The thyroid gland originates from the ventral floor of the foregut as a thickening of the endodermal cell layer. The molecular mechanisms underlying the early steps of thyroid morphogenesis are not known. Gene targeting experiments have contributed to the identification of several transcription factors, in general playing a role in the proliferation, survival, and migration of the thyroid cell precursors. The experiments reported here analyze the expression of the transcription factors Titf1, Hhex, Pax8, and Foxe1 in the thyroid primordium of null mutants of each of them. We found that most of these transcription factors are linked in an integrated regulatory network, each of them controlling the presence of other members of the network. The expression of Foxe1 is regulated in an intriguing fashion as it is strongly dependent on the presence of Pax8 in thyroid precursor cells, while the expression of the same gene in the pharyngeal endoderm surrounding the primordium is dependent on Sonic hedgehog (Shh)-derived signaling. Moreover, by the generation of mouse mutants expressing Foxe1 exclusively in the thyroid primordium, we provide a better understanding of the role of Foxe1 in these cells in order to acquire the competence to migrate into the underlying mesenchyme. In conclusion, we provide the first evidence of gene expression programs, controlled by a hierarchy of transcription factors expressed in the thyroid presumptive gut domain and directing the progression of thyroid morphogenesis.

The thyroid-stimulating hormone/thyrotropin (TSH) is the most relevant hormone in the control of thyroid gland physiology in adulthood. TSH effects on the thyroid gland are mediated by the interaction with a specific TSH receptor (TSHR). We studied the role of TSHTSHR signaling on gland morphogenesis and differentiation in the mouse embryo using mouse lines deprived either of TSH (pit(dw)pit(dw)) or of a functional TSHR (tshr(hyt)tshr(hyt) and TSHR-knockout lines). The results reported here show that in the absence of either TSH or a functional TSHR, the thyroid gland develops to a normal size, whereas the expression of thyroperoxidase and the sodium/iodide symporter are reduced greatly. Conversely, no relevant changes are detected in the amounts of thyroglobulin and the thyroid-enriched transcription factors TTF-1, TTF-2, and Pax8. These data suggest that the major role of the TSH/TSHR pathway is in controlling genes involved in iodide metabolism such as sodium/iodide symporter and thyroperoxidase. Furthermore, our data indicate that in embryonic life TSH does not play an equivalent role in controlling gland growth as in the adult thyroid.

Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists demonstrate antitumor activity likely through transactivating genes that regulate cell proliferation, apoptosis, and differentiation. The PAX8/PPARgamma fusion oncogene, which is common in human follicular thyroid carcinomas appears to act via dominant negative suppression of wild-type PPARgamma, suggesting that it may be a tumor suppressor gene in thyroid cells. We have identified a novel high-affinity PPARgamma agonist (RS5444) that is dependent upon PPARgamma for its biological activity. This is the first report of this molecule and its antitumor activity. In vitro, the IC50 for growth inhibition is approximately 0.8 nM while anaplastic thyroid carcinoma (ATC) tumor growth was inhibited three- to fourfold in nude mice. siRNA against PPARgamma and a pharmacological antagonist demonstrated that functional PPARgamma was required for growth inhibitory activity of RS5444. RS5444 upregulated the cell cycle kinase inhibitor, p21WAF1/CIP1. Silencing p21WAF1/CIP1 rendered cells insensitive to RS5444. RS5444 plus paclitaxel demonstrated additive antiproliferative activity in cell culture and minimal ATC tumor growth in vivo. RS5444 did not induce apoptosis but combined with paclitaxel, doubled the apoptotic index compared to that of paclitaxel. Our data indicate that functional PPARgamma is a molecular target for therapy in ATC. We demonstrated that RS5444, a thiazolidinedione (Tzd) derivative, alone or in combination with paclitaxel, may provide therapeutic benefit to patients diagnosed with ATC.

