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Mol. indicate that intact COG complexes are required to maintain Golgi dynamics and its associated functions. According to the current CDG nomenclature, this newly identified deficiency is usually designated CDG-IIj. INTRODUCTION The Golgi apparatus is an important relay station in the secretory pathway as it plays a pivotal role in targeting proteins and lipids to distinct post-Golgi compartments (1). During transit through the Golgi apparatus, most of the newly synthesized secretory and membrane-bound proteins undergo major modifications, mainly involving different types of glycosylation. One of these, polarity (3). A tightly regulated organization of transport is required in order to mediate cargo transit as well as to maintain the organization. The exact mechanism of this transit is still not clarified, though it will most likely be a combination of the vesicular transport model, which implicates fixed cisternae with vesicles transporting cargo forward and recycling escaped proteins to earlier cisternae or the ER (4C7) and the cisternal maturation model. In the latter model, the cisternae mature towards the gene combined with a deletion around the maternal allele. Experiments performed on this patient’s fibroblasts yielded comparable defects albeit less severe as found in the cells of the previously described COG-deficient patients. Moreover, we present an updated overview of the different mutations identified thus far in which we attempt to correlate for the first time the respective clinical phenotypes with the severity in glycosylation and trafficking defects as well as with the Golgi integrity using Cyanidin chloride transmission electron microscopy (TEM). Our analysis underscores the high importance of an intact COG complex in both intra-Golgi trafficking and the maintenance of the normal morphology of the Golgi apparatus. Furthermore, we provide novel insights in the steady-state localization of both full and partial complexes with implications around the action mechanism of the complex. With this study, the number of patients harbouring mutations in individual COG genes rises to ten, which is about one-third of the total number of CDG-II cases in which a mutation has been identified making mutations one of the Cyanidin chloride Cyanidin chloride most frequent causes of CDG-II. Furthermore, given the insights that the different individual studies have generated on COG complex formation and functioning, we are now at a point where a comparison of all mutant subunits along different criteria reveals more specific or even as yet unknown functions of not only the full complex, but also of different subunits and subcomplexes. RESULTS Genetic and molecular analysis of COG4 The identification of several CDG type II patients harbouring mutations in individual subunits of the octameric COG complex fostered a strong interest in the functional role this Golgi tethering complex plays in the glycosylation process. By direct sequencing of the genes in a cohort of unsolved CDG-II patients, we identified a novel patient carrying a seemingly homozygous C>T point mutation at position 2185 in the genomic DNA encoding the gene (Fig.?1A). The mutation was not found after sequencing of over BMP4 100 alleles of a randomly chosen European control population. At the protein level, this mutation converts a highly conserved arginine 729 (Fig.?1B) into a tryptophan residue (p.R729W). Open in a separate window Physique?1. Genetic and molecular characterization of the described COG4 patient. (A) Sequencing revealed a heterozygous C>T missense mutation in the patient and the absence of this mutation in the mother. The fluorescence hybridization (FISH) image shows the deletion of fosmid G24P85580E2 (red) around the Cyanidin chloride maternal allele, whereas the control subtelomeric 16q fosmid (green) shows a normal signal. A schematic representation of the mutations present in the patient is usually given, the green and red asterisk around the maternal allele indicate, respectively, the last heterozygous SNP and the first hemizygous SNP in the patient, the black asterisk around the paternal allele indicates the position of the missense mutation, green regions indicate genes (>?>: sense/