Recent genetic studies revealed crucial roles of JNK (c-jun N-terminal kinase) activation in cell death. However, the molecular mechanisms underlying JNK-mediated cell death are largely unknown. We present one of the JNK-mediated apoptotic mechanism is regulated by a ubiquitine-proteasome system.
The pars tuberalis has been generally understood as a simple forward elongation of the glandular pituitary that develops into an architecturally similar structure. In rats, it is also believed that the pars tuberalis completely encircles the infundibular stalk at the ventral portion of hypothalamus. Intact Wistar-Imamichi rats were used in the present study, and frontal and sagittal serial sections of the pituitary gland/brain complex were prepared. Serial sections were stained with hematoxylin-eosin and with antibodies to LH-RH, S-100 protein or LH-RH receptor. Electron microscopic analyses were also conducted. The anatomical end of the epithelial structure of the pars tuberalis was observed at approximately 1 mm behind the optic chiasm. At this point, both the capillaries and the pars tuberalis spread and interdigitated over the median eminence. The pars tuberalis did not, however, completely encircle the pituitary stalk. Electron microscopic observations revealed some profiles of neuroendocrine nerve elements that were also present between the agranular cells of the pars tuberalis. A few LH-RH-positive nerve fibers were initially found just behind the optic chiasm, while the number of LH-RH-positive reactions increased around the capillary vessels. These reactions then decreased significantly and were sparsely distributed both in the diencephalon and in the area near the pituitary stalk where the two separated. LH-RH receptors were observed on S-100 protein-positive cells in the pars tuberalis. The present observations show the significance of the pars tuberalis and its relationship between the anterior pituitary gland and the hypothalamus as organs that possibly form another collaborating mechanism for the regulation of hormone secretion of the anterior pituitary gland.
To investigate the properties of endocytosis of the epithelial cells in the intermediate portion of the endolymphatic sac (ES), we infused cationized ferritin (CF), microperoxidase (MPO), and horseradish peroxidase (HRP), as endocytosis tracers, into the endolymphatic space of the ES. Thirty minutes after infusion, the tissues were fixed and the distributions of HRP, MOP and CF were observed by transmission electron microscopy. The results at 30 min after tracer infusion were as follows. Concerning CF, endocytosis showed different activity depending on the area of the ES. In one area, CF was hardly observed within the epithelial cells, while in another area, it was observed within the epithelial cells. The CF-loaded vesicles were mainly coated vesicles. These results suggested that infusion of the artificial endolymphatic sac endolymph with CF may not stimulate the whole signal system of the ES. Concerning HRP, it bound to the apical membrane and was observed in the vesicles and the sorting endosomes. The diameters of these vesicles were of two types: one had a smaller diameter (less than 200 nm), while the other had a larger diameter (over 200 nm) and originated from macropinocytosis. Concerning MPO, it was much less observed in the vesicles than HRP. We discuss the different activities of endocytosis among these tracers, and suggest that a large molecular weight substance, i.e. HRP, might stimulate the fluid-phase endocytosis and/or adsorptive pinocytosis.
ZAKI-4 is a thyroid hormone-responsive gene which encodes two isoforms, ZAKI-4 α and β, both of which belong to a family of proteins that inhibit calcineurin activity. Calcineurin is a calcium/calmodulin-dependent phosphatase and is known to play crucial roles in brain development and function. Using in situ hybridization and immunohistochemistry, the present study aimed to demonstrate regional distribution of ZAKI-4 mRNAs and proteins in the mouse brain. Both ZAKI-4 mRNA isoforms showed similar spatial expression in the brain. Although they were widely expressed throughout the entire brain, the highest expression was observed in neurons in olfactory bulb, hippocampus and cerebellum. Consistent with the expression of ZAKI-4 mRNA isoforms, ZAKI-4 proteins were widely, but not evenly, distributed in the brain; the most intense immunoreactivity was found in the olfactory bulb, cerebral neocortex, hippocampus and cerebellum. As for the subcellular localization, ZAKI-4 immunoreactivity was confined to neuronal somata, with higher expression in the soma than in dendrites, and was not detected in glia. The double immunostaining of ZAKI-4 proteins and calcineurin revealed that they were co-localized in the periphery of the soma and dendrites of neurons. These results indicate that ZAKI-4 proteins are localized in the area where they are able to inhibit calcineurin activity.
Calcitonin (CT) enhances calcium excretion by inhibition of renal tubular calcium resorption, but the precise functions of CT remain poorly understood. We carried out in situ hybridization (ISH) for the calcitonin receptor (CTR) to evaluate the site that expresses CTR mRNA in the rat kidney. The intense signal was observed in the straight tubule of the cortex and the outer stripe of the outer medulla, but not in the inner medulla. A less intense signal was observed in the convoluted and collecting tubules, glomeruli, and renal tubule of the inner stripe of the outer medulla. Although CTR expression in the proximal straight tubule was suggested based on the physiological evidence, CTR localization was not proven. We demonstrated CTR expression in the proximal straight tubule, in addition to the distal straight tubule reported in previous studies using autoradiography. It was not possible to distinguish two CTR isoforms (C1a and C1b) by ISH, because a new probe recognized the common sequence of these isoforms. As only C1a was confirmed in kidney by RT-PCR, it seems reasonably certain that the ISH signal is of the C1a type. This new CTR probe can be an important tool for analyzing CTR expression in various tissues.
The present study investigated the localization of inducible NOS (iNOS), heat shock protein (HSP) 27, HSP60 and HSP70 in 25 cases of pleomorphic adenoma. Immunohistochemical staining for iNOS and HSPs was widely observed in neoplastic epithelia. In the stromal tissues, the cells showed both positive and negative staining with iNOS or HSPs. Staining for HSP27 was limited to the cytoplasm, and was more intense for HSP60 and 70. Both iNOS and HSPs were presumed to be localized mainly in myoepithelial cells in pleomorphic adenoma, and their localizations were mostly overlapped. These results indicated that iNOS and HSPs may be involved, at least in part, in the development of pleomorphic adenoma.