Transcription factors of the Pax family bind to their target genes via the paired domain which is known to be composed of two subdomains each recognizing distinct half-sites in adjacent major grooves of the DNA helix. We now demonstrate that the mammalian Pax8 gene gives rise, by alternative mRNA splicing, to a protein isoform containing an extra serine residue in the recognition alpha-helix 3 of the paired domain. This Pax8(S) protein does not interact with bipartite paired domain-binding sites, indicating that inactivation of the N-terminal DNA-binding motif severely restricts the sequence specificity of the paired domain. However, the Pax8(S) protein binds in vitro and in vivo to the 5aCON sequence which was previously identified as a high-affinity binding site for the Pax6(5a) splice variant carrying a 14-amino-acid insertion in the paired domain. The 5aCON sequence is shown to consist of four interdigitated 5' half-sites of the bipartite consensus sequence and is thus bound by four Pax8(S) molecules via the intact C-terminal DNA-binding motif of the paired domain. Together these data suggest that inactivation of the N-terminal region of the paired domain by alternative splicing is used in vivo to selectively target Pax transcription factors to gene regulatory regions containing highly specialized 5aCON-like sequences.

Recent evidence indicates a crucial role for paired box genes in mouse and human embryogenesis. The murine Pax8 gene encodes a sequence-specific transcription factor and is expressed in the developing secretory system as well as in the developing and adult thyroid. This restricted expression pattern suggested involvement of the Pax8 gene in the morphogenesis of the above organs and prompted us to investigate the PAX8 gene in humans. In this report, we describe the isolation and characterization of PAX8 cDNAs from a human adult kidney cDNA library. An open reading frame of 450 amino acids contains the 128 amino acid paired domain at its amino-terminal end. The predicted human and mouse Pax8 proteins show 97.8% conservation and are identical in their paired domains. Two independent cDNA clones reveal differential splicing of the PAX8 transcripts resulting in the removal of a 63 amino acid serine-rich region from the carboxy end of the predicted Pax8 protein. The truncated Pax8 protein becomes more similar to the predicted murine Pax2 protein, that is also expressed during kidney development and lacks the serine rich region. RNAse protection analysis shows the presence of both PAX8 transcripts in human thyroid, kidney and five Wilms' tumors. No truncated Pax8 transcripts could be detected in mouse kidney. In situ hybridization to sections of human embryonic and fetal kidney showed expression of PAX8 in condensed mesenchyme, comma-shaped and S-shaped bodies. In contrast, PAX2 expression was present mainly in the very early stages of differentiation, in the induced, condensing mesenchyme. This restricted expression pattern suggests a specific role for both genes during glomeruli maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

A subset of follicular thyroid carcinomas contains a balanced translocation, t(2;3)(q13;p25), that results in fusion of the paired box gene 8 (PAX8) and peroxisome proliferator-activated receptor gamma (PPARG) genes with concomitant expression of a PAX8-PPARgamma fusion protein, PPFP. PPFP is thought to contribute to neoplasia through a mechanism in which it acts as a dominant-negative inhibitor of wild-type PPARgamma. To better understand this type of follicular carcinoma, we generated global gene expression profiles using DNA microarrays of a cohort of follicular carcinomas along with other common thyroid tumors and used the data to derive a gene expression profile characteristic of PPFP-positive tumors. Transient transfection assays using promoters of four genes whose expression was highly associated with the translocation showed that each can be activated by PPFP. PPFP had unique transcriptional activities when compared with PAX8 or PPARgamma, although it had the potential to function in ways qualitatively similar to PAX8 or PPARgamma depending on the promoter and cellular environment. Bioinformatics analyses revealed that genes with increased expression in PPFP-positive follicular carcinomas include known PPAR target genes; genes involved in fatty acid, amino acid, and carbohydrate metabolism; micro-RNA target genes; and genes on chromosome 3p. These results have implications for the neoplastic mechanism of these follicular carcinomas.

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.

