Predation at a snail's pace: what's time to a gastropod?

Summary Predation by naticid gastropods shows evidence of adaptation to maximize the rate of energy intake. The predation rate of Polinices duplicatus feeding on artificially altered, thin-shelled Mercenaria mercenaria was faster than the predation rate on normal Mercenaria. The rate of energy intake was limited by handling time. The time saved by predation on thin-shelled prey was used to forage. Thus time was shown to be valuable to P. duplicatus, and cost-benefit functions using time and energy as currencies are appropriate for estimating dietary efficiency and predicting prey choice.Despite the clear superiority of thin-shelled prey, P. duplicatus did not learn to prefer this novel prey type, suggesting that predator choices are sterotyped, reflecting optima selected over evolutionary time.     

Organization of the ribosomal ribonucleic acid genes in various wild-type strains and wild-collected strains of Neurospora

Summary The organization of the ribosomal DNA (rDNA) repcat unit in the standard wild-type strain of Neurospora crassa, 74-OR23-1A, and in 30 other wild-type strains and wild-collected strains of N. crassa, N. tetrasperma, N. sitophila, N. intermedia, and N. discreta isolated from nature, was investigated by restriction enzyme digestion of genomic DNA, and probing of the Southern-blotted DNA fragments with specific cloned pieces of the rDNA unit from 74-OR23-1A. The size of the rDNA unit in 74-OR23-1A was shown to be 9.20 kilobase pairs (kb) from blotting data, and the average for all strains was 9.11+0.21 kb; standard error=0.038; coefficient of variation (C.V.)=2.34%. These data indicate that the rDNA repeat unit size has been highly conserved among the Neurospora strains investigated. However, while all strains have a conserved HindIII site near the 5 end of the 25 S rDNA coding sequence, a polymorphism in the number and/or position of HindIII sites in the nontranscribed spacer region was found between strains. The 74-OR23-1A strain has two HindIII sites in the spacer, while others have from 0 to at least 3. This restriction site polymorphism is strain-specific and not species-specific. It was confirmed for some strains by restriction analysis of clones containing most of the rDNA repeat unit. The current restriction map of the 74-OR23-1A rDNA repeat unit is presented.     

Purine phosphoribosyltransferase (EC 2.4.2.7 and 2.4.2.8) and purine de novo synthesis activity in rat testicular tissue at different stages of development, and their correlation with the circulating levels of gonadotrophins and testosterone, and with structural changes

The overall activity of the purine de novo synthesis pathway and the activities of purine phosphoribosyltransferase in the rat testis were measured at different ages and were correlated with histological observations. Similar studies of the concentration of circulating gonadotrophins and testosterone were performed. The purine phosphoribosyltransferase activities were between two and three orders of magnitude greater than purine de novo synthesis. The peak activity of the purine de novo synthesis pathway coincided with the first appearance of meiosis in the spermatocytes immediately before the luteinising hormone (LH) level rose to its peak. The highest activity of the hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8) - catalysed purine salvage pathway coincided with the first appearance of mature spermatozoa in the tubules just after the occurrence of peak levels of follicle-stimulating hormone (FSH). These findings are linked to the development of testicular atrophy in cases of severe HPRT deficiency in man.     

Broad-Host-Range Agrocin of Agrobacterium tumefaciens

Eighteen strains of Agrobacterium tumefaciens isolated from crown galls were tested for agrocin production. Of six agrocin-producing strains, one (D286) produced a broad-host-range agrocin active against strains carrying nopaline, octopine, and agropine type Ti plasmids. Sensitivity to agrocin D286 was found to map in the 11- to 18-megadalton region of the nopaline Ti plasmid pTiC58. The agrocin was partially purified, and its physical characteristics were consistent with its being a nucleotide, as is agrocin 84. Agrocin D286 was shown to inhibit DNA, RNA, and protein syntheses. Strain D286 spontaneously lost its pathogenicity, and its potential for use in the biological control of crown gall is discussed.     

The inhibition of nucleic acid synthesis by mycophenolic acid

1. Mycophenolic acid, an antibiotic of some antiquity that more recently has been found to have marked activity against a range of tumours in mice and rats, strongly inhibits DNA synthesis in the L strain of fibroblasts in vitro. 2. The extent of the inhibition of DNA synthesis is markedly increased by preincubation of the cells with mycophenolic acid before the addition of [(14)C]thymidine. 3. The inhibition of DNA synthesis by mycophenolic acid in L cells in vitro is reversed by guanine in a non-competitive manner, but not by hypoxanthine, xanthine or adenine. 4. The reversal of inhibition by guanine can be suppressed by hypoxanthine, 6-mercaptopurine and adenine. 5. Mycophenolic acid does not inhibit the incorporation of [(14)C]thymidine into DNA in suspensions of Landschütz and Yoshida ascites cells in vitro. 6. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into cold-acid-soluble and -insoluble guanine nucleotides in Landschütz and Yoshida ascites cells and also in L cells in vitro. There is some increase in the radioactivity of the adenine fraction in the presence of the antibiotic. 7. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into xanthine and guanine fractions in a cell-free system from Landschütz cells capable of converting hypoxanthine into IMP, XMP and GMP. 8. Preparations of IMP dehydrogenase from Landschütz ascites cells, calf thymus and LS cells are strongly inhibited by mycophenolic acid. The inhibition showed mixed type kinetics with K(i) values of between 3.03x10(-8) and 4.5x10(-8)m. 9. Evidence was also obtained for a partial, possibly indirect, inhibition by mycophenolic acid of an early stage of biosynthesis of purine nucleotides as indicated by a decrease in the accumulation of formylglycine amide ribonucleotide induced by the antibiotic azaserine in suspensions of Landschütz and Yoshida ascites cells and L cells in vitro.     

