Prelude to a Division

Bhalla, Needhi; Dernburg, Abby F.

doi:10.1146/annurev.cellbio.23.090506.123245

Cited by 123 publications

(162 citation statements)

References 150 publications

(169 reference statements)

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“…Such considerations could help to explain why, in several situations, in two of the most robust cases of ''region-specific'' pairing, for the XY chromosomes of Drosophila and for ''pairing centers'' in C. elegans, specificity is conferred by clusters containing multiple nontandem repeats of short sequences (1,11). For Drosophila, where 50 copies of a Ͻ250-bp repeat are normally involved in pairing, it has further been shown that, when pairing site sequences are moved to locations where flanking homology is absent, eight copies are largely sufficient to confer detectable pairing but two copies are not (1).…”

Section: Discussionmentioning

confidence: 99%

“…In some instances, whole chromosomes pair via multiple interactions all along their lengths (1-9) or via any region present in duplicate copies (10). In other cases, pairing occurs preferentially or exclusively in particular localized regions (''pairing sites''), which tend to involve repeated sequences, specific proteins (for establishment and/or maintenance of pairing) and/or heterochromatic regions (characterized by a paucity of genes and a less ''open'' chromatin structure) (1,(11)(12)(13)(14)(15).In contrast to recombination-related processes that are known to involve protein-mediated Watson-Crick basepairing interactions between a ssDNA and a ssDNA or dsDNA partner, the fundamental basis for ''recombination-independent'' pairing remains mysterious. The most obvious possibility is direct DNA/DNA interactions.…”

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confidence: 99%

“…Recombinational double-strand break repair and programmed homologous recombination during meiosis all involve complex series of biochemical reactions in which single-stranded DNA (ssDNA) plays a prominent role. There also exist homologous pairing reactions that seem to involve interactions between chromosomal regions whose DNAs are chemically intact double-stranded DNA (dsDNA) (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). In some instances, whole chromosomes pair via multiple interactions all along their lengths (1)(2)(3)(4)(5)(6)(7)(8)(9) or via any region present in duplicate copies (10).…”

mentioning

confidence: 99%

“…In some instances, whole chromosomes pair via multiple interactions all along their lengths (1)(2)(3)(4)(5)(6)(7)(8)(9) or via any region present in duplicate copies (10). In other cases, pairing occurs preferentially or exclusively in particular localized regions (''pairing sites''), which tend to involve repeated sequences, specific proteins (for establishment and/or maintenance of pairing) and/or heterochromatic regions (characterized by a paucity of genes and a less ''open'' chromatin structure) (1,(11)(12)(13)(14)(15).…”

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confidence: 99%

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Single molecule detection of direct, homologous, DNA/DNA pairing

Danilowicz¹,

Lee²,

Kim

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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Using a parallel single molecule magnetic tweezers assay we demonstrate homologous pairing of two double-stranded (ds) DNA molecules in the absence of proteins, divalent metal ions, crowding agents, or free DNA ends. Pairing is accurate and rapid under physiological conditions of temperature and monovalent salt, even at DNA molecule concentrations orders of magnitude below those found in vivo, and in the presence of a large excess of nonspecific competitor DNA. Crowding agents further increase the reaction rate. Pairing is readily detected between regions of homology of 5 kb or more. Detected pairs are stable against thermal forces and shear forces up to 10 pN. These results strongly suggest that direct recognition of homology between chemically intact B-DNA molecules should be possible in vivo. The robustness of the observed signal raises the possibility that pairing might even be the ''default'' option, limited to desired situations by specific features. Protein-independent homologous pairing of intact dsDNA has been predicted theoretically, but further studies are needed to determine whether existing theories fit sequence length, temperature, and salt dependencies described here.dsDNA ͉ sequence-dependent P airing of homologous DNA/chromosome regions is a central feature of many biologically important processes. Recombinational double-strand break repair and programmed homologous recombination during meiosis all involve complex series of biochemical reactions in which single-stranded DNA (ssDNA) plays a prominent role. There also exist homologous pairing reactions that seem to involve interactions between chromosomal regions whose DNAs are chemically intact double-stranded DNA (dsDNA) (1-15). In some instances, whole chromosomes pair via multiple interactions all along their lengths (1-9) or via any region present in duplicate copies (10). In other cases, pairing occurs preferentially or exclusively in particular localized regions (''pairing sites''), which tend to involve repeated sequences, specific proteins (for establishment and/or maintenance of pairing) and/or heterochromatic regions (characterized by a paucity of genes and a less ''open'' chromatin structure) (1,(11)(12)(13)(14)(15).In contrast to recombination-related processes that are known to involve protein-mediated Watson-Crick basepairing interactions between a ssDNA and a ssDNA or dsDNA partner, the fundamental basis for ''recombination-independent'' pairing remains mysterious. The most obvious possibility is direct DNA/DNA interactions. Theoretical models have proposed that homology recognition arises from non-Watson-Crick hydrogen bond interactions between bases in the major or minor grooves (16). Local melting could also occur, permitting recognition via standard Watson-Crick base pairing. Other theories suggest that homology recognition can occur due to interactions between sequencedependent charge distributions associated with neighboring DNA helices, where the charge distributions include not only the phosphates in the DNA but also other ...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Single molecule detection of direct, homologous, DNA/DNA pairing

