Regulation of Germ cell to maternal transition

Abstract The gametes arise either from germ cells or germline stem cells (GSCs), by undergoing differentiation and meiosis. The gametes help launch the next generation by sustaining early development prior to zygotic genome activation by contributing specific components to the zygote. In particular, the mature oocyte, in addition to a haploid genome, contains a “maternal contribution” of RNAs, proteins, complexes, and organelles that is critical to establish a totipotent zygote. Moreover, the oocyte cytoplasm is also sufficient to reprogram a quiescent somatic cell nucleus to totipotency. Thus, the oocyte's maternal contribution is essential and critical for totipotency. Germ cells undergoing differentiation and meiosis to eventually synthesize maternal contribution is conserved up to human. Nevertheless, the mechanisms that establish this highly potent oocyte cytoplasm during oogenesis are incompletely understood. Using Drosophila as a model system, my lab has discovered a germ cell-to-maternal transition, wherein germ cell-specific programs, such as those that promote GSC self-renewal, differentiation, and entry into meiotic cell cycle, are silenced once the oocyte is specified. Our work reveals that this silencing of the germ cell program is critical to establishing the “correct” maternal contribution by excluding transcripts that could interfere with development of the early embryo. We find that this silencing is is mediated by heterochromatin formation to and removal of perduring RNAs by RNA degradation pathways. Although, we are beginning to understand how germ cell specific programs are silenced during the germ cell-to-maternal transition several aspects remain poorly characterized. The objective of the proposal is to uncover how the germ cell-to-maternal transition is regulated by addressing the following questions: 1. How do the changes in gene expression during the germ cell-to-maternal transition relate to reorganization of the genome?, 2. How are germ cell-specific genes targeted for silencing? and 3. How is silencing of germ cell-specific genes coordinated with oocyte specification? The rationale for the proposed work identifying regulators of this transition and the underlying molecular mechanisms could reveal new etiologies and therapies for human infertility and novel concepts in developmental biology.