On a daily basis, multitudes of molecules enter each cell in our body. These can be nutrients or signal molecules or pathogenic microorganisms. An organelle in the cell directs these molecules to other stations for further processing. This organelle is called the endosome. If the pathways by which this sorting occurs fails at any stage, several diseases such as neurodegenerative diseases and certain cancers can occur. Thus, a better understanding of the steps in these pathways is of utmost importance.
In a recent study published in Communications Biology, a group of scientists from Japan and Austria, led by Prof Jiro Toshima from the Tokyo University of Science, reports a new finding regarding the maintenance and functioning of the endosome.
Conventional knowledge is that two processes are necessary for the upkeep of endosomes: a) sacs of molecules constantly form at the cell membrane, are transported to the endosome, and fuse into it; b) protein-containing vesicles transported from the Golgi (another cell organelle) fuse with the endosome.
The researchers of this study claim that this is not the case.
They introduce genetic mutations and drugs into yeast cells to inhibit each of these transport processes at a time. When transport from the Golgi does not occur, a protein essential to the upkeep of the endosome, Rab5, is not activated, and endosome formation is affected. When cell transport from the membrane is inhibited, there is no effect on the endosome. Thus, essentially, transport from the Golgi is necessary and that from the cell membrane is dispensable, or not as crucial. "Our results provide a different view of endosome formation and identify the Golgi as critical for the optimal maintenance and functioning of endosomes," Prof Toshima says. This study clarifies only a fraction of the molecule-sorting pathway in cells. But, this is certainly one giant step in the research in this field. Perhaps, the insights from this study will soon appear on the pages of cell biology textbooks.
About the Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.
With a mission of "Creating science and technology for the harmonious development of nature, human beings, and society", TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.
About Professor Jiro Toshima from the Tokyo University of Science
Dr Jiro Toshima is at present a Professor with the Department of Biological Science and Technology at the Tokyo University of Science, Japan. Having begun research in cell biology and related fields in 1999, he has co-authored over 41 publications, and is the lead author of the present paper. From September 2017 to August 2019, he served as a Councillor in the Japanese Biochemical Society.
This research was supported by grants to Junko Y. Toshima (JSPS KAKENHI Grant #26440067, the Takeda Science Foundation, the Novartis Foundation, Japan) and to Jiro Toshima (JSPS KAKENHI Grant #19K06571, the Life Science Foundation of Japan, the Uehara Memorial Foundation and the Takeda Science Foundation).