Question

52. During neuronal pathfinding, the growth cone of the neuron chemotaxes to the target cell in the brain it needs to reach. At that point, the growth cone touches the target cell and responds to it by creating an adhesions junction. What type of signaling activates chemotaxis? What type of signaling activates formation of the adhesions junction. Suggest a biochemical pathway that would activate and form the adhesions junction.

Answer 1

Neuronal chemotaxis is the movement of of axons in the direction of chemical gradients. Gradients of diffusible and substrate‐bound molecules play an important role in guiding axons to appropriate targets & in the development of nervous systems responses.

concentration gradient of the particular chemical is sensed by the axonal receptors which leads to the development of growth cone towards the target the particular cells. Then, the growth cone touches the target cell and responds to it by creating an adhesions junction. special type of signaling that involves the detection of this concentration gradient of chemical attractant or repellent by the G protein coupled receptors present on the cell surface which gets activated by the binding of these specific molecules.

signaling that activates formation of the adhesions junction arises from the axonal growth cone which projects to a specific targets based on positional information encoded by chemical gradients in both source and target areas. It is brought in tern by the activation of several transmembrane receptor proteins.

A biochemical pathway that activate and form the adhesions junction are as follows:-

Adherene junction consist of two basic adhesive subunits the cadherin/catenin & nectin/afadin complexes. It requires one of these adhesion complex to function. During adherens belt formation it is the E cadherin complex that gets involved. It consists of an extracellular domain , a transmembrane domain, and two cytoplasmic domains. The EC domain forms a trans-cadherin interaction between adjacent cells, initiates weak cell-cell adhesion, and forms adhesion molecule linkages. The Ca2+ binding in the EC domain ensures the correct conformation of the extracellular domain of cadherin. The cytoplasmic domain includes a highly phosphorylated region that mediates the binding of E-cadherin to β-catenin and participates in signal transduction.When this highly-conserved cytosolic domain of E-cadherin binds to the intracellular ligand β-catenin, this in turn anchors the E-cadherin on the surface of the cell membrane to the cytoskeleton through α-catenin, forming an adhesive junction E-cadherin/β-catenin complex. This E-cadherin/β-catenin complex is the core for the formation of the adhesion belt, which mediates homologous adhesion, maintaining the polarity and integrity of normal cells bringing about the required response.