Environmental stress sensing and signal transduction in fungi; Antifungal drug targets
The capacity for regulation of gene expression enables successful adaptation of organisms to the environment. Modulation of gene expression in response to the environment has at least three components: (1) external signals are recognized and converted into information that can be transmitted to genes in need of regulation (signal transduction); (2) DNA binding proteins with the ability to activate transcription (transcriptional activators) recognize specific DNA binding sites in the regulatory regions of appropriate genes; and (3) transcriptional activators trigger transcription by interacting with the transcriptional machinery. Our research uses molecular, genetic and biochemical techniques in investigating the mechanics of signal detection and transcriptional activation in response to external stimuli using the single-cell model eukaryote, Saccharomyces cerevisiae (yeast) and the opportunistic pathogen, Cryptococcus neoformans.
We use a variety of approaches including genetic screens, biochemical assays, and microarray analysis to identify signaling molecules involved, to learn more about the stimuli and how they are sensed, and to identify the target genes of the pathways. We continue to investigate issues including: (1) how information is transferred between molecules of the pathway; (2) which additional environmental, physical and chemical signals activate the pathway; and (3) the functional relationship between the two branches of the pathway.
We are also capitalizing on existing protein structure information for signaling molecule complexes in essential signal transduction pathways to design inhibitory peptides corresponding to the protein-protein interface setting the stage for the future identification of small molecule inhibitors with related specificity. Even partial inhibition of activity is expected to substantially compromise the fitness and virulence of fungal pathogens by simultaneously altering normal environmental stress responses. The identification of inhibitory peptides that are toxic to Cryptococcus will provide a foundation with which to propose screening for peptidomimetics or isolation of structurally related small molecule inhibitors each of which might constitute a valid lead compound for a novel antifungal drug.
The evolution of animals via gene loss and outsourcing of genetic function
Developmental biologist Lewis Wolpert emphasized the morphogenetic process that organizes the multicellular body plan of the animal into distinct layers giving rise to nervous system, intestines, and musculature in the following statement: "It is not birth, marriage, or death, but gastrulation which is truly the most important time in your life." While other organisms also evolved multicellularity, they neither gastrulate nor have the genes that drive this process. Thus, animal evolution research has focused on genes unique to animals. However, with full genome sequences from all domains of life, we are now asking a different question and thus re-evaluating what it means to be an animal. In a collaborative project by the Fassler and Erives laboratories, we have been using eukaryotic genome data sets to understand the quintessential aspects of animal physiology by asking NOT what genes are uniquely present in animals, which has been well covered, but by asking instead what genes have been lost. In preliminary computational genomic studies, we identified highly conserved eukaryotic genes that were lost in stem-metazoans, i.e., the organisms that led to the first animal. Such gene losses may point to important constraints that interfered with the evolutionary innovation of new developmental programs and/or that were rendered superfluous.
Poly-glutamine tract length variation in the Gal11 proteins of wine yeast
The yeast GAL11 gene, encodes a subunit of the RNA polymerase II mediator complex, and plays important roles in eukaryotic transcriptional activation. The amino acid composition of the Gal11 protein is unusual in that it has many long tracts of glutamine (also called Q). Inspection of the GAL11 locus in yeast strains with sequenced genomes cataloged in the “Saccharomyces Genome Database” reveals extreme variation in these poly-Q regions. We speculate that Q-rich proteins may encode a rich source of genetic variation that may contribute to the adaptation of strains to novel environments. By introducing GAL11 variants from wild wine yeast strains with differing poly-Q content into a laboratory strain lacking the GAL11 locus, we are investigating the extent to which poly-Q variation may affect Gal11 function and the fitness of yeast strains in various stressful environments. The study of poly-Q repeat length changes in yeast may have clinical relevance. Nine human neurodegenerative disorders, all of them inherited gain-of-function diseases, are caused by the expansion of the CAA or CAG triplet repeat sequences, which encode glutamine. In these proteins poly-Q stretches expand beyond a critical threshold length, which results in an aggregation-prone conformation and cellular toxicity.