Worm Breeder's Gazette 16(5): 28 (February 1, 2001)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Using Caenorhabditis elegans as a model to study autophagy

Willisa Liou

Department of Anatomy, Chang Gung University, Taiwan. e-mail : liouw@mail.cgu.edu.tw

Autophagy is the bulk degradation of cytoplasmic components with the lysosomal enzymes. This physiological process can be upregulated by starvation and has been best studied in the liver. With the advent of molecular genetics, the autophagic pathway is now being dissected at the molecular level using yeast as a model system. Despite of exciting results, the use of yeast is not without its caveat for it is a single-cell organism and the data of which require prudent extrapolation to the mammalian cells in the light of complex physiological melieu of the multicellular organism. Furthermore, the fine structural features of autophagic vacuoles in yeast are, to a certain extent, different from those in the mammalian cells. For example, the sequestration apparatus of the nascent autophagic vacuoles, namely phagophore, found no counter part in the yeast.

By analogy to the ease of genetic manipulation and the complete genomic sequence now available in the yeast, I proposed another organism, the nematode Caenorhabditis elegans, as a model for the molecular dissection of the autophagic pathway.  In this study I employed ultrathin cryosectioning method and demonstrated that the autophagic vacuoles - in all its likeness to that of the mammalian cells - indeed are present in the intestinal cells of the C. elegans. Figures 1, 2 and 3 shows the characteristic nascent autophagic vacuoles. They are isolated pieces of cytoplasm circumscribed by whorl-like membranous structure, namely phagophore.  In an attempt to mark the autophagic vacuoles of later stages, i.e. degradative vacuoles, I then immunostained the ultrathin cryosections of the worms with antibodies against cathepsin D, a lysosomal enzyme. The result, shown in Figure 4, is somewhat surprising in that this hydrolytic enzyme is localized in the lumen of the gut in association with the bacteria being digested, instead of being intracellularly localized as in the case of human liver cells (Figure 5).

In conclusion, this study demonstrated for the first time the presence of autophagic vacuoles and the establishment of the ultracryomicrotomy technique in combination with immunoelectron microscopy in C. elegans. The significance of the extracellular localization of cathepsin D awaits further investigation.