Tubular Cyst Formation Research Articles

Towards an Understanding of Kidney Diseases Associated with Inhibition of Notch Signaling Pathway by Transmission Electron Microscopy

Transmission electron microscopy (TEM) of samples prepared by ultramicrotomy provides detailed structural information for interrogation of processes at the cellular level. In this work, we are using mouse models and cell culture systems to understand how Notch signaling suppresses renal tubular cyst formation and microadenoma (a tumor) formation. These studies are likely to reveal how Notch signaling is linked to primary cilia and the cell cycle, and will provide insights into the mechanisms by which Notch functions as a tumor suppressor in epithelial cancers. By performing electron microscopy, we are investigating the structure of cilia to understand their role in Notch signaling deficient kidney cells. By analyzing TEM images, we are able to detect normal 9+0 microtubule doublets within the axoneme of primary cilia in both wild type and mutant type cells. After analyzing mutant kidney cells, we detected cilia which have unusual arrangements of microtubules. These abnormal structures may be due to alterations in “posttranslational modifications”. We believe that the Notch signaling deficiency may alter the posttranslational modifications of the microtubules in mutant cells. In the future, we plan to determine the posttranslational modifications in Notch signaling deficient cells by performing a quantitative analysis by western blotting. Also, by performing tem tomography, we can confirm that the abnormal structures are real and not artifacts.

Effects of Increased Renal Tubular Vascular Endothelial Growth Factor (VEGF) on Fibrosis, Cyst Formation, and Glomerular Disease

The role of vascular endothelial growth factor (VEGF) in renal fibrosis, tubular cyst formation, and glomerular diseases is incompletely understood. We studied a new conditional transgenic mouse system [Pax8-rtTA/(tetO)(7)VEGF], which allows increased tubular VEGF production in adult mice. The following pathology was observed. The interstitial changes consisted of a ubiquitous proliferation of peritubular capillaries and fibroblasts, followed by deposition of matrix leading to a unique kind of fibrosis, ie, healthy tubules amid a capillary-rich dense fibrotic tissue. In tubular segments with high expression of VEGF, cysts developed that were surrounded by a dense network of peritubular capillaries. The glomerular effects consisted of a proliferative enlargement of glomerular capillaries, followed by mesangial proliferation. This resulted in enlarged glomeruli with loss of the characteristic lobular structure. Capillaries became randomly embedded into mesangial nodules, losing their filtration surface. Serum VEGF levels were increased, whereas endogenous VEGF production by podocytes was down-regulated. Taken together, this study shows that systemic VEGF interferes with the intraglomerular cross-talk between podocytes and the endocapillary compartment. It suppresses VEGF secretion by podocytes but cannot compensate for the deficit. VEGF from podocytes induces a directional effect, attracting the capillaries to the lobular surface, a relevant mechanism to optimize filtration surface. Systemic VEGF lacks this effect, leading to severe deterioration in glomerular architecture, similar to that seen in diabetic nephropathy.

Renal Tubular Cyst Formation in Newborn Rats Treated with p-Cumylphenol

In this study, we investigated the sequential changes in the development of renal tubular cysts in newborn rats treated with p-cumylphenol (PCP). Fifteen animals per sex were treated orally with 300 mg/kg/day of PCP for up to 18 days from postnatal day (PND) 4 and were sacrificed on PNDs 8, 12, 19 and 22 and after a 7 day recovery period. On PNDs 8 and 12, slight dilatation of the collecting ducts was frequently observed in the medulla and slight papillary necrosis was also noted in some cases. These dilated collecting ducts were lined with slightly hyperplastic epithelial cells. On PNDs 19 and 22, multiple large cystic changes arising from the collecting ducts in the outer medulla were seen. These cystically dilated ducts were also lined with hyperplastic epithelial cells. During the dosing period, the labeling index of proliferating cell nuclear antigen in the collecting duct epithelium was higher in the PCP-treated group than in the control group at all time points. After a 7 day recovery period, the cystic change still remained, although the cell density was decreased and the epithelial cells became flattened. On the other hand, basophilic tubules with peritubular lymphoid cell infiltration were multifocally observed in the cortex. In conclusion, PCP induced multiple renal cysts that developed in the collecting ducts of the outer medulla in neonatal rats, and it is suggested that epithelial cell proliferation may play some roles in the induction of cystic lesions.

