Yoichiro Takashima

Early oogenesis in the ascidian Ciona savignyi

Summary Morphology of the germinal epithelium and the early follicular oocyte in the ascidian Ciona savignyi as examined by electron microscopy. The oogenetic part of the germinal epithelium contains oocytes at two different stages and the dark and clear cells. The smaller oocyte contains synaptonemal complexes. The larger oocyte in the initial phase of growth has a conspicuous nucleolus, electron-dense materials and some mitochondria close to the nuclear envelope. The nucleus of the larger oocyte is round and has the smooth contour. The dark cell contains a relatively large nucleus and is sometimes connected to each other by an intercellular bridge. Therefore, the dark cell, which has been suggested to be the progenitor cell of two kinds of accessory cells, may be also the oogonium. The early follicular oocyte just after migration from the germinal epithelium retains most of cytological features similar to those of the larger oocyte. However, the nuclear contour of the early follicular oocyte is uneven. ...

Redistribution and fate of colchicine-induced alkaline phosphatase in rat hepatocytes: possible formation of autophagosomes whose membrane is derived from excess plasma membrane.

The redistribution and fate of colchicine-induced alkaline phosphatase (ALPase) in rat hepatocytes were investigated by electron microscopic enzyme cytochemistry and biochemistry. ALPase activity markedly increased in rat hepatocytes after colchicine treatment (2.0 mg/kg body weight, intraperitoneal injection). At 20–24 h after colchicine treatment, the liver showed the highest activity of ALPase. Thereafter, ALPase activity decreased and returned to normal levels at 48 h. In normal hepatocytes from control rats, ALPase activity was seen only on the bile canalicular membrane. However, at 20–24 h after colchicine treatment, colchicine-induced ALPase was redistributed in the sinusoidal and lateral (basolateral) membranes as well as in the bile canalicular membrane. At 30–36 h after colchicine treatment, ALPase activity on the basolateral membrane gradually decreased. In contrast, ALPase in the bile canalicular membrane increased along with the enlargement of bile canaliculi, suggesting that ALPase in the basolateral membrane had been transported to the bile canalicular membrane. Furthermore, ALPase-positive vesicles, cisternae and autophagosome-like structures were frequently seen in the cytoplasm. ALPase was also positive in some lysosomal membranes. ALPase in hepatocytes at 48 h after colchicine treatment returned to almost the same location as in control hepatocytes. Altogether, it is suggested that excessively induced ALPase is at least partially retrieved by invagination of the bile canalicular membrane and then transported to lysosomes for degradation. In addition, this study indicates that excess plasma membrane might be a possible origin of autophagosomal membrane.

Cytochemical demonstration of NPPase activity for detecting proton-translocating ATPase of Golgi complex in rat pancreatic acinar cells.

SummaryAn attempt at cytochemical demonstration of acidification proton-translocating ATPase (H+-ATPase) of Golgi complex in rat pancreatic acinar cells has been made by using p-nitrophenylphosphatase (NPPase) cytochemistry which is used for detecting of Na+-K+-ATPase (Mayahara et al. 1980) and gastric H+-K+-ATPase (Fujimoto et al. 1986). K+-independent NPPase activity was observed on the membrane of the trans cisternae of Golgi complex, but not inside of cisternae. The localization of NPPase activity is different from that of acid phosphatase activity where reaction products were seen on the inside of the trans Golgi cisternae. Since this activity was insensitive to vanadate, ouabain and independent of potassium ions, it was distinct from plasma membranous ATPases such as Na+-K+-ATPase and Ca2+-ATPase. The K+-independent NPPase activity was diminished by the inhibitors of H+-ATPase such as N-ethylmaleimide (NEM) and 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS). The NPPase reaction products were also seen on the membranes of other acidic organelles, i.e., lysosomes, endosomes, autophagosomes and coated vesicles. These results suggest that NPPase activity on the membrane of the Golgi complex and other acidic organelles corresponds with H+-ATPase which plays a role in acidification.

The shape and distribution of lysosomes and endocytosis in the ciliary epithelial cells of rats.

The shape and distribution of lysosomes in the ciliary epithelium of rat eyes were examined by electron microscopy combined with acid phosphatase (ACPase) cytochemistry and three-dimensional observation of 2 μm-thick sections. ACPase activity was cytochemically localized in lysosomes and trans Golgi cisternae in the non-pigmented epithelial (NPE) and pigmented epithelial (PE) cells. In NPE cells, it was shown three-dimensionally, that most lysosomes had an elongate form, up to 5 μm in length, and a diameter of 70–100 nm. These elongate lysosomes (nematolysosomes) were predominantly located in the basal region of the cells. In contrast, PE cells had spherical lysosomes distributed at random throughout the cytoplasm. However, no nematolysosomes were seen in the PE cells. When the isolated ciliary processes were incubated in a medium containing horseradish peroxidase (HRP), HRP was incorporated into the nematolysosome-like structures by pinocytosis from the basal surface of the NPE cells. These findings suggest that nematolysosomes are associated with the pinocytotic activity of NPE cells. The pinocytosis-nematolysosomal route may be involved in the uptake and degradation of macromolecules from the aqueous humor in the posterior chamber.