Induction of proliferation or transformation of neuroretina cells by the mil and myc viral oncogenes

The genome of the avian retrovirus MH2 contains, in addition to the v-myc oncogene shared with three other avian retroviruses (MC29, CMII and OK-10), a second cell-derived oncogene, v-mil (refs 1-3). Like the three other viruses, which contain only v-myc, MH2 induces mainly liver and kidney carcinomas in fowl and transforms fibroblasts and macrophages in vitro. However, MH2 and MC29 differ in their biological properties when assayed on cultures of chicken embryo neuroretina (NR) cells. Indeed, NR cells, which normally do not multiply in vitro, are induced to proliferate and become transformed upon infection with MH2, whereas infection with MC29 has no apparent effect on these cells. To analyse the functions of the two oncogenes of MH2, we isolated spontaneous and in vitro-constructed mutants of this virus and investigated their effects on NR cell multiplication and transformation. We report here that expression of v-mil is sufficient to induce NR cell proliferation, although it does not result in cell transformation. In addition, viruses expressing only the v-myc oncogene fail to induce any detectable change in NR cells. However, cooperation of the two oncogenes is required to achieve transformation of NR cells by MH2.     

Equilibrium: the intracellular distribution of steroid receptors

Data are presented which suggest that there are unbound receptors for oestrogen in nuclei of the smooth muscle cells of the myometrium. A new model for the distribution of unbound receptors is proposed in which unbound receptor is in equilibrium, partitioned between nucleus and cytoplasm according to the free water content of these intracellular compartments.     

Identification of a new class of steroid hormone receptors

The gonads and adrenal glands produce steroids classified into five major groups which include the oestrogens, progestins, androgens, glucocorticoids and mineralocorticoids. Gonadal steroids control the differentiation and growth of the reproductive system, induce and maintain sexual characteristics and modulate reproductive behaviour. Adrenal steroids also influence differentiation as well as being metabolic regulators. The effects of each steroid depend primarily on its specific receptors, the nature of which could therefore provide a basis for classification of steroid hormone action. The successful cloning, sequencing and expression of the human glucocorticoid (hGR) (ref. 1), oestrogen (hER), progesterone (hPR), and mineralocorticoid (hMR) receptors, complementary DNA, plus homologues from various species, provides the first opportunity to study receptor structure and its influence on gene expression. Sequence comparison and mutational analysis show structural features common to all groups of steroid hormone receptors. The receptors share a highly conserved cysteine-rich region which functions as the DNA-binding domain. This common segment allows the genome to be scanned for related gene products: hMR cDNA for example, was isolated using an hGR hybridization probe. In this study, using the DNA-binding domain of the human oestrogen receptor cDNA as a hybridization probe, we have isolated two cDNA clones encoding polypeptides with structural features suggestive of cryptic steroid hormone receptors which could participate in a new hormone response system.     

略论俄语词类转化的本质和原因

通过对构词法和词类转化的对比分析，阐明了词类转化的性质，即词类转化是词的功能运作，它的发生是有规律、有条件的，它依赖于情境因素，是言语层次上的现象。词类转化的外部原因是社会的变化、语言交际的特点和情景的作用；内部原因是词的省略、词的搭配和词的某一语法形式游离以及句法功能改变的结果。     

Common non-hormone binding component in non-transformed chick oviduct receptors of four steroid hormones

Steroid hormones produce a response in target cells by binding to hormone-specific soluble receptors, which undergo a transformational change, leading to their interaction with chromatin and to modified gene expression. In a previous paper, we described a monoclonal antibody, BF4, that specifically recognizes and binds the non-transformed '8S' form of chicken oviduct progesterone receptor (8S-PR). We now show that BF4 does not form an immune complex with the 4S transformed form of 3H-progestin-labelled progesterone receptor, but does interact with the 8S non-transformed forms of the oestrogen, androgen and glucocorticosteroid receptors. Our results suggest that the antigenic determinant recognized by BF4 is present on a non-hormone binding unit, which we identify as a polypeptide of molecular weight (MW) 90,000 in the case of the progesterone receptor, and that this unit is common to other 8S non-transformed chicken steroid receptors.     

The receptors and cells for mammalian taste

The emerging picture of taste coding at the periphery is one of elegant simplicity. Contrary to what was generally believed, it is now clear that distinct cell types expressing unique receptors are tuned to detect each of the five basic tastes: sweet, sour, bitter, salty and umami. Importantly, receptor cells for each taste quality function as dedicated sensors wired to elicit stereotypic responses.     

T-cell receptors of human suppressor cells

Cells which can suppress the immune response to an antigen (TS cells) appear to be essential for regulation of the immune system. But the characterization of the TS lineage has not been extensive and many are sceptical of studies using uncloned or hybrid T-cell lines. The nature of the antigen receptor on these cells is unclear. T cells of the helper or cytotoxic lineages appear to recognize their targets using the T-cell receptor (TCR) alpha beta-CD3 complex. TCR beta-gene rearrangements are also found in some murine and human suppressor cell lines but others have been shown not to rearrange or express the beta-chain or alpha-chain genes. We previously established TS clones derived from lepromatous leprosy patients which carry the CD8 antigen and recognize antigen in the context of the major histocompatibility complex (MHC) class II molecules in vitro. We here report the characterization of additional MHC-restricted TS clones which rearrange TCR beta genes, express messenger RNA for the alpha and beta chains of the TCR and express clonally unique CD3-associated TCR alpha beta structures on their cell surface but do not express the gamma chain of the gamma delta TCR on the cell surface. We conclude that antigen recognition by at least some human CD8+ suppressor cells is likely to be mediated by TCR alpha beta heterodimers.     

