to block translation from both start sites, and four additional MOs were designed to target different exon-intron boundaries to block splicing. Injection of MOs, individually and in various combinations, generated similar phenotypes. Otic induction was impaired, and otic vesicles were small. Regional ear markers were expressed correctly, but hair cell production was significantly reduced. This phenotype was strongly enhanced by simultaneously disrupting either of the co-inducers fgf3 or fgf8, or another early regulator, dlx3b, which is thought to act in a parallel pathway. In contrast, the phenotype caused by disrupting foxi1, which is required for pax8 expression, was not enhanced by simultaneously disrupting pax8. Disrupting pax8, pax2a and pax2b did not further impair otic induction relative to loss of pax8 alone. However, the amount of otic tissue gradually decreased in pax8-pax2a-pax2b-deficient embryos such that no otic tissue was detectable by 24 hours post-fertilization. Loss of otic tissue did not correlate with increased cell death, suggesting that otic cells dedifferentiate or redifferentiate as other cell type(s). These data show that pax8 is initially required for normal otic induction, and subsequently pax8, pax2a and pax2b act redundantly to maintain otic fate.

nlz gene family is required for hindbrain patterning in the zebrafish

This study describes the conserved nlz gene family whose members encode unusual zinc finger proteins. In the zebrafish neurectoderm, both nlz1 and the newly isolated nlz2 are expressed in the presumptive hindbrain and midbrain/hindbrain boundary, where expression of nlz1 is dependent on pax2a. In addition, nlz2 is uniquely expressed more anteriorly, in the presumptive midbrain and diencephalon. Overexpression of Nlz proteins during gastrula stages inhibits hindbrain development. In particular, ectopically expressed Nlz1 inhibits formation of future rhombomeres 2 and 3 (r2, r3), whereas neighboring r1 and r4 are not affected. Conversely, simultaneous reduction of Nlz1 and Nlz2 protein function by expression of antisense morpholino-modified oligomers leads to expansion of future r3 and r5, with associated loss of r4. These data indicate that one function of the nlz gene family is to specify or maintain r4 identity, and to limit r3 and r5 during hindbrain formation.

Angiotensin II increases Pax-2 expression in fetal kidney cells via the AT2 receptor

Although both the renin angiotensin system (RAS) and the paired homeobox 2 gene (Pax-2) seem critically important in renal organogenesis, whether and how they might interact has not been addressed. The present study asked whether a link between the RAS and Pax-2 exists in fetal renal cells, speculating that such an interaction, if present, might influence renal development. Embryonic kidney explants and embryonic renal cells (mouse late embryonic mesenchymal epithelial cells [MK4] and mouse early embryonic mesenchymal fibroblasts [MK3]) were used. Pax-2 protein and Pax-2 mRNA were detected by immunofluorescence, Western blot, reverse transcription-PCR, and real-time PCR. Angiotensin II (AngII) upregulated Pax-2 protein and Pax-2 mRNA expression via the AngII type 2 (AT(2)) receptor in MK4 but not in MK3 cells. The stimulatory effect of AngII on Pax-2 gene expression could be blocked by PD123319 (AT(2) inhibitor), AG 490 (a specific Janus kinase 2 inhibitor), and genistein (a tyrosine kinase inhibitor) but not by losartan (AT(1) inhibitor), SB203580 (specific p38 mitogen-activated protein kinase inhibitor), PD98059 (specific MEK inhibitor), SP600125 (JNK inhibitor), and diphenyleneiodonium chloride (an NADPH oxidase inhibitor). Moreover, embryonic kidney explants in culture confirmed that AngII upregulates Pax-2 gene expression via the AT(2) receptor. These studies demonstrate that the stimulatory effect of AngII on Pax-2 gene expression is mediated, at least in part, via the Janus kinase 2/signal transducers and activators of transcription signaling transduction pathway, suggesting that RAS and Pax-2 interactions may be important in renal development.

