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 (<italic>BRCA2</italic>) are at increased risk for developing breast and ovarian cancer; however, the relationship between <italic>BRCA2</italic> mutation and these cancers is not understood. Studies of <italic>Brca2</italic> mutation by gene targeting in mice are limited, as homozygous <italic>Brca2</italic> mutation typically leads to early embryonic lethality. We established a zebrafish line with a nonsense mutation in <italic>brca2</italic> exon 11 (<italic>brca2</italic><super>Q658X</super>), a mutation similar in location and type to <italic>BRCA2</italic> mutations found in humans with hereditary breast and ovarian cancer. <italic>brca2</italic><super>Q658X</super> homozygous zebrafish were viable and survived to adulthood; however, juvenile homozygotes failed to develop ovaries during sexual differentiation. Instead, <italic>brca2</italic><super>Q658X</super> homozygotes developed as infertile males with meiotic arrest in spermatocytes. Germ cell migration to the embryonic gonadal ridge was unimpaired in <italic>brca2</italic><super>Q658X</super> homozygotes; thus, failure of ovarian development is not due to defects in early establishment of the embryonic gonad. Homozygous <italic>tp53</italic> mutation rescued ovarian development <italic>brca2</italic><super>Q658X</super> homozygous zebrafish, reflecting the importance of germ cell apoptosis in gonad morphogenesis. In adulthood, <italic>brca2</italic><super>Q658X</super> homozygous zebrafish were predisposed to testicular neoplasias. Additionally, tumorigenesis in multiple tissues was significantly accelerated in combination with homozygous <italic>tp53</italic> mutation in both <italic>brca2</italic><super>Q658X</super> homozygous and <italic>brca2</italic><super>Q658X</super> heterozygous zebrafish. These studies reveal a critical role for <italic>brca2</italic> in zebrafish ovarian development, demonstrate a conserved association for <italic>brca2</italic> mutation in reproductive tumorigenesis in zebrafish, and indicate that <italic>tp53</italic> mutation is an important contributor to <italic>brca2</italic>-associated carcinogenesis. The <italic>brca2</italic><super>Q658X</super>-mutant zebrafish line is an important resource for studying both gonadogenesis and <italic>brca2</italic>-associated carcinogenesis.