Cell Differentiation and Organogenesis in Aspergillus
The filamentous fungus Aspergillus nidulans has multiple developmental programs, each with a unique set of differentiated cell types that are organized into tissues, organs and higher order structures. Devel-opmental landmarks include spore germination and the establishment of true filamentous hyphae, the ac-quisition of developmental competence (Tc), and the asexual (mitotic) and sexual (meiotic) reproductive cycles. Fundamental processes required for these events include the ability to correctly respond to diverse extrinsic and intercellular signals and to correctly transduce this information to elicit necessary changes in gene expression. In addition, development-specific gene expression must be correctly integrated with al-terations in cell polarity and cell cycle regulation and specialized nuclear movement events. A. nidulans is a classical model organism for developmental genetics and a representative of a major group of Asco-mycete fungi that include important animal and plant pathogens. Also included are human pathogens that are increasingly problematic as the population of immunosuppressed persons increases. Potential out-comes of the work include a comparative approach to understanding how diverse fungal species use con-served regulatory proteins and signaling mechanisms in different ways to control biological processes such as self/non-self recognition at both the cellular and nuclear level, zygote formation (karyogamy) and gametogenesis (meiosis and ascosporogenesis). From a broader perspective, this project's objectives ad-dress mechanistic questions concerning the regulation of cell differentiation and organogenesis, processes that are fundamental developmental events in all complex eucaryotic organisms.
Recent studies indicate that the filamentous fungi possess a regulatory network linking signal molecules to cell differentiation events that differs from the budding yeast paradigm. This is consistent with the more complex life cycle of fungi that form diverse multicellular structures. This project's central hypothe-sis is that a study of organogenesis in A.nidulans will identify new genes and regulatory mechanisms that will provide novel models for eucaryotic multicellular development and reproductive biology. The spe-cific goals of this project are to use a key transcriptional regulator, SterileA, as an entry point into path-ways controlling the initiation of meiotic reproduction and the differentiation of sexual reproductive structures. SteA (Sterile) controls fertilization events and ascogenous tissue development. steA is con-stiuitively expressed, indicating that SteA interacting proteins control SteA function in response to signal-ing pathways. Interacting proteins will be identified by co-immunoprecipitation of protein complexes (a proteomic approach) and by screening a yeast two-hybrid library expressing A. nidulans developmentally regulated cDNAs. Specific interactions with MpkB (ERK1 type MAPK) and cAMP-dependent protein kinases will also be tested. Direct SteA target genes representing the downstream effects of SteA activa-tion, will be identified using chromatin co-immunoprecipitation (ChIP) analysis. This class of target genes likely represents key components of the regulatory network controlling foci formation, fertilization and ascogenous tissue differentiation.
For over 50 years, A.nidulans has been a valuable tool for teaching classic eucaryotic genetics and, more recently molecular genetics, to young scientists at the undergraduate, graduate and postdoctoral levels. A project goal is to train productive new scientists. Therefore, this project includes young scientists at all levels and will provide them with research opportunities and learning experiences in the areas of molecu-lar genetics and cellular and developmental biology. They will also have the opportunity to hone commu-nication skills through daily interactions with other colleagues, and to the larger scientific community, through publications, posters and oral presentations at regional and national meetings.