MODELING GERMLINE BRCA2 MUTATIONS IN ZEBRAFISH

Abstract

Human ovarian cancer is a leading cause of morbidity and mortality in women, but the pathophysiology of this disease is not well-defined. Humans with inherited mutations in the breast cancer 2 gene (BRCA2) are at increased risk for developing breast and ovarian cancer; however, the relationship between BRCA2 mutation and these cancers is not understood. Studies of Brca2 mutation by gene targeting in mice are limited, as homozygous Brca2 mutation typically leads to early embryonic lethality. We established a zebrafish line with a nonsense mutation in brca2 exon 11 (brca2Q658X), a mutation similar in location and type to BRCA2 mutations found in humans with hereditary breast and ovarian cancer. brca2Q658X homozygous zebrafish were viable and survived to adulthood; however, juvenile homozygotes failed to develop ovaries during sexual differentiation. Instead, brca2Q658X homozygotes developed as infertile males with meiotic arrest in spermatocytes. Germ cell migration to the embryonic gonadal ridge was unimpaired in brca2Q658X homozygotes; thus, failure of ovarian development is not due to defects in early establishment of the embryonic gonad. Homozygous tp53 mutation rescued ovarian development brca2Q658X homozygous zebrafish, reflecting the importance of germ cell apoptosis in gonad morphogenesis. In adulthood, brca2Q658X homozygous zebrafish were predisposed to testicular neoplasias. Additionally, tumorigenesis in multiple tissues was significantly accelerated in combination with homozygous tp53 mutation in both brca2Q658X homozygous and brca2Q658X heterozygous zebrafish. These studies reveal a critical role for brca2 in zebrafish ovarian development, demonstrate a conserved association for brca2 mutation in reproductive tumorigenesis in zebrafish, and indicate that tp53 mutation is an important contributor to brca2-associated carcinogenesis. The brca2Q658X-mutant zebrafish line is an important resource for studying both gonadogenesis and brca2-associated carcinogenesis.