Pictilisib-Induced Resistance Is Mediated through FOXO1-Dependent Activation of Receptor Tyrosine Kinases in Mucinous Colorectal Adenocarcinoma Cells.

The phosphatidylinositol (PI3K)/AKT/mTOR axis represents an important therapeutic target to treat human cancers. A well-described downstream target of the PI3K pathway is the forkhead box O (FOXO) transcription factor family. FOXOs have been implicated in many cellular responses, including drug-induced resistance in cancer cells. However, FOXO-dependent acute phase resistance mediated by pictilisib, a potent small molecule PI3K inhibitor (PI3Ki), has not been studied. Here, we report that pictilisib-induced adaptive resistance is regulated by the FOXO-dependent rebound activity of receptor tyrosine kinases (RTKs) in mucinous colorectal adenocarcinoma (MCA) cells. The resistance mediated by PI3K inhibition involves the nuclear localization of FOXO and the altered expression of RTKs, including ErbB2, ErbB3, EphA7, EphA10, IR, and IGF-R1 in MCA cells. Further, in the presence of FOXO siRNA, the pictilisib-induced feedback activation of RTK regulators (pERK and pAKT) was altered in MCA cells. Interestingly, the combinational treatment of pictilisib (Pi3Ki) and FOXO1i (AS1842856) synergistically reduced MCA cell viability and increased apoptosis. These results demonstrate that pictilisib used as a single agent induces acute resistance, partly through FOXO1 inhibition. Therefore, overcoming PI3Ki single-agent adaptive resistance by rational design of FOXO1 and PI3K inhibitor combinations could significantly enhance the therapeutic efficacy of PI3K-targeting drugs in MCA cells.

Bilateral blockade of MEK- and PI3K-mediated pathways downstream of mutant KRAS as a treatment approach for peritoneal mucinous malignancies.

Mucinous colorectal adenocarcinomas (MCAs) are clinically and morphologically distinct from nonmucinous colorectal cancers (CRCs), show a distinct spectrum of genetic alterations (higher KRAS mutations, lower p53, high MUC2), exhibit more aggressive behavior (more prone to peritoneal dissemination and lymph node involvement) and are associated with poorer response to chemotherapy with limited treatment options. Here, we report the effectiveness of combinatorial targeting of two KRAS-mediated parallel pathways in reducing MUC2 production and mucinous tumor growth in vitro and in vivo. By knockdown of mutant KRAS we show that, mutant KRAS (a) is necessary for MUC2 production in vitro and (b) synergistically engages PI3K/AKT and MEK/ERK pathways to maintain MUC2 expression in MCA cells. These results define a novel and a previously undescribed role for oncogenic KRAS in mucinous cancers. MCA cells were sensitive to MEK inhibition suggesting cellular dependence ('addiction') of KRAS-mutant MCA cells on hyperactivation of the MEK-driven pathway. Interestingly, MCA cells, though initially sensitive, were later resistant to PI3K single agent inhibition. Our studies suggest that this resistance involves dynamic rewiring of signaling circuits mediated through relief of RTK inhibition and MEK-ERK rebound activation. This resistance however, could be overcome by co-targeting of PI3K and MEK. Our studies thus provide a rational basis for MEK- and PI3K-targeted combination therapy for not only KRAS mutant MCA but also for other related mucinous neoplasms that overproduce MUC2 and have a high rate of KRAS mutations such as pseudomyxoma peritonei.

Patient-derived xenograft mouse models of pseudomyxoma peritonei recapitulate the human inflammatory tumor microenvironment.

