PhD Exit Seminar – Alex Sin (Harrison lab)

PhD Exit Seminar

Tuesday December 13^th, 2:10 pm – Room SW 403, University of Toronto at Scarborough

Alex Sin (Harrison lab)

“Growth of the Mammalian Golgi Apparatus During Interphase“

Abstract

The Golgi apparatus is an important processing station in all eukaryotic cells, where proteins and lipids are glycosylated and sent to their final destinations. For this reason, it is expected that the Golgi apparatus must be duplicated during the cell cycle to ensure subsequent daughter cells have sufficient Golgi content following mitosis. In mammalian systems, extensive research has been focused on the Golgi apparatus’ inheritance process during mitosis, yet research investigating its growth during interphase has been limited. Challenges in monitoring mammalian Golgi growth have been attributed to its elaborate ribbon structure, thus any theories of its growth have mostly been based on observations in lower eukaryotes. The aims of my thesis were to definitively characterize the growth of the mammalian Golgi apparatus during interphase, and elucidate the underlying mechanisms regulating this process. To circumvent the challenges associated with the intricacies of the mammalian Golgi structure, I employed a combination of flow cytometry, fluorescent microscopy and transmission electron microscopy to measure different aspects of its growth. Here I demonstrate the growth of the mammalian Golgi apparatus in its protein content and volume during interphase. Through ultrastructural analyses, physical growth of the mammalian Golgi apparatus was revealed to occur by cisternal elongation of the individual Golgi stacks contrary to previous speculations. By examining the timing and regulation of Golgi growth, I establish that Golgi growth starts after passage through the cell growth checkpoint at late G1 phase and continues growing in a manner highly correlated with cell size growth. Finally, by identifying S6 kinase 1 as a major player in Golgi growth, I reveal the coordination between cell size and Golgi growth via activation of the protein synthesis machinery in early interphase.