Pituitary hypoplasia in Pttg-/- mice is protective for Rb+/- pituitary tumorigenesis

Pituitary tumor transforming gene (Pttg) is induced in pituitary tumors and associated with increased tumor invasiveness. Pttg-null mice do not develop tumors, but exhibit pituitary hypoplasia, whereas mice heterozygous for the retinoblastoma (Rb) deletion develop pituitary tumors with high penetrance. Pttg-null mice were therefore cross-bred with Rb+/- mice to test the impact of pituitary hypoplasia on tumor development. Before tumor development, Rb+/-Pttg-/- mice have smaller pituitary glands with fewer cycling pituitary cells and exhibit induction of pituitary p21 levels. Pttg silencing in vitro with specific short hairpin interfering RNA in AtT20 mouse corticotrophs led to a marked induction of p21 mRNA and protein levels, decreased RB phosphorylation, and subsequent 24% decrease in S-phase cells. Eighty-six percent of Rb+/-Pttg+/+ mice develop pituitary adenomas by 13 months, in contrast to 30% of double-crossed Rb+/-Pttg-/- animals (P < 0.01). Pituitary hypoplasia, associated with suppressed cell proliferation, prevents the high penetrance of pituitary tumors in Rb+/- animals, and is therefore a protective determinant for pituitary tumorigenesis.     

Mutations of N-terminal regions render the retinoblastoma protein insufficient for functions in development and tumor suppression.

To assess biological roles of the retinoblastoma protein (RB), four independent transgenic mouse lines expressing human RB with different deletions in the N-terminal region (RBdeltaN) were generated and compared with mice expressing identically regulated, full-length RB. Expression of both RB and RBdeltaN caused developmental growth retardation, but the wild-type protein was more potent. In contrast to wild-type RB, the RBdeltaN proteins were unable to rescue Rb-/- mice completely from embryonic lethality. Embryos survived until gestational day 18.5 but displayed defects in the terminal differentiation of erythrocytes, neurons, and skeletal muscle. In Rb+/- mice, expression of the RBdeltaN transgenes failed to prevent pituitary melanotroph tumors but delayed tumor formation or progression. These results strongly suggest that N-terminal regions are crucial for embryonic and postnatal development, tumor suppression, and the functional integrity of the entire RB protein. Furthermore, these transgenic mice provide models that may begin to explain human families with low-penetrance retinoblastoma and mutations in N-terminal regions of RB.     

p18Ink4c, but not p27Kip1, collaborates with Men1 to suppress neuroendocrine organ tumors

Mutant mice lacking both cyclin-dependent kinase (CDK) inhibitors p18(Ink4c) and p27(Kip1) develop a tumor spectrum reminiscent of human multiple endocrine neoplasia (MEN) syndromes. To determine how p18 and p27 genetically interact with Men1, the tumor suppressor gene mutated in familial MEN1, we characterized p18-Men1 and p27-Men1 double mutant mice. Compared with their corresponding single mutant littermates, the p18(-/-); Men1(+/-) mice develop tumors at an accelerated rate and with an increased incidence in the pituitary, thyroid, parathyroid, and pancreas. In the pituitary and pancreatic islets, phosphorylation of the retinoblastoma (Rb) protein at both CDK2 and CDK4/6 sites was increased in p18(-/-) and Men1(+/-) cells and was further increased in p18(-/-); Men1(+/-) cells. The remaining wild-type Men1 allele was lost in most tumors from Men1(+/-) mice but was retained in most tumors from p18(-/-); Men1(+/-) mice. Combined mutations of p27(-/-) and Men1(+/-), in contrast, did not exhibit noticeable synergistic stimulation of Rb kinase activity, cell proliferation, and tumor growth. These results demonstrate that functional collaboration exists between p18 and Men1 and suggest that Men1 may regulate additional factor(s) that interact with p18 and p27 differently.     

Cell-autonomous and non-cell-autonomous functions of the Rb tumor suppressor in developing central nervous system.

