Exemplars and the reproduction of everyday life: The Amherst affair

Frederick Errington is Aaaociate Professor of Anthropology, at Keene State College, New Hampshire. Deborah Gewertz is Professor of Anthropology, at Amherst College, Massachusetts.     

Chemotaxis in the Marine Fungus Rhizophydium littoreum

Zoospores of the marine chytrid Rhizophydium littoreum are attracted to a variety of substances common to their environment. In general, carbohydrates and polysaccharides elicited strong concentration-dependent positive responses. There was no direct correlation between all substances used as foods and those stimulating positive responses. The chemotactic activities of this organism should, however, tend to bring it toward concentrated food sources.     

Collagenous substrata regulate the nature and distribution of glycosaminoglycans produced by differentiated cultures of mouse mammary epithelial cells

We have investigated the influence of culture substrata upon glycosaminoglycans produced in primary cultures of mouse mammary epithelial cells isolated from the glands of late pregnant mice. Three substrata have been used for experiments: tissue culture plastic, collagen (type I) gels attached to culture dishes, and collagen (type I) gels that have been floated in the culture medium after cell attachment. These latter gels contract significantly. Cells cultured on all three substrata produce hyaluronic acid, heparan sulfate, chondroitin sulfates and dermatan sulfate but the relative quantities accumulated and their distribution among cellular and extracellular compartments differ according to the nature of the culture substratum. Notably most of the glycosaminoglycans accumulated by cells on plastic are secreted into the culture medium, while cells on floating gels incorporate almost all their glycosaminoglycans into an extracellular matrix fraction. Cells on attached collagen gels secrete approx. 30% of their glycosaminoglycans and assemble most of the remainder into an extracellular matrix. Hyaluronic acid is produced in significant quantities by cells on plastic and attached gels but in relatively reduced quantity by cells on floating gels. In contrast, iduronyl-rich dermatan sulfate is accumulated by cells on floating gels, where it is primarily associated with the extracellular matrix fraction, but is proportionally reduced in cells on plastic and attached gels. The results are discussed in terms of polarized assembly of a morphologically distinct basal lamina, a process that occurs primarily when cells are on floating gels. In addition, as these cultures secrete certain milk proteins only when cultured on floating gels, we discuss the possibility that cell synthesized glycosaminoglycans and proteoglycans may play a role in the maintenance of a differentiated phenotype.     

Genetic structure of natural populations of the red-spotted newt,Notophthalmus viridescens

Genetic variation is described at 15 loci in 2 neotenic and 12 nonneotenic populations of red-spotted newts. Though high levels of genetic similarity (I=0.990) were found among all populations, allele frequencies at six of the eight most polymorphic loci show significant heterogeneity across populations. Change in allele frequencies at two of these loci (Pep-2 and Ldh-1) is significantly correlated with latitude. Interspecific homologies are established for newt peptidases based on substrate specificities and lactate dehydrogenases based on tissue distribution, thermal stability, and kinetic properties. Nonneotenic populations are highly variable (H=0.157) and neotenic populations are only slightly, but significantly, less variable (H=0.120). The high levels of heterozygosity detected in nonneotenic populations may result from large effective population size and/or environmental heterogeneity. The unexpectedly high heterozygosity values obtained for the neotenic populations may indicate adult dispersal or the presence of some previously undetected red efts at these localities. In any case, a major change in life history has apparently had little effect on the genetic structure of these populations.This research was supported by grants from the Blakeslee Fund of Smith College.     

Frequency distribution studies of epipelic diatoms along an intertidal shore

Live and dead cell counts of epipelic diatoms were analysed at 16 sites along a transect crossing a saltmarsh, sandflat, and mudflat at Berrow Flats, Somerset, U.K. Replicate monthly samples were taken from January 1982 to June 1984. The ratio of dead to live cells varied according to position along the transect. Temporal changes of the ratios did not display a cyclic seasonal pattern. The clustered mosaic of live cells and empty frustules on surface sediments was quantitatively assessed. Graphing variance against seasonal mean cell counts showed that the variance was proportional to the square of the mean. The Neyman Type A equation is suggested as a possible model to explain this relationship.     

Beneficial effects of activated charcoal on bulblet production in tissue cultures of Muscari armeniacum

Production of bulblets of Muscari armeniacum through tissue culture is enhanced when 1 g/l activated charcoal is added to a modified Murashige and Skoog (MS) medium. Bulblet regeneration is direct from bulb scale explants with no intermediate callus growth. Bulblets can be transferred successfully to a greenhouse environment directly from aseptic culture.     

