Synthesis of alpha subunit of human chorionic gonadotrophin by presumptive HeLa cells

Summary Several cell lines, originally thought to be derived from a human placenta at term but possibly HeLa-contaminated, have been studied. These cells secrete a protein indistinguishable immunochemically from the alpha subunit of chorionic gonadotropin but not the beta subunit of chorionic gonadotropin or placental lactogen. Complete chorionic gonadotropin was detected but amounted to less than 1% of the level of the alpha subunit. The cells also produce an alkaline phosphatase similar to placental alkaline phosphatase in immunochemical, gel-electrophoretic, and heat-denaturation properties. They induce tumor growth when inoculated into nude mice. These cells are aneuploid and have a model chromosome number of 66. The common HeLa karyologic markers, designated 1, 2, and 3, and A-type glucose-6-phosphate dehydrogenase are present in these cells. HeLa cells have not previously been shown to secrete theα subunit of hCG.     

PINEAL SEROTONIN N-ACETYLTRANSFERASE ACTIVITY: PROTECTION OF STIMULATED ACTIVITY BY ACETYL-CoA AND RELATED COMPOUNDS

—Rat pineal serotonin N—acetyltransferase activity increases 30–70-fold at night in the dark and then decreases rapidly when animals are exposed to light. Activity of the enzyme is also stimulated by l -norepinephrine in organ culture. When homogenates of glands stimulated by dark in vivo or NE in vitro are incubated at 37°C, enzyme activity will also rapidly decrease. This decrease can be prevented by one of the cosubstrates of the enzyme, acetyl–CoA. Protection can also be conferred by cysteamine (β-mercaptoethylamine, HS–CH₂–CH₂–NH₂) which is the terminal portion of the CoA molecule. This protection mechanism could be involved in the physiological control of enzyme activity.     

DNA sequence organization in the genomes of five marine invertebrates

The arrangement of repetitive and non-repetitive sequence was studied in the genomic DNA of the oyster (Crassostrea virginica), the surf clam (Spisula solidissima), the horseshoe crab (Limulus polyphemus), a nemertean worm (Cerebratulus lacteus) and a jelly-fish (Aurelia aurita). Except for the jellyfish these animals belong to the protostomial branch of animal evolution, for which little information regarding DNA sequence organization has previously been available. The reassociation kinetics of short (250-300 nucleotide) and long (2,000-3,000 nucleotide) DNA fragments was studied by the hydroxyapatite method. It was shown that in each case a major fraction of the DNA consists of single copy sequences less than about 3,000 nucleotides in length, interspersed with short repetitive sequences. The lengths of the repetitive sequences were estimated by optical hyperchromicity and S1 nuclease measurements made on renaturation products. All the genomes studied include a prominent fraction of interspersed repetitive sequences about 300 nucleotides in length, as well as longer repetitive sequence regions.     

The isolation of a soluble type III collagen precursor from rat skin

A soluble form of type III collagen has been isolated from the 1.0 M NaCl neutral salt soluble extract of rat skin. This component has a molecular weight of 350,000 and is converted by reduction and alkylation to three identical α-chains with molecular weight 118,000. Segment-long-spacing precipitates produced from the renatured disulfide-linked component are about 300 Å longer than collagen with extensions at both the amino and carboxyl terminal ends. Pepsin treatment removes both amino and carboxyl terminal extensions. These and radioisotope incorporation data lead to the conclusion that this component is a precursor of the [αl(III)₃] collagen.     

Effect of protease inhibitors on mitogen stimulation of hamster lymphoid cells

Hamster lymph node and spleen cells can be stimulated to incorporate tritiated thymidine ([³H]TdR) in vitro under serum-free conditions by the proteases trypsin and chymotrypsin. Under similar conditions, thymocytes could be stimulated by concanavalin A (ConA) but not lipopolysaccharide (LPS) or the proteases. The subpopulation of cells responding to the proteases correlated with the cells responding to LPS on fractionation of spleen and lymph node cells on discontinuous bovine serum albumin (BSA) gradients or on nylon-wool columns. The stimulation induced by trypsin was completely blocked by soybean trypsin inhibitor (SBTI) while that induced by chymotrypsin was only partially blocked. The inhibition by SBTI of protease activation was not effective when added 24 h after initiation of stimulation. On the other hand, addition of clarified isologous serum to protease activated cultures after 24 h still lead to greater than 50% inhibition of [³H]TdR incorporation.     

Practising Conservation Biology in a Virtual Rainforest World

The interdisciplinary science of conservation biology provides undergraduate biology students with the opportunity to connect the biological sciences with disciplines including economics, social science and philosophy to address challenging conservation issues. Because of its complexity, students do not often have the opportunity to practise conservation biology. To increase exposure to this science, this paper describes a virtual rainforest island on which students collect data related to forest carbon storage, while also confronting ethical issues. Students are asked to independently make decisions, collect data and explore the island before writing a research report with recommendations for the future management of the island’s forests. The ethics of decision-making are addressed in the students’ research reports and are reinforced through guided class discussion. Students will complete this activity with increased ethical awareness, as well as a better understanding of the challenges associated with the practise of conservation biology.     

DLG1: Chromosome Location of the Closest Human Homologue of the Drosophila Discs Large Tumor Suppressor Gene

The Drosophila discs large tumor suppressor protein, Dlg, is the prototype of a newly discovered family of proteins termed MAGUKs (membrane-associated guanylate kinase homologues). MAGUKs are localized at the membrane-cytoskeleton interface, usually at cell-cell junctions, where they appear to have both structural and signaling roles. They contain several distinct domains, including a modified guanylate kinase domain, an SH3 motif, and one or three copies of the DHR (GLGF/PDZ) domain. Recessive lethal mutations in the discs large tumor suppressor gene interfere with the formation of septate junctions (thought to be the arthropod equivalent of tight junctions) between epithelial cells, and they cause neoplastic overgrowth of imaginal discs, suggesting a role for cell junctions in proliferation control. A homologue of the Dlg protein, named Hdlg, has been isolated from human B lymphocytes. It shows 65-79% identity to Dlg in the different domains, and it binds to the cytoskeletal protein 4.1. Here, we report that the gene for lymphocyte Hdlg, named DLG1, is located at chromosome band 3q29. This finding identifies a novel site for a candidate tumor suppressor on chromosome 3.