Pseudomyxoma peritonei (PMP) is a neoplastic syndrome characterized by peritoneal tumor implants with copious mucinous ascites. The standard of care for PMP patients is aggressive cytoreductive surgery performed in conjunction with heated intraperitoneal chemotherapy. Not all patients are candidates for these procedures and a majority of the patients will have recurrent disease. In addition to secreted mucin, inflammation and fibrosis are central to PMP pathogenesis but the molecular processes that regulate tumor-stromal interactions within the peritoneal tumor microenvironment remain largely unknown. This knowledge is critical not only to elucidate PMP pathobiology but also to identify novel targets for therapy. Here, we report the generation of patient-derived xenograft (PDX) mouse models for PMP and assess the ability of these models to replicate the inflammatory peritoneal microenvironment of human PMP patients. PDX mouse models of low- and high-grade PMP were generated and were of a similar histopathology as human PMP. Cytokines previously shown to be elevated in human PMP were also elevated in PDX ascites. Significant differences in IL-6 and IL-8/KC/MIP2 were seen between human and PDX ascites. Interestingly, these cytokines were mostly secreted by mouse-derived, tumor-associated stromal cells rather than by human-derived PMP tumor cells. Our data suggest that the PMP PDX mouse models are especially suited to the study of tumor-stromal interactions that regulate the peritoneal inflammatory environment in PMP as the tumor and stromal cells in these mouse models are of human and murine origins, respectively. These mouse models are therefore, likely to be useful in vivo surrogates for testing and developing novel therapeutic treatment interventions for PMP.

Malignant Peritoneal Mesothelioma: Characterization of the Inflammatory Response in the Tumor Microenvironment.

BACKGROUND: Malignant peritoneal mesothelioma (MPM) is a rare cancer arising from mesothelial cells lining the peritoneal surface. Little is known about the tumor microenvironment in regulating MPM oncogenesis. The current study defined the chemokine/cytokine expression profile and inflammatory responses within the MPM microenvironment. METHODS: Levels of 10 cytokines (Fractalkine, IFNγ, IL-6, IL-8, IP-10, MCP-1, MIP-1α, MIP-1ß, TNFα, VEGF) in matched ascites and sera from 15 MPM patients were measured using Milliplex immunoassays. Sera from six normal control sera were included. Statistical analyses included the Wilcoxon signed-rank test, the Mann-Whitney U test, bivariate analysis, and the R (2) coefficient of correlation. RESULTS: The median levels of IL-6 (3190 vs 3.18 ng/ml; p < 0.001), IL-8 (118 vs 4.93 ng/ml; p < 0.001), IP-10 (3923 vs 384 ng/ml; p < 0.001), and MCP-1 (2886 vs 544 ng/ml; p = 0.005) were significantly higher in the MPM ascites than in the matched MPM serum. In the MPM serum samples, the levels of IL-8 (4.93 vs 1.52 ng/ml; p = 0.002), MIP-1ß (53.8 vs 22.3; p = 0.016), TNFα (9.97 vs 4.5 ng/ml; p = 0.013), and VEGF (277 vs 105.4 ng/ml; p = 0.036) were significantly higher than in the control sera. CONCLUSION: The chemokines/cytokines in the MPM tumor microenvironment are distinct from those associated with inflammatory responses to infection or injury (e.g., IL-1, IL-2, TNFα, IFNγ). These local changes reflect active reciprocal communication between tumor and associated stroma, which the authors predict is integral to MPM oncogenesis. Future studies will test this hypothesis and identify potential serum biomarkers for MPM.

The endocytic recycling regulatory protein EHD1 Is required for ocular lens development.

The C-terminal Eps15 homology domain-containing (EHD) proteins play a key role in endocytic recycling, a fundamental cellular process that ensures the return of endocytosed membrane components and receptors back to the cell surface. To define the in vivo biological functions of EHD1, we have generated Ehd1 knockout mice and previously reported a requirement of EHD1 for spermatogenesis. Here, we show that approximately 56% of the Ehd1-null mice displayed gross ocular abnormalities, including anophthalmia, aphakia, microphthalmia and congenital cataracts. Histological characterization of ocular abnormalities showed pleiotropic defects that include a smaller or absent lens, persistence of lens stalk and hyaloid vasculature, and deformed optic cups. To test whether these profound ocular defects resulted from the loss of EHD1 in the lens or in non-lenticular tissues, we deleted the Ehd1 gene selectively in the presumptive lens ectoderm using Le-Cre. Conditional Ehd1 deletion in the lens resulted in developmental defects that included thin epithelial layers, small lenses and absence of corneal endothelium. Ehd1 deletion in the lens also resulted in reduced lens epithelial proliferation, survival and expression of junctional proteins E-cadherin and ZO-1. Finally, Le-Cre-mediated deletion of Ehd1 in the lens led to defects in corneal endothelial differentiation. Taken together, these data reveal a unique role for EHD1 in early lens development and suggest a previously unknown link between the endocytic recycling pathway and regulation of key developmental processes including proliferation, differentiation and morphogenesis.

