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1301. The pathogenesis of cancer metastasis.
Metastases do not result from random survival of cells released from the primary tumour but from the selective growth of specialised subpopulations of highly metastatic cells endowed with specific properties that befit them to complete each step of the metastatic process.
1302. Protein methylation in behavioural control mechanisms and in signal transduction.
In both prokaryotes and eukaryotes methyl groups can be added to and removed from the carboxyl groups of proteins. Recent work has revealed that these reactions have a role in several behavioural phenomena. The nature of this role has been uncovered in one case--that of bacterial chemotaxis.
1303. Hormonal regulation of peptide receptors and target cell responses.
Regulation of plasma membrane receptors for peptide hormones by the prevailing ligand concentration often causes altered target cell function. Receptor number is determined by hormone-induced changes in membrane conformation, irreversible ligand binding, and processing of ligand-receptor complexes during hormone action.
1304. A unifying model for the G1 period in prokaryotes and eukaryotes.
A model to explain the cell division cycle in both prokaryotes and eukaryotes is presented. No specific 'G1 functions' take place during the G1 period, which is merely part of a larger period for the preparation of DNA synthesis which began at the previous initiation of DNA synthesis. A G1 period exists merely because the doubling time of the cells is greater than the sum of the S and G2 periods.
1305. Cell-surface antigens induced by RNA tumour viruses.
Host animals show an immune response to the surface of cells infected with RNA tumour viruses. An element of this response is due to expression of viral structural antigens, but the major part is due to virus-induced cell-surface antigens (CSAs). This article compares the properties of CSAs of the avian, murine and feline retrovirus systems.
1309. Steroid-induced meiotic division in Xenopus laevis oocytes: surface and calcium.
Progesterone reinitiates meiotic maturation in Xenopus oocytes. Evidence is reported which indicates that the steroid acts at the level of the cell surface and suggests that an induced change of Ca2+ distribution triggers in turn a cascade of cytoplasmic events including protein synthesis and germinal vesicle (nucleus) breakdown. These novel features of steroid hormone action in amphibian oocytes are discussed in relation to presently accepted views of the mechanism of action of steroid hormones in somatic cells.
1310. Fibronectins--adhesive glycoproteins of cell surface and blood.
A recently characterised class of adhesive, high molecular weight glycoproteins is present on the surfaces of cells, in connective tissue matrices, and in extracellular fluids. These proteins may have important roles in cellular adhesion, malignant transformation, reticuloendothelial system function, and embryonic differentiation.
1311. 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.
1312. Chemotherapy of parasite infections.
Although several good antiparasitic agents are available, new drugs are needed for the treatment of diseases such as chloroquine-resistant malaria, Chagas' disease, leishmaniasis and filariasis. The 'semirational approach' should be the basis for their synthesis.
1313. The pathology, pathobiology and pathogenesis of schistosomiasis.
Although the general pathology of schistosomiasis has been well understood for more than 70 years, it is only recently that it has been possible to analyse the disease at the molecular level and to understand the relationship between the number of parasites in an infected individual and the appearance of overt disease.
1314. Identification of economically important parasites.
The taxonomy of a parasite can be an important guide to its pathogenic characteristics. A wide range of anatomical, biochemical and behavioural tests is now being developed to define different strains and subspecies of the main tropical parasites.
1315. Epidemiology and ecology of leishmaniasis in Latin-America.
Of the diseases caused by protozoal parasites, leishmaniasis is probably second in importance only to malaria. Chemotherapeutic drugs are toxic, expensive and not 100% effective. This, and the absence of any non-living vaccine against the disease, means that control depends on eliminating either reservoirs or insect vectors, or both. Recently, a greatly increased knowledge of the Leishmania species involved, and of their natural hosts, has helped to define the nature and extent of the problem.
1316. Mammals, resources and reproductive strategies.
The breeding systems of mammalian species are strongly influenced by the density and dispersion of their populations. These in turn are affected by variations in the distribution of resources. Through quantitative comparisons, it is possible to trace evolutionary relationships between feeding behaviour, population dispersion, breeding systems and morphology.
1317. Repair deficient human disorders and cancer.
The analysis of the repair of damage to DNA in mammalian cells leads not only to a knowledge of which environmental agents are deleterious to living creatures, but also to an understanding of which reaction products in DNA are potentially carcinogenic and which tissues are the more sensitive.
1318. Chromatin.
The approximate shape of the chromatin subunit called the nucleosome is now known, but its internal architecture is not well understood. Recent studies reveal details of the organisation of DNA within the nucleosome, and show that the arginine-rich histones are essential to DNA folding. Nucleosomes or structures related to them seem to be present at points of DNA replication and transcription; interactions within and between nucleosomes are likely to play a critical part in these processes.
1319. Prediction of protein structure from amino acid sequence.
In principle, it is possible to predict theoretically the three-dimensional structure of a protein from its amino acid sequence. Recently substantial progress towards this goal has been made by the use of simple models to represent protein conformation and interatomic interactions, together with the knowledge gained form analyses of know protein structures.
1320. Study of membrane permeability changes by fluctuation analysis.
The molecular basis of the changes in membrane permeability that underlie the nerve impulse can be studied by statistical analysis of the random fluctuations in current through the nerve membrane. Such "noise analysis" has already begun to clarify the nature of the gating mechanisms that control the flow of ions across the membrane at the neuromuscular junction.
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