Tagging an organelle

In the early 1980s, cell biologists kept slamming into the same obstacle when they tried deploying antibodies to elucidate the working of the Golgi complex. True, use of antibodies to identify proteins (Bader et al., 1982; de Camilli et al., 1983a,b; Huttner et al., 1983; Weiss et al., 1984; Woodcock-Mitchell et al., 1982; Yen and Fields, 1981), localize cellular structures (Levine and Willard, 1981), and differentiate cell types (Schnitzer et al., 1981; Skene and Willard, 1981) was booming. The difficulty was crafting antibodies to target exclusively proteins from the Golgi complex, recalls Graham Warren (now at Yale University, New Haven, CT). Even the purest mixtures of Golgi membranes contained contaminants, such as shards of cell membrane, and stimulated production of antibodies that labeled non-Golgi structures. Warren and his colleagues Daniel Louvard and Hubert Reggio, all then at the European Molecular Biology Laboratory in Heidelberg, Germany, devised a technique for weeding out the unwanted antibodies.

To the “raw” antibody solution they added debris they had initially separated from the Golgi membranes. This junk was mainly plasma membranes and bits of endoplasmic reticulum. After letting the combination incubate, they again removed the membrane gunk—and in the process eliminated many of the unwanted antibodies (Louvard et al., 1982). The researchers then performed the step again with rat plasma, which sopped up antibodies against secretory proteins. Using immunofluorescence, the researchers showed that the leftover mixture labeled only the perinuclear region, where the Golgi complex forms. Meanwhile, cells tagged with the “raw” antibody concoction glowed all over. “This was a dramatic demonstration that you could make high-affinity antibodies to organelles,” says Warren. Cell biologists expressed their approval in the usual way, he says: “They asked us for samples.”

The researchers determined that the antibodies were recognizing one Golgi protein—though they weren't sure of its identity or location. Subsequent work revealed that it was mannosidase II, a key Golgi enzyme. Louvard and colleagues applied the same technique to uncover four markers for the endoplasmic reticulum. Their discovery helped researchers better understand the anatomy and activity of the Golgi complex. But it also sparked a controversy—over whether the complex forms spontaneously or requires a template—that hasn't abated today (Wells, 2001).