Katrina Velle

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Current: University of Massachusetts Amherst | Fritz-Laylin Lab 

 I'm a cell biologist interested in actin-driven phenotypes and microbial pathogenesis. As a postdoc, I am investigating the contributions of the actin cytoskeleton to cell migration, cell division, and osmoregulation in Naegleria gruberi—a non-pathogenic model system for the "brain-eating amoeba." My work is currently supported by an NIH NIGMS K99 award. 

Former: University of Connecticut | Campellone Lab

During my PhD, I studied how and why pathogenic E. coli hijack the actin cytoskeleton of their mammalian host cells. I defined a pathway of actin nucleator collaboration, and an actin-driven mechanism for cell-to-cell transmission. 

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Why use Naegleria as a model system?

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Unique cytoskeletal features

Almost every known eukaryotic cell relies on both actin and microtubule cytoskeletons to drive cellular processes. Crosstalk between these systems is extensive and of growing interest, but what happens if a cell lacks one of these systems? As interphase amoebae, Naegleria cells have no microtubules at all, providing an opportunity to study actin phenotypes in the absence of microtubule crosstalk. 

While Naegleria lack microtubules most of the time, these cells do use microtubules under two circumstances: (1) during closed mitosis, Naegleria assembles a spindle from mitotic-specific tubulins (cyan, top/left cell), and (2) as a stress response, amoebae transiently differentiate into swimming flagellates, which requires the assembly of a pellicle microtubule array and two flagella (yellow, lower/right cell). After cytokinesis, and upon flagellates returning to an amoeboid state, tubulin and tubulin transcripts are degraded.

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Insights into eukaryotic evolution

Much of the cell biology we know has come from studies of model organisms within the "yeast to human" opisthokont lineage (pink) and the related amoebozoa. Naegleria (blue) last  shared an ancestor with this opisthokont lineage over a billion years ago. Due to this evolutionary distance, we cannot assume that any basic cell biology conserved in yeasts and human cells is also conserved in Naegleria without rigorous testing. However, any traits shared by Naegleria and opisthokonts can provide clues as to what the last common eukaryotic ancestor may have looked like.

Implications for human health

One species of Naegleria, Naegleria fowleri, is also known as the "brain-eating amoeba." A current lack of reliable treatments has lead to a case fatality rate of over 90%. A more complete understanding of Naegleria's basic cell biology may lead to the discovery of new treatment targets to combat this deadly infection.