Poster abstracts

Poster number 52 submitted by Dongju Park

Multiple functions of BRCA1 during spermiogenesis

Dongju Park (Molecular, Cellular and Developmental Biology, The Ohio State University), Reena Shakya (Comprehensive Cancer Center, The Ohio State University), Jonathan Lee (Department of Molecular and Cellular Biochemistry, The Ohio State University), Vedud Purde (Ohio State Biochemistry Program, The Ohio State University), Thomas Ludwig (Department of Molecular and Cellular Biochemistry, The Ohio State University)

Abstract:
Spermatogenesis is a highly complicated process involving mitosis, meiosis and spermiogenesis. After mitotic division of germ cells (spermatogoinal stem cells), some daughter cells undergo meiosis and others maintain germ cell population. During the first meiotic division, massive DNA double strand breaks (DSB) are induced by SPO11 and repaired by homology-directed repair (HDR). Haploid cells (round spermatids) produced from meiosis form tail and acrosome which covers the anterior portion of sperm head containing digestive enzymes to penetrate the oocyte.
Breast cancer susceptibility gene 1 (Brca1) play essential roles for genome integrity by involving multiple cellular processes including cell cycle check point control, DSB repair and ubiquitination. Mice with missense mutation (Brca1 S1655F or Brca1 M1717R) in C-terminal BRCT domain that disrupts interaction with phospho-ligand showed mitotic HDR defect resulting in tumor development, while mice with Brca1 I26A in N-terminal RING domain that have no E3 ubiquitin ligase activity had functional mitotic HDR. Interestingly, all mutant mice show a common phenotype, infertility. Here, we report multiple functions of BRCA1 during spermatogenesis. First, full-length BRCA1 is absolutely essential for self-renewal of spermatogonial stem cells. BRCA1 truncation mutant mice (Brca1 ex11tr) have completely empty testes showing proliferation defects of germ cells and extensive apoptosis. Second, surprisingly, both E3 ubiquitin ligase activity and BRCT phosphoprotein binding are dispensable for meiotic HDR. All three missense mutant mice can form sex-body and finish meiosis. Lastly, both E3 ubiquitin ligase activity and BRCT phosphoprotein binding are required to inhibit amplification of pericentriolar material (PCM) during spermiogenesis. We observed that PCM is amplified in round spermatids of all three missense mutant mice, and the amplified-extra-PCM display diffuse area having no centriole. Based on this observation, we are currently working on that the extra-PCM which have no centriole could nucleate microtubule disrupting microtubule organization.

References:
Shakya, R. et al, BRCA1 Tumor Suppression Depends on BRCT Phosphoprotein Binding, But Not Its E3 Ligase Activity, Science 334, 525-528

Keywords: Spermatogenesis, BRCA1, Centriole