The Polycystic Kidney Disease-1 Gene Is a Target for p53-mediated Transcriptional Repression

The Polycystic Kidney Disease-1 Gene Is a Target for p53-mediated Transcriptional Repression

Segment-Specific c-ErbB2 Expression in Human Autosomal Recessive Polycystic Kidney Disease

c-ErbB2 (also referred to as Neu or HER2), a transmembrane glycoprotein with intrinsic tyrosine kinase activity, is structurally related to epidermal growth factor receptor (EGFR) and forms active heterodimers with EGFR as well as other members of the EGFR family. c-ErbB2 is reported to mediate differentiation and proliferation in epithelial cells and is expressed in a tissue-specific and developmental stage-specific manner. Given the role of EGFR in cystic renal epithelial hyperplasia and the immature phenotype of cystic renal epithelial cells, the segment-specific expression pattern of c-ErbB2 in human autosomal recessive polycystic kidney disease (ARPKD) was examined in nine ARPKD kidney specimens ranging from gestational age 17 wk through postnatal age 4 wk. c-ErbB2 staining of human ARPKD samples showed increased expression with increasing gestational age compared with normal human fetal and postnatal kidneys. This increased c-ErbB2 expression was primarily localized to the apical surfaces of cystic collecting tubule cells, similar to the pattern of EGFR expression, and paralleled collecting tubular cyst formation and growth.

Postnatal development and progression of renal dysplasia in cyclooxygenase-2 null mice

Genetic ablation of cyclooxygenase-2 (COX-2) resulted in cystic renal dysplasia and early death in adult mice. The ontologic development of the renal pathology and the biochemical and physiological abnormalities associated with the dysplasia are unknown. Mice homozygous for a targeted deletion of COX-2 (-/-) were compared with wild-type littermates (+/+). Somatic and kidney growth and renal histology were studied at the day of birth and at a number of postnatal ages. Systolic blood pressure, urinalysis, urine osmolality, serum and urine chemistries, and inulin clearance were evaluated in adult animals. Beginning at postnatal day 10 (PN10), kidney growth was suppressed in -/- animals, while somatic growth and heart growth were unaffected. By PN10, -/- kidneys had thin nephrogenic cortexes and crowded, small, subcapsular glomeruli. The pathology increased with age with progressive outer cortical dysplasia, cystic subcapsular glomeruli, loss of proximal tubular mass, and tubular atrophy and cyst formation. Adult -/- kidneys had profound diffuse tubular cyst formation, outer cortical glomerular hypoplasia and periglomerular fibrosis, inner cortical nephron hypertrophy, and diffuse interstitial fibrosis. The glomerular filtration rate was reduced by more than 50% in -/- animals (6.82 +/- 0.65 mL/min/kg) compared with wild-type controls (14.7 +/- 1.01 mL/min/kg, P < 0. 001). Plasma blood urea nitrogen and creatinine were elevated in null animals compared with controls. Blood pressure, urinalysis, urine osmolality, and other plasma chemistries were unaffected by the deletion of COX-2. Deficiency of COX-2 results in progressive and specific renal architectural disruption and functional deterioration beginning in the final phases of nephrogenesis. Tissue-specific and time-dependent expression of COX-2 appears necessary for normal postnatal renal development and the maintenance of normal renal architecture and function.

Proximal tubular cysts in fetal human autosomal recessive polycystic kidney disease.

Standard texts describe human autosomal recessive polycystic kidney disease (ARPKD) as a cystic kidney disease in which lesions are localized to collecting tubules. Murine models of ARPKD consistently demonstrate an early phase of proximal tubular (PT) cystic involvement, which disappears shortly after birth. This is followed by a phase of collecting tubular (CT) cyst formation and progressive enlargement leading to compromise of renal function and death. Because the description of cystic lesions in human ARPKD has been largely based on postnatal specimens, PT cyst formation was hypothesized to be a characteristic feature of fetal human, as well as murine, ARPKD. This study examines nephron segment-specific cyst localization histochemically by lectin binding in 11 human ARPKD specimens obtained at different fetal and postnatal ages. PT cysts were found in human fetal specimens from gestational age 14 wk to 26 wk. The percentage of cysts involving PT segments ranged from 2 to 41%. The cystic index of PT cysts ranged from 2 to 5. In all specimens in which PT cysts were found, both the percentage of CT cysts and their cystic index were equal to or greater than the percentage of PT cysts and the associated PT cystic index. PT cysts were absent in all kidney specimens older than 34 wk gestational age. It is concluded that human ARPKD, like murine ARPKD, has a transient phase of PT cyst formation during early fetal development.