FISHing for chick genes: Triple-label whole-mount fluorescence in situ hybridization detects simultaneous and overlapping gene expression in avian embryos

Multi-color whole-mount in situ hybridization is a powerful technique for comparing the spatial expression patterns of two or more genes in developing embryos. We have developed an amplified triple-label whole-mount fluorescence in situ hybridization (FISH) protocol that permits detection of three different mRNAs in a single embryo. Our protocol uses simultaneous in situ hybridization to haptenylated riboprobes, followed by sequential antibody detection using anti-hapten antibodies conjugated to horseradish peroxidase, and the tyramide signal amplification (TSA) fluorescence detection system. Conventional fluorescence microscopy identifies areas of overlapping gene expression at the tissue level, whereas confocal fluorescence microscopy permits single-cell resolution and differentiates specialized cell types within a given tissue. This protocol will provide researchers engaged in the use of FISH with a solid starting point for adapting their own in situ hybridization protocols, either alone or in combination with immunohistochemistry or green fluorescence protein colocalization.

Islet-1 expression in the developing chicken inner ear

The cell types of the inner ear originate from the otic placode, a thickened layer of ectoderm adjacent to the developing hindbrain. The placode invaginates and forms the otic pit, which pinches off as a small vesicle called the otocyst. Presumptive cochleovestibular neurons delaminate from the anterior ventral part of the otocyst and form the cochleovestibular ganglion of the inner ear. Here we show that the LIM/homeodomain protein islet-1 is expressed in cells of the ventral part of the otic placode and that this ventral expression is maintained at the otic pit and the otocyst stages. Auditory and vestibular neurons originate from this islet-1-positive zone of the otocyst, and these neurons maintain islet-1 expression until adulthood. We also demonstrate that islet-1 becomes up-regulated in the presumptive sensory epithelia of the inner ear in regions that are defined by the expression domains of BMP4. The up-regulation of islet-1 in developing inner ear hair and supporting cells is accompanied by down-regulation of Pax-2 in these cell types. Islet-1 expression in hair and supporting cells persists until early postnatal stages, when the transcriptional regulator is down-regulated in hair cells. Our data is consistent with a role for islet-1 in differentiating inner ear neurons and sensory epithelia cells, perhaps in the specification of cellular subtypes in conjunction with other LIM/homeodomain proteins.

Correlation of Pax-2 expression with cell proliferation in the developing chicken inner ear

In vertebrates, the paired-box transcription factor Pax-2 is one of the earliest markers of the developing inner ear and is robustly expressed in the otic placode and the otic vesicle. Mutations in the Pax-2 gene result in developmental defects of the vestibular and auditory apparatus. We set out to investigate whether regions of Pax-2 expression in the developing otic vesicle correlate with areas of cell proliferation or cell death, which would indicate a possible role of Pax-2 in these processes. Regionalized proliferation and local apoptosis are the principal mechanisms that lead to the complex morphogenesis of the highly compartmentalized inner ear starting from a simple vesicle. We found a high correlation of Pax-2 expression with proliferating cells in the walls of the early otic vesicle. Apoptotic cells were mostly localized outside of the Pax-2-expressing regions. At later stages, we found the highest intensity of proliferating and Pax-2-positive cells in areas of the developing sensory epithelia. When hair cells begin to differentiate, they maintain a lower level of Pax-2 expression than neighboring cells for a brief period, before they completely down-regulate expression of this transcription factor. We conclude that a significant proportion of proliferating cells in the developing otocyst express Pax-2, in particular in regions that include developing sensory patches. This implicates Pax-2 as a marker for proliferating hair and supporting cell progenitors. Furthermore, the likelihood that Pax-2-expressing cells in the otocyst die by apoptosis is much lower when compared with cells residing in Pax-2-negative regions.

The role of Pax2 in mouse inner ear development

The paired box transcription factor, Pax2, is important for cochlear development in the mouse inner ear. Two mutant alleles of Pax2, a knockout and a frameshift mutation (Pax21Neu), show either agenesis or severe malformation of the cochlea, respectively. In humans, mutations in the PAX2 gene cause renal coloboma syndrome that is characterized by kidney abnormalities, optic nerve colobomas and mild sensorineural deafness. To better understand the role of Pax2 in inner ear development, we examined the inner ear phenotype in the Pax2 knockout mice using paint-fill and gene expression analyses. We show that Pax2-/- ears often lack a distinct saccule, and the endolymphatic duct and common crus are invariably fused. However, a rudimentary cochlea is always present in all Pax2 knockout inner ears. Cochlear outgrowth in the mutants is arrested at an early stage due to apoptosis of cells that normally express Pax2 in the cochlear anlage. Lack of Pax2 affects tissue specification within the cochlear duct, particularly regions between the sensory tissue and the stria vascularis. Because the cochlear phenotypes observed in Pax2 mutants are more severe than those observed in mice lacking Otx1 and Otx2, we postulate that Pax2 plays a key role in regulating the differential growth within the cochlear duct and thus, its proper outgrowth and coiling.

