The coatomer is a cytosolic protein complex that binds to dilysine motifs and reversibly associates with Golgi non-clathrin-coated vesicles, which further mediate biosynthetic protein transport from the ER, via the Golgi up to the trans Golgi network. Coatomer complex is required for budding from Golgi membranes, and is essential for the retrograde Golgi-to-ER transport of dilysine-tagged proteins. Required for limiting lipid storage in lipid droplets. Involved in the expansion of luminal extracellular matrices and apical membrane during tubulogenesis. Required in the tracheal epithelium for luminal protein secretion and diametric tube growth. In salivary glands, required for deposition of O-glycans and luminal extracellular matrix assembly. Required for epidermal morphogenesis and cuticle development. Oligomeric complex that consists of at least the alpha, beta, beta', gamma, delta, epsilon and zeta subunits. The coatomer is cytoplasmic or polymerized on the cytoplasmic side of the Golgi, as well as on the vesicles/buds originating from it. Expressed in ovary, testis, testis tip, young spermatocytes, germ cells and follicle cells. Up-regulated expression within centrally to posteriorly located germarial cysts and in migrating follicle cells. Widespread expression in imaginal disks including eye-antennal disk, wing disk, third leg and haltere disk. Expressed during spermatogenesis and at later stages of oogenesis. During embryonic and larval development, expressed ubiquitously. Starting at stage 10 embryos and lasting until the end of embryonic development, strongly expressed in the salivary glands and in cells of the presumptive proventriculus. Maternal expression abundant in early embryos. Zygotic expression commences in the epidermis and salivary glands from stage 11, initiates in the trachea at stage 13, and at early stage 15 is also detected in the foregut and hindgut tubes. Narrow tracheal tubes and thin salivary glands with reduced tube diameter and impaired tube elongation. Fails to complete dorsal closure. Fails to efficiently secrete luminal components and assemble the luminal chitinous matrix during tracheal tube expansion. In salivary glands, fails in the luminal deposition and assembly of a distinct, transient intraluminal matrix. Disrupted endoplasmic reticulum and Golgi in embryos. Null mutants die late in embryogenesis with a poorly differentiated cuticle and denticle. Defects in cell rearrangements, in branch elongation, in tube dilation and tube fusion. Belongs to the COPG family.