Septate junction

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Septate junction

Septate junctions are specialized intercellular connections found in invertebrates, particularly in arthropods and annelids. These junctions are analogous to the tight junctions found in vertebrates and play a crucial role in maintaining the paracellular barrier and regulating the passage of molecules between cells.

Structure

Septate junctions are characterized by their ladder-like appearance when viewed under an electron microscope. They consist of parallel rows of septa, which are proteinaceous structures that span the intercellular space. These septa are composed of various proteins, including neurexin IV, contactin, and neuroglian, which are essential for the formation and function of the junction.

Function

The primary function of septate junctions is to create a barrier that regulates the movement of ions and molecules between cells, thereby maintaining the homeostasis of the extracellular environment. They also play a role in cell signaling and the establishment of cell polarity.

Types

There are two main types of septate junctions:

• **Pleated septate junctions (pSJs)**: Found primarily in epithelial cells, these junctions have a pleated or folded appearance.
• **Smooth septate junctions (sSJs)**: Found in glial cells and other non-epithelial cells, these junctions have a smooth appearance.

Comparison with Tight Junctions

While septate junctions and tight junctions serve similar functions in maintaining the paracellular barrier, they differ in their molecular composition and structure. Tight junctions are found in vertebrates and are composed of proteins such as claudins, occludin, and junctional adhesion molecules (JAMs).

Role in Development and Disease

Septate junctions are crucial for the proper development and function of tissues in invertebrates. Mutations or disruptions in the proteins that form these junctions can lead to developmental abnormalities and diseases. For example, mutations in the gene encoding neurexin IV can result in defects in the blood-brain barrier in Drosophila melanogaster.

Research

Ongoing research aims to further elucidate the molecular mechanisms underlying the formation and function of septate junctions. Understanding these processes can provide insights into the evolution of intercellular junctions and their roles in health and disease.

See also

• Tight junction
• Adherens junction
• Gap junction
• Desmosome
• Hemidesmosome