The small GTPase Rheb is required for spermatogenesis but not oogenesis

The process of germ cell development is under the tight control of various signaling pathways, among which the PI3K-Akt-mTOR pathway is of critical importance. Previous studies have demonstrated sex-specific roles for several components of this pathway. In the current study, we aimed to evaluate the role of Rheb, a member of the small GTPase superfamily and a critical component for mTORC1 activation, in male and female gametogenesis. The function of Rheb in development and the nervous system has been extensively studied, but little is known about its role in the germ line. We have exploited genetic approaches in the mouse to study the role of Rheb in the germ line and have identified an essential role in spermatogenesis. Conditional knockout (cKO) of Rheb in the male germ line resulted in severe oligoasthenoteratozoospermia and male sterility. More detailed phenotypic analyses uncovered an age-dependent meiotic progression defect combined with subsequent abnormalities in spermiogenesis as evidenced by abnormal sperm morphology. In the female, however, germ-cell specific inactivation of Rheb was not associated with any discernible abnormality; these cKO mice were fertile with morphologically unremarkable ovaries, normal primordial follicle formation, and subsequent follicle maturation. The absence of an abnormal ovarian phenotype is striking given previous studies demonstrating a critical role for the mTORC1 pathway in the maintenance of primordial follicle pool. In conclusion, our findings demonstrate an essential role of Rheb in diverse aspects of spermatogenesis but suggest the existence of functionally redundant factors that can compensate for Rheb deficiency within oocytes.

Cooperation between p53 and the telomere-protecting shelterin component Pot1a in endometrial carcinogenesis

Type II endometrial cancer (EMCA) represents only 10% of all EMCAs, but accounts for 40% of EMCA-related mortality. Previous studies of human tumors have shown an association between Type II tumors and damaged telomeres. We hypothesized that the lack of murine Type II EMCA models is due to the extremely long telomeres in laboratory mouse strains. We previously showed that telomerase-null mice with critically short telomeres developed endometrial lesions histologically resembling endometrial intraepithelial carcinoma (EIC), the accepted precursor for Type II EMCA. However, these mice did not develop invasive endometrial adenocarcinoma, and instead succumbed prematurely to multi-organ failure. Here, we modeled critical telomere attrition by conditionally inactivating Pot1a, a component of the shelterin complex that stabilizes telomeres, within endometrial epithelium. Inactivation of Pot1a by itself did not stimulate endometrial carcinogenesis, and did not result in detectable DNA damage or apoptosis in endometrium. However, simultaneous inactivation of Pot1a and p53 resulted in EIC-like lesions by 9 months indistinguishable from those seen in late generation telomerase-null mice. These lesions progressed to invasive endometrial adenocarcinomas as early as 9 months of age with metastatic disease in 100% of the animals by 15 months. These tumors were poorly differentiated endometrial adenocarcinomas with prominent nuclear atypia, resembling human Type II cancers. Furthermore, these tumors were aneuploid with double-stranded DNA breaks and end-to-end telomere fusions and most were tetraploid or near-tetraploid. These studies lend further support to the hypothesis that telomeric instability has a critical role in Type II endometrial carcinogenesis and provides an intriguing in-vivo correlate to recent studies implicating telomere-dependent tetraploidization as an important mechanism in carcinogenesis.

Impaired nonhomologous end-joining provokes soft tissue sarcomas harboring chromosomal translocations, amplifications, and deletions

Although nonhomologous end-joining (NHEJ) deficiency has been shown to accelerate lymphoma formation in mice, its role in suppressing tumors in cells that do not undergo V(D)J recombination is unclear. Utilizing a tumor-prone mouse strain (ink4a/arf(-/-)), we examined the impact of haploinsufficiency of a NHEJ component, DNA ligase IV (Lig4), on murine tumorigenesis. We demonstrate that lig4 heterozygosity promotes the development of soft-tissue sarcomas that possess clonal amplifications, deletions, and translocations. That these genomic alterations are relevant in tumorigenesis is supported by the finding of frequent mdm2 amplification, a known oncogene in human sarcoma. Together, these findings support the view that loss of a single lig4 allele results in NHEJ activity being sufficiently reduced to engender chromosomal aberrations that drive non-lymphoid tumorigenesis.