Astrocyte-endothelial cell relationships during human retinal vascular development

PURPOSE

To evaluate evidence for the presence of vascular precursor cells (angioblasts) and astrocyte precursor cells (APCs) in the developing human retina and determine their relationship.

METHODS

Pax-2/GFAP/CD-34 triple-label immunohistochemistry was applied to four retinas aged 12, 14, 16, and 20 weeks of gestation (WG) to label APCs, astrocytes, and patent blood vessels. APCs are Pax-2(+)/GFAP(-), whereas astrocytes are Pax-2(+)/GFAP(+). Adenosine diphosphatase (ADPase) enzyme histochemistry, which identifies endothelial cells and vascular precursors, was applied to human retinas aged 12, 16, 17, and 19 WG. Nissl stain, a nonspecific cell soma marker, was applied to 14.5-, 18-, and 21-WG retinas. Established blood vessels were visualized with CD34 and ADPase.

RESULTS

Topographical analysis of the distribution of Nissl-stained spindle cells and ADPase(+) vascular cells showed that these two populations have similar distributions at corresponding ages. ADPase(+) vascular precursor cells preceded the leading edge of patent vessels by more than 1 millimeter. In contrast, Pax-2(+)/GFAP(-) APCs preceded the leading edge of CD34(+) blood vessels by a very small margin, and committed astrocytes (Pax-2(+)/GFAP(+)) were associated with formed vessels and nerve fiber bundles. Two populations of ADPase(+) cells were evident, a spindle-shaped population located superficially and a deeper spherical population. The outer limits of these populations remain static with maturation.

CONCLUSIONS

A combination of Pax-2/GFAP/CD34 immunohistochemistry, Nissl staining, and ADPase histochemistry showed that the vascular precursor cells (angioblasts), identified using ADPase and Nissl, represent a population distinct from Pax-2(+)/GFAP(-) APCs in the human retina. These results lead to the conclusion that formation of the initial human retinal vasculature takes place through vasculogenesis from the prior invasion of vascular precursor cells.

Molecular anatomy of placode development in Xenopus laevis

We analyzed the spatiotemporal pattern of expression of 15 transcription factors (Six1, Six4, Eya1, Sox3, Sox2, Pax6, Pax3, Pax2, Pax8, Dlx3, Msx1, FoxI1c, Tbx2, Tbx3, Xiro1) during placode development in Xenopus laevis from neural plate to late tail bud stages. Out of all genes investigated, only the expression of Eya1, Six1, and Six4 is maintained in all types of placode (except the lens) throughout embryonic development, suggesting that they may promote generic placodal properties and that their crescent-shaped expression domain surrounding the neural plate defines a panplacodal primordium from which all types of placode originate. Double-labeling procedures were employed to reveal the precise position of this panplacodal primordium relative to neural plate, neural crest, and other placodal markers. Already at neural plate stages, the panplacodal primordium is subdivided into several subregions defined by particular combinations of transcription factors allowing us to identify the approximate regions of origin of various types of placode. Whereas some types of placode were already prefigured by molecularly distinct areas at neural plate stages, the epibranchial, otic, and lateral line placodes arise from a common posterior placodal area (characterized by Pax8 and Pax2 expression) and acquire differential molecular signatures only after neural tube closure. Our findings argue for a multistep mechanism of placode induction, support a combinatorial model of placode specification, and suggest that different placodes evolved from a common placodal primordium by successive recruitment of new inducers and target genes.

Potential role of Pax-2 in retinal axon navigation through the chick optic nerve stalk and optic chiasm

The degree of fiber decussation at the optic chiasm differs between species, ranging from complete crossing in lower vertebrates to highly complex patterns of intermingling of the fibers from the two eyes seen in mammals and birds. Understanding the genetic control of fiber guidance through the chiasm is therefore important to unravel the developmental mechanisms within the visual system. Here we first report on early stages of chiasm formation, with pioneering axons from the left eye consistently arriving earlier than their counterparts from the right eye. This initial left-right asymmetry is transient and no functional significance is assigned to it yet. Secondly, we examined formation of the chiasm in relation with the expression of the transcription factor Pax-2 along the ventral eye cup and optic nerve stalk. Finally, in order to examine causal involvement of Pax-2 in chiasm formation, the gene was overexpressed along the neuraxis and in the eye cup at embryonic stages preceding the exit of axons from the eye, and hence arrival of axons at the chiasm. When studied with neuroanatomical tracing, Pax-2 overexpression resulted in visibly anomalous decussation of axons at the chiasm. A likely consequence of this perturbation was erroneous arrival of axons at the tectum, as observed by anterograde staining from the retina. These data suggest that balanced expression of Pax-2 results in the correct formation of the chick chiasm at early stages by imposing accurate pathfinding within the optic stalk and the midline.