Recent molecular studies have provided new insights into thyroid carcinogenesis. In thyroid papillary carcinomas at least three initiating events may occur, which are point mutations in the BRAF and RAS genes and RET/PTC rearrangements. Tumors harboring mutant BRAF and RAS are prone to progression to poorly differentiated and anaplastic carcinoma, but most likely require additional mutations to trigger this process. In thyroid follicular carcinomas, two known initiating events are RAS mutations and PAX8-PPARgamma rearrangements, and RAS predisposes to dedifferentiation of follicular carcinomas. p53 and beta-catenin mutations, found with increasing incidence in poorly differentiated and anaplastic carcinomas but not in well-differentiated tumors, may serve as a direct molecular trigger of tumor dedifferentiation. Additional evidence for progression from a preexisting well-differentiated carcinoma to poorly differentiated and anaplastic carcinoma comes from the studies of loss of heterozygosity and comparative genomic hybridization. Molecular studies, although limited by the lack of uniform histologic criteria for poorly differentiated carcinomas, revealed no genetic mutations or chromosomal abnormalities that are unique for poorly differentiated carcinoma and not present in well-differentiated or anaplastic carcinomas. This suggests that poorly differentiated carcinoma, as a group, represents a distinct step in the evolution from well-differentiated to anaplastic thyroid carcinoma, rather than an entirely separate type of thyroid malignancy.

Ovarian serous neoplasms can have morphologic overlap with malignant mesothelioma. The distinction is clinically important, yet most studies have failed to identify immunostains that reliably distinguish these 2 tumor types. Recently, transcription factor PAX8 was shown to be a sensitive and relatively specific marker for Müllerian tumors. In addition, some studies suggest that h-caldesmon is sensitive and specific for mesothelioma when compared with serous ovarian tumors. The goal of this study was to evaluate whether PAX8 and h-caldesmon expression can successfully distinguish mesothelioma from serous ovarian tumors. Immunohistochemistry was carried out using PAX8 and h-caldesmon antibodies on archival tissue from 254 ovarian serous tumors and 50 mesothelial tumors. Nuclear and cytoplasmic immunoreactivity were considered positive for PAX8 and h-caldesmon, respectively. PAX8 staining was present in 99% of high-grade serous ovarian carcinomas and all (100%) low-grade ovarian carcinomas and serous borderline tumors; however, only 74% of these cases (188/254) were diffusely positive in more than 50% of tumors cells, and intensity ranged from strong to weak. None of the pleural malignant mesotheliomas were reactive with PAX8. However, 2/23 (9%) peritoneal malignant mesotheliomas showed focal and/or weak staining for PAX8; the remaining cases were negative. Two well-differentiated papillary mesotheliomas and 1 multicystic mesothelioma each showed some staining for PAX8. h-caldesmon was negative in all serous neoplasms and all mesothelial neoplasms, except 1 pleural malignant mesothelioma which showed patchy immunoreactivity. Strong PAX8 staining is highly specific (P<0.00001) for ovarian serous tumors when compared with malignant mesotheliomas of the peritoneum and pleura. The presence of weak staining for PAX8 in the 3 "noninvasive" mesotheliomas questions the use for PAX8 in this differential diagnosis. On the basis of this study, h-caldesmon is not a useful marker for mesothelioma.

BACKGROUND

In their previous analysis of papillary thyroid carcinomas (PTCs) from an Ukrainian-American cohort that was exposed to iodine-131 ((131) I) from the Chernobyl accident, the authors identified RET/PTC rearrangements and other driver mutations in 60% of tumors.

METHODS

In this study, the remaining mutation-negative tumors from that cohort were analyzed using RNA sequencing (RNA-Seq) and reverse transcriptase-polymerase chain reaction to identify novel chromosomal rearrangements and to characterize their relation with radiation dose.

RESULTS

The ETS variant gene 6 (ETV6)-neurotrophin receptor 3 (NTRK3) rearrangement (ETV6-NTRK3) was identified by RNA-Seq in a tumor from a patient who received a high (131) I dose. Overall, the rearrangement was detected in 9 of 62 (14.5%) post-Chernobyl PTCs and in 3 of 151 (2%) sporadic PTCs (P = .019). The most common fusion type was between exon 4 of ETV6 and exon 14 of NTRK3. The prevalence of ETV6-NTRK3 rearrangement in post-Chernobyl PTCs was associated with increasing (131) I dose, albeit at borderline significance (P = .126). The group of rearrangement-positive PTCs (ETV6-NTRK3, RET/PTC, PAX8-PPARγ) was associated with significantly higher dose response compared with the group of PTCs with point mutations (BRAF, RAS; P < .001). In vitro exposure of human thyroid cells to 1 gray of (131) I and γ-radiation resulted in the formation of ETV6-NTRK3 rearrangement at a rate of 7.9 × 10(-6) cells and 3.0 × 10(-6) cells, respectively.