Tyrosine kinase activity of the EGF receptor in murine metanephric organ culture

Epidermal growth factor (EGF) and its fetal form, transforming growth factor alpha (TGF-alpha) are renal mitogens which induce epithelial hyperplasia, proximal tubular cyst formation (TC), and accelerated distal nephron differentiation in metanephric organ culture. To delineate the intracellular mechanisms mediating these growth factor effects, we studied the specific role of the epidermal growth factor receptor (EGF-R), the common receptor for both ligands, as an activated tyrosine kinase in TC formation and nephrogenesis. Fetal murine metanephric explants were incubated for 120 hours in control, and EGF (15 ng/ml)/TGF-alpha (10 ng/ml) supplemented medium with and without EGF-R blocking monoclonal antibody (50 mg/ml), or tyrosine kinase inhibitor. EGF-R tyrosine kinase inhibition was achieved by incubation with a synthetic tyrphostin (TP B42) (0.1 microM) or genestein (5.5 micrograms/ml). The following parameters were assessed: (a) segment-specific nephron development using morphometry and immunohistology; (b) tubular epithelial hyperplasia by protein content and BrdU uptake; and (c) TC formation by morphometric cystic index. Both growth factors produced hyperplastic proximal TC, significantly increased explant growth, and significantly increased distal nephron differentiation. Inhibiting the ligand-EGF-R interaction with EGF-R blocking monoclonal antibody abolished all growth factor-induced effects and resulted in increased amounts of undifferentiated mesenchyme and decreased distal nephron differentiation. Inhibition of EGF-R tyrosine kinase activity with either Tyrphostin B42 or genestein blocked TC formation and produced nodular blastemal hyperplasia and decreased distal nephron differentiation.

Epidermal growth factor receptor expression is abnormal in murine polycystic kidney

Renal tubular cyst formation and progressive enlargement in autosomal recessive polycystic kidney disease (ARPKD) are mediated by increased epithelial cell proliferation and altered transtubular fluid transport. Epidermal growth factor (EGF)-like peptides have been proposed to play roles in normal nephrogenesis and cystic tubular mitogenesis. Therefore, renal expression of EGF receptor (EGFR) protein and mRNA was examined in an animal model for ARPKD, the C57BL/6Jcpk/cpk (CPK) mouse. Both quantitative and qualitative abnormalities of EGFR expression were demonstrated. While both control and cystic proximal tubules, as well as control collecting tubules, demonstrated exclusive basalateral EGFR protein expression, cystic collecting tubules exhibited significant apical-lateral receptor localization. During nephrogenesis, EGFR protein expression was elevated in CPK renal tissue when compared to developmentally staged controls. Control and CPK kidneys expressed the same species of EGFR mRNA. Levels increased with developmental age, but were significantly higher at each stage of development in CPK kidneys. Overexpression of both EGFR protein and mRNA in CPK mice suggests altered control of EGFR protein and/or gene expression. EGFR mislocalization and overexpression may be mechanisms whereby the EGF-like factors in cyst fluid stimulate cystogenesis through an autocrine-paracrine cycle in ARPKD.

Epithelial polarity and differentiation in polycystic kidney disease.

Renal cysts are central pathological features in a number of human congenital and acquired diseases, and produce significant morbidity and mortality. This review describes our laboratory's efforts to identify specific alterations in epithelial cell polarity and differentiation associated with renal tubular cyst formation and progressive enlargement. Studies in a murine model of human autosomal recessive polycystic kidney disease, the C57BL/6J cpk/cpk (CPK) mouse have demonstrated quantitative (increased activity) and qualitative (apical membrane distribution) alterations in Na+,K(+)-adenosine triphosphatase activity that mediate tubular cyst formation. Proximal tubular cyst formation in CPK kidneys is characterized by increased activity of a basolateral Na+,K(+)-ATPase, which drives organic anion secretion and consequent tubular fluid secretion. In contrast, collecting tubule cyst formation is characterized by increased apical membrane Na+,K(+)-ATPase expression, which may be a marker of the relatively undifferentiated phenotype of cyst lining cells. If such apically expressed enzyme is active, it may have pathogenic import in collecting tubule cyst formation and enlargement by mediating net basal to apical vectorial solute and fluid transport.

Abnormal sodium pump distribution during renal tubulogenesis in congenital murine polycystic kidney disease.

