Question

Axon growth. 1-2 sentences per molecule, short paragraph/annotated diagram for experiment. Briefly explain the role of the following molecules in neural development.

- netrins

- nerve growth factor

- semaphorins

For ONE of these molecules, explain an experiment that shows its importance in development.

Answer 1

Netrin are a class of proteins involved in axon guidance.Structuraly they resembles the extra cellular matrix protein laminin. They are chemotropric ;a growing axon will either move towards or away from a higher concentration of netrin.Netrin attraction is mediated through UNC-40/DCC cell surface receptors and reception is mediated through UNC-5 receptors.Netrins act as growth factors ,encouraging cell growth activities in target cells.Mice defecient in netrin fail to form hippocampal comissure .

NGF or Nerve growth factor is neuropeptide and neurotrophic factor involved in growth ,maintenence,proliferation,and survival of certain target neurons.The biological process involving NGF are survival of pancreatic beta cells and the regulation of the immune system.

Semaphorin is a guidence cues ensuring axon targetting ,they also act as key regulators of cell migration,cell death or synapse formation during nervous system develepment.It is the soluble Sema3A.It act as repulsive factor on chicken DRG neurons by inducing the collapse and retraction of their growth cones.It mediates axon repulsion.

Experiment showing importance of NGF in neural system :

Studies are carried out in laboratory animals and isolated cells have demonstrated protective action of NGF not only on survival of degenerating peripheral nerve cells but also on regulation of neurotransmitters and neuropeptide synthesis of sympathetic and sensory nerve cells.