The optic chiasm, or optic chiasma, is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebrates, although in cyclostomes, it is located within the brain.
Semaphorins are a class of secreted and membrane proteins that were originally identified as axonal growth cone guidance molecules. They primarily act as short-range inhibitory signals and signal through multimeric receptor complexes. Semaphorins are usually cues to deflect axons from inappropriate regions, especially important in the neural system development. The major class of proteins that act as their receptors are called plexins, with neuropilins as their co-receptors in many cases. The main receptors for semaphorins are plexins, which have established roles in regulating Rho-family GTPases. Recent work shows that plexins can also influence R-Ras, which, in turn, can regulate integrins. Such regulation is probably a common feature of semaphorin signalling and contributes substantially to our understanding of semaphorin biology.
Neuropilin is a protein receptor active in neurons.
A plexin is a protein which acts as a receptor for semaphorin family signaling proteins. It is classically known for its expression on the surface of axon growth cones and involvement in signal transduction to steer axon growth away from the source of semaphorin. Plexin also has implications in development of other body systems by activating GTPase enzymes to induce a number of intracellular biochemical changes leading to a variety of downstream effects.
Neuropilin-1 is a protein that in humans is encoded by the NRP1 gene. In humans, the neuropilin 1 gene is located at 10p11.22. This is one of two human neuropilins.
Semaphorin-3A is a protein that in humans is encoded by the SEMA3A gene.
Semaphorin-4D (SEMA4D) also known as Cluster of Differentiation 100 (CD100), is a protein of the semaphorin family that in humans is encoded by the SEMA4D gene.
Plexin B1 is a protein of the plexin family that in humans is encoded by the PLXNB1 gene.
Semaphorin-3F is a protein that in humans is encoded by the SEMA3F gene.
Rnd1 is a small signaling G protein, and is a member of the Rnd subgroup of the Rho family of GTPases. It is encoded by the gene RND1.
Semaphorin-3C is a protein that in humans is encoded by the SEMA3C gene.
Plexin-A1 is a protein that in humans is encoded by the PLXNA1 gene.
Plexin-B2 is a protein that in humans is encoded by the PLXNB2 gene.
Semaphorin 7A, GPI membrane anchor (SEMA7A) also known as CD108, is a human gene.
Plexin-A2 is a protein that in humans is coded by the PLXNA2 gene.
Plexin-A4 is a protein that in humans is encoded by the PLXNA4 gene.
Semaphorin-4G is a protein that in humans is encoded by the SEMA4G gene.
Collapsin response mediator protein family or CRMP family consists of five intracellular phosphoproteins of similar molecular size and high (50–70%) amino acid sequence identity. CRMPs are predominantly expressed in the nervous system during development and play important roles in axon formation from neurites and in growth cone guidance and collapse through their interactions with microtubules. Cleaved forms of CRMPs have also been linked to neuron degeneration after trauma induced injury.
The growth cone is a highly dynamic structure of the developing neuron, changing directionality in response to different secreted and contact-dependent guidance cues; it navigates through the developing nervous system in search of its target. The migration of the growth cone is mediated through the interaction of numerous trophic and tropic factors; netrins, slits, ephrins and semaphorins are four well-studied tropic cues (Fig.1). The growth cone is capable of modifying its sensitivity to these guidance molecules as it migrates to its target; this sensitivity regulation is an important theme seen throughout development.
Semaphorin 3E is a protein that in humans is encoded by the SEMA3E gene.