Congenital polycystic kidney disease is characterized by the formation of large fluid-filled cysts in kidney tubules. It has been postulated that increased epithelial cell proliferation and altered transtubular fluid transport are necessary for cyst formation. To address the latter problem, we have studied the plasma membrane distribution of the alpha 1 and beta 1 subunits of Na+/K(+)-ATPase during progressive stages of proximal and collecting tubular cyst formation in the CPK mouse, a murine model of autosomal recessive polycystic kidney disease. In both control and cystic proximal tubules, Na+/K(+)-ATPase distribution was restricted to the basal-lateral membrane of cells. However, in newborn through day 5 kidney tissue, 16% of control vs. 47% of cystic outer cortical, 6% of control vs. 46% of cystic inner cortical, and 2% of control vs. 63% of cystic medullary collecting tubules demonstrated apical and lateral membrane distribution of Na+/K(+)-ATPase. In all nephrogenic zones, the percentage of control or cystic collecting tubules demonstrating apical membrane distribution of Na+/K(+)-ATPase decreased over time, but the percentage of cystic collecting tubules with apical membrane Na+/K(+)-ATPase remained significantly greater than in developmentally matched controls. No alterations in the normal distributions of other apical or basal-lateral membrane marker proteins were noted at any stage of control or cystic proximal or collecting tubule development. We conclude that apical-lateral membrane Na+/K(+)-ATPase expression is a normal transient feature of early collecting tubule development. However, apical membrane Na+/K(+)-ATPase persists in cystic kidneys, suggesting that such expression may be a manifestation of the relatively undifferentiated phenotype of epithelial cells lining collecting tubule cysts. The persistence of apical membrane Na+/K(+)-ATPase, if the enzyme is functional, may have pathogenic important in abnormal transtubular fluid transport in polycystic kidney disease.

Pathophysiology of renal tubular cyst formation in murine models of polycystic kidney disease.

Pathophysiology of renal tubular cyst formation in murine models of polycystic kidney disease.

In vitro modulation of tubular cyst regression in murine polycystic kidney disease

Recent studies in a murine model of genetically-determined polycystic kidney disease, the CPK mouse, have suggested that alterations in renal Na-K ATPase activity in concert with tubular epithelial hyperplasia have pathogenic import in proximal tubular cyst formation. In the current study, we therefore studied the relative roles of Na-K ATPase activity, tubular epithelial hyperplasia, and basal lamina alterations during in vitro modulation of proximal tubular cyst regression during serum-free organ culture of newborn CPK kidneys. Under basal in vitro conditions, regression of CPK proximal tubular cysts was demonstrated in association with progressive decreases in Na-K ATPase activity and tubular epithelial hyperplasia. The pattern of proximal tubular cyst regression was modified by: a) Na-K ATPase activity induction with triiodothyronine, which promoted proximal tubular cystogenesis; and b) Na-K ATPase activity inhibition with ouabain, which blocked the effects of T3 on the process of cyst formation. Modulation of proximal tubular cystogenesis by Na-K ATPase induction and inhibition were accomplished without significant changes in proximal tubular epithelial hyperplasia or expression of basal lamina components. We conclude that increased Na pump activity may have a significant role in proximal tubular cyst formation and progressive enlargement in the CPK mouse.

Effect of vitamin C supplementation on renal oxalate deposits in five-sixths nephrectomized rats.

We have previously reported that hyperoxalemia can be aggravated by vitamin C supplementation in regular hemodialysis patients. The present study was undertaken to examine the validity of this observation in an experimental setting. Fifty five-sixths nephrectomized rats were divided into two groups: 30 rats were allowed free access to water containing 8 mg/ml of vitamin C (100-160 mg/100 g/24 h) and the remainder given tap water without vitamin C. The serum creatinine increased and the Hct decreased gradually; however, there was no difference between the two groups. Plasma vitamin C, oxalate and urinary oxalate levels were higher in the vitamin -treated group than the nontreated rats. Histological examination revealed glomerular and interstitial fibrosis and round cell infiltration as well as tubular cyst formation. Oxalate deposits in renal tubules were found only in vitamin C-treated rats with advanced renal failure. Nontreated animals with equally advanced renal impairment showed no oxalate deposits. These results confirm our previous clinical findings that vitamin C supplementation aggravates the secondary oxalosis of chronic renal failure.

Congenital murine polycystic kidney disease. II. Pathogenesis of tubular cyst formation.