Comparison of cytoreductive surgery and hyperthermic intraperitoneal chemotherapy with mitomycin or carboplatin for diffuse malignant peritoneal mesothelioma.

Diffuse malignant peritoneal mesothelioma is a rare, aggressive disease. Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) have improved outcomes where systemic chemotherapy has not succeeded. In this study, we compare outcomes of patients treated with mitomycin or carboplatin as perfusate. In this retrospective study, 47 procedures (CRS + HIPEC) were conducted on 44 patients between March 2003 and August 2010 with either mitomycin or carboplatin. χ(2) and Student's t test were used for comparison of clinicopathological variables and Kaplan-Meier curves and log rank test were used to compare overall survival. Median survival of the mitomycin group was 18 months with 1- and 5-year survivals of 72.3 and 27.3 per cent, respectively. Median survival of the carboplatin group was not reached and 1- and 5-year survivals were 89.7 and 62.5 per cent, respectively (P = 0.014). Mean hospital and intensive care unit length of stay was 18.9 and 8.7 days in the mitomycin group and 12.5 and 2.3 days in the carboplatin group (P = 0.0069). Mean number of packed red blood cell units transfused was higher in the mitomycin group compared with the carboplatin group (3.54 vs 0.83, P < 0.05). There was no postoperative mortality. HIPEC with carboplatin in diffuse malignant peritoneal mesothelioma is associated with improved overall survival and shorter hospital stay compared with HIPEC with mitomycin.

Pseudomyxoma peritonei: inflammatory responses in the peritoneal microenvironment.

BACKGROUND: Pseudomyxoma peritonei (PMP), a peritoneal mucinous neoplasm of appendiceal origin, is associated with inflammation and fibrosis, which is central to its biology. The significance of the microenvironment in PMP has not been well characterized. METHODS: Immunoassays were used to measure cytokines and C-reactive protein (CRP). Forty-two cytokines were initially measured in 23 PMP ascites and 10 PMP peritoneal washings. On the basis of these results, matching serum and ascites samples were analyzed for ten relevant cytokines (n = 32) and CRP (n = 28). Immunohistochemistry was performed on formalin-fixed tissue sections. Statistical analysis was by Wilcoxon signed rank test, Mann-Whitney U-test, and bivariate analysis. RESULTS: Serum CRP was elevated in PMP and correlated to CRP level in ascites. Interleukin (IL)-6, IL-8 (CXCL8), interferon gamma-induced protein 10 (IP-10), (CXCL10), monocyte chemotactic protein (MCP)-1 (CCL2), and macrophage inflammatory protein (MIP)-1α (CCL3) levels were grossly elevated in ascites but did not correlate with serum levels. Cytokines normally associated with infection or tissue injury (e.g., IL-1, IL-2, interferon gamma) were not elevated. Immunohistochemistry localized IL-6 to stroma, IP-10, and MCP-1 to tumor cells and IL-8 to adipose tissue. There were complex interactions among cytokines. IL-6, in particular, had many significant correlations in ascites. Serum IL-8, MIP-1ß, and CRP were higher in PMP compared to controls. CONCLUSIONS: The pattern of cytokines in PMP is distinct from infection- or injury-associated inflammation. The results support peritoneal synthesis for cytokines. CRP, IL-8, and MIP-1ß are potential serum markers for PMP. IL-6 appears to play a central role in PMP biology. This study provides new details about PMP tumor biology and identifies possible therapeutic targets.

Proposed classification of pseudomyxoma peritonei: influence of signet ring cells on survival.