The retinoblastoma tumor suppressor (RB) plays an important role in the regulation of cell cycle progression and terminal differentiation of many cell types. Rb(-/-) mouse embryos die at midgestation with defects in cell cycle regulation, control of apoptosis and terminal differentiation. However, chimeric mice composed of wild-type and Rb-deficient cells are viable and show minor abnormalities. To determine the role of Rb in development more precisely, we analyzed chimeric embryos and adults made with marked Rb(-/-) cells. Like their germline Rb(-/-) counterparts, brains of midgestation chimeric embryos exhibited extensive ectopic S-phase entry. In Rb-mutants, this is accompanied by widespread apoptosis. However, in chimeras, the majority of Rb-deficient cells survived and differentiated into neuronal fates. Rescue of Rb(-/-) neurons in the presence of wild-type cells occurred after induction of the p53 pathway and led to accumulation of cells with 4n DNA content. Therefore, the role of Rb during development can be divided into a cell-autonomous function in exit from the cell cycle and a non-cell-autonomous role in the suppression of apoptosis and induction of differentiation.     

Extensive contribution of Rb-deficient cells to adult chimeric mice with limited histopathological consequences.

Homozygosity for a mutation in the Rb tumor suppressor gene causes mid-gestation embryonic lethality in the mouse. Using a two-step targeting protocol, we have constructed Rb homozygous mutant mouse embryonic stem cells and used them to create chimeric animals partially composed of Rb-deficient cells. Analysis of these chimeras demonstrates widespread contribution of the mutant cells to adult tissues, including the retina and mature erythrocytes. Despite the presence of large numbers of Rb-deficient cells in most tissues of these mice, they are remarkably normal but do exhibit certain histological defects including cataracts, hyperplasia of the adrenal medulla, and enlarged cells in the cerebellum and the liver. Like animals heterozygous for the Rb mutation, the chimeras develop tumors of the intermediate lobe of the pituitary, and the rate of pituitary tumorigenesis is greatly accelerated.     

Hmga1 is required for normal sperm development

The Hmgi protein family of chromosomal architectural factors is extensively studied for its roles in embryogenesis and its association with benign mesenchymal tumors. Although the biochemical function of Hmga1 has been studied in vitro, to provide in vivo insight into its biological function, a targeted disruption of Hmga1 was initiated. Chimeric founder mice were derived from embryonic stem (ES) cells harboring a targeted mutation in a single Hmga1 allele. These 14 different chimeric founders produced 494 black progeny. Since none of these 494 progeny were agouti, none of them were derived from ES cells. Control injections of the wild-type ES cell lines resulted in ES cell derived agouti mice, indicating that the ES cells were totipotent. Therefore, our results indicate that one intact Hmga1 allele was not sufficient for germ-line transmission of the ES cells. Seven chimeric founder mice that were examined histologically demonstrated aberrant regions in their reproductive organs. Aberrant regions of seminiferous tubules were reduced in diameter, demonstrated vacuolated Sertoli cells, and had an absolute deficiency of sperm. While the Hmga1(+/-) ES cells were shown to contribute to the formation of the epididymides, they did not significantly contribute to the testes of chimeric founder mice. No sperm isolated from any of the Hmga1(+/-) chimeric mice were shown to arise from the ES cells, as none of them contained the targeted disruption of the Hmga1 gene. Our results suggest that both alleles of Hmga1 are required for normal sperm production in the mouse.     

Deficiency of phospholipase C-gamma1 impairs renal development and hematopoiesis.

Phospholipase C-gamma1 (PLC-gamma1) is involved in a variety of intracellular signaling via many growth factor receptors and T-cell receptor. To explore the role of PLC-gamma1 in vivo, we generated the PLC-gamma1-deficient (plc-gamma1(-/-)) mice, which died of growth retardation at embryonic day 8.5-9.5 in utero. Therefore, we examined plc-gamma1(-/-) chimeric mice generated with plc-gamma1(-/-) embryonic stem (ES) cells for further study. Pathologically, plc-gamma1(-/-) chimeras showed multicystic kidney due to severe renal dysplasia and renal tube dilation. Flow cytometric analysis and glucose phosphate isomerase assay revealed very few hematopoietic cells derived from the plc-gamma1(-/-) ES cells in the mutant chimeras. However, differentiation of plc-gamma1(-/-) ES cells into erythrocytes and monocytes/macrophages in vitro was observed to a lesser extent compared with control wild-type ES cells. These data suggest that PLC-gamma1 plays an essential role in the renal development and hematopoiesis in vivo.     

