Histology and Cell Biology Lab

Professor: Nobukazu ARAKI

Microscopy dates from the 17th century when Hooke and Malpighi employed simple lenses in the study of various structural features. Electron microscopes were first introduced in the field of microscopic anatomy in the middle of the 20th century. Utilizing this new instrument, cytological studies have clarified much of the structure of various subcellular elements. These revelations, combined with new knowledge from biochemistry and cell physiology, have led to a firmer basic understanding of many ongoing processes of the living cell. In this Department, various subcellular structures have been studied by electron microscopy to establish possible correlations between fine structure and function.

Research Activities.

The main research subject of the Department is the study of structure and function of cells and tissues by means of electron microscope and confocal laser microscope.

1. Electron microscopic study on the structure and function of the apical tubules in various absorbing epithelia.

We have discovered specific helical structure in the apical tubules of several absorbing epithelia (kidney proximal tubules, visceral yolk sacs and ductuli efferentes) by using a newly composed fixative for electron microscopy (J Electron Microsc 33: 292-293, 1984). This uniqe structure is thought to be commonly observed in the apical tubules of almost all absorbing epithelia, because a similar structure has also been found in other types of absorbing epithelia (Cell Tissue Res 244: 39-46, 1986, J Electron Microsc 39: 260-263, 1990). Our studies have revealed that the apical tubules are originated by budding off from the resorption vacuoles (endosomes) located in the apical cytoplasm, rather than being involved in the process of absorption (Cell Tissue Res 251: 511-521, 1988, Acta Histochem Cytochem 22:35-46, 1989). Our recent study by thick section and scanning electron microscopy further revealed that these tubules build up an extensive network in the apical cytoplasm of the yolk sac epithelial cell (Cell Tissue Res 278: 353-361, 1994) and kidney proximal tubule cells (Cell Tissue Res 288:317-325, 1997). Tubular networks of endosomes are now believed to represent the recycling endosomes (Eur J Cell Biol 74:41-48, 1997).

2. Electron microscopic study on the mosaic structure of the plasma membrane in various electrolyte-transporting epithelia.

A structural diversity of the plasma membrane has been described in a wide variety of cells. Such a diversity reflects chemical composition and molecular arrangement in the structure of the biological membrane. We have demonstrated a unique structural membrane differentiation in the cytoplasmic tubules of the lamprey chloride cells, kidney proximal tubule cells and intestinal absorbing cells which are engaged in electrolyte transport (J Cell Sci 56: 441-452, 1982, J Ultrastruct Res 85: 58-69, 1983, Cell Tissue Res 243: 461-468, 1986, J Electron Microsc 46: 93-95, 1997). This membrane differentiation consists of parallel arrays of small particles which wind helically on the membrane of the cytoplasmic tubules. These particles were thought to be the sites of enzyme activity, presumably Na-K-ATPase, related to the cells' overall function in electrolyte transport.

3. Studies on phagocytosis and pinocytosis in macrophages.

Our laboratory is also interested in various aspects of endocytosis in macrophages, including fluid-phase pinocytosis, phagocytosis and receptor-mediated endocytosis. Recently, we have identified a PI3kinase-dependent novel contractile activity in macrophages that mediates the closure of macropinosomes and phagosomes (J. Cell Biol 135:1249-1260, 1996). The contractile activity seems to be an actin-mediated mechanism that uses a mechanochemical myosin-like enzyme and actin-binding proteins. We are currently investigating the roles for myosins and actin-binding proteins in macrophage endocytosis using immunocytochemistry, confocal laser microscopy, electron microscopy, and video microscopic image analysis of living cells. The study of endocytosis in macrophages may reap practical benefits because of the crucial role of these cells as animal defense against microorganism and tumors.

Research Training

In this Department, the curriculum is arranged to give basic training to those who will be engaged in research in anatomy or teaching anatomy as well as to those who will be engaged in clinical medicine. The Department also offers an advanced course (lectures and laboratory exercise) of electron microscopy applied to cell biology and medicine to graduate students. The seminar is open from 5.00 to 7.00 p.m. every Monday throughout the year at the conference room. Original research results are presented every year at the annual meeting of the Japan Association of Anatomists or at the annual meeting of the Japan Society of Electron Microscopy.

Techniques Available

1. General techniques for transmission and scanning electron microscopy 2. Freeze fracture and replica techniques for electron microscopy 3. Rapid freeze and freeze substitution fixation techniques for electron microscopy 4. Ultrathin cryosection techniques for electron microscopy 5. Techniques for confocal laser microscopy and image analysis 6. Immunocytochemistry and enzyme cytochemistry