Septate Junction
In cell biology, septate junctions , rarely also referred to as septum junctions , are narrow bands of membrane proteins that completely girdle the epithelial cells of invertebrates . They are responsible for maintaining a paracellular barrier and controlling the paracellular transport of molecules across the epithelium.
Septate junctions occur in invertebrates and have been studied mainly in arthropods . In vertebrates , the tight junctions have an analogous function.
function
Septate junctions are responsible for maintaining a paracellular barrier and controlling the paracellular transport of molecules across the epithelium. They form a diffusion barrier, which ensures that the spaces between two cells are sealed and only certain molecules can pass. In this way, organs can create and maintain different chemical compositions inside them.
construction
Septate junctions differ structurally from tight junctions in that they are to be found as ladder-shaped "septae" in the lateral membrane and not as a compact structure at the apical end of the lateral membrane. They join the Adherens Junctions . The individual epithelial cells are surrounded by protein bands. The protein bands of neighboring plasma membranes are connected by regular parallel rows of membrane proteins. This gives the septate junctions the ladder-shaped appearance.
In Drosophila melanogaster , a distinction is made between pleated septate junctions , which in addition to the epithelial barrier of ectodermal epithelia also establish the blood-nerve barrier , and smooth septate junctions , which occur in mesodermal epithelia. Not much is known about the smooth septate junctions ; they differ in electron microscopic images from the pleated septate junctions in the absence of septa. They also lack the typical transmembrane components of the pleated septate junctions such as claudins or neurexin IV.
In vertebrates, paranodal septate junctions occur, which have structural similarities to the septate junctions of arthropods. It has not yet been clarified whether they are also made up of similar components or whether they emerged from the septate junction structures.
history
Septate junctions were first described as Septate Desmosomes by RL Wood in 1959 .
literature
- Alberts, B. et al .: Molecular Biology of the Cell . Garland Science, 4th edition, 2002. ISBN 0815340729 .