How the Fungi got into shape : cellular organization and morphogenetic gene evolution in phylum Chytridiomycota reveals mechanisms underlying the evolution of fungal body diversity

With their threadlike hyphal cells, fungi can invade the surface of a cheese, secreting digestive enzymes and soaking up the spoils. Although most fungi feed with hyphae, phylum Chytridiomycota produces various alternative cell shapes. Here I address three hypotheses regarding the evolution of cell shape. Firstly, Fungi inherited core genes for cellular morphogenesis from their most recent common ancestor and diversification of these genes through evolutionary time potentially contributed to morphological novelty. My phylogenomic surveys revealed duplications in seven families of actin-binding proteins predating the radiation of fungal phyla. Synthesizing previous studies of the function, localization and evolutionary history of septin, myosin, and actin-binding proteins in yeasts and hyphal fungi enabled me to further hypothesize their roles during development in Chytridiomycota. Since Chytridiomycota diverged from moulds and mushrooms, each group evolved unique mechanisms for constructing different cell shapes using a shared ancestral molecular toolkit. Hyphal growth and septation require actin. My second hypothesis was that actin, a major cytoskeletal component, is also involved in morphogenesis in Chytridiomycota. Using fluorescence microscopy, I documented rhodamine phalloidin-stained actin cables, patches, sheets and perinuclear shells through development in Chytriomyces hyalinus. I disrupted the actin cytoskeleton with the chemical inhibitor latrunculin B. Observing actin patches concentrated at rhizoid tips and at cytoplasmic cleavage planes, and finding that actin integrity was essential for rhizoid proliferation in C. hyalinus both support a conserved role for actin in polarized growth and cytokinesis. Thirdly, I hypothesized that sustained tip growth and nuclear migration underlie the convergent evolution of hyphae and hypha-like growth forms. Chytriomyces hyalinus shows determinate growth that ceases once a zoosporangium matures. Phylogenies indicate that filamentous species in Chytridiomycota with indeterminate growth arose independently from ancestors with a determinate growth mode. I determined that actin organization and nuclear migration patterns in each species differed from one another and from hyphae, most likely as a result of their independent origins. In combination, phylogenetic analyses, molecular genetics, and microscopy are tearing away the curtains of time that mask the ever-changing molecular machinery that gave rise to an astounding diversity of form and function in modern fungi.Science, Faculty ofBotany, Department ofGraduat

A different shade of hypha : cytological and molecular phylogenetic evidence for the independent rise of the hyphal habit in the class Monoblepharidomycetes (Chytridiomycota)

Once the ancestors of fungi stopped moving and instead started reaching out with hyphae, their filamentous growth made possible new variety in form and habitat. Hyphae mediated substrate colonization, absorptive nutrition, mating and reproduction. Although shared across most familiar terrestrial fungal lineages, little was known about where hyphae evolved in early fungi. In chapter one, I review the phylogenetic origins of hyphae and current understanding of the cytology of hyphal tips. Better understanding of fungal phylogeny and hyphal growth near the base of the fungal tree was needed. In Chapter 2, I investigated the phylogeny and cytology in the Class Monoblepharidomycetes (Chytridiomycota), a group of deeply diverging, zoosporic fungi, encompassing a range of body types. Species can be either crescent or rod-shaped unicells or sprawling hyphal growths. I inferred a phylogeny of the fungi based on 28S ribosomal DNA sequence data using maximum likelihood (ML) and Bayesian inference methods. I recovered the monophyly of modern fungal phyla and the topology was comparable to the most taxonomically diverse and gene–rich phylogeny of the fungi to date. I used likelihood methods to trace the origins of hyphae on my likelihood tree, concluding that hyphae arose independently in the Monoblepharidomycetes and at least three other times in the fungi. Next, I searched for evidence of convergent evolution in the cellular organization of hyphal Monoblepharidomycetes using fluorescence and transmission electron microscopy. I showed that the hyphae of Monoblepharidomycetes have a novel form with an unusual microtubule cytoskeleton and without a typical fungal Spitzenkörper. This constitutes the first report on the cytology of hyphae from the Chytridiomycota. In Chapter 3, I discuss the significance of my research and possible future directions including cytological experiments on the Monoblepharidomycetes cytoskeleton.Science, Faculty ofBotany, Department ofGraduat

Diverse organizations of actin and nuclei underpin the evolution of indeterminate growth in Chytridiomycota and Dikarya

Indeterminate growth, as in the hyphae of the “Humongous Fungus” of Michigan requires sustained nuclear migration and cell wall remodeling. We compare actin organization and patterns of nuclear positioning among four distantly related, indeterminate species of phylum Chytridiomycota: Cladochytrium replicatum, Physocladia obscura, Nowakowskiella sp., and Polychytrium aggregatum. We combined light microscopy, nuclear staining with DAPI, and actin staining with rhodamine phalloidin to analyze actin distribution and nuclear migration during somatic growth in the four Chytridiomycota species. Actin formed plaques, filaments, cables and perinuclear shells in patterns that varied across the four species. All four species initiated indeterminate growth by extending branching, anucleate rhizomycelium,The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Plexus 2024: Navigate

Welcome to the 25th anniversary edition of PLEXUS, UC Irvine School of Medicine’s annual student-organized Journal of Medical Humanities & Arts. To mark this celebratory milestone, it is with great pleasure that I present to you NAVIGATE. In the ever-evolving landscape of medicine, the ability to navigate through challenges and unforeseen obstacles is paramount. NAVIGATE serves as a timely invitation for our colleagues to reflect on the distances traversed and to envision the new horizons that lie ahead. We sought to highlight the constellation of tools utilized when we feel lost and to acknowledge the beacons that steer our actions. The subsequent pages offer its readers profoundinsights into the extraordinary journeys undertaken by the greater UCI Health community. We hope it delivers a sense of direction, solace, and clarity to all readers.As we celebrate our 25th anniversary, wehonor the visionaries, contributors, and readers that have propelled us forward on this remarkable voyage. Their collective support fuels our efforts to serve as a creative outlet for the community, catalyze meaningful discussions, and apply the tenets of medical humanities to foster a cohort of compassionate healers.We extend our deepest gratitude to our faculty advisors Dr. Juliet McMullin and Dr. TanNguyen for their invaluable guidance and for sharing their expertise within the field. We thank the UCISOM Medical Humanities & Arts Program and the UCI Department of Family Medicine for their unwavering support. I invite you to embark on this exploration with us, and witness the intricate tapestry of our contributors’ lived experiences that defines our shared journey in healthcare.Bon voyage,Christopher SahagianEditor-in-ChiefCreative Review — Caroline GeeCreative Review — Huan NguyenCreative Review — Sana ShahDesign — Nicole ParkerDesign — Britney WengFaculty Advisor — Dr. Juliet McMullinFaculty Advisor — Dr. Tan NguyenStaff Advisor — Leonora Naser-Saravia{Front Cover): NEW HEIGHTS Britney Weng, MS1San Pedro de Atacama, Chile(Inner Cover): TRAVERSING  Britney Weng, MS1Chile Route 2