Scott Keeney, PhD

Meiosis is a specialized cell division that generates gametes in every sexually reproducing organism, from fungi to humans. During meiosis in most sexual organisms, recombination helps homologous chromosomes pair and become physically connected, promoting accurate segregation. Recombination also alters genome structure by disrupting genetic linkage groups, and less often, by generating large-scale rearrangements between dispersed repetitive sequences. Meiotic recombination is thus a powerful determinant of germline genome stability, but also of genome diversity, evolution, and instability.

Meiotic recombination involves formation and repair of double-strand breaks (DSBs) generated by the Spo11 protein through a topoisomerase-like reaction in which a tyrosine severs the DNA backbone and attaches covalently to the 5' end of the cleaved strand. Endonucleolytic cleavage liberates Spo11 bound to short oligonucleotides and resection yields 3'-single-stranded tails. These tails are substrates for strand-exchange proteins that catalyze invasion of homologous duplexes, ultimately giving rise to recombinant products. DSB repair can result in either reciprocal exchange of flanking chromosome arms (a crossover), or no exchange (a noncrossover). If there are sequence polymorphisms in the repair region, then formation of heteroduplex DNA and mismatch correction can yield nonreciprocal transfer of information from one chromosome to the other (gene conversion).

DSBs are hazardous genomic damage that most cells avoid, but that each meiotic cell introduces in large numbers (approximately 160 on average in yeast, approximately 200 to 300 in mice). Recombination usually occurs between allelic sequences on homologs or between sister chromatids, but can involve non-allelic DNA with high-sequence identity. Such non-allelic homologous recombination (NAHR) can cause chromosome rearrangements. Furthermore, outright failure of DSB repair can lead to meiotic arrest or lethal aneuploidy in gametes. To minimize the risk of deleterious effects, cells regulate Spo11 activity to occur only at the right time and right place, but mechanisms of this regulation remain poorly understood.

The long-range objectives of our research are to understand the mechanism of meiotic recombination and to determine how this process is coordinated with other events of meiotic prophase. We focus much of our attention on Spo11 (the protein that makes the DNA DSBs that initiate recombination), the proteins that interact with Spo11, and the interactions of these proteins with meiotic chromosomes. We are also examining the mechanisms that regulate the timing, number, and location of DSB formation and the mechanisms that control the distribution of crossovers.