MITOTIC GOLGI CLUSTERS ARE NOT TUBULAR ENDOSOMES

HeLa cells were incubated with 15 nm BSA-gold for 1 or 2 hours to mark the endocytic pathway and mitotic cells were then isolated by shake-o ff. Thin, frozen sections were labelled with antibodies against two re sident Golgi markers, beta-(1,4)-galactosyltransferase and N-acetylglu cosaminyltransferase I. Detection of the latter was aided by the use o f a HeLa cell line stably expressing a myc-tagged version of the endog enous protein. The secondary antibodies were coupled to either 5 or 10 nm gold so that the distribution of each of the three markers could b e followed. Qualitative and quantitative studies showed that there wer e two populations of clusters, those described by us earlier and terme d Golgi clusters (Lucocq et al. (1987) J. Cell Biol. 104, 865-874), co ntaining either or both Golgi markers, and clusters of tubular endosom es containing BSA-gold. There was very little overlap showing that Gol gi clusters cannot be tubular endosomes as concluded by Tooze and Holl inshead (1992) Eur. J. Cell Biol. 58, 228-242.