The frequency of marker changes in sugarcane plants regenerated from callus culture

This study investigates the frequency of apparent and permanent expression of marker change following two types of tissue culture, conventional callus and direct regeneration cultures, and for two markers it relates this frequency to that following breeding. Each clone was used for only one marker. After conventional callus culture, plants of the sugarcane clone Arundoid B, a clone having a growth habit with shortened internodes and leaves, were freed of this marker at a rate of 1 in 172 plants. Marker remission in a second clone with a leaf blotch was enhanced in the presence of a mutagen. Callus culture alone gave a remission rate of 1/280 plants, while treatment of callus with ethyl methanesulfonate gave a remission rate of 1/42 plants. Of two markers subjected to vegetative and sexual transmission, the first, a leaf marker, was stable in callus culture with no remissions; crossing with non-marker parents produced progeny with 54% lacking the marker. The second, a stalk marker (multibud), showed epigenetic effects during two generations of vegetative propagation; plants lacking the multibud marker produced vegetative progeny in which the marker reappeared. Nine crosses to nonmarker parents produced progeny of which an average of 29% had the marker. The use of stalk chimeras as markers demonstrated that passage through conventional callus or direct regeneration culture resulted in the loss of the donor phenotype in all plants regenerated. Phenotypic variation in plants derived from callus culture appears to arise from several sources; chimeral segregants, epigenetic transients, and mutational variants.     

Preimplantation mammalian aggregation and injection chimeras

The preimplantation embryo is highly resilient to experimental manipulations. A specific manipulation that has revealed many clues to the developmental process is chimera production. Chimeras have been used to describe the importance of developmental characteristics of embryonic cells and how these characteristics are involved with developmental fate. These characteristics have been monopolized in the production of interspecific chimeras and the production of transgenic animals. This review attempts to discuss the major factors affecting preimplantation mammalian embryo chimera production.     

Phenotypic variation during micropropagation of the chimeralRhododendron ‘President Roosevelt’

The putative periclinal chimeraRhododendron xlimbatum President Roosevelt was used to study the origin of shoots in vitro. Genotypic segregation readily occurred in vitro. Numerous phenotypes were observed, although most shoots were either entirely green or maintained the original variegation pattern. Derivatives of the third apical layer were rarely involved in shoot formation. A reversed chimeral form was isolated. Adventitious shoots were usually miniaturized and rapidly proliferating, but axillary shoots had thicker stems, larger leaves and proliferated more slowly. Corolla tissue produced stunted, leafy shoots; no variegated shoots were produced from floret explants. In shoot tip cultures the addition of 40M 2iP without IBA resulted in the greatest number of shoots. Explant choice was the most critical factor for maintenance of foliar variegation.     

Chimeric aptamers in cancer cell-targeted drug delivery

Aptamers are single-stranded structured oligonucleotides (DNA or RNA) that can bind to a wide range of targets (“apatopes”) with high affinity and specificity. These nucleic acid ligands, generated from pools of random-sequence by an in vitro selection process referred to as systematic evolution of ligands by exponential enrichment (SELEX), have now been identified as excellent tools for chemical biology, therapeutic delivery, diagnosis, research, and monitoring therapy in real-time imaging. Today, aptamers represent an interesting class of modern pharmaceuticals which with their low immunogenic potential mimic extend many of the properties of monoclonal antibodies in diagnostics, research, and therapeutics. More recently, chimeric aptamer approach employing many different possible types of chimerization strategies has generated more stable and efficient chimeric aptamers with aptamer–aptamer, aptamer–nonaptamer biomacromolecules (siRNAs, proteins) and aptamer–nanoparticle chimeras. These chimeric aptamers when conjugated with various biomacromolecules like locked nucleic acid (LNA) to potentiate their stability, biodistribution, and targeting efficiency, have facilitated the accurate targeting in preclinical trials. We developed LNA-aptamer (anti-nucleolin and EpCAM) complexes which were loaded in iron-saturated bovine lactofeerin (Fe-blf)-coated dopamine modified surface of superparamagnetic iron oxide (Fe₃O₄) nanoparticles (SPIONs). This complex was used to deliver the specific aptamers in tumor cells in a co-culture model of normal and cancer cells. This review focuses on the chimeric aptamers, currently in development that are likely to find future practical applications in concert with other therapeutic molecules and modalities.     

Foldamers Derived From Nucleoside β-Amino Acids: Pna Or Dna? Can We Have Both In One Place?

The synthesis of a modified thymidine (nucleoside β-amino acid) monomer and preliminary investigations into the solid phase peptide synthesis of PNA/DNA chimeras containing a neutral, internucleoside amide linkage are described.     

On the concept and elucidation of endogenous retroviruses

Endogenous retrovirus (ERV) genomes integrated into the chromosomal DNA of the host were first detected in chickens and mice as Mendelian determinants of Gag and Env proteins and of the release of infectious virus particles. The presence of ERV was confirmed by DNA hybridization. With complete host genomes available for analysis, we can now see the great extent of viral invasion into the genomes of numerous vertebrate species, including humans. ERVs are found at many loci in host DNA and also in the genomes of large DNA viruses, such as herpesviruses and poxviruses. The evolution of xenotropism and cross-species infection is discussed in the light of the dynamic relationship between exogenous and endogenous retroviruses.     

Completion of the Vimentin Rod Domain Structure Using Experimental Restraints: A New Tool for Exploring Intermediate Filament Assembly and Mutations

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