Conversion of neurons and glia to external-cell fates in the external sensory organs of Drosophila hamlet mutants by a cousin-cousin cell-type respecification

The Drosophila external sensory organ forms in a lineage elaborating from a single precursor cell via a stereotypical series of asymmetric divisions. HAMLET transcription factor expression demarcates the lineage branch that generates two internal cell types, the external sensory neuron and thecogen. In HAMLET mutant organs, these internal cells are converted to external cells via an unprecedented cousin-cousin cell-fate respecification event. Conversely, ectopic HAMLET expression in the external cell branch leads to internal cell production. The fate-determining signals NOTCH and PAX2 act at multiple stages of lineage elaboration and HAMLET acts to modulate their activity in a branch-specific manner.

Expression of Pax2 in the intermediate mesoderm is regulated by YY1

The transcription factor Pax2 is essential for the development of the urogenital system. Pax2 expression can be detected by mouse embryonic day 8.5 (E8.5) in the region of intermediate mesoderm fated to become the nephric duct, pronephros, and mesonephros. Elements that direct Pax2 expression to nephrogenic precursor cells must be responding to positional information that controls nephrogenic fate. A 4.1-kb Pax2 promoter/enhancer fragment directs expression of a lacZ reporter to the nephrogenic region and the midbrain-hindbrain junction in transgenic mice. As kidney development proceeds, transgene expression is limited to the nephric duct and its derivatives, but not the metanephric mesenchyme. The early expression driven by the 4.1 promoter does not require the Pax2 protein, demonstrating that it receives positional information in the absence of a developing pro- or mesonephros. We have identified two DNAseI hypersensitive regions within this promoter, one at the start site of transcription initiation and a second approximately 2-kb upstream. Deletion of the more distal site significantly attenuates lacZ expression in the nephrogenic region but not in the midbrain-hindbrain region. DNA footprinting of this fragment revealed a highly conserved sequence between mouse and human Pax2 promoter sequences. Using fractionated nuclear extracts, we identified the transcription factor Yin Yang 1 (YY1) as the protein that binds to this conserved sequence. Deletion of the YY1 element significantly attenuated expression of a full-length 4.1 promoter. Moreover, inclusion of this YY1 binding element significantly enhanced expression of a minimal Pax2 promoter/enhancer transgene in E12 embryos. These data point to a novel role for YY1 in the establishment of high level tissue-specific expression within the intermediate mesoderm.

Pcp4l1, a novel gene encoding a Pcp4-like polypeptide, is expressed in specific domains of the developing brain

We report the cloning of a novel mouse gene (Pcp4l1) that encodes a polypeptide with significant sequence similarity to the Purkinje cell protein 4 gene (Pcp4) and describe its expression pattern during mouse development. Similar to Pcp4, the Pc4l1 gene product is characterized by the presence of an IQ domain and is highly conserved across evolution. RNA in situ hybridization reveals instead that Pcp4l1 has a distinct pattern of expression: it is only expressed in the central nervous system (CNS), and is first detected at E9.5 in the mesencephalic and metencephalic roof plate as well as in the isthmus, in a region that overlaps the expression domains of Pax2, Fgf8 and Wnt1. Thus, the early Pcp4l1 expression pattern coincides with the regional expression of well-characterized patterning molecules in the organizing centers of the developing brain. Starting at midgestation, Pcp4l1 is mainly expressed in the structures of the circumventricular organs, including the subcommissural organ, the rhombencephalic and telencephalic choroid plexi, and the pineal gland. In the adult brain, this transcript is also detected in laminar as well as in several nuclear structures of the CNS.

