Presentation Information
[SS17-06]Quantitative Insights into Intra-Golgi Secretory Transport and Cisternal Organization via Fluorescence Microscopy
*Lei Lu1, Hieng Chiong Tie1, Haiyun Wang1, Divyanshu Mahajan1, Yuen In Lam1, Yuguang Mu1 (1. School of Biological Sciences, Nanyang Technological University (Singapore))
Keywords:
Golgi,Fluorescence Imaging,Intra-Golgi Transport,Cisternal Progression Model,Stable Compartment Model
The Golgi apparatus is essential for membrane trafficking and post-translational modifications of secretory cargos in eukaryotic cells. Despite its significance, the molecular organization and cellular mechanisms of the Golgi remain poorly understood. To address these gaps, we developed three innovative imaging tools that enable quantitative analysis of cisternal localization and organization in nocodazole-induced Golgi ministacks using fluorescence microscopy (Tie et al., 2018; Tie et al., 2016; Tie et al., 2022).
Using these tools, we investigated intra-Golgi secretory transport, a subject of long-standing debate in membrane trafficking. Two competing models have been proposed: the stable compartment model, which posits that the Golgi stack is a stable entity with transport mediated by vesicular shuttling of cargos, and the cisternal progression model, which suggests that Golgi cisternae dynamically mature, carrying cargos as they progress. The cisternal progression model further posits uniform intra-Golgi transport velocities dictated by maturation and emphasizes the necessity of COPI-mediated retrograde transport for Golgi organization. While the cisternal progression model is currently more widely accepted, our findings challenge its core assumptions.
We observed that intra-Golgi transport velocities decrease as secretory cargos transit from the cis to the trans-side of the Golgi stack, with distinct velocities even for cargos within the same cisterna. Additionally, Golgi exit kinetics, measured by the Golgi residence time, varied significantly among cargos. Notably, truncation of the luminal domain of Tac (interleukin 2 receptor alpha subunit), a transmembrane secretory cargo lacking intra-Golgi recycling signals, extended its Golgi residence time from 16 minutes to a notable 3.4 hours. Moreover, inhibition of COPI-mediated retrograde transport with brefeldin A revealed that nocodazole-induced Golgi ministacks remained intact for 30–60 minutes, contradicting the cisternal progression model’s reliance on COPI for maintaining Golgi stacking.
These findings challenge the classical cisternal progression model and instead support the stable compartment model.
References
Tie, H.C., A. Ludwig, S. Sandin, and L. Lu. 2018. The spatial separation of processing and transport functions to the interior and periphery of the Golgi stack. Elife. 7.
Tie, H.C., D. Mahajan, B. Chen, L. Cheng, A.M. VanDongen, and L. Lu. 2016. A novel imaging method for quantitative Golgi localization reveals differential intra-Golgi trafficking of secretory cargoes. Mol Biol Cell. 27:848-861.
Tie, H.C., D. Mahajan, and L. Lu. 2022. Visualizing intra-Golgi localization and transport by side-averaging Golgi ministacks. J Cell Biol. 221.
Using these tools, we investigated intra-Golgi secretory transport, a subject of long-standing debate in membrane trafficking. Two competing models have been proposed: the stable compartment model, which posits that the Golgi stack is a stable entity with transport mediated by vesicular shuttling of cargos, and the cisternal progression model, which suggests that Golgi cisternae dynamically mature, carrying cargos as they progress. The cisternal progression model further posits uniform intra-Golgi transport velocities dictated by maturation and emphasizes the necessity of COPI-mediated retrograde transport for Golgi organization. While the cisternal progression model is currently more widely accepted, our findings challenge its core assumptions.
We observed that intra-Golgi transport velocities decrease as secretory cargos transit from the cis to the trans-side of the Golgi stack, with distinct velocities even for cargos within the same cisterna. Additionally, Golgi exit kinetics, measured by the Golgi residence time, varied significantly among cargos. Notably, truncation of the luminal domain of Tac (interleukin 2 receptor alpha subunit), a transmembrane secretory cargo lacking intra-Golgi recycling signals, extended its Golgi residence time from 16 minutes to a notable 3.4 hours. Moreover, inhibition of COPI-mediated retrograde transport with brefeldin A revealed that nocodazole-induced Golgi ministacks remained intact for 30–60 minutes, contradicting the cisternal progression model’s reliance on COPI for maintaining Golgi stacking.
These findings challenge the classical cisternal progression model and instead support the stable compartment model.
References
Tie, H.C., A. Ludwig, S. Sandin, and L. Lu. 2018. The spatial separation of processing and transport functions to the interior and periphery of the Golgi stack. Elife. 7.
Tie, H.C., D. Mahajan, B. Chen, L. Cheng, A.M. VanDongen, and L. Lu. 2016. A novel imaging method for quantitative Golgi localization reveals differential intra-Golgi trafficking of secretory cargoes. Mol Biol Cell. 27:848-861.
Tie, H.C., D. Mahajan, and L. Lu. 2022. Visualizing intra-Golgi localization and transport by side-averaging Golgi ministacks. J Cell Biol. 221.