CONCLUSIONS

The authors report the occurrence of ETV6-NTRK3 rearrangements in thyroid cancer and demonstrate that this rearrangement is significantly more common in tumors associated with exposure to (131) I and has a borderline significant dose response. Moreover, ETV6-NTRK3 rearrangement can be directly induced in thyroid cells by ionizing radiation in vitro and, thus, may represent a novel mechanism of radiation-induced carcinogenesis.

Lhx1 and Lhx5 are co-expressed in multiple interneuron cell types in the developing spinal cord. These include early-born dI4 and dI6 inhibitory interneurons, as well as late-born inhibitory dILA neurons (dILA), all of which express the paired-domain transcription factor Pax2. Although it appears that Lhx1 and Lhx5 do not control the initial specification of the neuronal cell types in which they are expressed, we have found a cell-autonomous requirement for either Lhx1 or Lhx5 to maintain the expression of Pax2, Pax5 and Pax8 in dorsal inhibitory neurons at later developmental stages. Lhx1; Lhx5 double-knockout mice exhibit a downregulation of Gad1 and Viaat (Slc32a1) from E13.5 onwards that is closely associated with a decrease in Pax2 expression. Pax2 is a key factor for dorsal GABAergic identity, with the expression of Pax5 and Pax8 being differentially dependent on Pax2 in the dorsal horn. In summary, our findings support a model in which the differentiation of GABAergic interneurons in the dorsal cord depends on Pax2, with Lhx1 and Lhx5 helping to activate and maintain Pax2 expression in these cells. Lhx1 and Lhx5 therefore function together with Pax2, Pax5 and Pax8 to establish a GABAergic inhibitory-neurotransmitter program in dorsal horn interneurons.

BACKGROUND

Lung cancer is the leading cause of cancer death in men and women in the United States and Western Europe. Over 160,000 Americans die of this disease every year. The five-year survival rate is 15% - significantly lower than that of other major cancers. Early detection is a key factor in increasing lung cancer patient survival. DNA hypermethylation is recognized as an important mechanism for tumor suppressor gene inactivation in cancer and could yield powerful biomarkers for early detection of lung cancer. Here we focused on developing DNA methylation markers for squamous cell carcinoma of the lung. Using the sensitive, high-throughput DNA methylation analysis technique MethyLight, we examined the methylation profile of 42 loci in a collection of 45 squamous cell lung cancer samples and adjacent non-tumor lung tissues from the same patients.

RESULTS

We identified 22 loci showing significantly higher DNA methylation levels in tumor tissue than adjacent non-tumor lung. Of these, eight showed highly significant hypermethylation in tumor tissue (p < 0.0001): GDNF, MTHFR, OPCML, TNFRSF25, TCF21, PAX8, PTPRN2 and PITX2. Used in combination on our specimen collection, this eight-locus panel showed 95.6% sensitivity and specificity.

CONCLUSIONS

We have identified 22 DNA methylation markers for squamous cell lung cancer, several of which have not previously been reported to be methylated in any type of human cancer. The top eight markers show great promise as a sensitive and specific DNA methylation marker panel for squamous cell lung cancer.

