Paternal age effect mutations as selfish drivers of germline stem cell clonality

PROJECT SUMMARY Spermatogonial stem cells (SSCs) maintain male fertility, but not all SSCs are created equal. Here, I propose to lineage trace the contributions of individual SSCs to sperm production across the fertile lifespan of an animal. My central hypothesis is that SSCs compete for dominance and that Paternal Age Effect (PAE) mutations in the RAS-MAPK pathway can confer autonomous advantage to SSCs at the cost of offspring health. In Aim 1, I will identify the contributions of individually labeled SSC clones to spermatogenesis throughout zebrafish adulthood using serial sperm sampling of male zebrafish from sexual maturity through the “elderly stage” when fertility begins to decline. In Aim 2, I will investigate whether PAE mutations drive the selection of individual SSCs. I will overexpress mutated PAE genes in a subset of SSC clones within the zebrafish testis and determine the consequences to clonal dynamics, measuring non-neutral clonal competition in a living animal. In Aim 3, I will determine the potentially “selfish” influence of PAE-containing clonal dominance by measuring mutation transmission and consequences for the next generation. Together, this proposal will illuminate developmental mechanisms that underlie male reproductive aging and may aid future efforts to design male-oriented reproductive interventions that improve birth outcomes. My interdisciplinary team of mentors will provide training in stem cell population analysis, genetic engineering, and modeling human disease in animals, complemented by clinical mentorship and shadowing in pediatrics and reproductive endocrinology. The training plan was developed in collaboration with my Sponsors to complete the central goals of conducting independent, collaborative research; advancing communication and grant-writing skills; learning how to effectively mentor and teach trainees in a supportive environment; and honing clinical skills in preparation for the return to medical school. This training is ideal for a future physician-scientist with the goal of improving patient care at the intersection of basic research and clinical reproductive interventions.