Extra-embryonic function of Rb is essential for embryonic development and viability

The retinoblastoma (Rb) gene was the first tumour suppressor identified. Inactivation of Rb in mice results in unscheduled cell proliferation, apoptosis and widespread developmental defects, leading to embryonic death by day 14.5 (refs 2-4). However, the actual cause of the embryonic lethality has not been fully investigated. Here we show that loss of Rb leads to excessive proliferation of trophoblast cells and a severe disruption of the normal labyrinth architecture in the placenta. This is accompanied by a decrease in vascularization and a reduction in placental transport function. We used two complementary techniques-tetraploid aggregation and conditional knockout strategies-to demonstrate that Rb-deficient embryos supplied with a wild-type placenta can be carried to term, but die soon after birth. Most of the neurological and erythroid abnormalities thought to be responsible for the embryonic lethality of Rb-null animals were virtually absent in rescued Rb-null pups. These findings identify and define a key function of Rb in extra-embryonic cell lineages that is required for embryonic development and viability, and provide a mechanism for the cell autonomous versus non-cell autonomous roles of Rb in development.     

Effects of an Rb mutation in the mouse.

The retinoblastoma gene is mutated in several types of human cancer and is the best characterized of the tumour-suppressor genes. A mouse strain has been constructed in which one allele of Rb is disrupted. These heterozygous animals are not predisposed to retinoblastoma, but some display pituitary tumours arising from cells in which the wild-type Rb allele is absent. Embryos homozygous for the mutation die between days 14 and 15 of gestation, exhibiting neuronal cell death and defective erythropoiesis.     

Rb基因表达与非小细胞肺癌关系的研究

采用mRNA原位杂交和免疫组织化学方法对31例非小细胞肺癌及相应的正常组织进行Rb基因表达的研究。结果显示Rb基因转录的阴性率为16．1％（5／31）,蛋白表达异常率为19．4％（6／31）。表明,非小细胞肺癌的发生与Rb基因的表达有关。     

Somatic misexpression of germline P granules and enhanced RNA interference in retinoblastoma pathway mutants

Caenorhabditis elegans homologues of the retinoblastoma (Rb) tumour suppressor complex specify cell lineage during development. Here we show that mutations in Rb pathway components enhance RNA interference (RNAi) and cause somatic cells to express genes and elaborate perinuclear structures normally limited to germline-specific P granules. Furthermore, particular gene inactivations that disrupt RNAi reverse the cell lineage transformations of Rb pathway mutants. These findings suggest that mutations in Rb pathway components cause cells to revert to patterns of gene expression normally restricted to germ cells. Rb may act by a similar mechanism to transform mammalian cells.     

Inactivation of the p53 pathway in retinoblastoma

Most human tumours have genetic mutations in their Rb and p53 pathways, but retinoblastoma is thought to be an exception. Studies suggest that retinoblastomas, which initiate with mutations in the gene retinoblastoma 1 (RB1), bypass the p53 pathway because they arise from intrinsically death-resistant cells during retinal development. In contrast to this prevailing theory, here we show that the tumour surveillance pathway mediated by Arf, MDM2, MDMX and p53 is activated after loss of RB1 during retinogenesis. RB1-deficient retinoblasts undergo p53-mediated apoptosis and exit the cell cycle. Subsequently, amplification of the MDMX gene and increased expression of MDMX protein are strongly selected for during tumour progression as a mechanism to suppress the p53 response in RB1-deficient retinal cells. Our data provide evidence that the p53 pathway is inactivated in retinoblastoma and that this cancer does not originate from intrinsically death-resistant cells as previously thought. In addition, they support the idea that MDMX is a specific chemotherapeutic target for treating retinoblastoma.     

Acute mutation of retinoblastoma gene function is sufficient for cell cycle re-entry

Cancer cells arise from normal cells through the acquisition of a series of mutations in oncogenes and tumour suppressor genes. Mouse models of human cancer often rely on germline alterations that activate or inactivate genes of interest. One limitation of this approach is that germline mutations might have effects other than somatic mutations, owing to developmental compensation. To model sporadic cancers associated with inactivation of the retinoblastoma (RB) tumour suppressor gene in humans, we have produced a conditional allele of the mouse Rb gene. We show here that acute loss of Rb in primary quiescent cells is sufficient for cell cycle entry and has phenotypic consequences different from germline loss of Rb function. This difference is explained in part by functional compensation by the Rb-related gene p107. We also show that acute loss of Rb in senescent cells leads to reversal of the cellular senescence programme. Thus, the use of conditional knockout strategies might refine our understanding of gene function and help to model human cancer more accurately.     