Xp11 translocation renal cell carcinoma (RCC) harbor various TFE3 gene fusions, and are known to underexpress epithelial immunohistochemical (IHC) markers such as cytokeratin and EMA relative to usual adult type RCC; however, their profile in reference to other IHC markers that are differentially expressed in other subtypes of RCC has not been systematically assessed. Few therapeutic targets have been identified in these aggressive cancers. We created 2 tissue microarrays (TMA) containing five 1.4-mm cores from each of 21 Xp11 translocation RCC (all confirmed by TFE3 IHC, 6 further confirmed by genetics), 7 clear cell RCC (CCRCC), and 6 papillary RCC (PRCC). These TMA were labeled for a panel of IHC markers. In contrast to earlier published data, Xp11 translocation RCC frequently expressed renal transcription factors PAX8 (16/21 cases) and PAX2 (14/21 cases), whereas only 1 of 21 cases focally expressed MiTF and only 5 of 21 overexpressed p21. Although experimental data suggest otherwise, Xp11 translocation RCC did not express WT-1 (0/21 cases). Although 24% of Xp11 translocation RCC expressed HIF-1alpha (like CCRCC), unlike CCRCC CA IX expression was characteristically only focal (mean 6% cell labeling) in Xp11 translocation RCC. Other markers preferentially expressed in CCRCC or PRCC, such as HIG-2, claudin 7, and EpCAM, yielded inconsistent results in Xp11 translocation RCC. Xp11 translocation RCC infrequently expressed Ksp-cadherin (3/21 cases) and c-kit (0/21 cases), markers frequently expressed in chromophobe RCC. Using an H-score that is the product of intensity and percentage labeling, Xp11 translocation RCC expressed higher levels of phosphorylated S6, a measure of mTOR pathway activation (mean H score=88), than did CCRCC (mean H score=54) or PRCC (mean H score=44). In conclusion, in contrast to prior reports, Xp11 translocation RCC usually express PAX2 and PAX8 but do not usually express MiTF. Although they may express HIF-1alpha, they only focally express the downstream target CA IX. They inconsistently express markers associated with other RCC subtypes, further highlighting the lack of specificity of the latter markers. TFE3 and Cathepsin K remain the most sensitive and specific markers of these neoplasms. Elevated expression of phosphorylated S6 in Xp11 translocation RCC suggests the mTOR pathway as an attractive potential therapeutic target for these neoplasms.

We identified four insertional alleles of foxi one (foo), an embryonic lethal mutation in zebrafish that displays defects in both otic placode and the jaw. In foo/foo embryos the otic placode is split into two smaller placodes and mutant embryos show a dorsoventral (DV) cartilage defect manifested as a reduced hyomandibular and reduced third and fourth branchial arches. We identified foxi one (foo), the zebrafish ortholog of Foxi1 (FREAC6, FKHL10, HFH-3, Fkh10) and a member of the forkhead domain transcriptional regulator family, as the gene mutated in foo/foo embryos. foo is expressed in otic placode precursor cells, and foo/foo embryos lack placodal pax8 expression and have disorganized otic expression of pax2.1 and dlx3. Third stream neural crest cell migration, detected by dlx2 and krox20 expression, is aberrant in that it invades the otic placode territory. foo is expressed in pharyngeal pouch endoderm and is required for pouch expression of pax8 and proper patterning of other markers in the pouch such as nkx2.3. In foo/foo embryos, we observed a failure to maintain fgf3 expression in the pouches, followed by apoptosis of neural crest cells in adjacent arches. We conclude that foo expression is essential for pax8 expression probably downstream of Fgf signaling in a conserved pathway jointly required for integrity of patterning in the otic placode and pharyngeal pouches. We propose that correct placement of survival/proliferation cues is essential for shaping the pharyngeal cartilages and that evolutionary links between jaw and ear formation can be traced to Fgf-Foxi1-Pax8 pathways.