Methylammonium uptake by Rhodobacter capsulatus

The ammonium uptake system of Rhodobacter capsulatus B100 was examined using the ammonium analog methylammonium. This analog was not transported when cells were grown aerobically on ammonium. When cultured on glutamate as a nitrogen source, or when nitrogen-starved, cells would take up methylammonium. Therefore, in cells grown under nitrogen-limiting conditions, a second system of ammonium uptake (or a modified form of the first) is present which is distinguished by its capacity for transporting the analog in addition to ammonium. The methylammonium uptake system exhibited saturation kinetics with a K _m of 22 M and a V _max of about 3 nmol per min · mg protein. Ammonium completely inhibited analog transport with a K _i in the range of 1 M. Once inside the cell methylammonium was rapidly converted to -N-methylglutamine; however, a small concentration gradient of methylammonium could still be observed. Kinetic parameters reflect the effects of assimilation.The methylammonium uptake system was temperature and pH dependent, and inhibition studies indicated that energy was required for the system to be operative. A glutamine auxotroph (G29) lacking the structural gene for glutanime synthetase did not accumulate the analog, even when nitrogen starved. The Nif^- mutant J61, which is unable to express nitrogenase structural genes, also did not transport methylammonium, regardless of the nitrogen source for growth. However, the mutant exhibited wild-type ammonium uptake and glutamine synthetase activity. These data suggest that transport of ammonium is required for growth on limited nitrogen and is under the control of the Ntr system in R. capsulatus.Abbreviations CCCP carbonyl cyanide-m-chlorophenyl hydrazone - CHES cyclohexylaminoethanesulfonic acid - DMSO dimethyl sulfoxide - GMAD -N-methylglutamine - GS glutamine synthetase - MES 2-(N-morpholino) ethanesulfonic acid - MSX methionine-Dl-sulfoximine - pCMB p-chloromercuribenzoate - Tricine N-tris(hydroxymethyl)methylglycine     

Glycopeptides of the Type-Common Glycoprotein gD of Herpes Simplex Virus Types 1 and 2

We have carried out detailed structural studies of the glycopeptides of glycoprotein gD of herpes simplex virus types 1 and 2. We first examined and compared the number of N-asparagine-linked oligosaccharides present in each glycoprotein. We found that treatment of either pgD-1 or pgD-2 with endo-β-N-acetylglucosaminidase H (Endo H) generated three polypeptides which migrated more rapidly than pgD on gradient sodium dodecyl sulfate-polyacrylamide gels. Two of the faster-migrating polypeptides were labeled with [³H]mannose, suggesting that both pgD-1 and pgD-2 contained three N-asparagine-linked oligosaccharides. Second, we characterized the [³H]mannose-labeled tryptic peptides of pgD-1 and pgD-2. We found that both glycoproteins contained three tryptic glycopeptides, termed glycopeptides 1, 2, and 3. Gel filtration studies indicated that the molecular weights of these three peptides were approximately 10,000, 3,900, and 1,800, respectively, for both pgD-1 and pgD-2. Three methods were employed to determine the size of the attached oligosaccharides. First, the [³H]mannose-labeled glycopeptides were treated with Endo H, and the released oligosaccharide was chromatographed on Bio-Gel P6. The size of this molecule was estimated to be approximately 1,200 daltons. Second, Endo H treatment of [³⁵S]methionine-labeled glycopeptide 2 reduced the molecular size of this peptide from approximately 3,900 to approximately 2,400 daltons. Third, glycopeptide 2 isolated from the gD-like molecule formed in the presence of tunicamycin was approximately 2,200 daltons. From these experiments, the size of each N-asparagine-linked oligosaccharide was estimated to be approximately 1,400 to 1,600 daltons. Our experiments indicated that glycopeptides 2 and 3 each contained one N-asparagine-linked oligosaccharide chain. Although glycopeptide 1 was large enough to accommodate more than one oligosaccharide chain, the experiments with Endo H treatment of the glycoprotein indicated that there were only three N-asparagine-linked oligosaccharides present in pgD-1 and pgD-2. Further studies of the tryptic glycopeptides by reverse-phase high-performance liquid chromatography indicated that all of the glycopeptides were hydrophobic in nature. In the case of glycopeptide 2, we observed that when the carbohydrate was not present, the hydrophobicity of the peptide increased. The properties of the tryptic glycopeptides of pgD-1 were compared with the properties predicted from the deduced amino acid sequence of gD-1. The size and amino acid composition compared favorably for glycopeptides 1 and 2. Glycopeptide 3 appeared to be somewhat smaller than would be predicted from the deduced sequence of gD-1. It appears that all three potential glycosylation sites predicted by the amino acid sequence are utilized in gD-1 and that a similar number of glycosylation sites are present in gD-2.