p18 Ink4c and Pten constrain a positive regulatory loop between cell growth and cell cycle control

Inactivation of the Rb-mediated G1 control pathway is a common event found in many types of human tumors. To test how the Rb pathway interacts with other pathways in tumor suppression, we characterized mice with mutations in both the cyclin-dependent kinase (CDK) inhibitor p18 Ink4c and the lipid phosphatase Pten, which regulates cell growth. The double mutant mice develop a wider spectrum of tumors, including prostate cancer in the anterior and dorsolateral lobes, with nearly complete penetrance and at an accelerated rate. The remaining wild-type allele of Pten was lost at a high frequency in Pten+/- cells but not in p18+/- Pten+/- or p18-/- Pten+/- prostate tumor cells, nor in other Pten+/- tumor cells, suggesting a tissue- and genetic background-dependent haploinsufficiency of Pten in tumor suppression. p18 deletion, CDK4 overexpression, or oncoviral inactivation of Rb family proteins caused activation of Akt/PKB that was recessive to the reduction of PTEN activity. We suggest that p18 and Pten cooperate in tumor suppression by constraining a positive regulatory loop between cell growth and cell cycle control pathways.     

Switching of melanocyte pigmentation associated with pituitary pars intermedia tumors in Rb+/- and p27-/- female mice with yellow pelage

As an incidental finding in a study of mammary tumorigenesis, two lines of genetically engineered mice were observed to develop pigmentation changes of the fur. Mice with targeted mutations of the Rb1 (Rb) and Cdkn1b (p27kip1) genes were crossed from C57BL/6 (black coat color; eumelanin) and 129Sv (wild-type agouti coat color) backgrounds, respectively, to one with a dominant yellow coat color (phaeomelanin) carrying a transgene for Agouti under a keratinocyte specific promoter. Both Rb+/- and p27-/- mice developed pituitary tumors of the pars intermedia that were associated with a switch to black (eumelanic) fur but were not observed in sibling Rb+/+ and p27+/+ mice. This phenomenon was observed first in the vibrissae and, subsequently one to two weeks later, as periorbital and dorsal patches, and was associated with pituitary lesions larger than four millimeters in the longest dimension. In Rb+/- mice, pigmentation change preceded a moribund state attributable to the tumors by two to four weeks, whereas in p27-/- mice, the pigmentation alteration was earlier, more gradual, and prolonged. The switch from phaeomelanin to eumelanin in the fur is most likely due to out-competition of the agouti gene product by alpha-melanocyte-stimulating hormone from the pituitary tumors, an effect masked in black or agouti mice.     

Generation of normal lymphocyte populations by Rb-deficient embryonic stem cells

BACKGROUND: Mice homozygous for a loss-of-function mutation of the recombination-activating gene-2 (RAG 2), which is required for the rearrangement of antigen receptor genes, do not produce mature B and T lymphocytes. But chimeric mice that result from injection of normal embryonic stem (ES) cells into blastocysts from RAG2-deficient mice develop normal mature lymphocyte populations, all of which are derived from the injected ES cells; we have called this process RAG2-deficient blastocyst complementation. Using ES cells with homozygous mutations, RAG-2-deficient blastocyst complementation could provide a physiological assay with which to determine the potential role of almost any gene in the development and/or function of lymphocytes. To test the general utility of this system, we have used it to test the differentiation-potential of ES cells that harbor homozygous loss-of function mutations of their retinoblastoma susceptibility (Rb) gene loci. We chose Rb for this analysis because of its widespread function in the control of the cell cycle and cell differentiation, the adverse effect of homozygous germline mutations of Rb on hematopoiesis in fetal liver, and the embryonic lethality that results when the homozygous Rb mutation is introduced into the germline. RESULTS: Homozygous Rb mutant ES cells can develop into phenotypically normal, mature B and T lymphocytes in the RAG-2-deficient background. Strikingly, Rb-deficient B and T cells do not have major defects in either activation or function. CONCLUSION: We have demonstrated the efficacy of the RAG-2-deficient blastocyst complementation system for evaluating the role of critical genes in lymphocyte development. Our results indicate that Rb expression is not intrinsically required for B-cell or T-cell function, despite the normally high levels of Rb expressed in lymphoid cells.     

