Wilhelm bernhard workshop on the cell nucleus

GENE EXPRESSION &

NUCLEUS-TO-CYTOPLASM TRANSPORT


TOPOLOGICAL ORGANIZATION OF GENE EXPRESSION IN DINOFLAGELLATES

Alverca E^1,2, Franca S² and Moreno Díaz de la Espina, S¹.

¹Nuclear Matrix Laboratory, CIB CSIC, Madrid, Spain, and ²Microbiology and Ecotoxicology Laboratory, INSA, Lisbon, Portugal
Dinoflagellates are the only eukaryotes lacking histones and nucleosomes. They contain low concentrations of basic proteins (HCc) without homology with histones, have condensed chromosomes in interphase and a unique nuclear organization. RNAPII activity is present in them, but the molecular characterization of the chromatin remodelling and transcription mechanisms is rudimentary. Only three proteins of Dinoflagellate transcription complexes (Dinap1, Dip1 and DapC) and a new class of transcription initiation factors (CcTBP) have been described, although snRNAs are conserved in them. Dinoflagellates are powerful models for the study of eukaryotic transcription without nucleosomes, and for the organization of the RNA nuclear network in their atypical nuclei. Chromatin remodelling, transcription, and RNA processing are spatially organized in dynamic nuclear domains that experience a constant flow of proteins. We investigated the spatial organisation of the transcription-splicing complexes in several Dinoflagellate species by western blot, confocal- and EM, and flow cytometry. Our data demonstrate for the first time the conservation of Cajal Bodies and of the sDMA protein domains, that distribute either in a perichromosomal layer around the condensed chromosomal cores, or in a diffuse pattern in the inter-chromosomal spaces, and in highly reactive CBs, but do not form speckles. Their distribution varies with the species and with the life cycle stages. EM revealed RNP fibrils intermingled with the decondensed DNA loops extruding from the chromosome cores, abundant interchromosomal granules, enriched in highly phosphorylated proteins, PGs and CBs. Cytochemical stainings for DNA, RNPs and immunogoldlabelling revealed that these structures are the counterpart of those detected by confocal microscopy. Our results confirm that in spite of the differences at the molecular level, the topological organization of the transcription/splicing complexes is conserved in Dinoflagellates.