Localization of the type 1 corticotropin releasing factor receptor (CRF-R1) in the embryonic mouse cerebellum

Corticotropin releasing factor (CRF) is present in the adult, as well as in the embryonic and postnatal rodent cerebellum. Further, the distribution of the type 1 CRF receptor has been described in adult and postnatal animals. The focus of the present study is to determine the distribution and cellular relationships of the type 1 CRF receptor (CRF-R1) during embryonic development of the cerebellum. Between embryonic day (E)11 and E12, CRF-R1 immunoreactive puncta are uniformly distributed in the ventricular zone, the site of origin of Purkinje cells, nuclear neurons, and GABAergic interneurons, as well as the germinal trigone, the birthplace of the precursors of granule cells. Between E13 and 18, the distribution of immunolabeled puncta decreases in both the ventricular zone and the germinal trigone and increases in the intermediate zone, as well as in the dorsal aspect of the cerebellar plate. Between E14 and 18, antibodies that label specific populations of cerebellar neurons were combined with the antibody for the receptor to determine the cellular elements that expressed CRF-R1. At E14, CRF-R1 immunoreactivity is co-localized in neurons immunolabeled with PAX-2, an antibody that is specific for GABAergic interneurons. These neurons continue to express CRF-R1 as they migrate dorsally toward the cerebellar surface. Between E16 and 18, Purkinje cells, immunolabeled with calbindin, near the dorsal surface of the cerebellum express CRF-R1 in their cell bodies and apical processes. CRF has been shown to have a depolarizing effect on adult and postnatal Purkinje cells. Further, CRF has been shown to contribute to excitability of hippocampal neurons during embryonic development by binding to CRF-R1; depolarization induced excitability appears to be critical for cell survival. The location of the type one CRF receptor and the presence of its primary ligand, CRF, in the germinal zones of the cerebellum and in migrating neurons suggest that this receptor/ligand interaction could be important in the regulation of neuronal survival through cellular mechanisms that lead to depolarization of embryonic cerebellar neurons.

Tlx3 and Tlx1 are post-mitotic selector genes determining glutamatergic over GABAergic cell fates

Glutamatergic and GABAergic neurons mediate much of the excitatory and inhibitory neurotransmission, respectively, in the vertebrate nervous system. The process by which developing neurons select between these two cell fates is poorly understood. Here we show that the homeobox genes Tlx3 and Tlx1 determine excitatory over inhibitory cell fates in the mouse dorsal spinal cord. First, we found that Tlx3 was required for specification of, and expressed in, glutamatergic neurons. Both generic and region-specific glutamatergic markers, including VGLUT2 and the AMPA receptor Gria2, were absent in Tlx mutant dorsal horn. Second, spinal GABAergic markers were derepressed in Tlx mutants, including Pax2 that is necessary for GABAergic differentiation, Gad1/2 and Viaat that regulate GABA synthesis and transport, and the kainate receptors Grik2/3. Third, ectopic expression of Tlx3 was sufficient to suppress GABAergic differentiation and induce formation of glutamatergic neurons. Finally, excess GABA-mediated inhibition caused dysfunction of central respiratory circuits in Tlx3 mutant mice.

Genetic determination of nephrogenesis: the Pax/Eya/Six gene network

Development of the kidney serves as a paradigm to understand the mechanisms underlying the formation of an organ. The first sign of kidney development is the interaction between two tissues derived from the intermediate mesoderm, the metanephrogenic mesenchyme and the nephric duct. Many of the genes that play a crucial role in early kidney development, such as Pax2, Eya1, Six1, Six2, Sall1, Foxc1, Wt1, and the Hox11 genes, are expressed in the mesenchyme and encode transcription factors that--with few exceptions--are involved in regulation of the Gdnf gene. Moreover, mutations in a number of these genes in humans are associated with kidney diseases. Interestingly, many of the components regulating early kidney development are conserved throughout evolution and are also involved in eye and muscle formation in mammals, as well as in eye development in Drosophila. Genetic and biochemical studies in Drosophila and mice indicate that these genes and their respective products act in a complex network of interdependencies and positive and negative feedback loops. Genetic experiments have allowed us to begin to characterize the complex interactions between the individual components, but it will require additional biochemical and functional experiments to eventually understand the molecular functions of each of the participating proteins.

