MODELING INFERTILITY: SINGLE GENE MUTATIONS AND CONSEQUENCES FOR GERM CELL DEVELOPMENT
Infertility is a growing global healthcare concern. Genetic causes account for a large percent of infertility cases, and in some instances, single-gene mutations are sufficient to cause infertility in humans. To further our understanding of certain single gene causes of infertility, we studied the function of three conserved genes, Trip13, Cyclin B3, and Flacc1, using knockout mouse lines. Trip13 is an ATPase that remodels HORMA-domain proteins and is essential for meiotic progression. Pathogenic mutations of TRIP13 are found in humans and cause infertility via oocyte maturation arrest. In Chapter 2, we used a genetic approach and imaging techniques to study the function of TRIP13 in meiotic prophase I in mice. We found that TRIP13 localizes to the synaptonemal complex (SC) in pachynema and to meiotic telomeres throughout prophase I. Trip13-/- spermatocytes arrest in pachynema and exhibit defective synapsis. TRIP13 localization in other mutant strains with defective synapsis, indicated that TRIP13 is likely recruited by a component of the SC during early synapsis. In Chapter 3, we examined CCNB3, a meiosis-specific cyclin, which is required for meiosis I in mice and for zygotic genome activation (ZGA) in Ciona intestinalis. In humans, CCNB3 mutations cause recurrent pregnancy loss. We explored meiotic and post-meiotic roles of CCNB3 using imaging studies, fertility tests, and pronuclei swap experiments. Ccnb3-/- females are sterile. Ccnb3-/- oocytes cannot complete meiosis I but can be fertilized. Resultant embryos are triploid, resulting in embryonic lethality. Cytoplasmic Ccnb3 was not required for embryonic development, and its function in ZGA is not conserved. In Chapter 4, we used varied approaches (microscopy, mating tests, histology, Western blot), to explore the function of the coiled-coil protein FLACC1. FLACC1, a testis-specific protein, was thought to be an important component of the sperm tail. However, Flacc1-/- males were fertile. FLACC1 Western blot showed testis specific expression, yet previous reports of localization to the sperm tail were not confirmed. Together, this work provides insights into the germ cell-specific function of three conserved genes, two of which are required for mammalian fertility.
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