Pathologic findings in eight cases of ovarian serous borderline tumors, three with foci of serous carcinoma, that preceded death or morbidity from invasive carcinoma

We sought to assess the frequency of previously reported adverse histopathologic findings in ovarian serous borderline tumors (SBTs) in cases that preceded a patient's death or caused serious morbidity due to invasive carcinoma. SBTs with foci of invasive carcinoma that occupied a minority of the tumor and were associated with similar outcomes were also studied for potential additional insights. Eight cases were found over a 22-year period. Ten tumors in 5 patients were purely SBT; at initial staging, 1 patient had invasive peritoneal implants; 3 had noninvasive peritoneal implants; 1 was stage I. At last follow-up 3 of the 5 patients had died of carcinoma, 1 was alive with carcinoma, and 1 had no clinical evidence of disease 4 years after a sigmoid colectomy for invasive serous carcinoma of the bowel wall. Four tumors in 3 patients had foci of invasion that were more than microinvasive; at initial staging, all 3 patients had invasive peritoneal implants, and all died of carcinoma. All 14 of the ovarian tumors in the 8 cases had surface involvement by tumor cells, and in 8 tumors in 5 cases they were confined primarily to the ovarian surface. Foci of "micropapillary serous carcinoma" accompanied more obvious areas of infiltrative carcinoma in 2 of the 4 ovarian tumors, the peritoneal implants in 1 of the cases with purely SBTs, and a recurrence in this case and 1 other case. No morphologic finding in the 10 purely SBTs was predictive of subsequent malignant behavior. We conclude that extraovarian invasive serous carcinomas, either following or concurrent with an ovarian SBT, develop from borderline foci that may originate in the ovary, but frequently are likely to have arisen independently in the peritoneum. The carcinomas may be preceded or accompanied by noninvasive-appearing micropapillary foci in the peritoneum in some cases, but micropapillary foci in the ovarian tumors are infrequent and not a necessary antecedent.

Discrimination of complete hydatidiform mole from its mimics by immunohistochemistry of the paternally imprinted gene product p57KIP2

The p57KIP2 protein is a cell cycle inhibitor and tumor suppressor encoded by a strongly paternally imprinted gene. We explored the utility of p57KIP2 as a diagnostic marker in hydatidiform mole, a disease likely the result of abnormal dosage and consequent misexpression of imprinted genes. Using a monoclonal antibody on paraffin-embedded, formalin-fixed tissue sections, the authors evaluated p57KIP2 expression in normal placenta and in 149 gestations including 59 complete hydatidiform moles, 39 PHMs, and 51 spontaneous losses with hydropic changes. p57KIP2 was strongly expressed in cytotrophoblast and villous mesenchyme in normal placenta, all cases of partial hydatidiform moles (39 of 39) and all spontaneous losses with hydropic changes (51 of 51). In contrast, p57KIP2 expression in cytotrophoblast and villous mesenchyme was absent or markedly decreased in 58 of 59 complete hydatidiform moles. In all gestations p57KIP2 was strongly expressed in decidua and in intervillous trophoblast islands, which served as internal positive controls for p57KIP2 immunostaining. p57KIP2 immunohistochemistry can reliably identify most cases of complete hydatidiform mole irrespective of gestational age and is thus a useful diagnostic adjunct, complementary to ploidy analysis, in the diagnosis of hydatidiform mole.

Loss of p16Ink4a with retention of p19Arf predisposes mice to tumorigenesis

The cyclin-dependent kinase inhibitor p16INK4a can induce senescence of human cells, and its loss by deletion, mutation or epigenetic silencing is among the most frequently observed molecular lesions in human cancer. Overlapping reading frames in the INK4A/ARF gene encode p16INK4a and a distinct tumour-suppressor protein, p19ARF (ref. 3). Here we describe the generation and characterization of a p16Ink4a-specific knockout mouse that retains normal p19Arf function. Mice lacking p16Ink4a were born with the expected mendelian distribution and exhibited normal development except for thymic hyperplasia. T cells deficient in p16Ink4a exhibited enhanced mitogenic responsiveness, consistent with the established role of p16Ink4a in constraining cellular proliferation. In contrast to mouse embryo fibroblasts (MEFs) deficient in p19Arf (ref. 4), p16Ink4a-null MEFs possessed normal growth characteristics and remained susceptible to Ras-induced senescence. Compared with wild-type MEFs, p16Ink4a-null MEFs exhibited an increased rate of immortalization, although this rate was less than that observed previously for cells null for Ink4a/Arf, p19Arf or p53 (refs 4, 5). Furthermore, p16Ink4a deficiency was associated with an increased incidence of spontaneous and carcinogen-induced cancers. These data establish that p16Ink4a, along with p19Arf, functions as a tumour suppressor in mice.