Retroviral transduction of T-cell antigen receptor beta-chain and myc genes

Support for multistage models of oncogenesis has been provided by several highly leukaemogenic retrovirus isolates that have transduced more than one host cell gene. Where functional studies have been performed, these retroviral oncogenes show synergy for in vitro transformation and leukaemogenesis. In naturally occurring feline leukaemias associated with feline leukaemia virus (FeLV), retroviral transduction of myc is a frequent oncogenic mechanism. But evidence suggesting that the FeLV v-myc genes might be insufficient for leukaemogenesis was provided by the latency (12 weeks) and clonality of FeLV/v-myc-induced tumours and the absence of demonstrable in vitro transformation by these viruses. In the search for secondary leukaemogenic events in FeLV/v-myc tumours, we have identified a case of FeLV transduction of a T-cell antigen receptor beta-chain gene. The proviruses carrying this gene (which we have named v-tcr) were a separate population from those carrying v-myc. In its normal role, the T-cell receptor beta-chain forms part of a multimeric complex involved in antigen recognition and T-cell activation. We suggest that v-tcr is a novel viral oncogene which assisted v-myc in the genesis of a naturally occurring case of thymic lymphosarcoma.     

Cellular transformation and the 'morphologic phenotype' of transformed cells.

Expression of the product of the transforming gene (src) of RNA tumour viruses promotes growth and usually alters the adhesion, appearance and surface properties of cultured fibroblasts. The latter group of properties termed the 'morphologic phenotype' of transformed cells is largely due to diminished cell-to-substratum adhesion. The role of cyclic AMP, cell surface protein (CSP), and other factors in producing the 'morphologic phenotype' are discussed. The effects of src expression bear a striking resemblance to the action of peptide hormones such as insulin on appropriate target cells.     

Identification of nuclear proteins encoded by viral and cellular myc oncogenes

The myelocytomatosis viruses are a family of replication-defective avian retroviruses that cause a variety of tumours in chickens and transform both fibroblasts and macrophages in culture through the activity of their oncogene v-myc. A closely related gene (c-myc) is found in vertebrate animals and is thought to be the progenitor of v-myc. Changes in the expression and perhaps the structure of c-myc have been implicated in the genesis of avian, murine and human tumours (for a review, see ref. 15). Elucidation of the mechanisms by which v-myc and c-myc might elicit tumorigenesis requires identification of the proteins encoded by these genes. To this end, we have expressed a portion of v-myc in a bacterial host and used the resulting protein to raise antisera that react with myc proteins. We report here that v-myc and c-myc encode closely related proteins with molecular weights (MWs) of approximately 58,000. Integration of retroviral DNA near or within c-myc in avian lymphomas apparently enhances expression of the gene. Here we have used cells from one such tumour to identify the protein encoded by c-myc and find that the coding domain for the gene is probably intact.     

Importance of IL-2 receptors in intra-thymic generation of cells expressing T-cell receptors

During development, lymphoid stem cells migrate into the thymic rudiment where they proliferate, rearrange their antigen receptor genes and become differentiated into functionally mature T cells. At present, the regulation of these processes is poorly understood, although recent studies have shown that early fetal and adult immature thymocytes express receptors for the T-cell growth factor, interleukin-2 (IL-2). We now present direct evidence that IL-2 receptors have a function in intra-thymic development by demonstrating that proliferation and the generation of cells expressing the T-cell antigen receptor (alpha beta TCR), which is responsible for the recognition of antigens in the context of MHC, are inhibited when antibodies to IL-2 receptors are added to fetal thymus organ cultures. The inhibition is specific in that it does not affect pre-thymic stem cells and can be partially reversed by addition of exogenous recombinant IL-2.     

三种大肠杆菌高效感受态的制备及转化

描述了一种改良的高效细菌感受态的制备和感受态细胞的保藏及细菌的转化方法.三种不同的大肠杆菌分别是DH5α,TG1和XL1blue,其中最有效的是XL1blue.每种菌株的感受态细胞制备的最佳光密度(OD600值)不同.对感受态细胞的存储时间及其与转化效率之间的关系也进行了研究,结果显示感受态细胞可以在-20℃存储7d,在-70℃存储15d.将常见的方法做了三种改进:首先是将CaCl2溶液改为TB溶液;其次是将培养基由LB换成S.O.C;再就是在质粒对感受态细胞的转化过程中加入DMSO或PEG8000.改良的细菌转化系统比常见的方法能提高转化效率约1000倍,是一种高效的细菌转化系统.     

Schwann cells induce morphological transformation of sensory neurones in vitro

Cell-cell interactions are thought to play a crucial part in determining the developmental fate of vertebrate cells and regulating their subsequent differentiation. In the peripheral nervous system, for example, signals from neuronal axons determine whether or not some Schwann cells wrap their plasma membrane concentricially around the axon to form a myelin sheath. Moreover, there is some evidence that the interactions between Schwann cells and neurones are not all one way: for example, Schwann cells are thought to provide signals for neuronal sprouting and regeneration. However, there are no clear examples in which Schwann cells have been shown to influence the normal development of neurones. Here I have used purified populations of embryonic sensory neurones and Schwann cells to demonstrate that Schwann cells have a dramatic influence on the development of these neurones. In the presence of Schwann cells, but not other cell types, the sensory neurones undergo a morphological transformation from an immature bipolar form to a mature pseudo-unipolar form. This provides a striking example of the importance of glial cells for neuronal development.