Pertussis Toxin Attenuates D2 Inhibition and Enhances D1 Stimulation of Adenylate Cyclase by Dopamine in Rat Striatum

The response of adenylate cyclase to GTP and to dopamine (DA) was investigated in synaptic plasma membranes isolated from rat striatum injected with pertussis toxin, which inactivates the inhibitory guanine nucleotide-binding regulatory protein (Ni) of adenylate cyclase. Pertussis toxin treatment reverted the inhibitory effects on the enzyme activity elicited by micromolar concentrations of GTP and reduced by 50% the DA inhibition of cyclase activity via D2 receptors. The toxin treatment enhanced the net stimulation of enzyme activity by DA in the presence of micromolar concentrations of GTP. However, the stimulatory effect of the selective D1 receptor agonist SKF 38393 was not significantly affected. The data indicate that Ni mediates D2 inhibition of striatal adenylate cyclase and participates in the modulation of D1 stimulation of the enzyme activity by DA.     

Energy-dependent formation of free ATP in yeast submitochondrial particles, and its stimulation by oligomycin

Yeast submitochondrial particles, in a P_i- and NADH-dependent reaction, produced low concentrations of free ATP in the absence of added ADP. This formation of free ATP, as measured by the luciferin-luciferase method, was strongly stimulated by oligomycin. For maximal stimulation, oligomycin was to be added not earlier than 5–10 min after the addition of NADH. Upon addition of antimycin or FCCP the system was completely inhibited. The amount of free ATP formed corresponded to one-third of the amount of bound ATP in submitochondrial particles. The stimulatory effect of oligomycin disappeared if the submitochondrial particles were spun down after oligomycin stimulation and then resuspended in the reaction medium, whereas submitochondrial particles with no oligomycin added initially were stimulated by oligomycin after the same procedure. A different picture emerged with addition of ADP. If the submitochondrial particles were preenergized with NADH in the presence of oligomycin before the addition of ADP the formation of free ATP upon subsequent addition of ADP was inhibited by oligomycin. In the presence of oligomycin, but lacking preenergization with NADH, a stimulation of free ATP formation was achieved with added ADP. A possible explanation for the stimulating effect of oligomycin on ATP formation in the absence of added ADP is that it enhances the release of bound ATP in an energy-requiring process. The release of only about one-third of the bound ATP could indicate that one of three nucleotide-binding subunits involved in the mechanism of ATP formation by ATP synthase is in a state suitable for such an energy-dependent release of ATP.     

Construction of an Unstable Ring-X Chromosome Bearing the Autosomal Dopa Decarboxylase Gene in Drosophila melanogaster and Analysis of Ddc Mosaics

An unstable Ring-X chromosome, Ddc⁺- Ring-X carrying a cloned Dopa decarboxylase (Ddc) encoding segment was constructed. The construction involved a double recombination event between the unstable Ring-X, R(1)w^vC and a Rod-X chromosome which contained a P-element mediated Ddc ⁺ insert. The resulting Ddc⁺-Ring-X chromosome behaves similarly to the parent chromosome with respect to somatic instability. The Ddc⁺-Ring-X chromosome was used to generate Ddc mosaics. Analyses of Ddc mosaics revealed that while there was no absolute requirement for the Ddc ⁺ expression in either the epidermis or the nervous system, very large mutant clones did affect the viability of the mosaic.     

Human carcinoma cell lines xenografted in athymic mice: biological and antigenic characteristics of an intraabdominal model

Summary In order to investigate in vivo clinical applications of murine monoclonal antibodies directed against human ovarian carcinoma a preclinical in vivo model was developed using BALB/c athymic mice. Three human carcinoma cell lines (MCF7, HT29, and SW626) were injected into the peritoneal cavity of pristane-primed animals and the biological and antigenic characteristics of the i.p. grown tumors were studied. The animals were killed when moribund or 6–8 weeks after tumor injection. At autopsy tumor take was observed in 85% of the injected animals, whereas palpable nodules were evident in only 83%. Examination of the peritoneal cavity revealed intraabdominal carcinomatosis with tumor masses varying in size between 0.2 and 0.5 cm in diameter and tumor sheets. The most frequently affected organs were the diaphragm, the liver, and the reproductive system. Ascitic fluid formation was rare and no animal developed tumors outside the peritoneal cavity. To determine whether the in vivo tumors retained the same antigenic characteristics as the in vitro cell lines, four monoclonal antibodies (MBrl, MOv2, MOv8, and MOv15) directed against ovarian carcinoma-associated antigens and two different experimental approaches (immunofluorescence and immunoblotting) were used. Variations at either a quantitative or a qualitative level were observed for some antigens, whereas no evident changes were apparent for others. In particular, the antigens detected by MBr1 and MOv15 on the MCF7 line both maintained high levels of expression and immunoblotting staining pattern, whereas the antigens detected by MOv2 on the HT29 and SW626 lines, although present at a high level, clearly changed their staining pattern. As regards the antigens recognized by MOv8 and MOv15 on the HT29 and SW626 lines, we observed a drastic decrease in the level of their expression and in many cases a drop below the threshold of detectability of the test. The intraabdominal carcinomatosis described partially mimics the growth characteristics of human ovarian cancer and maintains the expression of some antigenic markers associated with epithelial tumors of the ovary and may therefore be useful in devising immunodiagnostic and/or immunotherapeutic strategies for ovarian carcinoma.     

