肿瘤抑制基因APCmRNA在豚鼠脑中的分布

APC基因是1991年被发现的一类肿瘤抑制基因,它被定位于人第5号染色体5q21处。APC基因如发生缺失或突变,则易患直肠肿瘤,并伴有部分先天痴呆的病例。本工作在孟帆已获得的APC基因在豚鼠中的同源cDNA的基础上,完成了对它的亚克隆,并利用原位杂交和RNA酶保护分析的方法,对它在脑中的分布进行了研究。发现APCmRNA主要在海马、大脑和小脑中表达;嗅球中杂交信号稍弱,脑干中最弱。海马中阳性细胞主要是锥体细胞,小脑中则主要是内层颗粒细胞。在一个月大的豚鼠胚胎的脑中也观察到相似的表达型式。进一步的研究有助于我们更好地了解神经发育和先天痴呆发生的分子机制。     

The advantage of long-distance clonal spreading in highly disturbed habitats

Summary Classical theory states that cover of annual plants should increase relative to perennials as disturbance frequency increases. However, it has been suggested that long-distance clonal spreading can allow some perennial plants to survive in highly disturbed areas by quickly spreading into disturbed patches. To evaluate these hypotheses, we analysed data of plant distributions in two different ecosystems, a barrier island and a short-grass steppe. The disturbances studied were sand deposition during storms (overwash) on the barrier island and grazing by cattle in the short-grass steppe. In each case the disturbance frequency varied over the ecosystem; we categorized different areas in terms of their disturbance frequencies. All plant species in each area were categorized as one of four plant life forms (1) annual or biennial, (2) herbaceous perennial without long-distance clonal spreading (3) herbaceous perennial with long-distance clonal spreading (i.e guerilla form) and (4) woody plant. Percentage cover of each plant life form in each disturbance frequency category was calculated. In both ecosystems, (1) there was an increase in the relative cover of annuals as one moved from areas of low to moderate disturbance frequencies, but then a decrease in cover of annuals as one moved into the areas of highest disturbance frequency and (2) the guerilla forms showed the greatest relative increase in cover from moderately to highly disturbed areas. The combination of two factors can explain this pattern: (1) long-distance clonal spreading effectively reduces the time to colonization of recently disturbed sites and (2) effects of the disturbances in these two systems are probably more severe for seeds than for stems. We illustrate these effects using a spatially explicit simulation model of the population dynamics of plants in a disturbed landscape.     

Effects of substratum morphology on cell physiology

Among the host of substratum properties that affect animal cell behavior, surface morphology has received relatively little attention. The earliest effect of surface morphology on animal cells was discovered almost a century ago when it was found that cells became oriented in response to the underlying topography. This phenomenon is now commonly known as contact guidance. From then until very recentrly, little progress has been made in understanding the role of surface morphology on cell behavior, primarily due to a lack of defined surfaces with uniform morphologies. This problem has been solved recently with the development of photolithographic techniques to prepare substrata with well defined and uniform surface morphologies. Availability of such surfaces has facilitated systematic in vitro experiments to study influence of surface morphology on diverse cell physiological aspects such as adhesion, growth, and function. For example, these studies have shown that surfaces with uniform multipls parallel grooves can enhance cell adhesion by confining cells in grooves and by mechanically interlocking them. Several independent studies have demosterated that cell shape is a major determinant of cell growth and function. Because surface morphology has been shown to modulate the extent of cell spreading and cell shape, its effects on cell growth and function appear to be mediated via this biological coupling between cell shape and function. New evidence in the cell biology literature is emerging to suggest that surface morphology could affect other cell behavioral properties such as post-translational modifications. Further elucidation of such effects will enable better designs for implant and cell culture substrata.     

Single-cell cloning of a crown gall from protoplasts regenerated in hormone-free medium. Establishment of pure transformed cell-lines of Catharanthus roseus

Protoplasts enzymatically isolated from cell line of Catharanthus roseus G. Don crown gall, were cultured at high density (10⁵ P ml^-1) in modified B5 liquid medium (Gamborg et al. 1976). In the absence of growth regulators C. roseus protoplasts were able to regenerate a cell-wall, divide and, subsequently, yield very numerous clones in the absence of growth regulators. After two weeks, the cultures were greatly diluted in order to obtain clones of single-cell origin. Most of the clones individually transferred onto solid medium can proliferate indefinitely, without growth regulators. Among analyzed clones, 90% were nopaline positive. Their ajmalicine and serpentine content was compared with that of the parental crown gall line, and was found to be low. The CR10 protoplasts were very easy to grow, they were an interesting model for the development of pure tumorous lines. Moreover, we found that the tumorous protoplasts were useful for cell fusion experiments or for the delicate culture of tree protoplasts.Abbreviations B5 Gamborg et al. (1976) medium - 2,4-d 2,4-dichlorophenoxyacetic acid - Kin Kinetin - NAA naphthalene acetic acid - BA N⁶ (benzyl) adenine     

Latency of cathepsin B secreted by human colon carcinoma cells is not linked to secretion of cystacin C and is relieved by neutrophil elastase

