Fine Structure of Desmosomes, Hemidesmosomes, and an Adepidermal Globular Layer in Developing Newt Epidermis

Abstract

A B S T R A C TThe skin of late embryonic, larval, and young postmetamorphic newts, Taricha torosa, has been examined with particular reference to areas of cellular attachment. Stereo electron microscopic techniques and special staining methods for extracellular materials were utilized in addition to conventional avenues of ultrastructural study to investigate the fine architecture of desmosomes, hemidesmosomes, their associated filament systems, and extracellular materials. No evidence has been found that continuity of tonofilaments between adjacent cells exists at desmosomes. Rather, most of the tonofilaments which approach desmosomes (and perhaps also hemidesmosomes) course toward the "attachment plaque" and then loop, either outside the plaque or within it, and return into the main filament tracts of the cell. These facts suggest that the filamentous framework provides intracellular tensile support while adhesion is a product of extracellular materials which accumulate at attachment sites. Evidence is presented that the extracellular material is arranged as pillars or partitions which are continuous with or layered upon the outer unit cell membrane leaflets and adjoined in a discontinuous dense midline of the desmosome. A similar analysis has been made of extracellular materials associated with hemidesmosomes along the basal surface of epidermal cells. An adepidermal globular zone, separating the basal cell boundary from the underlying basal lamina and collagenous lamellae during larval stages, has been interpreted from enzyme and solvent extraction study as a lipid-mucopolysaccharide ccmplex, the function of which remains obscure. These observations are discussed in relation to prevailing theories of cellular adhesion and epidermal differentiation. They appear consistent with the concept that a wide range of adhesive specializations exists in nature, and that the more highly organized of these, such as large desmosomes and hemidesmosomes, serve as strong, highly supported attachment sites, supplemental in function to a more generalized aggregating mechanism.

Egfl7 knockdown causes defects in the extension and junctional arrangements of endothelial cells during zebrafish vasculogenesis

“…The desmosome (macula adherens) appears as a spot-like cell junction formed by transmembrane filaments linked at a central stratum in the ϳ25-nm-wide intercellular space. Desmosomes are sharply delineated by dense plaques connected to intermediate filaments (Farquhar and Palade, 1963;Kelly, 1966;Stokes, 2007). Although vascular endothelial cells in general do not display desmosomes (Bazzoni and Dejana, 2003), the junctional structures that we observed in this study meet all morphological criteria of desmosomes (Fig.…”

Rearrangement of the keratin cytoskeleton after combined treatment with microtubule and microfilament inhibitors.

“…A key organizational difference between cytokeratins and other intermediate filaments is the interaction of the keratins (tonofilaments) with desmosomes and related structures (5,6,11,(23)(24)(25)(26). Our results show that cytokeratin organization in HeLa cells depends on interactions with cell membrane structures which provide a peripheral network of stabilizing attachment sites for keratin filaments, as well as with microtubules and microfilaments, which may provide a cytoplasmic framework .…”

Cloning and sequence analysis of desmosomal glycoproteins 2 and 3 (desmocollins): cadherin-like desmosomal adhesion molecules with heterogeneous cytoplasmic domains.

“…This serves as a site for association of intermediate filaments (ITs). However, the IFs do not attach to the plaque directly but via filaments which extend into the cytoplasm from the inner face of the plaque (Kelly, 1966). Transmembrane desmosomal glycoproteins therefore require extracellular domains that participate in cell-cell adhesion and cytoplasmic domains that participate in plaque formation involving linkage, directly or indirectly, to IFs.…”