Thyroid dysgenesis (TD) is responsible for most cases of congenital hypothyroidism, a condition that affects about one in 4000 newborns. Mutations in PAX8, TITF1, or FOXE1 may account for congenital hypothyroidism in patients with either isolated TD or TD with associated malformations involving kidney, lung, forebrain, and palate. Pax8, titf1, and foxe1 are expressed in the mouse thyroid bud as soon as it differentiates on the pharyngeal floor. Because the spatio-temporal expression of these genes is unknown in humans, we decided to study them at different stages of human embryonic and fetal development. PAX8 and TITF1 were first expressed in the median thyroid primordium. Interestingly, PAX8 was also expressed in the thyroglossal duct and the ultimobranchial bodies. Human FOXE1 expression was detected later than in the mouse. PAX8 was also expressed in the developing central nervous system and kidney, including the ureteric bud and the main collecting ducts. TITF1 was expressed in the ventral forebrain and lung. FOXE1 expression was detected in the oropharyngeal epithelium and thymus. In conclusion, the expression patterns described here show some differences from those reported in the mouse. They explain the malformations associated with TD in patients carrying PAX8, TITF1, and FOXE1 gene mutations.

In the embryonic kidney, progenitors in the metanephric mesenchyme differentiate into specialized renal epithelia in a defined sequence characterized by the formation of cellular aggregates, conversion into polarized epithelia and segmentation along a proximal-distal axis. This sequence is reiterated throughout renal development to generate nephrons. Here, we identify global transcriptional programs associated with epithelial differentiation utilizing an organ culture model of rat metanephric mesenchymal differentiation, which recapitulates the hallmarks of epithelialization in vivo in a synchronized rather than reiterative fashion. We observe activation of multiple putative targets of beta-catenin/TCF/Lef-dependent transcription coinciding with epithelial differentiation. We show in cultured explants that isolated activation of beta-catenin signaling in epithelial progenitors induces, in a TCF/Lef-dependent manner, a subset of the transcripts associated with epithelialization, including Pax8, cyclin D1 (Ccnd1) and Emx2. This is associated with anti-apoptotic and proliferative effects in epithelial progenitors, whereas cells with impaired TCF/Lef-dependent transcription are progressively depleted from the epithelial lineage. In vivo, TCF/Lef-responsive genes comprise a conserved transcriptional program in differentiating renal epithelial progenitors and beta-catenin-containing transcriptional complexes directly bind to their promoter regions. Thus, beta-catenin/TCF/Lef-mediated transcriptional events control a subset of the differentiation-associated transcriptional program and thereby participate in maintenance, expansion and stage progression of the epithelial lineage.

BACKGROUND

Poorly differentiated carcinomas represent an aggressive group of thyroid tumors with controversial classification placement and poorly understood pathogenesis. Molecular data in this group of tumors are extremely heterogeneous, possibly reflecting different inclusion criteria. Recently homogeneous diagnostic criteria have been proposed by our group (Turin proposal) that need to be complemented by detailed molecular characterization.

OBJECTIVE

The objective of the study was to define a comprehensive molecular typing of poorly differentiated thyroid carcinomas classified following homogeneous diagnostic criteria.

METHODS

Sixty-five cases of poorly differentiated carcinoma selected following the Turin proposal have been screened for N-, K-, H-RAS, BRAF, RET/PTC1 and 3, and PAX8/PPARgamma mutations-rearrangements using alternative techniques and in two different laboratories. Molecular data were compared with clinical pathological parameters and survival by univariate and multivariate analysis.

RESULTS

RAS mutations in codon 61 were by far the most common genetic alteration in poorly differentiated carcinomas (23% of cases), with all mutation in NRAS except one in the HRAS gene. A single BRAF mutation was found in a poorly differentiated carcinoma with a residual component of a tall cell variant of papillary carcinoma. No KRAS, RET/PTC, or PAX8/PPARgamma genetic alteration was detected. In this series, the presence of RAS mutations was a unique negative prognostic parameter at multivariate analysis.

CONCLUSIONS

The present study demonstrates that strictly classified poorly differentiated carcinomas are genetically homogeneous, RAS mutations being the almost exclusive genetic event. Moreover, the detection of RAS mutations might be clinically relevant for the prognostic stratification of these tumors.

