Research Laboratory

The Laboratory of Dr. Ayelet Arbel-Eden in Collaboration with Emeritus Prof. Giora Simchen

Enhanced Occurrence of New Mutations During Meiosis

The ultimate sources of genetic variation in populations are mutation and recombination of genes and chromosomes. One major event leading to genetic variability in eukaryotes is the process of meiosis, which generates haploid gametes for sexual reproduction. In meiosis, higher mutation rates are observed compared to mitotic cell divisions. These meiosis-induced mutations are associated with recombination events. We focus our research on understanding the genetics and molecular mechanisms that underline this enhanced mutagenesis during meiosis. In our laboratory we use the budding yeast as a powerful eukaryotic model organism that can be genetically manipulated easily.

Mutation occurrence during meiosis has a direct impact on the transmission of genetic diseases from parents to offspring. Moreover, the issue of enhanced frequency of mutations during meiosis is of primary significance to evolutionary theory, as only germ-line mutations contribute to evolution.

Current Research Topics in Our Laboratory

• Timing of mutation occurrence during meiosis and the Role of the Trans-Lesion DNA Polymerases.
  Most mutations are introduced in the genome when new DNA is being synthesized by DNA polymerases. Therefore, DNA polymerases are prime candidates for introducing new mutations. We have investigated the time during meiosis at which the new mutations occur, and found that they coincide with the recombinational phases of meiosis. We have shown that most mutations do not occur during meiotic S-phase, but during prophase I, at the time of Double-strand breakage (DSBs) and recombination. We are investigating whether Trans-Lesion DNA Polymerases (TLSPs) may account for the enhanced mutagenicity observed in meiosis.

• Meiotic mutations that occur at recombination hot-spots, on a single molecule level.
  Meiotic recombination is triggered by DNA double-strand breaks (DSBs). DSBs are regularly induced throughout the genome during meiosis in yeast and other eukaryotes. Meiotic DSBs occur with high frequency in specific “hotspot” regions.  Among the strongest DSB hot spots in the yeast genome is the one located on chromosome III near the ARE1 gene.  In this project we wish to directly assess the relation between DSB-induced recombination and the occurrence of mutations during meiosis at the ARE1 hotspot. We use allele-specific primers to PCR amplify single recombinant DNA molecules from meiotic recombination events and from non-recombinant molecules following meiosis. The PCR products will be sequenced by Sanger sequencing. Mutation spectra, type and position will be determined as well as mutation’s distance from the actual breakage/crossover ARE1 site.

• The effect of recombination-deficient mutants on mutation arising during meiosis and during Return-to-growth.
  The molecular mechanism that underlines de novo mutagenicity is currently unknown, but the enhanced meiotic mutations are tightly associated with recombination events. Using recombination-deficient mutants, we examine the various steps during recombination where mutations may occur to pinpoint the stage at which mutations are arising.
  We have shown that mutations during meiosis are dependent upon the endonuclease Spo11, and that meiotic Double-strand breaks are required for the generation of these mutations.
  
  
• The involvement of replicative DNA polymerases in mutation occurrence during meiosis.

Contact Information: Dr. Ayelet Arbel-Eden