brca2 in zebrafish ovarian development, spermatogenesis, and tumorigenesis

Abstract

Humans with inherited mutations in 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, given that homozygous Brca2 mutation typically leads to early embryonic lethality. We established a zebrafish line with a nonsense mutation in brca2 exon 11 ( brca2 Q658X ), a mutation similar in location and type to BRCA2 mutations found in humans with hereditary breast and ovarian cancer. brca2 Q658X homozygous zebrafish are viable and survive to adulthood; however, juvenile homozygotes fail to develop ovaries during sexual differentiation. Instead, brca2 Q658X homozygotes develop as infertile males with meiotic arrest in spermatocytes. Germ cell migration to the embryonic gonadal ridge is unimpaired in brca2 Q658X homozygotes; thus, failure of ovarian development is not due to defects in early establishment of the embryonic gonad. Homozygous tp53 mutation rescues ovarian development in brca2 Q658X homozygous zebrafish, reflecting the importance of germ cell apoptosis in gonad morphogenesis. Adult brca2 Q658X homozygous zebrafish are predisposed to testicular neoplasias. In addition, tumorigenesis in multiple tissues is significantly accelerated in combination with homozygous tp53 mutation in both brca2 Q658X homozygous and brca2 Q658X heterozygous zebrafish. These studies reveal critical roles for brca2 in ovarian development and tumorigenesis in reproductive tissues.

Isolation and cytogenetic characterization of zebrafish meiotic prophase I mutants

“…All females in the same clutch of the mutant males produced offspring (Table S1), suggesting that mutant females were fertile (Table S1 is available online). However, there is the possibility that the mutants become male analogous to other reported zebrafish mutants with germ line defects (Kamminga et al, 2010;Rodriguez-Mari et al, 2010;Shive et al, 2010). Further analysis regarding the effects of these mutations on females will be facilitated by identification of the causative mutations.…”

“…To detected apoptosis signal transduction molecule Caspase-3, a commercially available antibody for zebrafish as described in Shive et al (2010) was used. For the immunohistochemical analysis of cleaved Caspase-3, the testes were fixed in Bouin's solution, and paraffin sections were prepared as described above.…”

Hooked on zebrafish: insights into development and cancer of endocrine tissues

“…TILLING has been used to isolate a missense mutation in the zebrafish brca2 ortholog (Shive et al 2010). Brca2 Q658X homozygous mutant zebrafish fail to undergo ovarian development and exhibit abnormal spermatogenesis.…”

Translation repression by maternal RNA binding protein zar1 is essential for early oogenesis in zebrafish

“…When oocytes are depleted in juveniles, zebrafish also develop into males (Dranow et al, 2013;Hartung et al, 2014;Houwing et al, 2008;Rodríguez-Marí et al, 2010Shive et al, 2010;White et al, 2011). Attenuation of apoptosis pathways by p53 deficiency restores ovarian development in otherwise all male fancl and brca2 mutants (Rodríguez-Marí et al, 2010Shive et al, 2010). In addition, germ cells and oocytes are also required to maintain female phenotype in adult zebrafish (Dranow et al, 2016(Dranow et al, , 2013.…”

“…Zebrafish without germ cells develop into male adults, indicating germ cells are essential for female development (Campbell et al, 2015;Draper et al, 2007;Houwing et al, 2007;Siegfried and Nüsslein-Volhard, 2008;Slanchev et al, 2005). When oocytes are depleted in juveniles, zebrafish also develop into males (Dranow et al, 2013;Hartung et al, 2014;Houwing et al, 2008;Rodríguez-Marí et al, 2010Shive et al, 2010;White et al, 2011). Attenuation of apoptosis pathways by p53 deficiency restores ovarian development in otherwise all male fancl and brca2 mutants (Rodríguez-Marí et al, 2010Shive et al, 2010).…”