The COPI vesicle transport system has been shown to function in most cells as an retrograde transport mechanism that returns golgi-modified proteins back to the ER where they function in cell signaling and metabolism [29, 30] . However, the COPI system has also been shown to function in anterograde transport in some secretory cells where it was found to be required for exocytosis of specific proteins [34] . The COPI vesicle transport system consists of seven coatomer subunits (alpha, beta, beta', gamma, delta, epsilon, zeta), which function as structural components that promote vesicle formation, a G protein that facilitates coatomer assembly and membrane budding (Arf), guanine nucleotide exchange factors (GEFs) that activate Arf proteins and thereby initiate coatomer assembly, and GTPase activating proteins (ArfGAPs) that stimulate GTP hydrolysis in Arf proteins and induce coatomer disassembly, which is required for vesicle membrane fusion. Based on our finding that loss of alpha-COPI expression in midgut epithelial cells of unfed mosquitoes disrupts RER whorl formation, without decreasing the total amount of RER membrane in cells ( Figure 6C and 6D) , we propose that COPI coatomer proteins directly contribute to whorl formation through subunit assembly. Further experiments are needed to directly test this idea, for example, by using immunogold EM analysis to determine if COPI coatomer proteins are tightly associated with RER whorls, and if so, which coatomer subunits are colocalized.