Isolated and purified plasma and thylakoid membranes of the cyanobacteriumAnacystis nidulans contain immunologically cross-reactive aa3-type cytochrome oxidase

Cell-free extracts ofAnacystis nidulans were fractionated by discontinuous sucrose density gradient centrifugation resulting in the separation of two distinct types of membranes, the heavier one containing the chlorophyll and the lighter one devoid of chlorophyll. Identity of the latter with plasma membrane was confirmed by labeling of intact cells with impermeant marker,³⁵S-diazobenzenesulfonate, prior to cell disruption. Both membrane fractions were purified individually by repeated recentrifugation on identical gradients. Purified membranes were subjected to dissociating polyacrylamide gel electrophoresis, either type of membranes yielding a distinct polypeptide pattern. After transfer of the polypeptides to nitrocellulose by Western blotting, two of the proteins, with molecular weights of approximately 55,000 and 32,000, respectively, gave strong and specifically complementary cross-reactions with antibodies raised against subunits I and II of the aa₃-type cytochrome oxidase fromParacoccus denitrificans. The findings will be discussed in terms of the presence of aa₃-type cytochrome oxidase in both plasma and thylakoid membranes ofAnacystis nidulans.     

The organization of repetitive sequences in the albumin and alpha-fetoprotein gene loci in the rat

Summary The distribution of middle repetitive sequences in the genic and extragenic regions of the rat albumin and -fetoprotein genes was analyzed. Their presence was determined by probing Southern blots of restriction fragments of albumin and -fetoprotein genomic subclones with ³²P-labeled total rat DNA. Repetitive sequences were detected in both genes. They were classified as weak, moderate and intense hybridizing elements according to the intensity of hybridization. Weak repetitive sequences were characterized as dG·dT repeats by using ³²P-labeled poly-(dG·dT)(dC·dA) oligomer probe. They occurred in 5 and 3 extragenic regions of the two genes and in introns 4 and 5 of the albumin gene. The moderate repetitive sequence present in intron 6 of the albumin gene was identified as the rat SINES element, 4D12. The intense repetitive sequence, localized in the 3 non-coding region of the albumin gene, corresponded to the terminal segment of a rat high repeat long interspersed DNA family, L1Rn. 4D12 and L1Rn sequences were also scattered throughout the -fetoprotein locus as moderate and intense repetitive elements, respectively, but their distribution was different from that of the albumin genomic region. These results indicate that repetitive sequences invaded the two loci in a non-conservative manner.     

De novo root formation in thin cell layers of tobacco: changes in free and bound polyamines

Thin cell layers excised from tobacco ( Nicotiana tabacum L. cv. Samsun) stem internodes, with an appropriate exogenous hormonal balance, were able to form a greater number of roots, and in a larger percentage of the explants (93%) than when they were excised from pedicels (40%). The developmental sequence of root formation and explant growth were followed by histological analysis. Free and bound [trichloroacetic acid (TCA)-soluble and -insoluble] putrescine and spermidine increased in the explants, particularly when root meristemoids appeared. These meristemoids originated in the superficial (day 6 in culture) or deep (days 10–11) layers and inside the newly formed callus (day 25). At those times, TCA-soluble and, to a lesser extent, TCA-insoluble bound putrescine predominated over the other polyamines. Spermine was always present in trace amounts. Polyamines decreased again when root and callus formation was completed (day 30). The involvement of these three classes of polyamines (free, TCA-soluble and -insoluble) in morphogenic processes is discussed.     

The association of H-2Ld with human beta-2 microglobulin induces localized conformational changes in the alpha-1 and- 2 superdomain

We have analyzed changes in the antigenicity of major histocompatibility complex class I molecules resulting from the association of human beta-2 micro-globulin (B2m) with the mouse class I heavy chain. In particular, the H-2L^d molecule exhibited enhanced crossreactivity for the 34-1-2 monoclonal antibody. In order to assess the nature of this structural alteration induced by human B2m, we utilized H-2 class I hybrid molecules in the mapping of the 34-1-2 determinant to the helical region of the alpha-1 domain. H-2L^d class I hybrid molecules were then used to establish the importance of the alpha-2 and- 3 domains in the observed increase of 34-1-2 cross-reactivity following exchange with human B2m. The H-2L^d hybrids suggest that alterations in interdomain contact are responsible for enhanced 34-1-2 cross-reactivity on the H-2L^d molecule. It is likely that this alteration arises through changes in class I conformation at regions of the molecule distant from points of contact between B2m and the class I molecule. This suggests that perturbations induced by association of human B2m with H-2L^d can affect the conformation of the alpha-1 and- 2 superdomain. That class I antigenic determinants are altered by the association of human B2m with mouse class I further suggests that the class I molecule is structurally flexible and may reflect the ability of the class I molecule to bind and present a vast array of disparate peptides to the T-cell receptor.