Basal laminas filaments

The second class of AChEs exists as heteromeric assemblies of catalytic and structural subunits. One form consists of up to 12 catalytic subunits linked by disulfide bonds to filamentous, collagen-containing structural subunits. These forms are often termed asymmetric, since the tail unit imparts substantial dimensional asymmetry to the molecule. The collagenous tail unit links by disulfide bonding at its proline rich N-terminus through a coiled coil arrangement to the C-terminus of two of the catalytic subunits [30]. The tail unit associates with the basal lamina of the synapse rather than the plasma membrane. 

While one end of the dystrophin molecule binds to actin filaments, the C-terminal domain associates with several additional proteins to form a dystrophin-glycoprotein complex (see figure)/1 k Dystrophin is linked directly to the membrane-spanning protein P-dystroglycan, which in the outer membrane surfaces associates with a glycoprotein a-dystroglycan. The latter binds to laminin-2 (Fig. 8-33), a protein that binds the cell to the basal lamina. Four... 

Fig. 7.11. Comparison of the fine structure of the membranes of the eggs of Hymenolepis diminuta and H. nana. Note in H. nana (in contrast to H. diminuta) (a) the embryophore is thin and incomplete - a feature which may facilitate hatching in the gut of the definitive host (b) there is an additional polar filament layer between the oncospheral membrane and the basal lamina. Gc, Golgi complex ger, granular endoplasmic reticulum /, lipid bodies m, mitochondria n, nucleus v, vacuoles. (After Fairweather Threadgold, 1981a Holmes Fairweather, 1982.)...

Plakin proteins link intracellular keratin intermediate filaments to hemidesmosomes of basal epidermal cells, or to desmosomes on suprabasal epidermal cells (Sect. 5.2.1), whereas type XVII collagen (the only collagen secreted by epithelial cells ) and integrins attach hemidesmosomes to a basal lamina. Three p 1 integrins (with al, a3 or a5 partners)... 

Many of the extracellular materials are filaments made from fibrous proteins, mainly collagen and elastin, and adhesion proteins such as fibronectin and laminin. Collagens form a family of proteins with a tissue-specific distribution, including types inifound in connective tissue such as filamentsand types IV and Vfound in basal laminae forming sheets of tissue. 

The basement membrane zone or epidermal-dermal junction is a thin extracellular matrix that separates the epidermis from the dermis. It is a highly specialized structure recognized with the light microscope as a thin, homogeneous band. Ultra-structurally, it can be divided into four component layers (1) the cell membrane of the basal epithelial cell, which includes the hemidesmosomes (2) the lamina ludda (lamina rara) (3) the lamina densa (basal lamina) and (4) the subbasal lamina (sublamina densa or reticular lamina), with a variety of fibrous structures (anchoring fibrils, dermal microfibril bundles, microthreadlike filaments) (Briggaman and Wheeler, 1975). The basement membrane has a complex molecular architecture with numerous components that play a key role in adhesion of the epidermis to the dermis. The macromolecules that are ubiquitous components of all basement membranes... 

Some parts of the tracheal epithelium of ageing mice invaginated into the lamina propria without any noticeable changes in either the epithelial cells or the basal lamina (Kawata and Fujita 1983). The lumen of the cyst-like structures usually formed characteristic concentric circles in the central portion and sometimes contained destructed cell debris at the periphery. The concentric circular materials consisted of entangled filaments of 15-20 nm in diameter. 

Branchial neuroepithelial cells are currently the best candidates for the O2 chemoreceptor cells that mediate the reflex responses to hypoxia in fish. In the gills, these cells are located in the primary epithelium of the giU filaments and he on the basal lamina between the inhalant water flowing over the gill and blood flow through the gill in an ideal anatomical location to function as O2 sensors. Branchial neuroepithelial cells share many of the characteristic anatomical features of mammalian O2 sensors (glomus and pulmonary neuroepithehal ceUs). Like mammalian cells, branchial neuroepithehal cells are innervated and possess a well-developed Golgi complex and numerous mitochondria and dense-cored... 

One form of cellular demise common to epithelial cells is detachment-initiated apoptosis, also referred to as anoikis (Frisch and Francis, 1994). Epidermal keratinocytes rely on signals derived from the surrounding extracellular matrix for survival. It is possible that loss of these signals plays a role in SM-induced epidermal cell injury, and that cell detachment from the basal lamina precedes cytotoxicity. Several lines of evidence support this possibility. First, SM can alter the dynamics of cytosolic proteins that exert control over the attachment of cells to the basement membrane. For example, SM can modify intracellular actin microfilaments and keratin intermediate filaments known to be important in maintaining epithelial cell connections with the basal lamina. Thus, Hinshaw et al. (1999) reported that SM causes changes in the actin microfilament architecture and morphology of human keratinocytes within 3h of... 

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