Zhang Liang
hughzl@yahoo.com.cn

Education

Biology, Sichuan University

Research summary

Meiotic recombination near the ends of eukaryotic chromosomes (telomeres) is poorly understood, but it may contribute significantly to the diversity of telomere-proximal genes, such as the olfactory receptors in humans and the major antigenic determinants of the malarial pathogen. Telomere-dependent silencing of transcription limits our ability to monitor crossing over and other modes of recombination reliably in most species, but these processes are accessible to analysis in the budding yeast, Saccharomyces cerevisiae. Preliminary tetrad dissection experiments in our lab suggest that the URA3 gene, when inserted into a site immediately adjacent to the telomere, recombines with a linked marker more frequently when telomeric silencing is partially blocked by selecting for expression of the URA3 gene or by altering histone modification. Because tetrad dissection is cumbersome, it has not yet been feasible to test various modifications on the sporulation protocol to learn how to maximize the effects on recombination. We are developing new strains that will enable us to get larger numbers of colonies that represent a random selection of spores. These methods depend on the use of two recessive drug resistance markers (can1 and cyh2) that are heterozygous in the diploid being sporulated. Plating the products of meiotic sporulation on the relevant drugs (canavanine and cyclohexamide, respectively) allows selection of can1 cyh2 cells, providing a convenient sample of the haploid spores. When the same strain is also heterozygous for telomere markers, we can thereby assay the extent of telomere-proximal recombination without having to perform tedious tetrad dissection. This will permit us to test many varied conditions for their effects on the rate of recombination and help clarify the relationship between telomeric silencing and crossing over.

Poster

Meiotic recombination near telomeres in yeast.
The 9th UW Undergraduate Research Symposium, Mary Grates Hall, May 2006