Microautophagy Recycles the Cell Nucleus

Researchers using a yeast model have found evidence that cells are able to break down and recycle parts of the nucleus, a process they termed piecemeal microautophagy of the nucleus (PMN). Their findings were reported in the January 2003 issue of Molecular Biology of the Cell.

It had long been recognized that cells frequently recycle various cell parts through a process known as autophagy, but it had been thought that the nucleus was inviolable. In the current report, investigators from the University of Rochester (New York, USA) found that in the yeast Sacchaaromyces cerevisiae nucleus-vacuole (NV) junctions were formed through specific interactions between Vac8p on the vacuole membrane and Nvj1p in the nuclear envelope. The NV junctions promoted PMN. During PMN, teardrop-like blebs were pinched from the nucleus, released into the vacuole lumen, and degraded by soluble hydrolases.

PMN occurred in rapidly dividing cells but was induced to higher levels by carbon and nitrogen starvation and was under the control of the Tor kinase nutrient-sensing pathway. Transmission electron microscopy revealed that portions of the granular nucleolus were often sequestered into PMN structures.

"In human society, the business of collecting and recycling garbage is not a very glamorous enterprise, but in the less prestige-oriented world of cells, it is invaluable,” explained senior author Dr. David Goldfarb, professor of biology at the University of Rochester. "We now know just how critical this process is, since a unique and elegant autophagic mechanism evolved to allow the piecemeal degradation of an otherwise essential organelle.”



Related Links:
University of Rochester