Location of B- and Z-DNA in the chromosomes of a primitive eukaryote dinoflagellate.

Abstract

Abstract. The usual conformation of DNA is a righthanded double helix (B-DNA). DNA with stretches of alternating purine-pyrimidine (G-C or A-T) can form a left-handed helix (Z-DNA). The transition B--'Z, facilitated by the presence of divalent cations, cytosine methylation, or constraints on DNA such as superhelicity may play a role in the regulation of gene expression and/or in DNA compaction (Zarling, D. A., D. J. Arndt-Jovin, M. Robert-Nicoud, L. P. Mclntosh, R. Tomae, and T. M. Jovin. 1984. J. Mol. Biol. 176:369--415). Divalent cations are also important in the structure of the quasi-permanently condensed chromosomes of dinoflagellate protists (Herzog, M., and M.-O. Soyer. 1983. Eur. J. Cell Biol. 30:33-41) which also have superhelicity in their DNA. The absence of histones in dinoflagellate chromosomes suggest that the search for Z-DNA sequences might be fruitful and could provide one indication of the physiological role of this particular DNA conformation.We report a complete immunofluorescent and immunogold analysis of the nuclei of the dinoflagellate Prorocentrum micans E. using monoclonal and polyclonal anti-B and anti-Z-DNA antibodies. Positive labeling was obtained with immunofluorescence using squash preparations and cryosections, both of which showed the intranuclear presence of the two DNA conformations. In ultrathin sections of aldehydeprefixed, osmium-fixed, and epoxy-embedded cells, we have localized B-DNA and Z-DNA either with single or double immunolabeling using IgG labeled with 5-and 7-rim gold particles, respectively. Chromosomal nucleofilaments of dividing or nondividing chromosomes, as seen in ultrathin sections in their archshaped'configuration, are abundantly labeled with anti-B-DNA antibody. Extrachromosomal anti-B-DNA labeling is also detected on the nucleoplasm that corresponds to DNA loops; we confirm the presence of these loops previously described external to the chromosomes (Soyer, M.-O., and O. K. Haapala. 1974. Chromosoma (Berl.). 47:179-192). B labeling is also visible in the nucleolus organizer region (NOR) and in the fibriUo-granular area (containing transcribing rDNA) of the nucleolus. Z-DNA was localized in limited areas inside the chromosomes, often at the periphery and near the segregation fork of dividing chromosomes. In the nucleolus, Z-DNA is observed only in the NOR area and never in the fibrillo-granular area. For both types of antibody experiments, controls using gold-labeled IgG without primary antibody were negative. A quantitative evaluation of the distribution of the gold-labeled IgG and a parametric test support the validity of these experiments. We also demonstrate the preservation of antibody activity on DNA molecules preincubated in OsO4 solutions. The role of the Z-DNA conformation as a possible site for unwinding and DNA processing in chromosomes that lack nucleosomes and that are permanently condensed is discussed. DNOFLAGELLATE protists are primitive eukaryotes, as demonstrated by ultrastructural, biochemical, and molecular biological studies (25,27...

Proliferating cell nuclear antigen (PCNA) as a marker of cell proliferation in the marine dinoflagellate Prorocentrum donghaiense Lu and the green alga Dunaliella salina Teodoresco

“…First, it is well known that dinoflagellates have an unusual chromosomal structure and the different size of the PCNA-like protein observed could be related to this variety in dinoflagellate chromosomal structure. It has been shown that dinoflagellates contain extensive stretches of Z-DNA (Soyer-Gobillard et al, 1990) and the C. cohnii PCNA could have a different structure and size to properly interact with the large amounts of Z-DNA (Leveson & Wong, 1999). It is also important to note that dinoflagellates are a transition group from prokaryotic to eukaryotic evolution and they are a very diverse group.…”

Telomeric DNA localization on dinoflagellate chromosomes: structural and evolutionary implications

“…This structure seems to be stabilized by metal cations and structural RNA (Kearns and Sigee, 1980;Dodge, 1985;Soyer-Gobillard and Herzog, 1985). Dinoflagellate DNA has a B configuration with some Z-DNA stretches mostly at the chromosome periphery and in NORs (Soyer-Gobillard et al, 1990). Structural inactive DNA forms the main body of the chromosomes while genetically active DNA localizes in peripheral DNA filaments (Sigee, 1986) where co-transcriptional splicing has also been localized (Alverca et al, 2001).…”

“…At the ultrastructural level, the nucleofilaments are arranged in a series of parallel nested arches providing a characteristic banding pattern, which has no homology to Q, G or C banding (Haapala and Soyer, 1974a). Transverse bands correspond to the DNA fibrils proceeding across the chromosome and interbands to the fibrils communicating with adjacent bands (Rizzo, 1982;Spector, 1984;Goyanes, 1987, 2005;Soyer-Gobillard et al, 1990). This structure seems to be stabilized by metal cations and structural RNA (Kearns and Sigee, 1980;Dodge, 1985;Soyer-Gobillard and Herzog, 1985).…”

Architecture and evolution of dinoflagellate chromosomes: an enigmatic origin

“…Longitudinal sections of chromosomes show bands of 0.8 Ìm diameter distributed in regular periods of around 100 nm (Costas and Goyanes, 1987). Fiber loops can also be found, protruding at the chromosome periphery (Livolant, 1978;Sigee, 1983Sigee, , 1986Soyer-Gobillard et al, 1990). Since the early studies of dinoflagellate chromosomes, the same question of how the chromatin fibers bend to organize in arches that finally build the dinoflagellate chromosome has arisen.…”