There are several nice things about this micrograph of a desmosomal mitochondrial tether (i.e. tethered via the intermediate filaments of the desmosome). One nice thing is the very rigid, and parallel membrane-leaflet quality of the plasmalemma where there is the desmosomal protein complex, and it also exhibits a very even and well defined separation of the outer and inner leafelets of the plasmalemma (at least this is what i think is shown in the micrograph below).  I have marked the two leaflets on the cell membranes on the adjacent cells with black lines. There are obvious periodicities within the inner and outer membrane leaflets too… not withstanding the density of the lead citrate and uranyl acetate stains and the quality of fixation) which seems to present overall patterning in the entire micrograph. I have marked the extracellular lines (which are not likely to be random as they appear, but more likely to be organized attached wishbone shapes (mirrored vertically and copied horizontally) shown in an earlier post but the lines here have been drown over actual densities in the extracellular (intercellular) space of the desmosome. Green blobs mark periodicities within the two leaflets of the plasmalemma, and the pink blobs mark the densities which are extracellular but likely adjacent, maybe even part of (like the cadherins in desmosomes) those proteins. (green blobs are INTERcellular, the pink blobs are within the plasmalemma (transmembrane). Electron micrograph on left is unretouched, on right, contrast and brightness enhanced and vector overlays show densities which can be matched to image on the left. This stub-tail monkey hepatocyte came from an animal that received two test doses of perfluorodecalin (a very small amount) a year prior, which in my experience has nothing to do with these tethers. Shown immediately below the outer leaflet of the plasmalemma is what appears to be a regular compartmentalization (shown as rectangles) likely representing a highly structure arrangement of plakophilin and plakglobin and maybe some desmoplakin and a bit of vimentin.  The number of densities (green or pink, and likely connected parts of the cadherin dimers, turn out in this micrograph to be about 9 nm…  a little close than found in mouse micrographs so far. 

This is just a micrograph to justify the idea that the desmosomal mitochondrial tethering, or junction or des-mites as i have aptly named them (as opposed to pore-mites) for nuclear pore mitochondrial tethering, are pretty universal. Here a single tether is in a stub tail monkey hepatocyte, from tissue taken back in the 1970s while studying the effects of infusing artificial blood emulsions (perfluorochemical based blood substitutes) . This particular monkey (Maccaca speciosa, probably female) did receive two test doses of a perfuorodecaline emulsion, just a tiny amount, 0.05cc/kg of a 10% emulsion PP5ct and 5% F68) (Lee Clark Jr named all his emulsions, this was EM#750428). no perfluorochemical droplets were seen in this hepatocyte. Sac date was 5 10 76.

So desmosomal mitochondrial junctions are here. Mitochondrion is in top part of micrograph, desmosome is attached to the down pointing portion.

Here is another pseudocolored desmosome with portions of two mitochondria top and bottom parts of this electron micrograph. It was difficult to determine exactly where the plasmalemma from each of these two cells went at the point of the desmosome, but I thought long and hard about which part of the structure they were. It seemed to me that there was a slight electron lucency just under the plasmalemma on each side, therefore this is the way I pseudocolored (with pink) the cell membranes.  The densities within the desmosome itself looks like there are three rows… the central dotted (periodic) line where the cadherin molecules knot together (my guess is this is a totally symmetric arrangement, not at all random like suggested by some) and perhaps another periodicity (well not perhaps…. it is pretty striking) which lies a little separated from the plasmalemma.  I don’t know if any of the models of the cadherins show a “lump” structure before the transmembrane part… ? That will take some searching.

Top image is unretouched transmission electron micrograph of a desmosome, as mentioned, mitochondria portion seen top and bottom.  The box in this image is what is enlarged in the second image. There are two very prominent intramitochondrial granules, especially the one in the mitochondria at the bottom of the micrograph.
This image is from the boxed area above, thus enlarged, pink is the plasmalemma, orange is the area just under the plasmalemma of each cell and into the space of the desmosome. Blue is what I see as the possible densities of cadherin molecules.

In this inset the periodicity of the outer part of the desmosome (probably still cadherin molecules) is a spacing about 1/15nm  not too different from that found in a previous post at something around 1 density for each 13-14nm spacing.  The periodicities on the central dense line of the desmosome in this micrograph might be something around 18nm spacing… I would have preferred if the densities came out one-to-one, but anticipate that in other assessments that it might do just that. But for now, i just count what shows up. 6102_5070_mouse_female_control.

I don’t know much about desmosomes, but they do make unique junctions with nuclear pore intermediate filaments and also very definite connections with mitochondria. The mitochondria – intermediate filament connections with desmosomes show a couple nice ultrastructural changes from the routine: 1) the mitochondrial outer membrane is flattened, or straightened in the area of connection with the intermediate filaments over the desmosome, and it is also a little darker. and 2) the mitochondrial body itself is drawn towards (at least that is the way it looks… as if there was a dragging force) the desmosomal intermediate filaments. The central line of the desmosome is not always visible when i see these tethers (often with two mitochondria in adjacent cells and a single desmosome, but there are molecular models of the cadherins (several) that I cut pasted masked and reduced to fit in the appropriate intercellular space where they would appear. It is a good lesson is relative “size” and “shape”.

Micrograph: Pale green semitransparent mask is over two mitochondria, one each in two adjacent cells. Red arrow points to the inner dense layer (maybe i will add the known proteins there “in scale), the white arrows point to the plasmalemma of the two separate cells, the black arrow points to the center dense “knotted” region, (maybe i will measure distances between visible knots) and the molecules (several taken from the internet, look similar and were pasted into the intercellular region (see demarcation from right hand side transparent grey.