In the current study, the pathogenesis of proximal tubular cyst formation was studied in an animal model of polycystic kidney disease, the CPK mouse. The specific roles of (a) sodium-potassium adenosine triphosphatase (Na-K ATPase) activity, determined by an enzyme-linked kinetic microassay, (b) proximal tubular epithelial hyperplasia, determined by calculation of mitotic indices, and (c) altered proximal tubular basal lamina formation, determined by immunohistological localization of basal lamina glycoproteins, were investigated at progressive developmental stages of CPK proximal tubular cyst formation. Increases in renal Na-K ATPase were present at the earliest fetal stages of proximal tubular cyst formation, and subsequently paralleled the course of proximal tubular cyst progression. Proximal tubular epithelial hyperplasia, although not present at the earliest stages of cyst formation, was a consistent feature of progressive proximal tubular cystic enlargement. Abnormalities in basal lamina glycoprotein expression were not present at any stage of proximal tubular cyst development. We conclude that increased Na-K ATPase and tubular epithelial hyperplasia are significant features of proximal tubular cyst formation in the CPK mouse.

Immunocytochemical localization of gamma-glutamyltranspeptidase during fetal development of mouse kidney.

In the fully developed kidney, gamma-glutamyltranspeptidase is localized predominantly to the apical plasma membrane of the proximal tubules. The appearance of this activity during murine fetal nephrogenesis was quantitated using a sensitive fluorometric assay, and development of membrane polarity was assessed by immunocytochemistry. Specific activity of the transpeptidase in 13-day fetal kidney was approximately 1 mU/mg protein. Between 13-21 days of gestation, total transpeptidase activity increased 7500-fold, whereas specific activity increased 50-fold. At 13 days of gestation, gamma-glutamyltranspeptidase immunoreactivity is localized to the apical surfaces of developing renal vesicles and the proximal segment of the S-shaped tubules. The organized cell structures have tight tubular junctions but lack a well-defined brush-border membrane. By 15 days of gestation, immunostaining of the apical surface of developing proximal segments is more prominent, and slight reactivity of the basolateral membrane is evident. By 17 days of gestation, the kidney is organized into discrete zones. The large increase in gamma-glutamyltranspeptidase activity correlates with the appearance of increased immunostaining of the developing brush-border membranes of the proximal tubules contained in the inner cortex. A very similar although somewhat delayed pattern of appearance of transpeptidase activity and immunostaining was observed in metanephric organ culture. Induction of proximal tubular cyst formation had no effect on the increase in transpeptidase activity that occurred during organotypic nephrogenesis.

Congenital murine polycystic kidney disease. I. The ontogeny of tubular cyst formation.

In the current study, the ontogeny of tubular cyst formation was studied in the CPK mouse, a murine strain with autosomal recessive polycystic kidney disease. Utilizing the technique of intact nephron microdissection in addition to standard light and transmission electron microscopy, the earliest morphologic alterations in CPK kidneys were localized in fetal tissue at 17 days of gestation to the distal portion of developing proximal tubules. During disease progression, from birth to 21 days of postnatal age, there was a shift in the site of cystic nephron involvement from proximal tubule to collecting tubules without involvement of other nephron segments. Cysts were enlarged tubular segments which remained in continuity with other portions of the nephron and were not associated with abnormalities in the overall pattern of nephron growth or differentiation. Analysis suggested that alterations in transtubular transport in abnormally shortened proximal tubular segments of juxtamedullary nephrons may have pathogenic importance in the early stages of cyst formation, and that epithelial hyperplasia and cytoskeletal alterations may have a role in progressive proximal tubular cystic enlargement. Cellular hyperplasia of epithelial walls of normally formed tubules was a prominent feature of cyst formation and progressive enlargement in collecting tubules. Such data form the basis for future studies into specific pathophysiological processes which may be operative in specific nephron segments during different stages of cyst formation in the CPK mouse.

Triiodothyronine-induced cyst formation in metanephric organ culture: the role of increased Na-K-adenosine triphosphatase activity.