The nomenclature and classification of pseudomyxoma peritonei (PMP) is confusing and controversial. Numerous classification systems have been proposed, none of which are easily reproducible or a useful guide for treatment. Patients with PMP of appendiceal origin were identified from our institution's database. Kaplan-Meier analyses were performed based on a proposed new PMP classification, a three-tiered grading system designated PMP1, PMP2, and PMP3. These results were compared with the established schemes by Ronnett and Bradley et al. There were 211 patients included in the analysis with a mean age of 51 ± 12 years at diagnosis. For PMP1, 86 patients (40.8%) included cases with abundant extracellular mucin and columnar nonstratified epithelium without dysplasia or atypia. For PMP3, 50 patients (23.7%) consisted of PMP with any percentage of signet ring cells (SRCs), For PMP2, 75 patients (35.5%) included all other patients. The mean age (± standard deviation) for PMP 1, 2, and 3 were 51 ± 12, 51 ± 12, and 51 ± 10 years, respectively (P = 0.90). The three groups had similar sex distribution (P = 0.24) and resection status (P = 0.47). Kaplan-Meier analyses showed median survivals of 120, 88, and 40 months and 5-year survival rates of 85.7, 63.05, and 32.2 per cent (P < 0.0001) for PMP 1, 2, and 3, respectively. Three distinct categories, PMP1, 2, and 3, were identified, which provide better stratification in terms of overall survival and represent differences in tumor biology that may impact treatment recommendations.

Histone posttranslational modifications and cell fate determination: lens induction requires the lysine acetyltransferases CBP and p300.

Lens induction is a classical embryologic model to study cell fate determination. It has been proposed earlier that specific changes in core histone modifications accompany the process of cell fate specification and determination. The lysine acetyltransferases CBP and p300 function as principal enzymes that modify core histones to facilitate specific gene expression. Herein, we performed conditional inactivation of both CBP and p300 in the ectodermal cells that give rise to the lens placode. Inactivation of both CBP and p300 resulted in the dramatic discontinuation of all aspects of lens specification and organogenesis, resulting in aphakia. The CBP/p300(-/-) ectodermal cells are viable and not prone to apoptosis. These cells showed reduced expression of Six3 and Sox2, while expression of Pax6 was not upregulated, indicating discontinuation of lens induction. Consequently, expression of αB- and αA-crystallins was not initiated. Mutant ectoderm exhibited markedly reduced levels of histone H3 K18 and K27 acetylation, subtly increased H3 K27me3 and unaltered overall levels of H3 K9ac and H3 K4me3. Our data demonstrate that CBP and p300 are required to establish lens cell-type identity during lens induction, and suggest that posttranslational histone modifications are integral to normal cell fate determination in the mammalian lens.

Spry1 and Spry2 are necessary for eyelid closure.

Sproutys (Sprys) are downstream targets and negative feedback regulators of the FGF-Ras-ERK signaling pathway. Our previous studies have shown that Spry1 and Spry2, through negative modulation of FGF-ERK signaling, allow lens vesicle separation from the overlying ectoderm and regulate corneal epithelial proliferation. Here we show that Spry1 and Spry2 are necessary for eyelid closure. Murine palpebral conjunctival epithelial cells that differentiate as inner eyelids and adjacent mesenchymal cells express Spry1 and Spry2 prior to eyelid closure. Conditional deletion of both Spry1 and Spry2, but not either one alone, in the ocular surface epithelial cells result in the "EOB" (eyes open at birth) phenotype suggesting redundant roles for these proteins during eyelid closure. Spry mutant eyelids show increased proliferation of conjunctival epithelial cells with concomitant induction of FGF targets, Erm, Pea3 and Dusp6 and elevated ERK phosphorylation. Peridermal cells at the leading edge of Spry-mutant eyelids showed reduced c-Jun, but not ERK, phosphorylation, reduced F-actin polymerization and reduced motility in vitro. Spry mutant eyelids also showed disruptions in epithelial mesenchymal interactions reflected in the enhanced mesenchymal Spry1 and Spry4 expression, disaggregation of BMP4-positive mesenchymal cells and loss of Shh in the eyelid epithelium. Spry mutant eyelids also showed increased Wnt signaling and reduced expression of Foxc1 and Foxc2, two transcription factors previously shown to be necessary for eyelid closure. Collectively, our results show that conjunctival epithelial Spry1 and Spry2 redundantly promote eyelid closure by (a) stimulating ERK-independent, c-Jun-mediated peridermal migration, (b) suppressing conjunctival epithelial proliferation through FGF-ERK signaling, (c) mediating conjunctival epithelial-mesenchymal interactions and (d) maintaining expression of Foxc1 and Foxc2.

