The delivery of mannose 6-phosphate receptors carrying lysosomal hydrolases from 
the trans-Golgi network (TGN) to the endosomal system is mediated by selective 
incorporation of the receptor-hydrolase complexes into vesicular transport 
carriers (TCs) that are coated with clathrin and the adaptor proteins, GGA and 
AP-1. Previous electron microscopy (EM) and biochemical studies have shown that 
these TCs consist of spherical coated vesicles with a diameter of 60-100 nm. The 
use of fluorescent live cell imaging, however, has revealed that at least some 
of this transport relies on a subset of apparently larger and highly 
pleiomorphic carriers that detach from the TGN and translocate toward the 
peripheral cytoplasm until they meet with distally located endosomes. The 
ultrastructure of such long-range TCs has remained obscure because of the 
inability to examine by conventional EM the morphological details of rapidly 
moving organelles. The recent development of correlative light-EM has now 
allowed us to obtain ultrastructural 'snapshots' of these TCs immediately after 
their formation from the TGN in live cells. This approach has revealed that such 
carriers range from typical 60- to 100-nm clathrin-coated vesicles to larger, 
convoluted tubular-vesicular structures displaying several coated buds. We 
propose that this subset of TCs serve as vehicles for long-range distribution of 
biosynthetic or recycling cargo from the TGN to the peripheral endosomes.