BPOZ基因纯合缺失ES细胞系的建立及其生长和分化研究

研究BPOZ基因缺失对细胞生长和分化的影响.以高浓度的G418筛选BPOZ基因杂合缺失型ES细胞,PCR鉴定抗高浓度G418细胞克隆基因型;半定量RTPCR分析3种基因型ES细胞BPOZ基因的表达情况,分析3种基因型ES细胞Oct34基因的表达以明确ES细胞分化状态.利用3种基因型ES细胞进行细胞生长曲线和3H胸嘧啶核苷参入实验比较其生长速度和增殖能力.以裸鼠荷瘤实验和类胚体形成实验比较BPOZ基因纯合缺失型ES细胞与野生型ES细胞生长分化能力.结果表明,筛选获得两个BPOZ基因剔除的纯合ES细胞克隆;筛选得到的纯合ES细胞中BPOZ基因表达完全缺失,细胞处未分化状态.与野生型ES细胞相比,BPOZ基因纯合缺失型ES细胞生长受抑,增殖能力减弱.BPOZ基因纯合缺失型ES细胞可分化形成类胚体和具备来自3个不同胚层的细胞和组织的畸胎瘤.BPOZ基因剔除使ES细胞生长受抑,对ES细胞分化发育没有明显影响.     

四倍体补偿技术的建立及其应用

常规基因剔除小鼠的获得主要是利用ES细胞的全能性先获得嵌合体小鼠,再利用:ES细胞的生殖系传递能力,通过嵌合体与野生型小鼠的交配获得杂合子小鼠.而四倍体补偿技术则可绕过嵌合体小鼠阶段,直接获得基因修饰杂合子小鼠.利用电融合技术和Piezoelectric microinjecfion显微注射技术建立了四倍体补偿技术,小鼠四倍体胚胎的获得率(电融合率)为(93.01±l.37)%,经体外培养囊胚形成率为(82.49±2.08)%.通过显微注射方法将2种129品系小鼠来源的ES细胞(CJ7和SCR012)注射到四倍体囊胚腔中,获得了完全ES细胞来源的小鼠,ES鼠的获得率分别为2.7%和8.3%.经微卫星DNA检测,成体小鼠的10个被检测组织均为129小鼠来源的.同时,也利用基因修饰的ES细胞进行了研究,获得了2种基因修饰的完全ES细胞来源的杂合子小鼠,部分小鼠具有繁殖能力,经繁育已获得了纯合子,其中凝血因子Ⅷ基因敲除小鼠获得了预期的血友病小鼠表型.上述结果说明四倍体补偿技术可应用于基因修饰小鼠的制备.     

p19Ink4d Is a Tumor Suppressor and Controls Pituitary Anterior Lobe Cell Proliferation

Pituitary tumors develop in about one-quarter of the population, and most arise from the anterior lobe (AL). The pituitary gland is particularly sensitive to genetic alteration of genes involved in the cyclin-dependent kinase (CDK) inhibitor (CKI)–CDK-retinoblastoma protein (Rb) pathway. Mice heterozygous for the Rb mutation develop pituitary tumors, with about 20% arising from the AL. Perplexingly, none of the CKI-deficient mice reported thus far develop pituitary AL tumors. In this study, we show that deletion of p19^Ink4d (p19), a CKI gene, in mice results in spontaneous development of tumors in multiple organs and tissues. Specifically, more than one-half of the mutant mice developed pituitary hyperplasia or tumors predominantly in the AL. Tumor development is associated with increased cell proliferation and enhanced activity of Cdk4 and Cdk6 and phosphorylation of Rb protein. Though Cdk4 is indispensable for postnatal pituitary cell proliferation, it is not required for the hyperproliferative pituitary phenotype caused by p19 loss. Loss of p19 phosphorylates Rb in Cdk4^−/− pituitary AL cells and mouse embryonic fibroblasts (MEFs) and rescues their proliferation defects, at least partially, through the activation of Cdk6. These results provide the first genetic evidence that p19 is a tumor suppressor and the major CKI gene that controls pituitary AL cell proliferation.     