Kras mutations and p53 overexpression in pseudomyxoma peritonei: association with phenotype and prognosis.

BACKGROUND: Little information exists on Kras mutations and p53 overexpression in pseudomyxoma peritonei (PMP). These genetic alterations are associated with poorer prognoses in colorectal cancer. We postulated that these mutations might be more frequent in high-grade (HG) PMP (peritoneal mucinous carcinomatosis) versus low-grade (LG) PMP (disseminated peritoneal adenomucinosis/peritoneal mucinous carcinomatosis), for which survival differences are well documented. METHODS: We collected data retrospectively on patients with PMP of appendiceal origin tested for Kras mutation (commercial assay) and p53 overexpression (immunohistochemistry). We used Fisher's exact test, chi-square test, and Kaplan-Meier survival curves for analysis. RESULTS: Of 64 cases with Kras mutations, 25 were classified as LG and 39 as HG PMP. Median age at diagnosis was 53 ± 11.5 y. We detected Kras mutations in 37 of 64 patients (57.8%). In LG PMP, 15 of 25 (60%) were Kras mutant versus 22 of 39 (56.4%) in HG PMP (P=0.80). Nearly 89% of mutations were seen in codon 12. We noted overexpression of p53 in 44.3% (86 of 194) of patients overall, which was significantly different between LG PMP and HG PMP: 35.5% (37 of 104) versus 54.4% (49 of 90), respectively (P=0.009). Kras mutations did not affect prognosis. Overexpression of p53 was associated with a worse outcome. CONCLUSIONS: Kras mutation and p53 overexpression rates are comparable to those of colorectal adenomas and mucinous colorectal cancer. Codon 12 mutations may be associated with mucin production. Kras mutation status is not prognostic for overall survival. Overexpression of p53 was significantly correlated with female sex, higher-grade disease, and worse survival.

Spry1 and Spry2 are necessary for lens vesicle separation and corneal differentiation.

PURPOSE: The studies reported here were performed to analyze the roles of Sproutys (Sprys), downstream targets and negative feedback regulators of the fibroblast growth factor (FGF) signaling pathway, in lens and corneal differentiation. METHODS: Spry1 and -2 were conditionally deleted in the lens and corneal epithelial precursors using the Le-Cre transgene and floxed alleles of Spry1 and -2. Alterations in lens and corneal development were assessed by hematoxylin and eosin staining, in situ hybridization, and immunohistochemistry. RESULTS: Spry1 and -2 were upregulated in the lens fibers at the onset of fiber differentiation. FGF signaling was both necessary and sufficient for induction of Spry1 and -2 in the lens fiber cells. Spry1 and -2 single- or double-null lenses failed to separate from the overlying ectoderm and showed persistent keratolenticular stalks. Apoptosis of stalk cells, normally seen during lens vesicle detachment from the ectoderm, was inhibited in Spry mutant lenses, with concomitant ERK activation. Prox1 and p57(KIP2), normally upregulated at the onset of fiber differentiation were prematurely induced in the Spry mutant lens epithelial cells. However, terminal differentiation markers such as ß- or γ-crystallin were not induced. Corneal epithelial precursors in Spry1 and -2 double mutants showed increased proliferation with elevated expression of Erm and DUSP6 and decreased expression of the corneal differentiation marker K12. CONCLUSIONS: Collectively, the results indicate that Spry1 and -2 (1) through negative modulation of ERKs allow lens vesicle separation, (2) are targets of FGF signaling in the lens during initiation of fiber differentiation and (3) function redundantly in the corneal epithelial cells to suppress proliferation.

Clinical implications of novel activating EGFR mutations in malignant peritoneal mesothelioma.

