262 research outputs found
Рецензія на монографію І.С. Чекмана «Нанофармакологія»
Рецензія на монографію І.С. Чекмана «Нанофармакологія» К.: Задруга, 2011. – 424 с
Chromosome and DNA methylation dynamics during meiosis in autotetraploid Arabidopsis arenosa
Variation in chromosome number due to
polyploidy can seriously compromise meiotic stability. In
autopolyploids, the presence of more than two homologous
chromosomes may result in complex pairing patterns
and subsequent anomalous chromosome
segregation. In this context, chromocenter, centromeric,
telomeric and ribosomal DNA locus topology and DNA
methylation patterns were investigated in the natural
autotetraploid, Arabidopsis arenosa. The data show that
homologous chromosome recognition and association
initiates at telomeric domains in premeiotic interphase,
followed by quadrivalent pairing of ribosomal 45S RNA
gene loci (known as NORs) at leptotene. On the other hand, centromeric regions at early leptotene show pairwise
associations rather than associations in fours. These
pairwise associations are maintained throughout prophase
I, and therefore likely to be related to the diploid-like
behavior of A. arenosa chromosomes at metaphase I,
where only bivalents are observed. In anthers, both cells
at somatic interphase as well as at premeiotic interphase
show 5-methylcytosine (5-mC) dispersed throughout the
nucleus, contrasting with a preferential co-localization
with chromocenters observed in vegetative nuclei. These
results show for the first time that nuclear distribution
patterns of 5-mC are simultaneously reshuffled in meiocytes
and anther somatic cells. During prophase I, 5-mC
is detected in extended chromatin fibers and chromocenters
but interestingly is excluded from the NORs what
correlates with the pairing patter
Life histories of the copepods Pseudocalanus minutus, P. acuspes (Calanoida) and Oithona similis (Cyclopoida) in the Arctic Kongsfjorden (Svalbard)
The year-round variation in abundance and stage-specific (vertical) distribution of Pseudocalanus minutus and Oithona similis was studied in the Arctic Kongsfjorden, Svalbard. Maxima of vertically integrated abundance were found in November with 111,297 ind m−2 for P. minutus and 704,633 ind m−2 for O. similis. Minimum abundances comprised 1,088 ind m−2 and 4,483 ind m−2 in June for P. minutus and O. similis, respectively. The congener P. acuspes only occurred in low numbers (15–213 ind m−2), and successful reproduction was debatable. Reproduction of P. minutus took place in May/June, and stage distribution revealed a 1-year life cycle with copepodids CIII, CIV, and CV as the overwintering stages. Oithona similis exhibited two main reproductive peaks in June and August/September, respectively. Moreover, it reproduced more or less continuously throughout the whole year with all stages occurring during the entire sampling period, suggesting two generations per year. Both species migrated towards greater depth in November, but O. similis preferred to stay longer in the upper 100 m as compared to Pseudocalanus. The reproduction of the two species in Kongsfjorden seemed to be linked to phytoplankton dynamics
Postembryonic establishment of megabase-scale gene silencing in nucleolar dominance
Nucleolar dominance is an epigenetic phenomenon in plant and animal genetic hybrids that describes the expression of 45S
ribosomal RNA genes (rRNA genes) inherited from only one progenitor due to the silencing of the other progenitor’s rRNA genes.
rRNA genes are tandemly arrayed at nucleolus organizer regions (NORs) that span millions of basepairs, thus gene silencing in
nucleolar dominance occurs on a scale second only to X-chromosome inactivation in female mammals. In Arabidopsis suecica, the
allotetraploid hybrid of A. thaliana and A. arenosa, theA. thaliana –derived rRNA genes are subjected to nucleolar dominance and
are silenced via repressive chromatin modifications. However, the developmental stage at which nucleolar dominance is
established in A. suecica is currently unknown. We show that nucleolar dominance is not apparent in seedling cotyledons formed
during embryogenesis but becomes progressively established during early postembryonic development in tissues derived from
both the shoot and root apical meristems. The progressive silencing of A. thaliana rRNA genes correlates with the transition of A.
thaliana NORs from a decondensed euchromatic state associated with histone H3 that is trimethylated on lysine 4 (H3K4me3) to
a highly condensed heterochromatic state in which the NORs are associated with H3K9me2 and 5-methylcytosine-enriched
chromocenters. In RNAi-lines in which the histone deacetylases HDA6 and HDT1 are knocked down, the developmentally
regulated condensation and inactivation of A. thaliana NORs is disrupted. Collectively, these data demonstrate that HDA6 and
HDT1 function in the postembryonic establishment of nucleolar dominance, a process which recurs in each generatio
Assignment of genetic linkage maps to diploid Solanum tuberosum pachytene chromosomes by BAC-FISH technology
A cytogenetic map has been developed for diploid potato (Solanum tuberosum), in which the arms of the 12 potato bivalents can be identified in pachytene complements using multicolor fluorescence in situ hybridization (FISH) with a set of 60 genetically anchored bacterial artificial chromosome (BAC) clones from the RHPOTKEY BAC library. This diagnostic set of selected BACs (five per chromosome) hybridizes to euchromatic regions and corresponds to well-defined loci in the ultradense genetic map, and with these probes a new detailed and reliable pachytene karyotype could be established. Chromosome size has been estimated both from microscopic length measurements and from 4′,6-diamidino-2-phenylindole fluorescence-based DNA content measurements. In both approaches, chromosome 1 is the largest (100–115 Mb) and chromosome 11 the smallest (49–53 Mb). Detailed measurements of mega-base-pair to micrometer ratios have been obtained for chromosome 5, with average values of 1.07 Mb/μm for euchromatin and 3.67 Mb/μm for heterochromatin. In addition, our FISH results helped to solve two discrepancies in the potato genetic map related to chromosomes 8 and 12. Finally, we discuss the significance of the potato cytogenetic map for extended FISH studies in potato and related Solanaceae, which will be especially beneficial for the potato genome-sequencing project
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