Although osteocytes are the most abundant cells in bone, little is known about their function, and no specific marker protein for osteocytes has been described. Dentin matrix protein 1 (DMP1) is an acidic phosphoprotein expressed in tooth organ and bone. Our previous work showed that in the chicken, which is not capable of forming tooth, DMP1 messenger RNA (mRNA) is highly expressed in bone by Northern blot analysis. To clarify the significance of DMP1 expression in bone, the expression of DMP1 mRNA and its protein was examined in the chicken and rat. In the chicken, DMP1 mRNA was detected only in bone tissues and was localized in osteocytes and preosteocytes but not in osteoblasts. Similarly, in the rat, DMP1 mRNA was predominantly expressed in osteocytes and preosteocytes in bone matrix but not in osteoblasts located at the bone surface. Antiserum was raised against the peptide from rat DMP1, and the localization of DMP1 was examined by immunohistochemistry. In the development of bone, DMP1 was first detected in newly formed bone matrix after osteoblastic cells had been embedded within it. After the appearance of typical osteocytes, DMP1 was localized in the pericellular bone matrix of osteocytes, including their processes. These data show that DMP1 is a bone matrix protein specifically expressed in osteocytes and preosteocytes and suggest that DMP1 plays a role in bone homeostasis because of its high calcium ion-binding capacity.

Streptococcus pyogenes (group A streptococcus (GAS)) is a pathogen that invades non-phagocytic host cells, and causes a variety of acute infections such as pharyngitis. Our group previously reported that intracellular GAS is effectively degraded by the host-cell autophagic machinery, and that a cholesterol-dependent cytolysin, streptolysin O (SLO), is associated with bacterial escape from endosomes in epithelial cells. However, the details of both the intracellular behavior of GAS and the process leading to its autophagic degradation remain unknown. In this study, we found that two host small G proteins, Rab5 and Rab7, were associated with the pathway of autophagosome formation and the fate of intracellular GAS. Rab5 was involved in bacterial invasion and endosome fusion. Rab7 was clearly multifunctional, with roles in bacterial invasion, endosome maturation, and autophagosome formation. In addition, this study showed that the bacterial cytolysin SLO supported the escape of GAS into the cytoplasm from endosomes, and surprisingly, a SLOdeficient mutant of GAS was viable longer than the wild-type strain although it failed to escape the endosomes. This intracellular behavior of GAS is unique and distinct from that of other types of bacterial invaders. Our results provide a new picture of GAS infection and host-cell responses in epithelial cells. Streptococcus pyogenes (group A streptococcus; GAS)2 is the causative pathogen for a diverse collection of human diseases, such as pharyngitis, bacteremia, and necrotizing fasciitis (1). GAS strains produce a variety of pathogenic factors such as streptolysin O (SLO), superantigens, and DNase (2-4). Invasive GAS diseases occur in ϳ1/1000 cases, with associated mortality of 25% (5).Autophagy is defined as "self-eating," bulk degradation system for cytoplasmic components. During autophagy, double membrane structures are formed in the cytoplasm, in which cytoplasmic organelles and proteins are sequestered. These structures, called autophagosomes, subsequently fuse with lysosomes to degrade the components within them. This system is important for the physiological turnover of cytoplasmic components, and is involved in a number of clinical conditions and diseases (6, 7). Recently, we and others showed that GAS is captured and degraded by autophagy, not by the endosomelysosome system (8, 9). Some species of bacteria invade host non-phagocytic cells, such as epithelial cells, and are largely degraded by the endocytosis pathway (10 -12). However, some bacteria, including Listeria monocytogenes, Shigella flexneri, Mycobacterium tuberculosis, and Salmonella typhimurium, cannot be eliminated by endosomes, and replicate within the cytoplasm (13-15). The autophagic machinery is thought to act to remove these bacteria. However, it is still unclear under what circumstances the intracellular bacteria are sequestered by autophagosomes and what events in the infected cells lead to the degradation of bacteria by autophagy.A cholesterol-dependent cytolysin of GAS, SLO, is a homolog of listerio...

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It is generally accepted that living jawless vertebrates (lampreys and hagfishes) lack the capability of mounting an adaptive immune response. At the same time, however, there are reports describing histological evidence for the presence in agnathan tissues of lymphocytes, the key players in adaptive immunity. The question therefore arises whether the cells identified morphologically as lymphocytes are true lymphocytes in terms of their genetic developmental program. In this study, evidence is provided that the lampreys express a member of the purine box 1 (PU.1)/spleen focus-forming virus integration B (Spi-B) gene family known to be critically and specifically involved in the differentiation of lymphocytes in jawed vertebrates. The lamprey gene is expressed in the lymphocyte-like cells of the digestive tract and inexplicably also in the ovary.