Cytological aspects of haemoglobin and chlorocruorin synthesis in polychaete annelids

Summary The ultrastructure of the haematopoietic cells in the polychaetes Neoamphitrite figulus Dalyell, Lanice conchilega (Pallas), Arenicola marina (L.), Myxicola infundibulum Renier, Megalomma vesiculusom (Montagu), Sabella penicillus L., are compared: all show similarities in having well developed Golgi, granular endoplasmic reticulum and haemoglobin or chlorocruorin in vesicles, and numerous mitochondria. The porphyrin byproducts of synthesis are combined with iron as haematins within electrondense granules built up from multi-lamellar organelles. The structure of the basal lamina which alone separates the cells from the lumen of the vessels is described and evidence is presented for the method of release of the haem into the plasma by reverse pinocytosis. The cycle of synthesis within the cell is discussed and the process of haem synthesis in annelids is reviewed. The structure of the haemoglobin-containing coelomocytes of Neoamphitrite figulus is briefly described.This work was made possible by an award from the Science Research Council. We would also like to thank the Director and Staff of the Plymouth Laboratory, where some of the work was done, for their hospitality and facilities.     

CYTOPLASMIC DNA SYNTHESIS IN AMOEBA PROTEUS : I. On the Particulate Nature of the DNA-Containing Elements

The incorporation of tritiated thymidine in Amoeba proteus was reinvestigated in order to see if it could be associated with microscopically detectable structures. Staining experiments with basic dyes, including the fluorochrome acridine orange, revealed the presence of large numbers of 0.3 to 0.5 µ particles in the cytoplasm of all cells studied. The effect of nuclease digestion on the dye affinity of the particles suggests that they contain DNA as well as RNA. Centrifugation of living cells at 10,000 g leads to the sedimentation of the particles in the centrifugal third of the ameba near the nucleus. Analysis of centrifuged cells which had been incubated with H₃-thymidine showed a very high degree of correlation between the location of the nucleic acid-containing granules and that of acid-insoluble, deoxyribonuclease-sensitive labeled molecules and leads to the conclusion that cytoplasmic DNA synthesis in Amoeba proteus occurs in association with these particles.     

Primary culture of normal rat mammary epithelial cells within a basement membrane matrix. II. Functional differentiation under serum-free conditions

Summary A serum-free primary culture system is described which allows normal rat mammary epithelial cells (RMECs) embedded within a reconstituted basement membrane to undergo extensive growth and functional differentiation as detected by synthesis and secretion of the milk products casein and lipid. RMECs isolated from mammary glands of immature virgin rats were seeded within an extracellular matrix preparation derived from the Engelbreth-Holm-Swarm sarcoma and cultured in a serum-free medium consisting of Dulbecco's modified Eagle's medium-F12 containing insulin, prolactin, progesterone, hydrocortisone, epidermal growth factor, bovine serum albumin, transferrin, and ascorbic acid. Casein synthesis and secretion were documented at the electron microscopic level as well as by an enzyme-linked immunosorbent assay (ELISA) assay using a polyclonal antibody against total rat caseins. Numerous secretory vesicles with casein micelles were noted near the apical surface of the RMECs, and secreted casein was observed in the lumen. These ultrastructural data were confirmed by the ELISA assay which showed that microgram amounts of casein per well were synthesized by the RMECs and that the amount of casein increased with time in culture. Using immunoblot analysis it was demonstrated that the full complement of casein proteins was synthesized. In addition to casein protein, β-casein mRNA levels were shown to increase with time. Synthesized lipid was detected at both the light and electron microscopic levels. Phase contrast photomicrographs demonstrated extensive intracellular lipid accumulation within the ductal and lobuloalveolarlike colonies, and at the electron micrograph level, lipid droplets were predominantly localized near the apical surface of the RMECs. The lipid nature of these droplets was verified by oil red O staining. Results from this study demonstrate that RMECs from immature virgin rats proliferate extensively and rapidly develop the capacity to synthesize and secrete casein and lipid when grown within a reconstituted basement membrane under defined serum-free conditions. This unique system should thus serve as an excellent model in which the regulation of mammary development and gene expression can be investigated. This work was supported by grants CA 33240 and CA 35641 and by core grant CA 24538 from the National Institutes of Health, Bethesda, MD.