Spatial organization of theSchizosaccharomyces pombegenome within the nucleus

Abstract

The fission yeast Schizosaccharomyces pombe is a useful experimental system for studying the organization of chromosomes within the cell nucleus. S. pombe has a small genome that is organized into three chromosomes. The small size of the genome and the small number of chromosomes are advantageous for cytological and genomewide studies of chromosomes; however, the small size of the nucleus impedes microscopic observations owing to limits in spatial resolution during imaging. Recent advances in microscopy, such as super-resolution microscopy, have greatly expanded the use of S. pombe as a model organism in a wide range of studies. In addition, biochemical studies, such as chromatin immunoprecipitation and chromosome conformation capture, have provided complementary approaches. Here, we review the spatial organization of the S. pombe genome as determined by a combination of cytological and biochemical studies.

The biology and polymer physics underlying large‐scale chromosome organization

“…In many organisms, nuclear organization is constrained by the Rabl conformation in which centromeres and telomeres localize to opposite sides of the nucleus (Figure B). In yeast, this reflects the facts that all centromeres are clustered at the spindle pole body (centrosome equivalent) embedded in the nuclear envelope and telomere clusters are tethered at the membrane on the opposite side of the nucleus . This configuration results in an alignment of chromosome arms and increased intrachromosomal contacts that are more frequent near centromeres and to a lesser extent near telomeres, and on this basis have sometimes been referred to as territories …”

“…Many eukaryotes have both heterochromatin and euchromatin that are separately partitioned into compartments (Figure A). Human and other metazoan genomes are composed of large blocks of interspersed transcriptionally active euchromatin and inactive heterochromatin, whereas the compact genome of the fission yeast S. pombe is 95% euchromatic with heterochromatin concentrated primarily at the centromeres, telomeres, rDNA and mating type loci . In both cases, euchromatin and heterochromatin self‐interact and physically segregate within the nucleus into peripheral heterochromatin and central euchromatin (Figure ).…”

“…In yeast, this reflects the facts that all centromeres are clustered at the spindle pole body (centrosome equivalent) embedded in the nuclear envelope and telomere clusters are tethered at the membrane on the opposite side of the nucleus. [116][117][118] This configuration results in an alignment of chromosome arms and increased intrachromosomal contacts that are more frequent near centromeres and to a lesser extent near telomeres, and on this basis have sometimes been referred to as territories. [119][120][121][122][123][124][125] In addition, it is important to stress the fact that the yeast chromosomes are much smaller than human chromosomes.…”

“…In S. pombe, chromosomes are organized into "globules" or "crumples" 137 and in S. cerevisiae into "self-associating domains" 138 that depend on the cohesin complex, but there is no evidence that either of these structures influence transcription. These structures are even sometimes referred to as TADs, 117 although they are not loops. 138 In stark contrast to eukaryotes, prokaryotes such as E. coli and…”

The Inner Nuclear Membrane Protein Bqt4 in Fission Yeast Contains a DNA-Binding Domain Essential for Telomere Association with the Nuclear Envelope

“…Shelterin complex can prevent telomeres from being recognized as double-stranded breaks, and also regulate telomerase activity to control telomere extension (de Lange, 2009;Palm and de Lange, 2008). Telomeres are often anchored to the nuclear envelope (NE) (Matsuda et al, 2017;Taddei et al, 2010). Although the association with the NE has no effect on the functional integrity of telomeres, it plays important roles in the progression of mitosis and meiosis (Chikashige et al, 2010).…”