The Faculty


Dynamics of membrane domains; directed evolution of fluorescent proteins

BPHYS Student

Ivy Fitzgerald, PhD

Research interests

Our goal is to understand the processes that generate compartments of the secretory pathway, including transitional ER sites (also known as ER exit sites) and the cisternae of the Golgi apparatus. Self-organization models provide the conceptual framework. Specifically, we postulate that tER sites are generated together with early Golgi cisternae by an integrated self-organization pathway, and that early cisternae progressively mature into late cisternae.

For exploring these ideas, our main experimental system is a pair of budding yeasts. In Saccharomyces cerevisiae, Golgi cisternae are dispersed throughout the cytoplasm and the ER contains multiple small tER sites, whereas in Pichia pastoris, ordered Golgi stacks are located next to large, stable tER sites. These two yeasts have complementary advantages for testing specific hypotheses about the secretory pathway. We use a combination of genetics, molecular biology, 4D confocal microscopy, and electron tomography. This work is revealing evolutionarily conserved principles of cellular organization.

A second project in the lab involves optimizing fluorescent proteins, including the red fluorescent protein DsRed. Wild-type DsRed matures very slowly. We overcame this problem by using directed evolution to create the first rapidly maturing DsRed variants, one of which is marketed commercially as DsRed-Express. More recent work yielded a noncytotoxic variant called DsRed-Express2, as well as a far-red variant called E2-Crimson. These engineering efforts inspired a basic research project in which we clarified the pathway of DsRed chromophore formation. Current efforts are focused on creating improved monomeric green and red fluorescent proteins.

Selected publications

Day KJ, Casler JC, Glick BS. (2018). Budding yeast has a minimal endomembrane system. Dev Cell 44, 56–72. (Link)

Papanikou E, Day KJ, Austin J, Glick BS. (2015). COPI selectively drives maturation of the early Golgi. eLife 4, 13232. (PubMed)

Papanikou E, Glick BS. (2014). Golgi compartmentation and identity. Curr Opin Cell Biol. 29, 74-81. (PubMed)

Bharucha N, Liu Y, Papanikou E, McMahon C, Esaki M, Jeffrey PD, Hughson FM, Glick BS. (2013). Sec16 influences transitional ER sites by regulating rather than organizing COPII. Mol Biol Cell. 24, 3406-3419. (PubMed)

Day KJ, Staehelin LA, Glick BS. (2013). A three-stage model of Golgi structure and function. Histochem Cell Biol. 140, 239-249. (PubMed)