Establishment and Characterization of Cell Lines from Homozygous Brachyury (T/T) Embryos of the Mouse

Lethal mutations in the T/t complex cause stage-specific morphologic abnormalities during early embryogenesis of mice. Although mutant embryos are lethal at the early stages of development, we have succeeded in establishing several cell lines from one of these mutants ( T/T ). Mutant-specific abnormality was not observed in gross morphology and growth patterns of cells. They, however, retained the characters of freshly dissociated embryonic cells to form smaller aggregates than the wild-type in rotation-mediated aggregation.
One of the T/T cell lines (T-1) formed tumors when injected into one-day-old syngeneic and allogeneic host, Expression of H-2 antigens was serologically studied with H-2 specificity 5 as a marker antigen. All lines except T-1 were shown to have this specificity.     

Decomposition Patterns of Foliar Litter and Deadwood in Managed and Unmanaged Stands: A 13-Year Experiment in Boreal Mixedwoods

Litter decomposition is a major driver of carbon (C) and nitrogen (N) cycles in forest ecosystems and has major implications for C sequestration and nutrient availability. However, empirical information regarding long-term decomposition rates of foliage and wood remains rare. In this study, we assessed long-term C and N dynamics (12–13 years) during decomposition of foliage and wood for three boreal tree species, under a range of harvesting intensities and slash treatments. We used model selection based on the second-order Akaike’s Information Criterion to determine which decomposition model had the most support. The double-exponential model provided a good fit to C mass loss for foliage of trembling aspen, white spruce, and balsam fir, as well as aspen wood. These litters underwent a rapid initial phase of leaching and mineralisation, followed by a slow decomposition. In contrast, for spruce and fir wood, the single-exponential model had the most support. The long-term average decay rate of wood was faster than that of foliage for aspen, but not of conifers. However, we found no evidence that fir and spruce wood decomposed at slower rates than the recalcitrant fraction of their foliage. The critical C:N ratios, at which net N mineralisation began, were higher for wood than for foliage. Long-term decay rates following clear-cutting were either similar or faster than those observed in control stands, depending on litter material, tree species, and slash treatment. The critical C:N ratios were reached later and decreased for all conifer litters following stem-only clear-cutting, indicating increased N retention in harvested sites with high slash loads. Partial harvesting had weak effects on C and N dynamics of decaying litters. A comprehensive understanding of the long-term patterns and controls of C and N dynamics following forest disturbance would improve our ability to forecast the implications of forest harvesting for C sequestration and nutrient availability.     

In vivo restriction. Sequence and structure of endonuclease II-dependent cleavage sites in bacteriophage T4 DNA.

Endonuclease II of bacteriophage T4 is required for in vivo restriction of cytosine-containing DNA from its host, Escherichia coli, (as well as from phage mutants lacking cytosine modification), normally the first step in the reutilization of host DNA nucleotides for synthesis of phage DNA in infected cells. The phage cytosine-DNA is fragmented incompletely to yield genetically defined fragments. This restriction is different from that of type I, II, or III restriction enzymes. We have located seven major endonuclease II-dependent restriction sites in the T4 genome, of which three were analyzed in detail; in addition, abundant sites were cleaved in less than or equal to 5% of all molecules. Sites I, II, and III shared the sequence 5'-CCGNNTTGGC-3' and were cleaved in about 25% (I and III) and 65% (II) of all molecules, predominantly staggered around the first or second of the central unspecified base pairs to yield fragments with one 5' base. The less frequently cleaved sites I and III deviated from site II in predicted helical structure when viewed from the consensus strand, and in sequence when viewed from the opposite strand. Thus, interaction with a particular helical structure as well as recognition of the bases in DNA appears important for efficient cleavage.     

Cross reactive antigens of Acholeplasma laidlawii and L-form of Staphylococcus aureus]

We demonstrated that the membrane of Acholeplasma laidlawii PG8 and L-form of Staphylococcus aureus, both of which induce cellular immunity in BALB/c mice, were antigenically related each other. Foodpad responses of the mice immunized with a mixture of either antigen and Freund's complete adjuvant showed clearly a cross reaction when challenged with the other antigen. Cross responses to incorporate 3H-thymidine to the spleen lymphocytes of the mice immunized with either antigen occurred in the presence of the other antigen. Furthermore, the purified T cells, but not B cells, of the spleen were activated in the presence of antigen-presenting cells. These antigens existing in the membrane fractions of both microorganisms were purified by Razin's method. Finally, these membrane components of A. laidlawii and L-form of S. aureus were subjected to gel electrophoresis and transferring to nitrocellulose membrane and used to stimulate the spleen lymphocytes of the mice immunized with A. laidlawii or of non-immunized mice. The fractions representing molecular weights of approximately 45 kD, 25 kD, and 13 kD of both microorganisms consistently stimulated the lymphocytes of the immunized mice but not those of non-immunized mice.