Production Of Spheroids Research Articles

The production of dental plaque and caries by the bacterium Streptococcus salivarius in gnotobiotic WAG/RIJ rats

The abilities of ten strains of Streptococcus salivarius to colonize rat molars and to induce caries were determined using mono-infected germ-free rats. Scanning electron microscopy revealed the production of micro-colonies and spheroids by Strep. salivarius on exposed surfaces of molar teeth, and abundant dense plaque formation in fissures. Most strains colonized fissures and smooth surfaces as effectively as Streptococcus mutans NCTC 10832, yet produced no buccal or lingual lesions. The four K − strains of Strep. salivarius produced more approximal lesions than the K + strains but fewer lesions than Strep. mutans. All but one Strep. salivarius strain fell into the high-caries category, together with Strep. mutans. They were all more cariogenic than either Streptococcus milleri NCTC 11169 or Streptococcus faecalis 47.

L-Glutamic acid as a mediator of sexual morphogenesis in Volvox capensis

In Volvox capensis the development of sexual individuals is in response to low concentrations (68 nM) of L-glutamic acid rather than to such species-specific glycoproteins as have been isolated in Volvox carteri or are believed to exist in a number of other species. V. capensis grows equally as well in light and in darkness in a medium supplemented with sodium acetate; however, L-glutamic acid is active as an inducer of the sexual form only in populations grown in the light. The site of action of L-glutamic acid and its biochemical role in the sexual response are unknown. Attempts to induce the sexual response by using the other L-amino acids, various analogs of glutamic acid, compounds of similar structure (e.g., gamma-aminobutyric acid), and intermediates of biochemical pathways known to involve L-glutamic acid (e.g., alpha-ketoglutarate or pyroglutamic acid) have been unsuccessful. L-Glutamic acid is produced by V. capensis as a natural product of the digestion of the glycoproteinaceous parental matrix at the time young spheroids escape. As a population increases, so does the level of L-glutamic acid produced at each succeeding generation until the threshold of sensitivity is reached and the induction of sexual forms is effected. This serves as a mechanism for ensuring the production of sexual spheroids and their zygotes, the only phase in the life cycle resistant to drying. Thus, Volvox is especially adapted to an existence in ephemeral pools of water resulting from seasonal rains.

Production, growth and handling of multicellular tumor spheroids

Production, growth and handling of multicellular tumor spheroids

The pathogenicity of an entomopoxvirus fromOthnonius batesi [Col.: Scarabaeidae] and its possible use as a control agent

In a natural population ofOthnonius batesiOll. at Glen Innes, N.S.W., 4.0% of larvae in 1972 and 2.2% in 1973 were exhibiting symptoms of virus infection, whilst 0.8% of pupae and adults from the same population were infected in 1972. These figures, and field observations of infected larvae, suggested that the pathogenicity of the virus was low. In laboratory experiments withO. batesi the infection had little effect on mortality, and no significant effect on duration of the first instar, food intake, or larval growth. The vast accumulation of virus in the fat body probably results in mortality prior to, or during, the pupal period. Temperature had a marked effect on both % infection (optimum 30°C) and production of viral spheroids (optimum 25°C). Very little viral development occurred below 20°C. In a host range study onlyO. batesi, Rhopaea verreauxiBlanch. andR. morbillosaBlkb. were infectedper os. The possible use of the virus as a control agent is discussed.

Ultrastructure of brain and nerve biopsy tissue in Wilson disease.

A 14-year-old girl with psychomotor deterioration developed Wilson disease. Mild atrophy of the small hand muscles was an unusual feature. A cerebral cortex biopsy specimen disclosed exuberant spheroid production, chromatolytic changes, myelin and axonal degeneration, alterations of capillary basal lamina, Hirano bodies, Alzheimer type protoplasmic astrocytosis, and many neuropil-based nonneuronal elements (M cells) of heterogeneous derivation distinct from astrocytes and normal oligodendrocytes. On reviewing neuroglia cell changes in light of present findings, the following conclusions become obvious: Alzheimer type II astrocytosis is true cellular hyperplasia of a class of reactive protoplasmic astrocytes with variable cytologic features. Alzheimer type I astrocytes most probably do not exist; the designation should be dropped. M cells play an important role in the cytopathology of Wilson disease; some forms may generate the so-called Alzheimer type I astrocyte.

A working model for the control of differentiation during development of the embryo ofVolvox carterif.nagariensis

SummaryThe production of asexual, male, or female spheroids in Volvox carteri f. nagariensis depends on the pattern of development of the embryo. This pattern is determined by the presence or absence of a chemical substance produced in populations of male spheroids; it may also be determined by each of two different genetic loci which have been studied in spontaneous female spheroids. Using the JACOB-MONOD operon theory as a model, a system of genetic control is proposed, involving two interlocking repressible systems. The system explains the postulated action of the chemical substance from male spheroids, as well as the action of the two genetic loci. The proposed model is a working hypothesis useful in designing further experimentation.