Danilowicz¹,

Lee²,

Kim

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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“…When the telomeres are clustered, centromeres are oriented in the opposite direction than the telomeres, resulting in a telomere-centromere polarization of the meiocyte nucleus. The presence of the bouquet coincides with pairing of homologous chromosomes (3,5). In plants, mammals, and fungi, chromosome pairing depends upon the progression of meiotic recombination (5-7).…”

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confidence: 99%

Live imaging of rapid chromosome movements in meiotic prophase I in maize

Sheehan

Pawlowski

2009

Proc. Natl. Acad. Sci. U.S.A.

110

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The ability of chromosomes to move across the nuclear space is essential for the reorganization of the nucleus that takes place in early meiotic prophase. Chromosome dynamics of prophase I have been studied in budding and fission yeasts, but little is known about this process in higher eukaryotes, where genomes and chromosomes are much larger and meiosis takes a longer time to complete. This knowledge gap has been mainly caused by difficulties in culturing isolated live meiocytes of multicellular eukaryotes. To study the nuclear dynamics during meiotic prophase in maize, we established a system to observe live meiocytes inside intact anthers. We found that maize chromosomes exhibited extremely dynamic and complex motility in zygonema and pachynema. The movement patterns differed dramatically between the two stages. Chromosome movements included rotations of the entire chromatin and movements of individual chromosome segments, which were mostly telomere-led. Chromosome motility was coincident with dynamic deformations of the nuclear envelope. Both, chromosome and nuclear envelope motility depended on actin microfilaments as well as tubulin. The complexity of the nuclear movements implies that several different mechanisms affect chromosome motility in early meiotic prophase in maize. We propose that the vigorous nuclear motility provides a mechanism for homologous loci to find each other during zygonema.chromosome dynamics ͉ cytogenetics ͉ meiosis ͉ cell biology I n early meiotic prophase, the nucleus undergoes a major spatial reorganization, which includes a general repositioning of chromatin and juxtaposition of homologous chromosomes (1). In many species, including maize, the nucleolus is located in the center of the nucleus during leptonema, and at the onset of zygonema, moves to a peripheral position (1, 2). Concurrently with the nucleus migration, all chromosome ends attach to the nuclear envelope (NE) and cluster on a single site forming the ''telomere bouquet'' (3, 4), which has been observed in most plants, animals, and fungi, including budding and fission yeasts, mouse, and maize. The telomeres remain clustered throughout zygonema. When the telomeres are clustered, centromeres are oriented in the opposite direction than the telomeres, resulting in a telomere-centromere polarization of the meiocyte nucleus. The presence of the bouquet coincides with pairing of homologous chromosomes (3, 5). In plants, mammals, and fungi, chromosome pairing depends upon the progression of meiotic recombination (5-7). However, a recombination-driven homology recognition mechanism can only operate across a relatively short distance, probably Ϸ1.2 m (6). In large-genome species, such as maize, where the zygotene nucleus is Ϸ20 m in diameter, this mechanism may not be sufficient to reach across the chromatin mass in the nucleus, even when the chromosomes are brought together by the bouquet (6). These constraints suggest that homologous chromosome segments must first be positioned close to each other, before the homology search...

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