P. Cabello

Bio: P. Cabello is an academic researcher. The author has contributed to research in topics: Cellular differentiation & Organelle. The author has an hindex of 1, co-authored 1 publications receiving 6 citations.

Position-dependent NOR activity in barley

Abstract: Two types of intraspecific nucleolar dominance/suppression are described for barley,Hordeum vulgare L When the nucleolus organizing regions (NORs) originally belonging to chromosomes 6 and 7 are combined by translocation in one chromosome, NOR 6 is dominant over NOR 7 Neither significant loss of rDNA nor its hypermethylation is the reason for the reduced nucleolus forming activity of NOR 7 Intrachromosomal NOR suppression probably does not occur in isochromosome 6s, which has two NORs 6 in one chromosome Meiotic and somatic pairing of the homologous arms might be the reason for early fusion of their nucleoli and thus for the lower than expected maximum number of interphase nucleoli Variable suppression of a partial NOR (63) is described for descendants of crosses between translocation lines with split NORs 6 and 7 In these cases also, the reduced activity of the partial NOR 63 is not due to deletion of rDNA as shown by in situ hybridization Unstable methylation of NOR 63 in heterozygous F1 individuals is probably the cause of this phenomenon

Dominance of a NOR (Nucleolar Organizer Region) over its Allele and Over its Sister NOR After Asymmetric 5-Azacytidine Substitution in Plant Chromosomes

Abstract: Dominance of a 5-azacytidine-substituted nucleolar organizer region (AZA NOR) over another with normal DNA when confined to a common nucleus or to different nuclei in a common cell was studied in Allium cepa L. root meristems. AZA administration took place for one S period. The assessment of NOR dominance was done either in early G1 (nucleologenesis) or later in interphase (mature nucleoli). At the mitosis immediately preceding the second interphase after AZA, the segregated AZA and normal chromatids of each chromosome of the pair of homologues were confined to a single binucleate cell by inhibiting the formation of the cell plate. Anaphase segregation of the homologous AZA NORs was seen to occur at random. The AZA NORs completed nucleologenesis after a shorter time than normal NORs, independently of the intranuclear or intracellular presence of other NORs. After nucleologenesis was over in the AZA NORs, a few of the normal NORs, when in a common nucleus, remained permanently inefficient in developing a full-size mature nucleolus or any nucleolus at all (partial or total dominance, respectively). Dominance of an AZA NOR over its sister or allelic NOR with normal DNA led to the new nucleolar patterns of asymmetry and inverse symmetry, respectively, making their appearance in these binucleate cells.

Determination of the replication time of nucleolar organizer DNA after 5-azacytidine treatment for restricted parts of the S period

Abstract: In vivo exposure to 5-azacytidine (10−6M) depressed the incorporation of methyl groups to GC rich regions ofAllium cepa L. DNA. Nearly 22% of its 5-methylcytosine residues were under-methylated. The treatment stimulated 1.8 times the rate of [3H]uridine incorporation, as measured in meristems proliferating under steady state kinetics. Nucleologenesis was shortened from 2.7 to 1.6 h in synchronous binucleate cells after 5-azacytidine treatment lasting the whole S period of their previous interphase. By hypomethylating DNA sequences replicated at different times during the S period, it could be inferred that the cistron replication took place in early S. Thus, nucleogenesis was shortened to only 0.6 h after such treatment. Sequential short treatment periods using [3H]thymidine confirmed that the nucleolar organizer regions of the chromosomes replicate in early S.

Post-mitotic assembly of the nucleolus. I. The internal matrix network is a recruitment site for processing nucleolar components in prenucleolar bodies

Abstract: The aim of this work was to investigate whether the nuclear matrix could provide the nucleation sites for dispersed parental nucleolar components to form post-mitotic prenucleolar bodies (PNBs). For this purpose, nuclear matrices from asynchronous populations of onion cells were fractionated, and the distribution of the insoluble components of the nucleolar processing complexes in the matrices were analysed by fibrillarin immunolabelling. The ultra-structural organization of the nuclear matrix of cells from late telophase to late G1, corresponding to the period of nucleolar reassembly and activation, was also analysed. Our results demonstrate that PNBs are structural components of the telophasic nuclear matrix and that this structure provides recruitment and assembly sites for the components of the nucleolar processing machinery, and suggests that the telophasic matrix network is involved in the early steps of post-mitotic nucleologenesis.