Meiosis evolves: adaptation to external and internal environments

Cao

et al. 2017

Nucleus

RNF20/Bre1 mediated H2B ubiquitination (H2Bub) has various physiologic functions. Recently, we found that H2Bub participates in meiotic recombination by promoting chromatin relaxation during meiosis. We then analyzed the phylogenetic relationships among the E3 ligase for H2Bub, its E2 Rad6 and their partner WW domain-containing adaptor with a coiled-coil (WAC) or Lge1, and found that the molecular mechanism underlying H2Bub is evolutionarily conserved from yeast to mammals. However, RNF20 has diverse physiologic functions in different organisms, which might be caused by the evolutionary divergency of their domain/motif architectures. In the current extra view, we not only elucidate the evolutionarily conserved molecular mechanism underlying H2Bub, but also discuss the diverse physiologic functions of RNF20 during meiosis.

Section: Introductionmentioning

confidence: 99%

H2B ubiquitination: Conserved molecular mechanism, diverse physiologic functions of the E3 ligase during meiosis

Cao

et al. 2017

Nucleus

“…Diakinesis cells of the Thai KPS 01-01-25 sugarcane exhibited not only true chiasma bonds between homologs/homeologs, but also secondary chromosome associations resulting from loose bivalents in the absence of chiasmata (Thumjamras et al, 2016). This reduction in chiasma frequency may also indicate how sensitive the structural meiotic components are to disturbance, and could be a direct consequence of meiotic adaptation to genomic challenges (Bomblies et al, 2015). …”

Section: Discussionmentioning

confidence: 99%

Revisiting Meiosis in Sugarcane: Chromosomal Irregularities and the Prevalence of Bivalent Configurations

et al. 2018

Traditional sugarcane cultivars (Saccharum officinarum) proved highly susceptible to diseases, and this led breeders to progress to interspecific crosses resulting in disease resistance. A backcrossing program to S. officinarum was then required to boost sucrose content. Clonal selection across generations and incorporation of other germplasm into cultivated backgrounds established the (narrow) genetic base of modern cultivars (Saccharum spp.), which have a man-made genome. The genome complexity has inspired several molecular studies that have elucidated aspects of sugarcane genome constitution, architecture, and cytogenetics. However, there is a critical shortage of information on chromosome behavior throughout meiosis in modern cultivars. In this study, we examined the microsporogenesis of a contemporary variety, providing a detailed analysis of the meiotic process and chromosome association at diakinesis, using FISH with centromeric probes. Chromosomal abnormalities were documented by examining high quality preparations of pollen mother cells (700 in total). Approximately 70% of the cells showed abnormalities, such as metaphase chromosomes not lined up at the plate, lagging chromosomes and chromosomal bridges, and tetrad cells with micronuclei. Some dyads with asynchronous behavior were also observed. Due to the hybrid composition of the sugarcane genome, we suggest that bivalent incomplete pairing may occur in the first prophase leading to univalency. The presence of rod bivalents showing the lagging tendency is consistent with a reduction in chiasma frequency. Finally, the presence of chromatin bridges indicates the indirect occurrence of chromosomal inversions, although chromosome fragments were not clearly recognized. Possible reasons for such meiotic abnormalities and the large prevalence of bivalent formation are discussed.

“…The difference in RAD-51 foci between female/male vs. hermaphrodite/male species is not merely a consequence of the decrease in genome size attributed to hermaphroditism (Fierst et al 2015), as we observe two to three times the number of RAD-51 foci in C. remanei and C. brenneri, which have only 30% larger genomes compared to C. elegans and C. briggsae. Environmental differences, particularly temperature, have also been shown to influence recombination (Bomblies et al 2015), suggesting that the differences in DSBs could be a consequence of these species' ecology. However, the Caenorhabditis species examined here have been shown to cohabitate and are relatively cosmopolitan in their distribution, except C. brenneri, which is restricted to tropical zones (Kiontke et al 2011).…”

Section: Dsb Levels Vary Considerably Between Caenorhabditis Speciesmentioning

confidence: 99%

To Break or Not To Break: Sex Chromosome Hemizygosity During Meiosis in Caenorhabditis

2016

Meiotic recombination establishes connections between homologous chromosomes to promote segregation. Hemizygous regions of sex chromosomes have no homologous chromosome to recombine with, yet must be transmitted through meiosis. An extreme case of hemizygosity exists in the genus Caenorhabditis, where males have a single X chromosome that completely lacks a homologous partner. To determine whether similar strategies have evolved to accommodate hemizygosity of the X during male meiosis in Caenorhabditis with distinct modes of sexual reproduction, we examined induction and processing of meiotic double strand breaks (DSBs) in androdioecious (hermaphrodite/male) Caenorhabditis elegans and C. briggsae, and gonochoristic (female/male) C. remanei and C. brenneri. Analysis of the recombinase RAD-51 suggests more meiotic DSBs are induced in gonochoristic vs. androdioecious species. However, in late prophase in all species, chromosome pairs are restructured into bivalents around a single axis, suggesting that the holocentric nature of Caenorhabditis chromosomes dictates a single crossover per bivalent regardless of the number of DSBs induced. Interestingly, RAD-51 foci were readily observed on the X chromosome of androdioecious male germ cells, while very few were detected in gonochoristic male germ cells. As in C. elegans, the X chromosome in C. briggsae male germ cells undergoes transient pseudosynapsis and flexibility in DSB repair pathway choice. In contrast, in C. remanei and C. brenneri male germ cells, the X chromosome does not undergo pseudosynapsis and appears refractory to SPO-11-induced breaks. Together our results suggest that distinct strategies have evolved to accommodate sex chromosome hemizygosity during meiosis in closely related Caenorhabditis species.