The transcription factor Pax8 is expressed in the developing thyroid gland, inner ear, kidney, and mid-hindbrain region. Pax8 mutant mice die only postnatally due to a thyroid gland defect. Here we report the generation and expression analysis of a Pax8(cre) allele. Cre recombinase activity was detected in known Pax8 expression domains of Pax8(cre/+) and Pax8(cre/cre) embryos carrying the Z/AP transgene, which expresses alkaline phosphatase only after Cre-mediated excision of lacZ sequences. Alkaline phosphatase expression was additionally detected in the adrenal gland and in the facial, vestibulocochlear, and cuneate nerves, which have so far not been associated with Pax8 expression. Our data indicate that the Pax8(cre) allele provides a novel important tool for conditional gene manipulation and lineage tracing in different Pax8 expression domains.

It is currently a controversial issue whether epithelial ovarian cancers arise in the ovarian surface epithelium (OSE) or the fimbrial epithelium of the oviduct. The hypothesis presented here aims to reconcile these 2 views and provides a possible explanation for 2 questions arising: first, why tumors originating in the fimbriae and OSE, which are parts of different organs, express common features; second, why these epithelia are prone to neoplastic transformation whereas the remaining oviduct and the extraovarian mesothelium are not. We hypothesize that these questions relate to the common origin of the OSE and fimbriae in that region of the embryonic coelomic epithelium, which will eventually link the extraovarian mesothelium to the epithelium of the oviductal ampulla. OSE and fimbriae become separated during embryonic development but, like other transitional, interepithelial junctions in adults, this region might remain incompletely committed and thus prone to neoplastic progression. To define differentiation at the OSE-tubal junction, salpingo-oophorectomy specimens were stained immunohistochemically for mesenchymal differentiation markers of OSE and for epithelial markers and Pax8, characterizing oviductal fimbriae and ampullae. OSE and ampullae were distinctly different, but there was no sharp boundary between OSE and fimbriae. Rather, both mesenchymal and epithelial markers overlapped, and Pax8 and fimbrial epithelial markers diminished distally, near the OSE. The results support the hypothesis that the OSE and fimbriae are parts of a transitional epithelium of common origin rather than 2 independent sources of ovarian cancer, and suggest that their immature, incompletely determined phenotype contributes to their propensity to neoplastic transformation.

BACKGROUND

Pax2;5;8 transcription factors play diverse roles in vertebrate and invertebrate organogenesis, including the development of the inner ear. Past research has suggested various cochlear defects and some vestibular defects in Pax2 null mice but the details of the cochlear defects and the interaction with other Pax family members in ear development remain unclear.

RESULTS

We show that Pax2;8 double null mice do not develop an ear past the otocyst stage and show little to no sensory as well as limited and transient neuronal development, thus indicating that these two family members are essential for overall ear morphogenesis and sustained neurosensory development. In support of functional redundancy between Pax proteins, Pax2 can be substituted by a Pax5 minigene, a gene normally not expressed in the embryonic mouse ear. There is no detectable morphological defect in Pax8 null mice suggesting that Pax2 expression can compensate for Pax8. Conversely, Pax8 cannot compensate for Pax2 leading to a cochlear phenotype not fully appreciated previously: Cochlear development is delayed until E15.5 when the cochlea extrudes as a large sack into the brain case. Immunocytochemistry and tracing from the brain show that a cochlear spiral ganglia form as a small addition to the inferior vestibular ganglion. However, the empty cochlear sack, devoid of any sensory epithelium development as indicated by the absence of Sox2 or MyoVII expression, nevertheless develop a dense innervation network of small neurons situated in the wall of the cochlear sack.

CONCLUSIONS

Combined these data suggest that Pax2 is needed for organ of Corti formation and is directly or indirectly involved in the coordination of spiral ganglion formation which is partially disrupted in the Pax2 null ears. All three Pax genes can signal redundantly in the ear with their function being determined primarily by the spatio-temporal expression driven by the three distinct promoters of these genes.

Direct interactions between the genes that regulate development and those which regulate the cell cycle would provide a mechanism by which numerous biological events could be better understood. We have identified a direct role for PAX5 in the control of p53 transcription. In primary human diffuse astrocytomas, PAX5 expression inversely correlated with p53 expression. The human p53 gene harbours a PAX binding site within its untranslated first exon that is conserved throughout evolution. PAX5 and its paralogues PAX2 and PAX8 are capable of inhibiting both the p53 promoter and transactivation of a p53-responsive reporter in cell culture. Mutation of the identified binding site eliminates PAX protein binding in vitro and renders the promoter inactive in cells. These data suggest that PAX proteins might regulate p53 expression during development and propose a novel alternative mechanism for tumour initiation or progression, by which loss of p53 function occurs at the transcriptional level.