BACKGROUND: There is a paucity of information about the molecular perturbations involved in MPM tumor formation. We previously reported that EGFR-TK mutations in MPM were predictive of achieving optimal surgical cytoreduction, but the status of EGFR pathway activation potential of these mutations was not known. Here we present the mutant EGFR activating potential and the matured survival data of the EGFR mutant(mut+) relative to wild type EGFR(mut-) mesothelioma. METHODS: Twenty-nine patients were evaluated and their tumors were probed for mutations in the catalytic TK-domain. Twenty-five patients were treated with cytoreductive surgery and complete clinical data was available for comparison of the mut+ and mut- groups. A COS-7 cell expression model was used to determine mutation activating profiles and response to erlotinib. RESULTS: Functional mutations were found in 31%(9/29) of patients; 7 of these mutations were novel and another was the L858R mutation. All missense mutations were found to be activating mutations and responsive to erlotinib. Of the 25 patients managed surgically, there were 7 mut+ and 18 mut-. Two of 7 (29%) mut+ developed progressive disease and died with a median follow-up time of 22 months; while 13/18 (72%) mut- developed progressive disease and 10/18 (56%) died with median TTP of 12 months and median survival of 14 months. CONCLUSIONS: The novel EGFR mutations identified are activating mutations responsive to erlotinib. The mut+ subset have a 'relative' improved outcome. Erlotinib may have a role in MPM and exploration for mutations in a larger patient cohort is warranted.

The endocytic recycling regulator EHD1 is essential for spermatogenesis and male fertility in mice.

BACKGROUND: The C-terminal Eps15 homology domain-containing protein 1 (EHD1) is ubiquitously expressed and regulates the endocytic trafficking and recycling of membrane components and several transmembrane receptors. To elucidate the function of EHD1 in mammalian development, we generated Ehd1-/- mice using a Cre/loxP system. RESULTS: Both male and female Ehd1-/- mice survived at sub-Mendelian ratios. A proportion of Ehd1-/- mice were viable and showed smaller size at birth, which continued into adulthood. Ehd1-/- adult males were infertile and displayed decreased testis size, whereas Ehd1-/- females were fertile. In situ hybridization and immunohistochemistry of developing wildtype mouse testes revealed EHD1 expression in most cells of the seminiferous epithelia. Histopathology revealed abnormal spermatogenesis in the seminiferous tubules and the absence of mature spermatozoa in the epididymides of Ehd1-/- males. Seminiferous tubules showed disruption of the normal spermatogenic cycle with abnormal acrosomal development on round spermatids, clumping of acrosomes, misaligned spermatids and the absence of normal elongated spermatids in Ehd1-/- males. Light and electron microscopy analyses indicated that elongated spermatids were abnormally phagocytosed by Sertoli cells in Ehd1-/- mice. CONCLUSIONS: Contrary to a previous report, these results demonstrate an important role for EHD1 in pre- and post-natal development with a specific role in spermatogenesis.

Activated Ras alters lens and corneal development through induction of distinct downstream targets.

BACKGROUND: Mammalian Ras genes regulate diverse cellular processes including proliferation and differentiation and are frequently mutated in human cancers. Tumor development in response to Ras activation varies between different tissues and the molecular basis for these variations are poorly understood. The murine lens and cornea have a common embryonic origin and arise from adjacent regions of the surface ectoderm. Activation of the fibroblast growth factor (FGF) signaling pathway induces the corneal epithelial cells to proliferate and the lens epithelial cells to exit the cell cycle. The molecular mechanisms that regulate the differential responses of these two related tissues have not been defined. We have generated transgenic mice that express a constitutively active version of human H-Ras in their lenses and corneas. RESULTS: Ras transgenic lenses and corneal epithelial cells showed increased proliferation with concomitant increases in cyclin D1 and D2 expression. This initial increase in proliferation is sustained in the cornea but not in the lens epithelial cells. Coincidentally, cdk inhibitors p27Kip1 and p57Kip2 were upregulated in the Ras transgenic lenses but not in the corneas. Phospho-Erk1 and Erk2 levels were elevated in the lens but not in the cornea and Spry 1 and Spry 2, negative regulators of Ras-Raf-Erk signaling, were upregulated more in the corneal than in the lens epithelial cells. Both lens and corneal differentiation programs were sensitive to Ras activation. Ras transgenic embryos showed a distinctive alteration in the architecture of the lens pit. Ras activation, though sufficient for upregulation of Prox1, a transcription factor critical for cell cycle exit and initiation of fiber differentiation, is not sufficient for induction of terminal fiber differentiation. Expression of Keratin 12, a marker of corneal epithelial differentiation, was reduced in the Ras transgenic corneas. CONCLUSIONS: Collectively, these results suggest that Ras activation a) induces distinct sets of downstream targets in the lens and cornea resulting in distinct cellular responses and b) is sufficient for initiation but not completion of lens fiber differentiation.