Excessive tumor-elaborated VEGF and its neutralization define a lethal paraneoplastic syndrome

Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen and key regulator of both physiologic and pathologic (e.g., tumor) angiogenesis. In the course of studies designed to assess the ability of constitutive VEGF to block tumor regression in an inducible RAS melanoma model, mice implanted with VEGF-expressing tumors sustained high morbidity and mortality that were out of proportion to the tumor burden. Documented elevated serum levels of VEGF were associated with a lethal hepatic syndrome characterized by massive sinusoidal dilation and endothelial cell proliferation and apoptosis. Systemic levels of VEGF correlated with the severity of liver pathology and overall clinical compromise. A striking reversal of VEGF-induced liver pathology and prolonged survival were achieved by surgical excision of VEGF-secreting tumor or by systemic administration of a potent VEGF antagonist (VEGF-TRAP(R1R2)), thus defining a paraneoplastic syndrome caused by excessive VEGF activity. Moreover, this VEGF-induced syndrome resembles peliosis hepatis, a rare human condition that is encountered in the setting of advanced malignancies, high-dose androgen therapy, and Bartonella henselae infection. Thus, our findings in the mouse have suggested an etiologic role for VEGF in this disease and may lead to diagnostic and therapeutic options for this debilitating condition in humans.

Multimodality therapy in early-stage neuroendocrine carcinoma of the uterine cervix

OBJECTIVE

Patients with early-stage neuroendocrine cervical carcinoma (NECC) have a high mortality rate despite aggressive therapy. The rarity of this tumor precludes initiation of a randomized, prospective trial. We reviewed our experience in early stage disease and performed a meta-analysis of the literature to identify prognostic factors and determine optimal multimodality therapy.

METHODS

Eleven women with International Federation of Gynecology and Obstetrics (FIGO) early stage (IB--IIA) NECC were treated with surgery and chemotherapy at our institutions between 1978 and 1998. Administration of radiation therapy was recorded, but not required for inclusion in this study. A gynecologic pathologist reviewed all histopathologic sections. Medical records were retrospectively reviewed and clinical data obtained. Twenty-three early-stage NECC patients who were similarly treated during the study interval were identified by a Medline search of the English literature and included in the analysis. The Kaplan--Meier method and log-rank test were used for survival analysis.

RESULTS

The overall 2-year survival rate for the 34 patients was 38%. The median age was 37 years (range, 20--75 years). Median cervical tumor diameter was 3.2 cm (range 0.5--11.0 cm). Lymphovascular space invasion was present in 21 (78%) of 27 patients (7 unknown). Fifteen (52%) of twenty-nine had lymph node metastases (5 unknown). Fifteen patients received postoperative platinum/etoposide (PE), seven received vincristine/adriamycin/cyclophosphamide (VAC), two received alternating cycles of VAC and PE, and ten received other chemotherapy regimens. Twenty women were treated with radiation therapy. The presence of lymph node metastases was a poor prognostic factor (P < 0.001). PE and VAC chemotherapy was associated with increased survival (P < 0.01).

CONCLUSION

NECC is a highly lethal variant of cervical cancer. The presence of lymph node metastases is the most important prognostic variable. Postoperative VAC or PE appears most likely to improve chances for survival.

