RESUMEN
Despite the universal importance of meiotic recombination for generating genetic diversity, numbers and distribution of recombination events along chromosomes vary among species, genotypes within species, and between sexes. Some interspecies differences stem from the diversity of genome size and composition among eukaryotes. Large-genome species, such as humans and most crops, display recombination landscapes that are different from those of small-genome yeasts. Chromatin patterns, including histone modifications and DNA methylation, are also responsible for interspecies differences as well as differences between the sexes. Finally, despite the overall recombination pathway conservation, there are species-specific components that result in distinct recombination patterns. Consequently, characteristics that are defining for the recombination landscape and universally shared by all eukaryotes remain largely to be discovered.
Asunto(s)
Biodiversidad , Estudios de Asociación Genética , Meiosis/genética , Recombinación Genética , Cromatina/genética , Intercambio Genético , Recombinación Homóloga , Humanos , Poliploidía , Especificidad de la EspecieRESUMEN
During meiotic recombination, double-strand breaks (DSBs) are formed in chromosomal DNA and then repaired as either crossovers (COs) or non-crossovers (NCOs). In most taxa, the number of DSBs vastly exceeds the number of COs. COs are required for generating genetic diversity in the progeny, as well as proper chromosome segregation. Their formation is tightly controlled so that there is at least one CO per pair of homologous chromosomes whereas the maximum number of COs per chromosome pair is fairly limited. One of the main mechanisms controlling the number of recombination events per meiosis is CO homeostasis, which maintains a stable CO number even when the DSB number is dramatically altered. The existence of CO homeostasis has been reported in several species, including mouse, yeast, and Caenorhabditis elegans. However, it is not known whether homeostasis exists in the same form in all species. In addition, the studies of homeostasis have been conducted using mutants and/or transgenic lines exhibiting fairly severe meiotic phenotypes, and it is unclear how important homeostasis is under normal physiological conditions. We found that, in maize, CO control is robust only to ensure one CO per chromosome pair. However, once this limit is reached, the CO number is linearly related to the DSB number. We propose that CO control is a multifaceted process whose different aspects have a varying degree of importance in different species.
Asunto(s)
Intercambio Genético , Homeostasis/genética , Recombinación Homóloga , Zea mays/genética , Animales , Cromatina/genética , Cromatina/metabolismo , Cromosomas de las Plantas/genética , Cromosomas de las Plantas/metabolismo , Roturas del ADN de Doble Cadena , Meiosis/genética , Ratones , Microscopía Fluorescente , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Recombinasa Rad51/genética , Recombinasa Rad51/metabolismoRESUMEN
CRISPR/Cas9 has dramatically changed how we conduct genetic research, providing a tool for precise sequence editing. However, new applications of CRISPR/Cas9 have emerged that do not involve nuclease activity. In the accompanying article "A dCas9-based system identifies a central role for Ctf19 in kinetochore-derived suppression of meiotic recombination," Kuhl et al. utilize a catalytically dead Cas9 to localize proteins at specific genomic locations. The authors seek to understand the role of kinetochore proteins in the suppression of meiotic recombination, a phenomenon that has been observed in centromere regions. By harnessing the power of CRISPR/Cas9 to bind specific genomic sequences, Kuhl et al. localized individual kinetochore proteins to areas of high meiotic recombination and assessed their role in suppression. This primer article provides undergraduate students with background information on chromosomes, meiosis, recombination and CRISPR/Cas9 to support their reading of the Kuhl et al. study. This primer is intended to help students and instructors navigate the study's experimental design, interpret the results, and appreciate the broader scope of meiotic recombination and CRISPR/Cas9. Questions are included to facilitate discussion of the study.