There are some ultrastructural characteristics of this desmosome which are interesting. Having a desmosome sectioned opportunely is hit and miss.  This particular section has some structures that look to be the correct size of intermediate filaments that are trailing off the the upper right under the mitochondrion, and there are definite light-dark-and dotted portions of the desmosome (in and including the plasmalemma portion) which have a distinct vertical repeating pattern.

I squeezed the micrograph bottom to top to determine if this was just a shifting of the image during photography or whether these vertical striations would still be visible when i removed (in photoshop) that kind of vertical shift.  The answer was that even then the spacing and the effect of the alternating light and dark areas in the cell membrane portion of the desmosome remained.  Red dot=27nm as determined by ribosome size, and thus the alternating dark and light vertical areas in the section are about 10nm in width.

In addtion, there is a clear darkening of the outer mitochondrial membrane, and a slight darkening of the inner mitochondria membrane at the point of the desmosomal-mitochondrial tethering. One can suggest that there is a relationship between this patterning and the various protein families that comprise the full structure of the desmosome, intermediate filaments and mitochondrial connection.

Control animal (neg 5936 block 8830 baboon, f, #23, right lobe of the liver, control bx, modified Karnovsky’s fix, 1% osmium tetroxide, Epon 812, (9 28 1977)). There are a lot of smooth vesicles in this sample and just a little bit of RER, three lipid droplets, and part of a bile canaliculus, possible the space of Disse in the very upper most right part of the image, mitochondria look pretty normal) I was looking for desmosomal-mitochondrial tethers and found this pretty nice desmosome and I pseudocolored the plasmalemma from the two adjacent hepatocytes present at the desmosome purple. There was a clear the “outer dense layer” of the desmosome (which i think is so unfortunately named “outer” and should have been named “inner dense layer” of the desmosomal complex). It had a particularly “loopy” appearance that I highlighted in orange.  Top image is the original micrograph (two hepatocytes) and box is the area enlarged in the figure below  with a desmosome).

Here is a gallery sheet of desmosomal mitochondrial tethers, and some are double, some are double-doubles (haha) and some have three tethers.  I can’t overemphasize how interesting these little structures are and how critical they must be for cell function. Just considering how the desmosome itself has become a known mechanism of cell signaling, then the energy provided (mitochondria) and the movement of proteins and mitochondria and signaling proteins via the intermediate filaments, and the latter involved also in cell shape change…. makes these structures very very important.  This gallery (making the gallery itself) caused me great grief… ha ha.. my little desk top computer just didn’t want to handle composite images of over a gig.  Would that I had real equipment…  wonder of wonders.  Enjoy the image(s) of whatever these DES-MiTes  (desmosomal-mitochondrial-tethers)  will ultimately be called (dumber names exist in science).

34 pix, 43 desmosomes, at least 56 mitochondria, numerous species represented here (ferret, rat, guinea pig, stub tail monkey, rhesus monkey, maybe others, and all images are from hepatocyte-hepatocyte junctions)

Two tiny mitochondria associations with a tangential section of a desmosome. Hepatocyte. 5893_2222. Not a particularly stunning micrograph, but sure documentation that mitochondria associate with desmosomes in hampster liver parenchymal cells.

“Desmosomes are a complex assembly of protein molecules that form at the cell surface and mediate cell–cell adhesion. Much is known about the composition of desmosomes and there is an established consensus for the location of and interactions between constituent proteins within the assembly. Furthermore, X-ray crystallography has determined atomic structures of isolated domains from several constituent proteins. Nevertheless, there is a lack of understanding about the architecture of the intact assembly and the physical principles behind the adhesive strength of desmosomes therefore remain vague. We have used electron tomography to address this problem. In previous work, we investigated the in situ structure of desmosomes from newborn mouse skin preserved by freeze-substitution and imaged in resin-embedded thin sections. In our present work, we have isolated desmosomes from cow snout and imaged them in the frozen unstained state. Although not definitive, the resulting images provide support for the irregular groupings of cadherin molecules seen previously in mouse skin.” ABSTRACT from Gethin Rh. Owen, Devrim Acehan, K.D. Derr, William J. Rice, David L. Stokes . Some things might be right, others not…. the last idea that cadherin molecules are grouped irregularly i don’t like. (This article i wont read as it is pay-per-view, which really galls me particularly because most research is paid for by tax-dollars and should be free).

” I found a dimension for the width “wide intercellular space (~240 A)” at 24nm and a measurement of the intermediate filament at 8nm (i presume diameter). The 22-24nm (could be less in some instances more like 15nm) as the width of the desmosomal intercellular space (which includes the densities on the outer leaflet of the plasmalemma from both cells and the central dense line of the desmosome.  That measurement looks about right. From this I estimate the width of the electron lucent annulus of the desmosome (which is much more evident when there is a tight junction on either side of the desmosome) to be dependent upon where the section sectioned the spot desmosome, and whether the cut was equatorial or tangent to the spot itself. On one micrograph (stub tail monkey hepatocyte) in which one area of the desmosome is close to a tight junction, shows this lucent area (the outer annulus) to be about 35nm in its radius – that dimension applies to the edge of the central dense line extending to the tight junction. The width of that particular desmosome (where the central line was apparent) was @265nm.  This makes the ratio of the dense desmosomal central line density distance to lucent annulus distance in cross section about 3.5%.

That lucent area may not be a uniform annulus, but if it were even, this assumes pretty much a “round” desmosomal spot weld. In measuring the radius of the annulus (just in the part ring part) I understand that the central dense line of the desmosome will appear in any view with the spot perpendicular to the plane of section, and this doesn’t diminish the fact that closer cuts to the outer edge of the desmosome will have a greater annulus to spot ratio. Fuzzing of the central dense line in the desmosome occurs when the angle of the section is not perpendicular to the spot, and can happen either at an equatorial section or anywere past that equator. So. any question I can ask, someone has an answer to…. so here is the definition of calculating the area of an annulus.. ha ha “An annulus (Latin word for ring) is a two-dimensional region of space bounded by two concentric circles. The area of an annulus is the difference in the areas of the larger circle of radius R, and the smaller circle of radius r. Mean radius (ρ) is the average of the exterior (R) and interior (r) radii. Breadth (δ) is the width of the annulus. “ So I just have to figure out how to use the online calculator.

The ratio of lucent annulus to dense desmosome is not too apparent when there is no tight junction visible right next to it. But that said, I can see a slight increase in plasmalemmal density for a short distance (same type of annulus arrangement as if there were a tight junction there) on each end of the desomosome cross section.