Pax2 mutant mice display increased number and size of islets of Langerhans but no change in insulin and glucagon content

Pax2 is a paired box transcription factor expressed in a spatially and temporally restricted manner and its absence results in major developmental defects of the central nervous system, eyes, ears and urogenital system. We recently reported that Pax2 is expressed in pancreatic endocrine cell lines and adult islets of Langerhans and activates glucagon gene expression. We have shown here that the Pax2 gene is expressed during pancreas development as early as embryonic day 10.5. Its absence, as assessed in Pax2(1Neu) mutant mice, results in a two- to threefold increase in the average pancreas volume occupied by the islets in both heterozygous and homozygous mutant mice with a gene-dependent dosage effect. This increase, which is due to a change in the number of islets per unit pancreas volume and in the size of individual islets, is not accompanied by significant modification in the insulin or glucagon content of the pancreas, indicating that the content of these hormones per cell is decreased. We have concluded that Pax2 may be implicated in the prenatal determination of the relative proportion of the endocrine and exocrine tissues of the pancreas.

Rescue of Defective Branching Nephrogenesis in Renal-Coloboma Syndrome by the Caspase Inhibitor, Z-VAD-fmk

In renal-coloboma syndrome (RCS), null mutations of the PAX2 gene cause renal hypoplasia due to a congenital deficit of nephrons; affected individuals may develop renal insufficiency in childhood. During normal kidney development, PAX2, is expressed at high levels throughout the arborizing ureteric bud (UB); recent observations suggest that one of its key roles is to suppress apoptosis in this collecting duct lineage. The authors hypothesized that increased UB cell apoptosis due to PAX2 haploinsufficiency must directly influence the rate of branching morphogenesis in developing kidney and the number of nephrons that can be formed before birth, when nephrogenesis in humans comes to an end. If so, the authors reasoned that caspase inhibitors might be used to suppress unwanted UB cell apoptosis during kidney development in Pax2(1Neu) mutant mice and rescue the genetic UB branching defect. E17.5 kidneys from Pax2(1Neu) mutant mice had smaller (-25%) longitudinal cross-sectional area and 3.5-fold increase in collecting duct cell apoptosis versus wild-type littermates; mutant E13.5 kidney explants allowed to arborize for 50 h in vitro had 18% fewer terminal branches than wild-types. However, exposure to the caspase inhibitor, Z-VAD-fmk (25 micro M), significantly increased terminal branch number in mutant explants (23%). It also increased branching in wild-type explants, apparently reflecting an effect of Z-VAD-fmk on basal apoptosis induced by ex vivo culture conditions. Similarly, when pregnant mice were injected daily with Z-VAD-fmk (10 micro g/g weight from E10.5 to E17.5), apoptosis of Pax2(1Neu) fetal collecting duct cells was suppressed to 40% of untreated mutants; by E14, terminal branch number was increased to 152% that of untreated litters. These studies support the hypothesis that PAX2 normally optimizes the rate of branching morphogenesis in fetal kidney by suppressing UB apoptosis. Furthermore, it suggests that caspase inhibitors can rescue the branching defect caused by PAX2 mutations.

Groucho suppresses Pax2 transactivation by inhibition of JNK-mediated phosphorylation

Pax proteins are DNA-binding transcription factors that regulate embryonic development through the activation and repression of downstream target genes. The Pax2 gene is absolutely required for kidney development and for patterning specific regions of the nervous system such as the eye, ear and hindbrain. The Pax2/5/8 family of proteins contains both transcription activation and repression domains. The activation domain of Pax2 is phosphorylated by the c-Jun N-terminal kinase (JNK) to enhance Pax2-dependent transcription. In this report, we demonstrate that the Groucho/TLE family protein, Grg4, interacts with Pax2 to suppress transactivation. Grg4 is able to specifically inhibit phosphorylation of the Pax2 activation domain, even in the presence of activated JNK. Furthermore, the Grg4 interaction and suppression of phosphorylation depends on Pax2 binding to its target DNA sequence and is independent of histone deacetylation. These data suggest a new model for Groucho mediated suppression of transcription through the specific inhibition of modifications in the activation domain of a transactivator.

