Every organism starts out as a single fertilized cell, yet we do not fully understand the events that are essential for producing that cell because they take place within the ovary of the mother. Failure to form an egg that is capable of embryonic development can result in profound birth defects or miscarriage. In addition, cancers of the ovary can arise from uncontrolled proliferation of the germ cells, those cells that can become eggs, or the somatic cells, the cells that do not develop as eggs, of the ovary. In normal ovaries, these two types of cells communicate with one another to regulate the growth and survival of both cell populations. In most animals, the germ line stem cells undergo an asymmetric division to generate daughter cells that will remain stem cells and others, cystoblasts that divide and eventually form eggs. The divisions of the cystoblasts are unique because the cells do not completely separate from one another, but instead remain attached to each other. Studies in mammals show that the connections between cystoblasts prevent too many cells from becoming oocytes, and in humans uncontrolled and complete separation of cystoblasts has been correlated with germ cell neoplasias. However, since these events occur before or at the time of fertilization we understand little about how the genes that are involved. Therefore, understanding how the growth and survival of these cells is regulated has important consequences to both fertility and cancer formation.
To study relationships between interacting cells within adjacent tissues, such as germline and somatic follicle cells, we need to analyze an animal system in which we can manipulate genes and study early development. The zebrafish system has advantages that allow us to use embryological, biochemical, and genetic techniques to access maternally controlled processes during vertebrate animal development. Our studies exploit the powerful genetics and cell biological access in the zebrafish system to unravel the mechanisms that regulate oocyte polarization and follicle cell fate in a vertebrate. Several features of primary oocyte development are common among insects, and vertebrates, including humans, thus this architecture is likely fundamental for germline development and fertility.
Our genetic and biochemical studies of oocyte polarity have led us to genes involved in mRNA localization and polarized transport, including motor and RNA binding proteins. Like oocytes, neurons are highly polarized cells, which rely on trafficking and post-transcriptional regulation of mRNAs to ensure that gene products are only expressed in discrete locations. We are adapting Rob Singer's MS2:MCP system to visualize RNA trafficking in the living zebrafish embryo. Understanding how the individual transport mechanisms operating in neurons contribute to their function has potential to uncover novel pathological mechanisms underlying neurodegenerative diseases.