There is evidence accumulating for non-random segregation of one or more chromosomes during mitosis in different cell types. We use cell synchrony and two methods, to show that all chromatids of budding yeast segregate randomly and there is no mother-daughter bias with respect to Watson and Crick-containing strands of DNA.
"It is essential to develop techniques to determine segregation patterns of individual chromosomes of the genome. By labeling the budding yeast Saccharomyces cerevisiae genome for one cell cycle by incorporating 5- bromo-deoxyuridine nucleotide analog, then analyzing chromosomes of mother cells separated from those of daughter cells, it was recently reported that there is no mother–daughter bias in segregation of specific strands of any chromosome (Keyes et al. 2102). In contrast, it was recently reported that preexisting histones are selectively retained in Drosophila male germline stem cells, while newly synthesized histones are enriched in the differentiating daughter cell (Tran et al. 2012). "
[Show abstract][Hide abstract] ABSTRACT: The base complementarity feature (Watson and Crick in Nature 171(4356):737-738, 1953) and the rule of semi-conservative mode of DNA replication (Messelson and Stahl in Proc Natl Acad Sci U S A 44:671-682, 1958) dictate that two identical replicas of the parental chromosome are produced during replication. In principle, the inherent strand sequence differences could generate nonequivalent daughter chromosome replicas if one of the two strands were epigenetically imprinted during replication to effect silencing/expression of developmentally important genes. Indeed, inheritance of such a strand- and site-specific imprint confers developmental asymmetry to fission yeast sister cells by a phenomenon called mating/cell-type switching. Curiously, location of DNA strands with respect to each other at the centromere is fixed, and as a result, their selected segregation to specific sister chromatid copies occurs in eukaryotic cells. The yeast system provides a unique opportunity to determine the significance of such biased strand distribution to sister chromatids. We determined whether the cylindrical-shaped yeast cell distributes the specific chromosomal strand to the same cellular pole in successive cycles of cell division. By observing the pattern of recurrent mating-type switching in progenies of individual cells by microscopic analyses, we found that chromosome 2 strands are distributed by the random mode in successive cell divisions. We also exploited unusual "hotspot" recombination features of this system to investigate whether there is selective segregation of strands such that oldest Watson-containing strands co-segregate in the diploid cell at mitosis. Our data suggests that chromosome 2 strands are segregated independently to those of the homologous chromosome.
Chromosome Research 05/2013; 21(3):297-309. DOI:10.1007/s10577-013-9352-1 · 2.48 Impact Factor
"Biased segregation of budding yeast chromosomes was tested recently using a highly quantitative assay that followed the fate of all 16 chromosomes and their distribution to mother and daughter cells (Keyes et al. 2012). The experiments took advantage of improved strains for exogenous thymidine labeling where the cells utilize thymidine with greater efficiency (Lengronne et al. 2001; Viggiani and Aparicio 2006). "
[Show abstract][Hide abstract] ABSTRACT: The budding yeast Saccharomyces cerevisiae is characterized by asymmetric cell division and the asymmetric inheritance of spindle components during normal vegetative growth and during certain specialized cell divisions. There has been a longstanding interest in the possibility that yeast chromosomes segregate non-randomly during mitosis and that some of the differences between mother and daughter cells could be explained by selective chromatid segregation. This review traces the history of the experiments to determine if there is biased chromatid segregation in yeast. The special aspects of spindle morphogenesis and behavior in yeast that could accommodate a mechanism for biased segregation are discussed. Finally, a recent experiment demonstrated that yeast chromatids segregate randomly without mother-daughter bias in a common laboratory strain grown under routine laboratory conditions.
Chromosome Research 05/2013; 21(3):193-202. DOI:10.1007/s10577-013-9348-x · 2.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The semi-conservative nature of DNA replication has suggested that identical DNA molecules within chromatids are inherited by daughter cells after cell division. Numerous reports of non-random DNA segregation in prokaryotes and eukaryotes suggest that this is not always the case, and that epigenetic marks on chromatids, if not the individual DNA strands themselves, could have distinct signatures. Their selective distribution to daughter cells provides a novel mechanism for gene and cell fate regulation by segregating chromatids asymmetrically. Here we highlight some examples and potential mechanisms that can regulate this process. We propose that cellular asymmetry is inherently present, and it provides an opportunity during each cell division for moderating cell fates.
Seminars in Cell and Developmental Biology 05/2013; 24(8). DOI:10.1016/j.semcdb.2013.05.008 · 6.27 Impact Factor
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