Jon Lamb
Hometown:
Granville, Ohio
Undergraduate Degree:
BS Plant Genetics and Breeding, Brigham Young University, Utah
Additional Degrees:
Ph.D in Biology, University of Missouri
Postdoctoral Experience:
Texas A&M University, College Station
Research Synopsis:
Double-strand breaks (DSBs) which occur from DNA damage are repaired by several distinct pathways in eukaryotic cells, including mechanisms that lead to chromosome rearrangements or deletions. These mechanisms include homologous recombination (HR), non-homologous end joining (NHEJ), and de novo telomere formation (DNTF). These various repair systems compete for access to broken chromosome ends. Much is known about HR and NHEJ DNA repair mechanisms but DNTF has not been extensively studied in higher eukaryotes. However, DNTF is a common occurrence in cancer cells where genome instability leads to gross chromosomal rearrangements.
My work in the Shippen lab includes developing a system to cause DNTF in order to study the genetic requirements of this process. One approach to inducing DNTF is to transform plants with a transgene containing a telomere repeat array. When the transgene is integrated into the genome, the telomere repeat array can become a telomere. If this happens, the rest of the chromosome distal to the integration site is lost and a truncated chromosome is produced. Pierre Kobrossly, an undergraduate worker in the lab, and myself have recovered several truncated chromosomes resulting form DNTF. We have found that more than 20% of lines transformed with the telomere repeat array contain DNTF events. We are currently characterizing several of the truncation events and are developing high throughput methods to screen for DNTF events.
Most chromosome deletions in Arabidopsis can not be transmitted through the gametophytic generation (the egg or pollen) so most chromosome truncation resulting form DNTF can not be recovered in a diploid organism. To overcome this difficulty, we transformed tetraploid plants so that the genetic buffering provided by the extra chromosome copies allows for recovery of DNTF products. To test the genetic requirements of DNTF, we will transform tetraploids with mutations in various genes involved in telomere maintenance. Then the frequency of DNTF events compared to a standard transgene insertion will be compared to wild-type levels. We will first transform plants that lack a functional telomerase to see if transgenic telomere repeat array mediated DNTF requires telomerase extension. We have also generated tetraploid lines with mutations in Lig4, a gene involved in double-strand break repair, and TBP1, a telomere double-strand binding protein. We predict that DNTF events will increase in frequency in the Lig4 background because other DNA repair pathways are less efficient. In the TBP1 background, the DNTF frequency is predicted to decrease. Additional tetraploid lines will be generated and transformed.