A new Drosophila Pax gene, sparkling (spa), implicated in eye development, was isolated and shown to encode the homolog of the vertebrate Pax2, Pax5, and Pax8 proteins. It is expressed in the embryonic nervous system and in cone, primary pigment, and bristle cells of larval and pupal eye discs. In spa(pol) mutants, a deletion of an enhancer abolishes Spa expression in cone and primary pigment cells and results in a severely disturbed development of non-neuronal ommatidial cells. Spa expression is further required for activation of cut in cone cells and of the Bar locus in primary pigment cells. We suggest close functional analogies between Spa and Pax2 in the development of the insect and vertebrate eye.

Thyroid-specific transcription factors, Pax8, TTF-1, and TTF-2, are crucial for thyroid organogenesis and differentiation. Compared with TTF-1, the other two markers have scarcely been investigated in surgical pathology. The goal of this study is to evaluate the expressions of these markers in thyroid tumors of the full spectrum of differentiation, with special emphasis on anaplastic carcinomas. A total of 94 cases of thyroid neoplasms were studied: 17 papillary carcinomas, 18 follicular adenomas, 16 follicular carcinomas, 7 poorly differentiated carcinomas, 28 anaplastic carcinomas, and 8 medullary carcinomas. Immunostains for these three markers were performed. The antibodies to Pax8 and TTF-2 were also applied on 147 lung carcinomas as well as a variety of normal tissues and malignant tumors. All three markers were seen in papillary carcinomas, follicular adenomas and carcinomas, and poorly differentiated carcinomas in a diffuse manner, whereas their expressions in medullary carcinomas were variable. Pax8 was expressed in 79% of anaplastic carcinomas to a variable extent, whereas TTF-1 and TTF-2 were seen only in 18 and 7% of anaplastic carcinomas, respectively. TTF-2 was negative in all other neoplastic and non-neoplastic tissues including those of the lung. Pax8 was expressed in renal tubules, fallopian tubes, ovarian inclusion cysts, and lymphoid follicles as well as renal carcinoma, nephroblastoma, seminoma, and ovarian carcinoma, but not in normal tissue and carcinomas of the lung. Pax8 is a useful marker for the diagnosis of anaplastic carcinomas, particularly when the differential diagnosis includes pulmonary carcinoma. In differentiated thyroid neoplasms, no significant difference in expression was seen in all the three transcription factors.

BACKGROUND

Orthotopic mouse models of human cancer represent an important in vivo tool for drug testing and validation. Most of the human thyroid carcinoma cell lines used in orthotopic or subcutaneous models are likely of melanoma and colon cancer. Here, we report and characterize a novel orthotopic model of human thyroid carcinoma using a unique thyroid cancer cell line.

METHODS

We used the cell line 8505c, originated from a thyroid tumor histologically characterized by anaplastic carcinoma cell features. We injected 8505c cells engineered using a green fluorescent protein-positive lentiviral vector orthotopically into the thyroid of severe combined immunodeficient mice.

RESULTS

Orthotopic implantation with the 8505c cells produced thyroid tumors after 5 weeks, showing large neck masses, with histopathologic features of a high-grade neoplasm (anaplasia, necrosis, high mitotic and proliferative indexes, p53 positivity, extrathyroidal invasion, lymph node and distant metastases) and immunoprofile of follicular thyroid cell origin with positivity for thyroid transcription factor-1 and PAX8, and for cytokeratins.

CONCLUSIONS

Here we describe a novel orthotopic thyroid carcinoma model using 8505c cells. This model can prove to be a reliable and useful tool to investigate in vivo biological mechanisms determining thyroid cancer aggressiveness, and to test novel therapeutics for the treatment of refractory or advanced thyroid cancers.