Date of Award

Spring 1-1-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Gia Voeltz

Second Advisor

Greg Odorizzi

Third Advisor

Tin Tin Su

Fourth Advisor

Amy Palmer

Fifth Advisor

Mark Winey

Abstract

The Endoplasmic Reticulum (ER) forms a dynamic network that spans throughout the cell. In addition to the well characterized roles in lipid synthesis, protein folding, and calcium handling, the ER coordinates important functions at stable membrane contact sites formed with other organelles. Recent work from the lab demonstrated that ER tubules circumscribe mitochondrial constrictions and define the position of mitochondrial fission. We predicted that mechanisms of membrane fission are conserved between various organelles. Here we hypothesized and tested whether ER contacts define the timing and the position of endosome fission. Endocytic cargo and Rab GTPases are segregated to distinct domains of an endosome that maintain their identity until they undergo fission to traffic cargo. It is not fully understood how segregation of cargo or Rab proteins is maintained along the continuous endosomal membrane, or what machinery is required for fission. Endosomes form contact sites with the ER that are maintained during trafficking. We show that stable contacts form between the ER and endosomes at constricted sorting domains and that free diffusion of cargo is limited at these positions. We demonstrate that the site of constriction and fission for early and late endosomes is spatially and temporally linked to contact sites with the ER. Lastly, we show that altering ER structure and dynamics reduces the efficiency of endosome fission. Together these data reveal a surprising role for ER contact in defining the timing and position of endosome fission.

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