Role of Pax genes in eye evolution: a cnidarian PaxB gene uniting Pax2 and Pax6 functions

PaxB from Tripedalia cystophora, a cubomedusan jellyfish possessing complex eyes (ocelli), was characterized. PaxB, the only Pax gene found in this cnidarian, is expressed in the larva, retina, lens, and statocyst. PaxB contains a Pax2/5/8-type paired domain and octapeptide, but a Pax6 prd-type homeodomain. Pax2/5/8-like properties of PaxB include a DNA binding specificity of the paired domain, activation and inhibitory domains, and the ability to rescue spa(pol), a Drosophila Pax2 eye mutant. Like Pax6, PaxB activates jellyfish crystallin and Drosophila rhodopsin rh6 promoters and induces small ectopic eyes in Drosophila. Pax6 has been considered a "master" control gene for eye development. Our data suggest that the ancestor of jellyfish PaxB, a PaxB-like protein, was the primordial Pax protein in eye evolution and that Pax6-like genes evolved in triploblasts after separation from Cnidaria, raising the possibility that cnidarian and sophisticated triploblastic eyes arose independently.

WT1 is a modifier of the Pax2 mutant phenotype: cooperation and interaction between WT1 and Pax2

Metanephric kidney development requires an inductive interaction between the ureteric bud and progenitor mesenchyme, where the early expression of two genes, Wilms' tumour 1 (WT1) and paired box 2 (Pax2), establishes critical but unknown developmental pathways. Indeed, transgenic mice with deregulated overexpression of Pax2 exhibit structural kidney defects and impaired renal function, as do mice harboring targeted disruptions and/or spontaneous mutations of either the Pax2 or WT1 genes. WT1 and Pax2 are thought to regulate each other's expression during renal development. To better define the relationship between WT1 and Pax2, we generated mouse embryos containing heterozygous mutations in both genes. WT1(+/-)/Pax2(1Neu/+) kidneys were 50% smaller than wild-type kidneys. They were characterized by severe attenuation of the renal medulla, and reduced development of calyces and the renal pelvis. Renal cortex development in compound heterozygotes culminated in fewer nephrons than in WT1(+/-), Pax2(1Neu/+) or wild-type mice. Only minor variations in the mesenchymal expression pattern of Pax2 protein, and the mRNA expression levels of Pax2 and WT1, were noted in mutant kidneys. We show that WT1 and Pax2 proteins interact in vitro and in vivo, demonstrating that WT1 and Pax2 can form a molecular complex. Our data suggest that WT1 is a modifier of the Pax2 mutant phenotype.

DNA-binding characteristics of cnidarian Pax-C and Pax-B proteins in vivo and in vitro: no simple relationship with the Pax-6 and Pax-2/5/8 classes

Cnidarians are the simplest animals in which distinct eyes are present. We have previously suggested that cnidarian Pax-Cam might represent a precursor of the Pax-6 class. Here we show that when expressed in Drosophila imaginal discs, Pax-Cam chimeric proteins containing the C-terminal region of EY were capable of eye induction and driving expression of a reporter gene under the control of a known EY target (the sine oculis gene). Whilst these results are consistent with a Pax-6-like function for Pax-Cam, in band shift experiments we were unable to distinguish the DNA-binding behaviour of the Pax-Cam Paired domain from that of a second Acropora Pax protein, Pax-Bam. The ability of a Pax-Bam/EY chimera to also induce eye formation in leg imaginal discs, together with the in vitro data, cast doubt on previously assumed direct relationships between cnidarian Pax genes and the Pax-6 and Pax-2/5/8 classes of bilateral animals.

The Secreted Frizzled Related Protein 2 (SFRP2) Gene Is a Target of the Pax2 Transcription Factor

Despite their essential role in vertebrate development, the function of Pax proteins in gene regulation is not well understood. To identify potential genes regulated by the Pax2 protein, we screened embryonic kidney cells transformed with Pax2-expressing retroviruses for genes activated in response to Pax2 expression. In this system, the gene encoding the secreted frizzled related protein, Sfrp2, was strongly activated in all Pax2b-expressing cells. This activation of Sfrp2 expression correlated with changes in chromatin structure at the Sfrp2 locus, particularly in and around regions of Pax2 binding. Although the amount of Pax2-dependent transactivation was low in transient assays, the data suggests that local alterations of chromatin structure by Pax proteins can greatly enhance expression when presented in the right cellular context.