The human VASA gene is specifically expressed in the germ cell lineage

To understand the origins and function of the human germ cell lineage and to identify germ cell-specific markers we have isolated a human ortholog of the Drosophila gene vasa. The gene was mapped to human chromosome 5q (near the centromere) by radiation hybrid mapping. We show by Northern analysis of fetal and adult tissues that expression of the human VASA gene is restricted to the ovary and testis and is undetectable in somatic tissues. We generated polyclonal antibodies that bind to the VASA protein in formalin-fixed, paraffin-embedded tissue and characterized VASA protein expression in human germ cells at various stages of development. The VASA protein is cytoplasmic and expressed in migratory primordial germ cells in the region of the gonadal ridge. VASA protein is present in fetal and adult gonadal germ cells in both males and females and is most abundant in spermatocytes and mature oocytes. The gene we have isolated is thus a highly specific marker of germ cells and should be useful for studies of human germ cell determination and function.

UbcD1, a Drosophila ubiquitin-conjugating enzyme required for proper telomere behavior

The end-to-end association of chromosomes through their telomeres has been observed in normal cells of certain organisms, as well as in senescent and tumor cells. The molecular mechanisms underlying this phenomenon are currently unknown. We show here that five independent mutant alleles in the Drosophila UbcD1 gene cause frequent telomere-telomere attachments during both mitosis and male meiosis that are not seen in wild type. These telomeric associations involve all the telomeres of the D. melanogaster chromosome complement, albeit with different frequencies. The pattern of telomeric associations observed in UbcD1 mutants suggests strongly that the interphase chromosomes of wild-type larval brain cells maintain a Rab1 orientation within the nucleus, with the telomeres and centromeres segregated to opposite sides of the nucleus. The UbcD1 gene encodes a class I ubiquitin-conjugating (E2) enzyme. This indicates that ubiquitin-mediated proteolysis is normally needed to ensure proper telomere behavior during Drosophila cell division. We therefore suggest that at least one of the targets of UbcD1 ubiquitination is a telomere-associated polypeptide that may help maintain proper chromosomal orientation during interphase.

Control of male sexual behavior and sexual orientation in Drosophila by the fruitless gene

Sexual orientation and courtship behavior in Drosophila are regulated by fruitless (fru), the first gene in a branch of the sex-determination hierarchy functioning specifically in the central nervous system (CNS). The phenotypes of new fru mutants encompass nearly all aspects of male sexual behavior. Alternative splicing of fru transcripts produces sex-specific proteins belonging to the BTB-ZF family of transcriptional regulators. The sex-specific fru products are produced in only about 500 of the 10(5) neurons that comprise the CNS. The properties of neurons expressing these fru products suggest that fru specifies the fates or activities of neurons that carry out higher order control functions to elicit and coordinate the activities comprising male courtship behavior.

Diaphanous is required for cytokinesis in Drosophila and shares domains of similarity with the products of the limb deformity gene

We show that the Drosophila gene diaphanous is required for cytokinesis. Males homozygous for the dia1 mutation are sterile due to a defect in cytokinesis in the germline. Females trans-heterozygous for dia1 and a deficiency are sterile and lay eggs with defective eggshells; failure of cytokinesis is observed in the follicle cell layer. Null alleles are lethal. Death occurs at the onset of pupation due to the absence of imaginal discs. Mitotic figures in larval neuroblasts were found to be polyploid, apparently due to a defect in cytokinesis. The predicted 123 × 10(3) M(r) protein contains two domains shared by the formin proteins, encoded by the limb deformity gene in the mouse. These formin homology domains, which we have termed FH1 and FH2, are also found in Bni1p, the product of a Saccharomyces cerevisiae gene required for normal cytokinesis in diploid yeast cells.

Toward a molecular genetic analysis of spermatogenesis in Drosophila melanogaster: characterization of male-sterile mutants generated by single P element mutagenesis

We describe 83 recessive autosomal male-sterile mutations, generated by single P element mutagenesis in Drosophila melanogaster. Each mutation has been localized to a lettered subdivision of the polytene map. Reversion analyses, as well as complementation tests using available chromosomal deficiencies, indicate that the insertions are responsible for the mutant phenotypes. These mutations represent 63 complementation groups, 58 of which are required for spermatogenesis. Phenotypes of the spermatogenesis mutants were analyzed by light microscopy. Mutations in 12 loci affect germline proliferation, spermatocyte growth, or meiosis. Mutations in 46 other loci disrupt differentiation and maturation of spermatids into motile sperm. This collection of male-sterile mutants provides the basis for a molecular genetic analysis of spermatogenesis.