Regulation of retinal morphology and posterior segment amino acids by 8-isoprostaglandin E2 in bovine eyes ex vivo.

There is evidence that isoprostanes (IsoPs) can regulate exogenously applied excitatory amino acid neurotransmitters in bovine retina in vitro. However, the regulation of retinal morphology and endogenous neurotransmitter levels by IsoPs is unknown. We examined the effects of intravitreally injected 8-iso-PGE(2) on retinal tissue integrity and viability and amino acid neurotransmitters in bovine eye organ culture ex vivo. Exposure of bovine eyeballs to simulated experimental conditions revealed no retinal apoptosis and necrosis in TUNEL and DAPI staining and hematoxylin and eosin staining assays, respectively, and no changes in basal levels of amino acids in retina and vitreous humor. Furthermore, intravitreal injection of 8-iso-PGE(2) into bovine eyeballs had no effect on retinal apoptosis and integrity. Interestingly, 8-iso-PGE(2) caused a concentration-dependent attenuation of retinal glutamate and its metabolite glutamine and glycine levels, while GABA was unaffected. 8-Iso-PGE(2) (1 and 100 microM) significantly (P < 0.001) attenuated glutamate levels by 33.9% and 48.0%, respectively. 8-Iso-PGE(2) (100 microM) inhibited (P < 0.01) retinal glutamine and glycine levels by 37.7% and 35.5%, respectively. The IsoP exhibited no effect on vitreous humor glutamine and glycine levels, while glutamate and GABA were not detected. Thus, 8-iso-PGE(2) can regulate retinal amino acids without inducing cell death in bovine retina ex vivo.

Dominant inhibition of lens placode formation in mice.

The lens in the vertebrate eye has been shown to be critical for proper differentiation of the surrounding ocular tissues including the cornea, iris and ciliary body. In mice, previous investigators have assayed the consequences of molecular ablation of the lens. However, in these studies, lens ablation was initiated (and completed) after the cornea, retina, iris and ciliary body had initiated their differentiation programs thereby precluding analysis of the early role of the lens in fate determination of these tissues. In the present study, we have ablated the lens precursor cells of the surface ectoderm by generation of transgenic mice that express an attenuated version of diphtheria toxin (Tox176) linked to a modified Pax6 promoter that is active in the lens ectodermal precursors. In these mice, lens precursor cells fail to express Sox2, Prox1 and alphaA-crystallin and die before the formation of a lens placode. The Tox176 mice also showed profound alterations in the corneal differentiation program. The corneal epithelium displayed histological features of the skin, and expressed markers of skin differentiation such as Keratin 1 and 10 instead of Keratin 12, a marker of corneal epithelial differentiation. In the Tox176 mice, in the absence of the lens, extensive folding of the retina was seen. However, differentiation of the major cell types in the retina including the ganglion, amacrine, bipolar and horizontal cells was not affected. Unexpectedly, ectopic placement of the retinal pigmented epithelium was seen between the folds of the retina. Initial specification of the presumptive ciliary body and iris at the anterior margins of the retina was not altered in the Tox176 mice but their subsequent differentiation was blocked. Lacrimal and Harderian glands, which are derived from the Pax6-expressing surface ectodermal precursors, also failed to differentiate. These results suggest that, in mice, specification of the retina, ciliary body and iris occurs at the very outset of eye development and independent of the lens. In addition, our results also suggest that the lens cells of the surface ectoderm may be critical for the proper differentiation of the corneal epithelium.

Perinatal ablation of the mouse lens causes multiple anterior chamber defects.