Development of an siRNA-based method for repressing specific genes in renal organ culture and its use to show that the Wt1 tumour suppressor is required for nephron differentiation

Wt1 is a tumour suppressor gene, mutation of which is a cause of Wilms' tumour, a childhood renal nephroblastoma. Wt1 is expressed in a rich pattern during renal development suggesting that it acts at three stages: determination of the kidney area, the differentiation of nephrons and maturation of glomeruli. Wt1-/- mice confirm that Wt1 is essential for the inception of kidney development; cells that ought to form kidneys die by apoptosis instead. Specific human WT1 mutations cause defects of glomerular maturation (Denys-Drash and Frasier syndromes), providing circumstantial evidence for action of Wt1 during glomerular maturation. There is, however, no genetic evidence for a function during nephron differentiation because this stage is never reached in Wt1-/- mice. We have therefore developed a novel technique, based on small interfering RNA (siRNA), to repress the expression of Wt1 and other specific genes at different stages of kidney development in culture. We find that early repression of Wt1 phenocopies the Wt1-/- mouse, but later repression prevents cells differentiating into nephrons and causes them instead to proliferate abnormally, possibly mimicking aspects of Wilms' tumour. In line with established hypotheses about genetic pathways that control kidney development, we find that repressing Pax2 using siRNAs represses Wt1 expression and blocks both bud growth and nephron differentiation, but that repressing Wnt4 blocks nephron differentiation without affecting Wt1 expression. As well as illuminating previously inaccessible aspects of Wt1 biology, our results suggest that siRNA in organ culture will be a powerful method for analyzing other developmental pathways and testing the effects of stage-specific loss of tumour suppressor genes.

Role of Pax2 in apoptosis resistance and proinvasive phenotype of Kaposi's sarcoma cells

In this study, we found that Kaposi's sarcoma cells but not human microvascular endothelial cells expressed PAX2, a gene coding for a transcription factor involved both in organogenesis and tumorigenesis. Moreover, Pax2 was frequently expressed, on spindle-shaped cells, in Kaposi's sarcoma lesions. We cloned PAX2 from Kaposi's sarcoma cells and obtained antisense and sense DNA. Transfection of Kaposi's sarcoma cells with antisense DNA, which suppressed Pax2 protein expression, reduced cell growth and survival and enhanced the sensitivity of Kaposi's sarcoma cells to apoptosis induced by serum deprivation or vincristine treatment. In addition, antisense transfection inhibited the cell motility, the invasion of Matrigel, and the spindle shape morphology, which are characteristics of Kaposi's sarcoma cells. Moreover, the alphavbeta3 integrin, known to be involved in tumor invasion, was down-regulated. To evaluate the possible role of Pax2 expression in the endothelial origin of Kaposi's sarcoma cells, human microvascular endothelial cells were transfected with sense DNA. Endothelial cells transfected with sense PAX2 acquired spindle shape morphology, showed enhanced motility and Matrigel invasion, and displayed an enhanced expression of alphavbeta3 integrin. In conclusion, the expression of Pax2 by Kaposi's sarcoma cells correlated with an enhanced resistance against apoptotic signals and with the proinvasive phenotype. Moreover, PAX2-transfected endothelial cells acquired a phenotype resembling that of Kaposi's lesional cells, suggesting a role of this embryonic gene in tumorigenesis.

Possible regulation of Wilms' tumour gene 1 (WT1) expression by the paired box genes PAX2 and PAX8 and by the haematopoietic transcription factor GATA-1 in human acute myeloid leukaemias

Overexpression of the embryonic transcription factor, Wilms' tumour protein 1 (WT1), is common in acute myeloid leukaemias (AML). Mutations of Wilms' tumour gene 1 (WT1) in AML are rare and WT1 expression may be increased by other transcription factors. PAX2, PAX8 and GATA-1 are known physiological regulators of WT1. In the present study, we analysed either bone marrow or blood samples of 43 AML patients for the expression levels of WT1, PAX2, PAX8 and GATA-1 by real-time reverse transcription polymerase chain reaction (LightCycler). Bone marrow samples of patients without haematological malignancies and stem cell preparation samples from healthy donors and lymphoma patients served as controls. PAX2 expression was found in 11 of 43 AML samples, with a clear correlation of PAX2 with WT1 expression levels observed. PAX8 expression was found in two additional samples. GATA-1 expression was detectable in 41 of 43 AML samples and also in all control samples; no significant differences between these groups were observed and no correlation of GATA-1 expression with WT1 expression levels was apparent. In conclusion, PAX2, and possibly PAX8, appears to be a candidate for the upregulation of WT1 in a proportion of AML, whereas GATA-1 expression cannot be explained as an inducer of WT1. In two-thirds of leukaemias from our series, the basis of WT1 upregulation cannot be explained by the simple upregulation of the known WT1 activators.