Tag: Nicole Kurhanewicz

Investigating the role of H3K9 methyl transferases in heat-induced DNA damage

Presenter: Philip Nosler – Biology

Faculty Mentor(s): Nicole Kurhanewicz, Diana Libuda

Session: (In-Person) Oral Panel—Bio-Zebrafish and DNA

Exposure to elevated temperature is a major cause of male infertility observed across both animals and plants. A primary consequence of heat stress is the accumulation of unusually high levels of DNA damage in developing sperm. Previous work from the Libuda Lab demonstrated that, similarly to humans, a single acute heat exposure is sufficient to produce high levels of DNA damage in developing sperm, but not in developing eggs in the model organism Caenorhabditis elegans. Further, mobilization of transposons, segments of DNA that can move autonomously throughout the genome, was associated with heat-induced DNA damage specifically in sperm. Normally, transposon movement is strictly repressed in the germline via chromatin modifications, which affect chromosome structure and regulate gene expression. Specifically, transposon genes are silenced in the germline via a particular chromatin modification: methylation of histone H3 lysine 9 by the methyltransferases SET-25, SET-32, and MET-2. Using an existing mutant strain for set-25 and a double mutant for met- 2;set-25, I found that DNA damage is elevated following heat stress, suggesting set-25 and met-2 repress heat-induced DNA damage. Currently, I am further assessing the roles of set-25, set-32, and met-2 in heat-induced DNA damage using single and double mutant strains. Overall, this work will further our understanding of the mechanisms underlying heat-induced male infertility.

Piwi-piRNA pathway protein PRG-1 represses in temperature-induced DNA damage in spermatocytes

Presenter(s): Fountane Chan

Faculty Mentor(s): Diana Libuda & Nicole Kurhanewicz

Oral Session 3 M

Poster 47

Session: Sciences

Half of infertility cases worldwide involve male-factor subfertility. As awareness and frequency of male infertility has grown, it is increasingly important to understand the underlying mechanisms of these major human health concerns. Developing sperm are particularly sensitive to fluctuations in temperature, requiring a narrow isotherm of 2-7°C below core body temperature. Although both oocytes and spermatocytes undergo meiosis, the specialized form of cell division that produces haploid sex cells, elevated gonadal temperatures have been shown both to impair only male fertility and produce excess DNA damage specifically in spermatocytes. Preliminary work using the powerful roundworm model Caenorhabditis elegans suggests the Piwi-piRNA pathway, a highly conserved genome maintenance pathway, is involved in temperature-induced DNA damage. Absence of worm-specific Argonaute proteins (WAGO), primary effector proteins of the Piwi pathway, results in considerably elevated DNA damage upon heat-shock. Interestingly, a panel of mutants deficient in the C. elegans Piwi protein, PRG-1, which functions upstream of WAGOs, demonstrate highly variable degrees of heat-induced DNA damage. This variability is likely due to acquired mutations stemming from inadequate germline surveillance over multiple generations. To circumvent this issue by controlling the number of generations a strain is without PRG-1, we generated a conditional knockdown mutant of PRG-1. Utilizing this mutant, we found that in the absence of PRG-1 after one generation, spermatocytes demonstrate exacerbated levels of heat-induced DNA damage, similar to WAGO null mutants. Taken together, my data suggest a key role for PRG-1 and male-specific components of the Piwi pathway in heat-induced DNA damage in spermatocytes.