Cytoplasmic dense bodies

The molecular mechanisms that couple the contractile filaments to the dense bodies are not established. Dense bodies contain the actin-cross-linking protein, a-actinin, as do the Z-lines of skeletal muscle. Dense bodies also contain actin and probably calponin, although it is currently unclear whether the a and y ( smooth muscle ) isoforms of actin (See Section 4.2) are both present in dense bodies or only the p non-muscle isoform (Small 1995, North et al 1994a, 1994b, Mabuchi et d 1996). Ultras-tructural and biochemical data obtained by Mabuchi et al (1997) suggests that one function of calponin may be to couple actin filaments and intermediate filaments at dense bodies. 

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Thybeig, J., Friberg, U. Ultrastructure and phosphatase activity of matrix vesicles and cytoplasmic dense bodies in the epiphyseal plate. J. Ultrastruct. Res. 33, 554 (1970)... 

Desmin is a cytoplasmic IFP that is characteristically found in muscle cells and in the neoplasms associated with them. In smooth muscle cells, it is seen with cytoplasmic dense bodies and subplasmalemmal dense plaques in striated muscle, desmin filaments are linked to sarcomeric Z disks. 

Fig. 1. Organization of filaments in smooth muscle cells. A. Vas deferens smooth muscle cell shown in transverse section. Thick filaments are surrounded by multiple thin filaments throughout the cytoplasm. Dense bodies ("db ) are round or oval in shape in transverse section but elongated in shape in oblique sections. Arrow point to intermediate filaments (10 nm) that surround the dense bodies. B. Longitudinal section of portal anterior mesenteric vein smooth muscle cell. Thin filaments (arrows) can be seen inserting on both sides of the dense bodies (db). Intermediate filaments (arrowheads) extend laterally from dense bodies and sometimes connect a series of dense bodies to form a chain. Magnification x 70,000. Reproduced from Bond and Somlyo (1982) The Journal of Cell Biology 95 403-413 with permission of Rockefeller University Press...

Cytosolic electron dense areas are also observed in smooth muscle cells that are referred to as dense bodies. Dense bodies are distributed relatively uniformly throughout the cytoplasm (Tsukita and Ishikawa 1983, Bond and Somlyo 1982, Fay et al 1983). They are obliquely oriented elongated structures that can appear circular or oval in shape under electron microscopy depending on the plane of section (See Figure 1). Cytoplasmic dense bodies have been measured up to 1.5 pm in length (Bond and Somlyo 1982, Tsukita and Ishikawa 1983, Ashton et al 1975, Fay et al 1983). 

PLATELETS. Platelets are nonnucleated discoid or elliptical cells that originate from the fragmentation of giant polyploid megakaryocytes located in the bone marrow. The average diameter of the platelet is 1.5 pm. Each platelet is surrounded by a trilaminar membrane, and its cytoplasm contains a dense body (delta granule), a surface-connected canalicular system,... 

Because there are no sarcomeres in smooth muscle, there are no Z lines. Instead, the actin filaments are attached to dense bodies. These structures, which contain the same protein as Z lines, are positioned throughout the cytoplasm of the smooth muscle cell as well as attached to the internal surface of the plasma membrane. Myosin filaments are associated with the actin filaments, forming contractile bundles oriented in a diagonal manner. This arrangement forms a diamond-shaped lattice of contractile elements throughout the cytoplasm. Consequently, the interaction of actin and myosin during contraction causes the cell to become shorter and wider. 

Although much of the focus has been on the DPC of striated muscle, it is likely that desmin attachments to dense plaques of smooth muscle play critical roles in regulating the transmission of contractile forces in this tissue as well. This is particularly relevant in light of the observed defects in smooth muscle of desmin-deficient mice, in which active force per cross-sectional area was reduced to 40% of controls of smooth muscle tissue (Sjuve et al, 1998). IFAP candidates for serving this linking function are plectin and other components of the actin-rich cortex, including calponin (which also plays a role in the cytoplasm of smooth muscle cell dense bodies see below), and the spectrin/ankyrin complex. 

Callus cultures derived from Jerusalem artichoke tubers are initially quiescent and have to be induced to divide. The induction of division is accompanied by a transformation in cell structure, which reflects changes in metabolism (e.g., Gamburg et al., 1999). Within an hour of the excision of Jerusalem artichoke tuber explants, ribosomes increase in abundance. They take the form of helices when scattered in the cytoplasm, and spirals when associated with the endoplasmic reticulum, and increase in frequency over time in line with the rate of protein synthesis (Yeoman and Street, 1973). Electron-dense bodies appear soon after in cell vacuoles, and to a lesser extent in the cytoplasm (Bagshaw et al., 1969), while crystal-containing bodies form in cells, which may contain hydrolytic enzymes (Bagshaw et al., 1969 Gerola and Bassi, 1964). Dormant Jerusalem artichoke tuber explants contain a variety of mitochondrial profiles, including distinctive cup-shaped... 

PEComas 40-50 yr—usually females. Various visceral organs and soft tissue. Epithelioid and spindle cells with perivascular arrangement, clear to granular cytoplasm HMB45+, melan-A+, but SI 00 negative EM glycogen, pre-melanosomes, occasional dense bodies... 

Amiodarone (formula [249]) and its desethyl metabolite desethylamiodarone (formula [250]) induced striking lamellated electron dense cytoplasmic inclusion bodies in human hepatocytes and Kupffer cells (Adams et al. 1983). 

The pineal glands of rats 12-28 months old exhibited regressive changes of different intensity with age (Boya and Calvo 1984). In type I pinealocytes there was a marked increase in dense bodies as well as the occasional appearance of wide cell profiles full of vesicles. Type II pinealocytes showed nuclear infoldings and cytoplasmic deposits of lipofuscin. 

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