At most three ES cells contribute to the somatic lineages of chimeric mice and of mice produced by ES-tetraploid complementation

Chimeric or entirely embryonic stem (ES) cell-derived mice ("ES mice") can be produced by injecting ES cells into diploid (2n) or tetraploid (4n) host blastocysts, respectively. Usually, between 10 and 15 ES cells are injected into the host blastocyst, but it is not clear how many of the injected cells contribute to the somatic lineages, thus serve as "founder cells" of the embryo proper. We have used genetically labeled ES cells to retrospectively determine the number of founder ES cells that generate the somatic lineages of chimeric and of ES mice. ES cell clones individually labeled with provirus were mixed in equal numbers and injected into 2n or 4n blastocysts to generate chimeric or ES mice. Southern analysis of DNA from the resulting animals indicated that the somatic lineages were most often derived from one or two and sometimes from up to three founder ES cells. The number of founder cells was independent of the total number of cells injected into the host blastocysts. Our results are consistent with the notion that constraints of the host embryo restrict the number of ES cells that can contribute to a chimeric or an ES mouse.     

Neural cells without functional N-Methyl-D-Aspartate (NMDA) receptors contribute extensively to normal postnatal brain development in efficiently generated chimaeric NMDA R1 -/- <--> +/+ mice

Embryonic stem (ES) cells have revolutionised our understanding of animal physiology. Analysis of chimaeric mice generated from these cells allows us to study the role of genes in development and function of the nervous system. The NMDA receptor, one of the two major ionotropic glutamate receptors, has been proposed to play fundamental roles in the survival, migration, differentiation, and activity-dependent maturation of neural cells. The NMDA receptor subunit 1 (NR1) gene is indispensable for receptor function, and knock-out mice die at birth, inhibiting the study of glutamate signalling in postnatal neurons. Homozygous NR1-/- ES cells were derived from matings of heterozygous mice under feeder-free conditions. Chimaeras were made by incorporating these ES cells into wild-type blastocysts and by the classical aggregation of morulae between wild-type and NR1-/- embryos. The resulting chimaeras survive and develop normally. NR1-/- neurons, identified by their lacZ label, were analysed and quantified in developing and adult brains with varying knock-out contributions in every single brain region. Specifically, postnatal ontogenesis of cerebellum and hippocampus was normal. Accordingly, in chimaeric mice, NMDA receptor-initiated signals are not required for the migration, differentiation, and survival of most types of neurons in the central nervous system, in a cell-autonomous way.     

Target-independent specification of proprioceptive sensory neurons

The c-fes protooncogene encodes a nonreceptor tyrosine kinase (Fes) implicated in cytokine receptor signal transduction, granulocyte survival, and myeloid differentiation. To study the role of c-fes during myelopoiesis, we generated embryonic stem (ES) cells with a targeted disruption of the c-fes locus. Targeted mutagenesis deletes the C-terminal SH2 and tyrosine kinase domains of c-fes (referred to as c-fes(Delta c/Delta c)). We demonstrate that the c-fes(Delta c/Delta c) allele results in a truncated Fes protein that retains the N-terminal oligomerization domain, but lacks both the SH2 and the tyrosine kinase domain. In vitro differentiation of c-fes(Delta c/Delta c) ES cells results in hyperproliferation of an early myeloid cell. Generation of c-fes(Delta c/Delta c) mutant chimeric mice causes lethality by E13.5 with embryos exhibiting pleiotropic defects, the most striking being cardiovascular abnormalities. These results establish that c-fes is an important regulator of myeloid cell proliferation and embryonic development.