Organelle transport and organization in mammalian oogenesis

University Of Missouri-Columbia, Columbia MO

Investigators

Abstract

In mammalian females, quiescent primary oocytes serve as the ovarian reserve supporting mature oocyte production and ovarian function. Primary oocytes differentiate in fetal ovaries and remain quiescent for years in adult ovaries, where a cohort of primary oocytes activates periodically to develop into mature oocytes. Quiescent primary oocytes undergo cell death continuously, leading to diminished ovarian function in adult females. Here, we propose to continue our study on how primary oocytes are determined among fetal germ cells during oocyte differentiation; and mechanisms underlying primary oocytes quiescence and loss in adult ovaries. Our previous study characterized roles of organelle dynamics in mouse oocyte differentiation and quiescence. We found that primary oocytes form via organelle transport within germline cysts, in which germ cells derived from the same progenitor are connected via intercellular bridges. ~20% of the germ cells collect organelles (Golgi, centrosomes, and mitochondria) from sister cyst cells to become primary oocytes, whereas the rest donate their organelles and undergo cell death. In the quiescent primary oocyte, enriched organelles organize into a Balbiani body (B- body), represented by a spherical configuration of Golgi complexes. The B-body is maintained by microtubules and actin, and regulates oocyte quiescence via RNA storage. These studies have laid a foundation for us to continue investigating oocyte determination and quiescence with a focus on organelle transport and organization in the next five years. We will continue our study on how the cell fate of collecting vs. donating organelles is determined among fetal germ cells. Our recent study suggests that organelle transport in cysts is conducted in a directional manner and facilitated by intercellular polarity between cyst germ cells. We will define the intercellular polarity by characterizing patterns of organelle (Golgi and mitochondria) transport, and the interactions between organelles, actin and microtubules in mouse and human germline cysts using advanced imaging approaches. We will identify functions of MACF1 (microtubule actin crosslinking factor 1) and microtubule minus-end-targeting protein CAMSAP3 (Calmodulin-regulated spectrin-associated proteins 3) in intercellular polarity, organelle transport and oocyte determination using inducible germ cell-specific conditional knockout mouse models. To further our knowledge of the structure and function of the B-body in mammals, we will unveil protein and organelle compositions of mouse and human B-bodies by protein profiling and imaging. We will conduct mechanistic study on B-body-mediated quiescence-senescence-cell death transitions in primary oocytes by investigating roles of the p53/TAp63 pathway in this process using in vitro ovary culture and mutant mouse models. We will also test the feasibility of protecting primary oocytes from chemotherapy drug-induced cell death by preserving the B-body function. Successful completion of the proposed study will advance our understanding of cell and developmental biology in mammalian oogenesis and have a positive impact on women’s health.