The lysosomal cystein proteinase cathepsin B is shown to be secreted by ten human colon carcinoma cell lines and to accumulate in culture media as a latent enzyme. The cell lines also secrete a physiological inhibitor of cathepsin B, cystatin C. A significant correlation was found between secretion of the latent enzyme and the inhibitor (r = 0.755, P < 0.01). The aim of the present study was to modulate the respective secretion of the two antagonists to test whether or not latency of cathepsin B was due to the concomitant secretion of the inhibitor. SW480 colon carcinoma cells were treated with the acidotropic agent ammonium chloride, phorbol 12-myristate 13-acetate, and the inflammatory cytokines TGF-β, TNF-α, and IL-1β. Ammonium chloride significantly increased latent cathepsin B levels without affecting the constitutive secretion of cystatin C. Phorbol 12-myristate 13-acetate induced a 4- to 5-fold increase in secreted latent cathepsin B, but did not alter significantly the accumulation of cystatin C in media. The cytokines, TGF-β, TNF-α, and IL-1β, had no major effect on the expression of these two antagonists. Latent cathepsin B released from human carcinoma cells could be efficiently activated by neutrophil elastate at neutral pH. It is concluded that latent cathepsin B is a true proenzyme rather than an enzyme-inhibitor comples. In addition, our data from neutrophil elastate activation experiments indicate that a proteolytic system for activation of the tumor cell-secreted latent enzyme may exist in vivo.     

胎盘型谷胱甘肽S－转移酶基因在胃癌中的表达

用Ｄｉｇ－ＧＳＴ－πｃＤＮＡ探针分子杂交方法,检测了正常胃组织,胃癌及相应癌旁正常组织中ＧＳＴ－πＤＮＡ和ＧＳＴ－πＲＮＡ水平,发现ＧＳＴ－πＤＮＡ水平没有明显变化,而ＧＳＴ－πＲＮＡ在８例胃癌组织中有６例高于正常胃组织,在１２例低分化腺癌中有７例癌旁正常组织高于相应癌组织,表明ＧＳＴ－π基因表达增加与胃癌有关,而且早于细胞形态的变化。     

P53，Rb和c－myc基因在人脑原发性肿瘤中的转录表达

采用RNA斑点杂交分析,对21例人脑原发性胶质瘤和11例人脑膜瘤中p53,Rb和c-myc基因转录水平的表达进行研究.发现48.4%的肿瘤中p53基因表达减弱,21.9%的肿瘤中Rb基因表达减弱;71.9%的肿瘤中c-myc基因表达增强.在p53基因表达减弱的15例病例中有13例(80%)c-myc基因表达增强.结果表明,p53基因表达减弱和c-myc基因表达增强与人脑原发性肿瘤的发生有关.     

Effects of magnetic fields on mammary tumor development induced by 7, 12-dimethylbenz(a)anthracene in rats

A series of epidemiological studies have indicated associations between exposure to magnetic fields (MFs) and a variety of cancers, including breast cancer. In order to test the possibility that MF acts as a cancer promoter or copromoter, four separate experiments have been conducted in rats in which the effects of chronic exposure to MFs on the development of mammary tumors induced by 7,12-dimethylbenz(a)anthracene (DMBA) were determined. Female rats were exposed in magnetic coils for 91 days (24 h/day) to either alternating current (AC; 50 Hz)-MF or direct current (DC)-MF. Magnetic flux density of the DC-MF was 15 mT. Two AC-MF exposures used a homogeneous field with a flux density of 30 mT (rms); one used a gradient field with flux density ranging from 0.3–1 μT. DMBA (5 mg) was administered orally at the onset of MF exposure and was repeated thrice at intervals of 1 week. In each experiment, 18–36 animals were exposed in 6 magnetic coils. The same number of rats were used as sham-exposed control. These control animals were treated with DMBA and were placed in dummy coils in the same room as the MF-exposed rats. Furthermore, groups of age-matched rats (reference controls) were treated with DMBA but housed in another room to exclude any MF exposure due to the magnetic stray field from the MF produced by coils. At the end of the exposure or sham-exposure period, tumor number and weight or size of tumors were determined at necropsy. Results were as follows: In sham-exposed animals or reference controls, the tumor incidence varied between 50 and 78% in the 4 experiments. The average number of mammary tumors per tumor-bearing animal varied between 1.6 and 2.9. In none of the experiments did MFs significantly alter tumor incidence, but in one of the experiments with AC-MF exposure at 30 mT, the number of tumors per tumor-bearing animal was significantly increased. Furthermore, exposure to a DC-MF at 15 mT significantly enhanced the tumor weight. Exposure to a gradient AC-MF at 0.3–1 μT exerted no significant effects. These experiments seem to indicate that MFs at high flux densities may act as a promoter or copromoter of breast cancer. However, this interpretation must be considered only a tentative conclusion because of the limitations of this study, particularly the small sample size used for MF exposure and the lack of repetition of data. © 1993 Wiley-Liss. Inc.     

Molecular cloning and expression of the gene for a major leucine-rich protein from human hepatoblastoma cells (HepG2)

Summary The human hepatoblastoma cell line, HepG2, exhibits an array of stable properties in culture that have made it a popular cell culture model for studies on regulation of liver-specific gene expression and properties of hepatoma cells. In contrast to other hepatoma cell lines, HepG2 cells overexpress a characteristic detergent-extractable, wheat germ lectin-binding protein with apparent molecular mass of 130 kDa. Using an antibody to screen a phage expression library of HepG2 complementary DNA (cDNA), we identified and cloned a 4734 base pair cDNA which codes for a 130-kDa leucine-rich protein (lrp130) when expressed in transfected cells. The deduced sequence of lrp130 exhibits sequences weakly homologous to the consensus sequence for the ATP binding site in ATP-dependent kinases and the protein kinase C phosphorylation site of the epidermal growth factor receptor. Consistent with the higher levels of expression of lrp130 antigen, Northern hybridization analysis indicated that HepG2 cells express high levels of the major 4.8 kilobase lrp130 mRNA relative to other hepatoma cells. Although currently of unknown function, lrp130 may be of utility as a marker for liver cell lineages represented by the HepG2 cell line.