Table 1.
Molecular components of the major categories (I–IV) and several other forms (1–7) of mammalian symmetrical (homotypic) junctions (JAM junction adhesion molecule, brackets not regularly seen in all cells, nd not decided as yet)
| Type | Occurrence | Associated filaments | Transmembrane proteins and glycoproteins | Specific plaque proteins (selection of hallmark representatives) |
|---|---|---|---|---|
| I. Desmosomes | ||||
| Maculae adhaerentes | Epithelial cells | Intermediate-sized filaments (keratins, vimentin, desmin) | Desmogleins Dsg 1–3a | Plakoglobin |
| Cardiomyocytes | Desmoplakins | |||
| Meningothelial cells | Desmocollins Dsc 1–3a | Plakophilins 1–3a | ||
| Reticulum cells of thymus and lymph follicles | ||||
| II. Adherens junctions | ||||
| Zonulae adhaerentes | Epithelial cells | Microfilaments (actin) | Typical cadherinsa (e.g., E-cadherin, N-cadherin, VE-cadherin, cadherin-11) nectin | α- and β-Catenin, plakoglobin, protein p120, protein ARVCF, protein p0071, neurojunginb, proteins ZO-1-3, afadin, vinculin |
| Endothelial cells | ||||
| Fasciae adhaerentes | Various types of cardiomyocytes | |||
| Puncta adhaerentia | Mesenchymal and neural cells | |||
| III. Tight junctions | ||||
| Zonulae occludentes | Epithelial cells | – d | Occludin | Proteins ZO-1-3 |
| Claudins 1–24a | ||||
| Endothelial cells | Tricellulin(s)c | Cingulin | ||
| JAM proteins | ||||
| IV. Gap junctions | ||||
| Nexus | All kinds of tissue-forming cells | – | Connexins 1-21a | Proteins ZO-1-3 |
| 1. Minimal dot junctions | ||||
| Puncta adhaerentia minima | Mesenchymal cells | Microfilaments (actin) | N-cadherin, cadherin-11 | α- and β-Catenin, proteins p120, p0071, ARVCF, (plakoglobine), afadin |
| 2. Taproot adherens junctions | ||||
| Manubria adhaerentia | Mesenchymal cells in culture | Microfilaments (actin) | N-cadherin, cadherin-11 | α- and β-Catenin, (plakoglobine), proteins p120, p0071, ARVCF, proteins ZO-1-3, afadin, vinculin |
| 3. Plakophilin-2-containing adherens junctions | ||||
| Coniunctiones adhaerentes | Mesenchymally derived cells of high proliferative activity | Microfilaments (actin) | N-cadherin, cadherin-11 (nectin) | α- and β-Catenin, plakoglobine, proteins p120 and p0071a, plakophilin-2, (plakophilin-3f), proteins ZO-1-3, afadin, vinculin |
| 4. Composite junctions | ||||
| Areae compositae | Cardiomyocytes of maturing and adult heart | Microfilaments (actin) | N-cadherin | Desmoplakin, α- and β-catenin, proteins p120, ARVCF and p0071, plakophilin-2, proteins ZO-1–3 |
| Cadherin-11 | ||||
| Intermediate-sized filaments | Desmoglein-2 | |||
| Desmocollin-2 | ||||
| 5. Adherens cortex | ||||
| Cortex adhaerens | Eye lens interior | ndd | N-cadherin, cadherin-11 | α- and β-Catenin, plakoglobin, protein p120, ezrin, periplakin, periaxin |
| 6. Sandwich junctions | ||||
| Iuncturae structae | Epidermal stratum spinosum or equivalent layers of other stratified epithelia | nd | Occludin, claudins | nd |
| 7. Complex junctions | ||||
| Complexus adhaerentes | Endothelial and virgultar cells of lymph node sinus | nd | N-cadherin | Desmoplakin, α- and β-catenin, protein p120, plakoglobin, proteins ZO-1–3, afadin |
| Cadherin-11 | ||||
| VE-cadherin | ||||
| Claudin-5 | ||||
| JAM proteins | ||||
aOne isoform or combinations of a few representatives, often with cell-type and cell-layer specificities
bOnly cell-type-specific combinations of the armadillo-type proteins underlined
cThere are two mRNA splice products of which only one protein has so far been localized
dActin microfilaments are seen near the junctions, but their specific association is not clear
ePlakoglobin has been demonstrated only in some cells and with markedly differing intensities, even in the same culture
fPlakophilin-3 has been seen only in a portion of plakophilin-2-positive cells