Previous organ culture investigations into the pathogenesis of renal cyst formation have demonstrated that glucocorticoid-induced proximal tubular cyst formation is associated with increases in renal sodium-potassium adenosine triphosphatase (Na-K-ATPase) activity. To explore the relationship between cyst production and transport enzyme induction, we examined the effects of the potent inducer of Na-K-ATPase activity, L-3,5,3'-triiodothyronine (T3), on renal tubular morphologic and enzymatic development in murine metanephric organ culture. The addition of T3 (2 X 10(-8) mol/L) to completely characterized, serum-free growth medium produced striking proximal tubular cystic abnormalities. Frank cyst development was preceded by ultrastructural alterations consisting of basolateral intercellular spreading, which increased with progressive tubular dilation. Ultrastructural analysis demonstrated no abnormalities of tubular cyst wall basal laminae, and immunohistologic staining with affinity-purified antibodies to the basal lamina glycoproteins fibronectin, laminin, and entactin, revealed no differences between cystic and control tissue. With use of an enzyme-linked kinetic microassay, T3-induced cystic organ culture explants (CY) showed significant increases in Na-K-ATPase when compared with controls from 72 to 120 hours of organ culture incubation. The initial differences in CY Na-K-ATPase occurred contemporaneously with the earliest ultrastructural evidence of cyst formation, and subsequent increases paralleled progressive tubular cyst formation. Tubular cyst formation in CY could be largely prevented by daily incubation of explants with ouabain, 0.2 mmol/L (final concentration) for 120 minutes without deleterious effects on overall metanephric development. We conclude that T3 induces proximal tubular cyst formation in metanephric organ culture, and that T3-induced increases in Na-K-ATPase have a primary role in the pathogenesis of tubular cyst formation in this model system.

Sodium-potassium ATPase activity mediates cyst formation in metanephric organ culture

To study the possible role of altered transtubular transport in renal tubular cyst formation, the ontogeny of renal Na-K ATPase was studied during glucocorticoid-induced cystic metanephric tubular development in serum-free, murine organ culture (SFMOC). Utilizing an enzyme-linked kinetic microassay, a developmental profile of total ATPase and specific Na-K ATPase activity was established for control (CON) and glucocorticoid-induced cystic organ culture (CY) explants. During 120 hr of CON and CY organ culture nephrogenesis total Na-K ATPase activity, specific Na-K ATPase activity, and the Na-K ATPase: total ATPase ratio progressively increased, simulating normal in vivo murine enzyme development. However, from 48 to 120 hr of organ culture, CY showed significant increases in Na-K ATPase activity when compared to CON at similar stages of development. Na-K ATPase activity (expressed as nmoles . min-1 . mg protein -1, mean +/- SD) was, at: 48 hr, CY 13.1 +/- 0.7 vs. CON 11.0 +/- 0.9 (P less than 0.01); 72 hr, CY 16.4 +/- 1.1 vs. CON 12.2 +/- 0.7 (P less than 0.001); 96 hr, CY 35.4 +/- 4.9 vs. CON 13.7 +/- 0.4 (P less than 0.001); and 120 hr, CY 26.1 +/- 1.4 vs. CON 16.3 +/- 0.9 (P less than 0.001). The initial differences in CY enzyme activity preceded the earliest ultrastructural evidence of cyst formation by 18 to 24 hr, while subsequent increases in Na-K ATPase activity in CY paralleled progressive tubular cyst formation. Tubular cyst formation in CY could be largely prevented by daily incubation of explants with ouabain, 0.2 mM (final concentration) X 120 min, without deleterious effects on overall metanephric development.(ABSTRACT TRUNCATED AT 250 WORDS)

1573 REGRESSION OF CONGENITAL MURINE POLYCYSTIC KIDNEY DISEASE (PKD) IN METANEPHRIC ORGAN CULTURE (MOC)

A form of autosomal recessive PKD naturally occurs in the mutant CPK strain of C57BL/6J mice. In order to examine the role of enviromental factors in the expression of genetically determined PKD, the organogenesis of CPK kidneys was studied in our previously described MOC system (In Vitro 18:675, 1982). In this system, advanced murine nephrogenesis occurs in a serum-free, completely controlled biochemical environment. Newborn kidneys from controls (CON) and CPK mice were microsliced into 100 μm explants and cultured in Ham's F-12: DMEM supplemented with insulin (8 × 10−7 M), T3 (2 × 10−9M), transferrin (6 × 10−8 M), PGE1(7 × 10−8 M), and Na2SeO3 (7 × 10−9 M) at 36 ± 0.5°C in mixed air:5% CO2. During 120 hours of culture:1) CON explants increased in size and demonstrated advanced tubular differentiation; and 2) CPK explants, which initially exhibited prominent proximal tubular dilatation and cyst formation, demonstrated total cyst regression in addition to overall growth and differentiation similar to CON. We conclude that in the CPK animal model of PKD: 1) early changes of proximal tubular cyst formation are totally reversible in vitro; and therefore that 2) genetically determined cyst formation can be modified by environmental factors. MOC of CPK kidneys provides a controlled experimental system in which the enviromental factors modulating cystic organogenesis may be isolated and further characterized.