PURPOSE: The purpose of this study was to reassess the role of the lens as an "embryonic organizer" of ocular tissues. METHODS: We ablated the lens in mice by lens-specific expression of an attenuated version of diphtheria toxin A subunit(Tox176) driven by a modified crystallin promoter. Alterations in the differentiation programs of ocular tissues were examined by hematoxylin and eosin staining, in situ hybridization, and immunohistochemistry. RESULTS: Transgenic mice in the family OVE1757 exhibited severe microphakia. Apoptotic lens fibers were seen by embryonic day 15 (E15) and the lenses were completely ablated by post natal day 8. Multiple defects were seen in the anterior chamber. Corneal endothelial cells did not differentiate properly. The mesenchymal cells that would normally give rise to the endothelial layer were found to express N-cadherin, but they failed to form tight junctions and undergo a mesenchymal-to-epithelial transition. Although early specification of the presumptive ciliary body and iris was detected, subsequent differentiation of the iris was blocked. No dramatic changes were seen in the development of the retina. CONCLUSIONS: These results support the hypothesis that an intact lens is essential for proper differentiation of both the corneal endothelium and the iris and that the lens "organizes" the development of tissues in the anterior chamber.

FGF9 can induce endochondral ossification in cranial mesenchyme.

BACKGROUND: The flat bones of the skull (i.e., the frontal and parietal bones) normally form through intramembranous ossification. At these sites cranial mesenchymal cells directly differentiate into osteoblasts without the formation of a cartilage intermediate. This type of ossification is distinct from endochondral ossification, a process that involves initial formation of cartilage and later replacement by bone. RESULTS: We have analyzed a line of transgenic mice that expresses FGF9, a member of the fibroblast growth factor family (FGF), in cranial mesenchymal cells. The parietal bones in these mice show a switch from intramembranous to endochondral ossification. Cranial cartilage precursors are induced to proliferate, then hypertrophy and are later replaced by bone. These changes are accompanied by upregulation of Sox9, Ihh, Col2a1, Col10a1 and downregulation of CbfaI and Osteocalcin. Fate mapping studies show that the cranial mesenchymal cells in the parietal region that show a switch in cell fate are likely to be derived from the mesoderm. CONCLUSION: These results demonstrate that FGF9 expression is sufficient to convert the differentiation program of (at least a subset of) mesoderm-derived cranial mesenchyme cells from intramembranous to endochondral ossification.

Intracorneal positioning of the lens in Pax6-GAL4/VP16 transgenic mice.

PURPOSE: The purpose of this study was to establish a GAL4/VP16-based binary transactivation system that was active in the lens and corneal epithelium of transgenic mice. METHODS: We generated transgenic mice with the transcriptional transactivator GAL4/VP16 driven by a modified Pax6 promoter that is active in lens and corneal epithelial cells. We also generated and tested UAS-lacZ reporter mice. Wild type and transgenic mice were analyzed by histological, in situ, and Southern hybridization techniques. RESULTS: Five families (OVE1931, OVE1934, OVE1935, OVE1936, and OVE1937) that carry the Pax6-GAL4/VP16 transgene were generated. Unexpectedly, mice from three of the transgenic lines showed ocular abnormalities. In the family OVE1936, cataracts were seen in the heterozygous mice at the time of eyelid opening and homozygotes showed microphthalmia. Transgenic mice in families OVE1931 and OVE1937 appeared normal. Histological analysis of ocular sections of OVE1934, OVE1935, and OVE1936 homozygous transgenic mice showed intracorneal positioning of the lens. The corneal stromal cells were disorganized and there was no distinctive corneal endothelial layer. In situ hybridizations showed robust expression of the GALVP16 transgene in the lens and corneal epithelial cells of the OVE1934, OVE1935, and OVE1936, but not in OVE1931 or OVE1937 families. Bigenic embryos generated by mating the Pax6-GAL4/VP16 mice to the UAS-lacZ mice showed that the GAL4/VP16 transgenic protein is functional and can induce eye-specific expression of a UAS-lacZ reporter gene. CONCLUSIONS: Our data suggest that (1) expression the GAL4/VP16 transgene induces changes in gene expression in lens cells, (2) that developmentally important genes are affected, and (3) that bigenic phenotypes will need to be interpreted with caution.