The cell biology of dynamic and stable intercellular bridges in situ

Every animal living on Earth is a collection of cells. Our human bodies contain trillions of cells. These cell building blocks are so tiny that over 1500 of them would fill a layer the size of the period at the end of this sentence. However, every animal living on Earth has developed from a single, exceptionally large cell, the egg. This large size is important for early development to proceed properly. We are studying the way in which the mother animal's body creates such big cells. We already know that this requires helper cells to donate their contents to the growing egg, via stable connections. Our ongoing research is on the maintenance of the stability of the window-like connections between helper cells and the egg. We are also studying how the connections are closed at the right time, so that the egg is finally autonomous. Education and outreach activities will include mentoring of K12 teachers, development and engagement of 2nd grade students in development, a math-biology hands on lab for undergraduates, and a novel approach for matching trainees with scientists and engineers. Also included are efforts to broaden participation of URM students and women in science.

The archetypical animal cell has one nucleus. However, in diverse organisms, this rule is broken by tissues such as syncytia. Syncytia are specialized tissues that contain multiple nuclei connected to a common cytoplasm via intercellular bridges. Syncytia are found in diverse contexts such as fruit fly egg chambers, filamentous fungi, mammalian muscle myotubes and plant seeds. In many animals, the egg- and sperm-producing organs are syncytial, and the maintenance of intercellular connections is essential for fertility. Our central aims are to determine the composition, dynamics and regulation of intercellular bridges that connect developing oocytes (egg cells) to a common syncytial cytoplasm. For the propose studies, the model system will be the egg-producing syncytium of the tiny free-living nematod worm, C. elegans. Egg production in the C. elegans syncytial germline is well described genetically and developmentally but has only begun to be explored with cell biology. The small size and transparency of C. elegans make it amenable to quantitative high-resolution in vivo imaging. In addition, quantitative image analysis, photo- and micro-manipulation, biochemistry, reverse genetics and corroborative modeling will be combined to study intercellular connections. C. elegans is highly suitable for dissecting molecular mechanism due to its well-annotated genome and the ease of protein depletion, and genome editing for fluorescent protein tagging. Syncytial intercellular bridges can be thought of as abortive cell division, wherein the cytokinetic ring failed to separate the daughter cells. Therefore, our vast knowledge about how cells pinch in half during cytokinesis has informed hypotheses about the structure and function of intercellular bridges. The high conservation of cell division machinery predicts our findings will be applicable across phylogeny. Furthermore, the conveyor belt-like arrangement of oocyte development from the distal to the proximal gonad will reveal spatio-temporal correlations that predict causal relationships.