Transporting cellular cargo with spatial and temporal precision is critical for many processes in all cells. Different cell types and organisms use diverse machineries for long-distance cargo transport. For example, mammalian cells and many filamentous fungi transport cargo using the microtubule-based motors dynein and kinesin, while yeast use myosin motors on actin cytoskeleton tracks. Despite a general understanding of cellular transport and the motors involved, little is known about how similar transport machineries are adapted by specific cell types or organisms. Dr. Christensen’s current research investigates canonical (motor-driven) and non-canonical cargo transport. In this proposal, she will investigate how both modes of transport have evolved in different organisms using an innovative approach in which evolutionary hypotheses are directly tested using comparative cell biology in fungal and mammalian cells. Defects in transport are particularly prevalent in neurological disorders such as Alzheimer’s, Huntington’s and ALS. Examining how diverse cell types differently use the transport machinery is directly applicable to understanding how transport defects lead to cell-specific diseases. In Aim 1, Dr. Christensen will investigate how regulators of motor-driven transport have evolved in fungi and human cells. In her current research and the K99 phase of this award, she will investigate how the gene expansion and functional diversification of the ‘FHF’ protein complex allows dynein to bind multiple cargos in human cells. For the R00 phase of this award, Dr. Christensen will identify and characterize novel dynein regulators using evolutionary analysis and comparative cell biology in A. nidulans and human cells. In Aim 2, Dr. Christensen will investigate a non-canonical form of transport known as ‘hitchhiking’. In hitchhiking, a cargo attaches to and is co-transported with another cargo to achieve motility. Hitchhiking has been demonstrated to occur in two evolutionarily divergent species of filamentous fungi, Aspergillus nidulans and Ustilago maydis. In the K99 phase of this award, she will investigate a potential evolutionary advantage of peroxisome hitchhiking in A. nidulans and determine if mRNA hitchhiking convergently evolved in A. nidulans and U. maydis. In the R00 phase of this award, she will determine if hitchhiking occurs in a third filamentous fungus, Ashbya gossypiii, a fungus lacking canonical microtubule-based transport. Dr. Christensen’s goal is to develop an independent research program at the interface of cell and evolutionary biology. To accomplish this, she will attend conferences spanning fields and participate in UCSD- sponsored and MOSAIC UE5 initiatives focused on lab management and the transition to independence. She will receive guidance from her mentoring committee (faculty listed below) and her primary mentor, Sam Reck- Peterson. This development plan, combined with training in evolutionary biology (with Matt Daugherty, UCSD), mammalian cell vesicle trafficking assays (with Susan Ferro-Novick, UCSD), and A. gossypii (with Amy Gladfelter, UNC Chapel Hill) will prepare her to excel in an independent position.

PROJECT NARRATIVE In the cell, many different cargos must be transported with spatial and temporal precision, and defects in intracellular transport are prevalent in many neurological disorders. There is an incredible diversity of cellular transport behavior and modalities in nature—how do different cells transport cargo, and how do they adapt the transport machinery for their specific needs? This proposal will investigate the evolution of different modes of cargo transport.