Form follows function in geminiviral minichromosome architecture.

A comprehensive survey on the viral minichromosomes of the begomoviruses Abutilon mosaic virus, tomato yellow leaf curl Sardinia virus, African cassava mosaic virus, Indian cassava mosaic virus (family Geminiviridae) during the course of infections in Nicotiana benthamiana is summarized. Using optimized one-dimensional and two-dimensional gel systems combined with blot hybridization and a standardized evaluation, discrete and heterogeneous virus-specific signals with different DNA forms were compared to trace functions of viral multiplication with inactive/active replication and/or transcription. A quantitative approach to compare the distantly related viruses during the course of infection with the aim to generalize the conclusions for geminiviruses has been developed. Focussing on the distribution of topoisomers of viral supercoiled DNA, which reflect minichromosomal stages, predominant minichromosomes with 12 nucleosomes, less with 13 nucleosomes and no with 11 nucleosomes were found. These results indicate that chromatin with only one open gap to bind transcription factors is the favourite form. The dynamics during infections in dependence on the experimental conditions is discussed with reference to the design of experiments for resistance breeding and molecular analyses.

Mapping of abutilon mosaic geminivirus minichromosomes.

The single-stranded circular DNA of Abutilon mosaic geminivirions is complemented to double-stranded DNA by host proteins after infecting cells. This double-stranded DNA serves as a template for replication as well as transcription and is assembled into host nucleosomes, yielding circular viral minichromosomes. Their chromatin structure was analyzed by use of isolated nuclei combining nuclease sensitivity assays with ligation-mediated PCR, evaluating nucleosomal ladders and topoisomer distributions in one- and two-dimensional gels by blot hybridization. Viral minichromosomes were found to exist in at least two defined structures covered with 11 or 12 nucleosomes, leaving open gaps accessible for interactions with other host factors. Nucleosome-free gaps were colocalized with promoter structures and the origin of replication in both components of genomic DNA (DNA A and DNA B). Nucleosomes were positioned over the entire viral DNA in at least two alternative phases with different periodicities. The distribution of topoisomers of monomeric viral circular double-stranded DNA confirmed the presence of variable chromatin structures revealing maximum frequencies of molecules with either 11, 12, or 13 superhelical turns (corresponding to respective numbers of nucleosomes) at maximal frequency at different stages during leaf development of infected plants. The role of variable chromatin structures for gene regulation of geminiviruses is discussed.

Adoptive transfer-experimental allergic neuritis in newborn Lewis rats results in inflammatory infiltrates, mast cell activation, and increased Ia expression with only minor nerve fiber degeneration.

Experimental allergic neuritis (EAN) induced in the Lewis rat by the adoptive transfer of a P2-specific T cell line (AT-EAN) is considered an animal model of Guillain-Barré syndrome. It is not yet known whether AT-EAN is inducible at early stages in the development of the peripheral nervous system (PNS) or whether disease activity is modified because of immaturity of either the nervous system or the immune system. We therefore compared the susceptibility of neo-natal and adult Lewis rats to AT-EAN induced by the adoptive transfer (intraperitoneally) of 10(6) activated P2-specific T cells. P2 antigen was already present in 7 day old Lewis rats and P2-specific T cell transfer into 3-day-old rats induced clinical disease associated with an inflammatory response (sciatic nerves and spinal ganglia). In injected newborn rats we observed local activation of mast cells, infiltration of the PNS by inflammatory cells, and induction of Ia antigen expression in Schwann cells. Unlike in adults, segmental or paranodal demyelination despite occasional nerve fiber degeneration did not occur. However, the difference between newborn and adult rats could not be ascertained statistically because of the relative rarity of the lesions, their focal character, the admixture of fiber demyelination and degeneration, and most importantly, size differences of the myelinated fibers, which result in a large developmental decrease in fiber density in adults compared to newborns.