多基因突变小鼠模型与动脉粥样硬化研究

目前己知人类有近 2 0 0 0 0种疾病 ,其发生与发展都与基因受损有着直接或间接的关系 ,其中相当一部分疾病的发病涉及到两个以上的基因功能异常。动脉粥样硬化 (AS)、肥胖、糖尿病、高血压等多基因疑难疾病是目前严重影响人类健康的重大疾病。在AS的发病过程中 ,血脂代谢异常是其重要原因之一。在载脂蛋白E(apoE)通过与低密度脂蛋白受体 (LDLR)和乳糜微粒受体的特异性结合 ,介导血浆脂蛋白的转运与清除 ,在脂质的代谢中起着非常重要的作用。瘦素受体 (OB R)在体内介导瘦素的信号传导 ,调节能量代谢与平衡与肥胖以及血脂代谢有关。通过…     

人参皂苷 Rb1 干预 DSS 诱导结肠炎模型小鼠转录组高通量测序及分析

摘要:目的 研究人参皂苷 Rb1 干预葡聚糖硫酸钠盐( Dextran Sulfate Sodium Salt,DSS)诱导结肠炎模型小鼠转录组学信息特征。 方法 C57BL / 6 雄性小鼠构建动物模型,将 15 只小鼠分为正常组、模型组和 Rb1 组,每组 5 只。 模型组和 Rb1 组给予 4% DSS 并自由饮水,第 2 天给 Rb1 组 40 mg / kg Rb1 进行干预。 持续 9 d,处死小鼠后,取结肠组织。 利用 Illumina 高通量测序平台分别对三组小鼠结肠组织进行转录组测序。 利用测定的转录组学数据对 Rb1 组和模型组两两比较之后进行重叠分析,筛选差异基因进行 GO 和 KEGG 分析。 结果 Rb1 干预后各项指标均有改善;GO 富集后其有 10 450 个有效差异表达基因得到 GO 注释,其中分子功能占 13. 5% ,生物过程占 68. 73% ,细胞组成占 17. 77% ;富集最显著的前 20 个 KEGG 通路中与 Rb1 干预后密切相关的有钙离子信号通路、神经活动配体-受体相互作用通路以及 cAMP 信号通路。 结论 人参皂苷 Rb1 能够缓解 DSS 诱导结肠炎模型小鼠的症状。 通过构建 Rb1 干预后 DSS 诱导结肠炎模型小鼠结肠组织转录组序列数据库,为以后 Rb1 功能基因的挖掘和参与代谢途径提供数据支撑,为临床应用提供新的思路。     

Developmental defects of the ear, cranial nerves and hindbrain resulting from targeted disruption of the mouse homeobox gene Hox-1.6.

Gene targeting in mouse embryo-derived stem cells has been used to generate mice with a disruption in the homeobox gene Hox-1.6. Mice heterozygous at the Hox-1.6 locus appear normal, whereas Hox-1.6-/Hox-1.6- mice die at or shortly after birth. These homozygotes exhibit profound defects in the formation of the external, middle and inner ears as well as in specific hindbrain nuclei, and in cranial nerves and ganglia. The affected tissues lie within a narrow region along the anteroposterior axis of the mouse but are of diverse embryonic origin. The set of defects associated with the disruption of Hox-1.6 is distinct from and nonoverlapping with that of the closely linked Hox-1.5 gene. But both mutations cause loss, rather than homeotic transformation, of tissues and structures.     

Abrogation by c-myc of G1 phase arrest induced by RB protein but not by p53.

Inactivating mutations of the retinoblastoma gene (RB) are found in a wide variety of tumour cells. Replacement of wild-type RB can suppress the tumorigenicity of some of these cells, suggesting that the RB protein (Rb) may negatively regulate cell growth. As activation of c-myc expression promotes cell proliferation and blocks differentiation, it may positively regulate cell growth. The c-myc protein is localized in the nucleus and can physically associate with RB protein in vitro, hence c-myc may functionally antagonize RB function. Microinjection of Rb in G1 phase reversibly arrests cell-cycle progression. Here we co-inject RB protein with c-myc, EJ-ras, c-fos or c-jun protein. Co-injection of c-myc, but not EJ-ras, c-fos or c-jun, inhibits the ability of Rb to arrest the cell cycle. The c-myc does not inhibit the activity of another tumour supressor, p53 (ref. 12). Thus, c-myc and RB specifically antagonize one another in the cell.     

A cellular protein that competes with SV40 T antigen for binding to the retinoblastoma gene product

Tumour-suppressor genes, such as the human retinoblastoma susceptibility gene (Rb), are widely recognized as being vital in the control of cell growth and tumour formation. This role is indicated, in part, by the suppression of tumorigenicity of human tumour cells after retrovirus-mediated Rb replacement. How Rb acts to bring about this suppression is not clear but one clue is that the Rb protein forms complexes with the transforming oncoproteins of several DNA tumour viruses, and that two regions of Rb essential for such binding frequently contain mutations in tumour cells. These observations suggest that endogenous cellular proteins might exist that bind to the same regions of Rb and thereby mediate its function. We report here the identification of one such human cellular Rb-associated protein of relative molecular mass 46,000 (46K) (RbAP46). Two lines of evidence support the notion that RbAP46 and simian virus 40 T antigen have homologous Rb-binding properties: first, several mutated Rb proteins that failed to bind to T also did not associate with RbAP46; and second, both T antigen and T peptide (amino acids 101-118) were able to compete with RbAP46 for binding to Rb. The apparent targeting of the RbAP46-Rb interaction by oncoproteins of DNA tumour viruses strongly suggests that formation of this complex is functionally important.