The organization and function of chromosomes

 

Baird DM, Farr CJ. The organization and function of chromosomes. EMBO Rep. 2006 Apr; 7 (4): 372-6. Epub 2006 Mar 17

The organization and function of chromosomes

Genomes, genes and junk, the large scale organization of chromosomes

 

Schmidt T, Heslop-Harrison JS. Genomes, genes and junk, the large scale organization of chromosomes. Trends Plant Sci. 1998 May; 3 (5): 195-9

Genomes, genes and junk, the large scale organization of chromosomes

 

Heterochromatin revisited

 

Grewal SI, Jia S. Heterochromatin revisited. Nat Rev Genet. 2007 Jan; 8 (1): 35-46

 

The formation of heterochromatin, which requires methylation of histone H3 at lysine 9 and the subsequent recruitment of chromodomain proteins such as heterochromatin protein HP1, serves as a model for the role of histone modifications and chromatin assembly in epigenetic control of the genome. Recent studies in Schizosaccharomyces pombe indicate that heterochromatin serves as a dynamic platform to recruit and spread a myriad of regulatory proteins across extended domains to control various chromosomal processes, including transcription, chromosome segregation and long-range chromatin interactions.

Heterochromatin revisited

Plant chromosomes from end to end: telomeres, heterochromatin and centromeres

 

Lamb JC, Yu W, Han F, Birchler JA. Plant chromosomes from end to end: telomeres, heterochromatin and centromeres. Curr Opin Plant Biol. 2007 Apr; 10 (2): 116-22. Epub 2007 Feb 8.

 

Recent evidence indicates that heterochromatin in plants is composed of heterogeneous sequences, which are usually composed of transposable elements or tandem repeat arrays. These arrays are associated with chromatin modifications that produce a closed configuration that limits transcription. Centromere sequences in plants are usually composed of tandem repeat arrays that are homogenized across the genome. Analysis of such arrays in closely related taxa suggests a rapid turnover of the repeat unit that is typical of a particular species. In addition, two lines of evidence for an epigenetic component of centromere specification have been reported, namely an example of a neocentromere formed over sequences without the typical repeat array and examples of centromere inactivation. Although the telomere repeat unit is quite prevalent in the plant kingdom, unusual repeats have been found in some families. Recently, it was demonstrated that the introduction of telomere sequences into plants cells causes truncation of the chromosomes, and that this technique can be used to produce artificial chromosome platforms.

 

Plant chromosomes from end to end

Planning for remodeling: nuclear architecture, chromotin and chromosomes

 

Heslop-Harrison JS. Planning for remodelling: nuclear architecture, chromatin and chromosomes. Trends Plant Sci. 2003 May; 8 (5): 195-7

 

DNA sequences occupy three-dimensional positions and their architecture is related to gene expression, gene-protein interactions and epigenetic processes. The recent analysis of chromosome 4 in Arabidopsis interphase nuclei reveals that gene-rich, undermethylated DNA is composed of active loops of 200 to 2000 kb associated with acetylated histones, providing a well-defined model system to study chromatin in its nuclear context.

Planning for remodeling-nuclear architecture, chromotin and chromosomes

Advances in plant chromosome identification and cytogenetic techniques

 

Kato A, Vega JM, Han F, Lamb JC, Birchler JA. Advances in plant chromosome identification and cytogenetic techniques. Curr Opin Plant Biol. 2005 Apr; 8 (2):148-54.

 

Recent developments that improve our ability to distinguish slightly diverged genomes from each other, as well as to distinguish each of the nonhomologous chromosomes within a genome, add a new dimension to the study of plant genomics. Differences in repetitive sequences among different species have been used to develop multicolor fluorescent in situ hybridization techniques that can define the components of allopolyploids in detail and reveal introgression between species. Bacterial artificial chromosome probes and repetitive sequence arrays have been used to distinguish each of the nonhomologous somatic chromosomes within a species. Such karyotype analysis opens new avenues for the study of chromosomal variation and behavior, as well as for the localization of individual genes and transgenes to genomic position.

Advances in plant chromosome identification and cytogenetic techniques

Reinterpreting pericentrimeric Heterochromatin

 

Topp CN, Dawe RK. Reinterpreting pericentromeric heterochromatin. Curr Opin Plant Biol. 2006 Dec; 9 (6): 647-53. Epub 2006 Oct 2

 

In fission yeast, pericentromeric heterochromatin is directly responsible for the sister chromatid cohesion that assures accurate chromosome segregation. In plants, however, heterochromatin and chromosome segregation appear to be largely unrelated: chromosome transmission is impaired by mutations in cohesion but not by mutations that affect heterochromatin formation. We argue that the formation of pericentromeric heterochromatin is primarily a response to constraints on chromosome mechanics that disfavor the transmission of recombination events in pericentromeric regions. This effect allows pericentromeres to expand to enormous sizes by the accumulation of transposons and through large-scale insertions and inversions. Although sister chromatid cohesion is spatially limited to pericentromeric regions at mitosis and meiosis II, the cohesive domains appear to be defined independently of heterochromatin. The available data from plants suggest that sister chromatid cohesion is marked by histone phosphorylation and mediated by Aurora kinases.

Reinterpreting pericentrimeric Heterochromatin

 

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