Research Projects
A. gossypii (“Ashbya” as we fondly refer to it) has the same set of core cell cycle proteins as found in its evolutionary cousin the budding yeast S. cerevisae. Despite these similar parts, this filamentous fungus seems to have a rather different basic cell cycle, presumably due to its special cell architecture and lifestyle (See a table showing the variable level of amino acid identity for these factors between the two species. See a movie made by Dr. Hans-Peter Schmitz of the University of OsnaBrueck in Germany comparing budding yeast and Ashbya growth) Notable features of the A. gossypii nuclear division cycle include asynchronous division of nuclei, an apparently stable pool of mitotic and G1 cyclins, and spatial regulation of the CDK-inhibitor Sic1p. See our recent paper in The Journal of Cell Biology describing the Ashbya gossypii cell cycle. For a complete listing of our papers, please use this link to PubMed. Here are some of the areas of research in the lab:
1. How are higher-order septin structures assembled and maintained in living cells?
The cell cortex links the cell interior and exterior by transmitting and responding to a variety of signals. The septins are a conserved class of proteins that organize and regulate the cortex in cells of diverse species, tissues and morphologies. Despite the widespread distribution and varied functions of septins, little is known about the molecular mechanisms that direct septin assembly and organization. A. gossypii is an attractive model system for examining mechanisms of septin organization because 1) many morphologically distinct septin complexes coexist within one cell and 2) we have generated a panel of mutants which perturb specific classes of structures. We are using quantitative fluorescence time-lapse imaging, biochemistry and reverse genetics to understand the rules of in vivo septin organization. This work is supported by a grant from the National Science Foundation.
2. How are autonomously dividing nuclei established in a common cytoplasm?
We have shown that nuclei divide asynchronously despite exposure to signals from a common cytoplasm. Our data indicated that sister nuclei-those born of the same mitosis-diverge in their cell cycle kinetics within G1. This divergence in timing requires the Retinoblastoma (Rb) tumor suppressor analogue, called Whi5. In this project we are examining novel mechanisms of Whi5 activation and regulation that lead to nuclear autonomous control of cell cycle commitment. This work is supported by the March of Dimes Foundation and the Prouty Foundation.
3. How are cell cycle signaling feedback loops generated within environments of significant biological noise?
Circular and highly regulated processes such as the cell division cycle and the circadian clock are driven by biochemical oscillators built of interconnected positive and negative feedback loops. These regulatory loops enable linear progression through and irreversible transitions between different states as well as coupling to other cellular networks. We study the cell cycle oscillator as a means to understand spatial control in the establishment and amplification of signaling feedback loops. In A. gossypii independent cell cycle oscillators co-exist out of sync in one cell. We are exploiting this as a model to understand how regulatory loops can be spatially compartmentalized and effectively locally concentrated within individual nuclei.
We combine quantitative fluorescence time-lapse microscopy, automated image tracking and analysis, statistical modeling, and genetic approaches to identify mechanisms of spatial insulation in cell cycle signaling pathways. In our initial work, we hypothesize that biological noise and asymmetric nuclear division (in which elements of the nuclear envelope are unequally partitioned) combine to generate nuclei of different fates in one cytoplasm. In collaboration with a statistical modeler and a mathematician, we have developed computational tools to test these hypotheses with large scale image data sets from which we track the division kinetics of related nuclei. Our long term goal is to understand the role of cell architecture in dictating the basic properties of signaling networks such as the cell cycle.