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The Robo proteins are critical regulators of midline crossing across species. In Drosophila embryos, Robo1 and Robo2 are required to keep ipsilaterally projecting axons from inappropriately crossing the midline, and to prevent contralateral axons from remaining stuck at the midline. Robo3, while it also binds Slit, does not appear to play a ...
Crossing of commissural axons across the midline in vertebrates is mediated by signaling in the floor plate of the neural tube. On the left panel an axon initiates its projection within the tube. On the right panel, the neuron initially receives chemoattractive signaling from netrin ligands and chemorepellents from slit ligands (1).
Comm promotes midline crossing by down-regulating Robo. A LPSY sorting signal motif has been shown to be required for Comm to sort Robo to endosomes, preventing it from accessing the surface of the growth cone. Thus, when Comm is expressed, axons are unaffected by the presence of Slit and are able to cross the midline. [27]
Comm expression turns off after the growth cone has crossed the midline; this permits Robo/Slit repulsion and prevents the growth cone from crossing the midline again. Vertebrates, on the other hand, do not possess a comm homolog ; instead they facilitate midline crossing through alternative splicing of Robo3 (aka.Rig-1).
This article is about the optic chiasm of vertebrates, which is the best known nerve chiasm, but not every chiasm denotes a crossing of the body midline (e.g., in some invertebrates, see Chiasm (anatomy)). A midline crossing of nerves inside the brain is called a decussation (see Definition of types of crossings).
The main function of Slit proteins is to act as midline repellents, preventing the crossing of longitudinal axons through the midline of the central nervous system of most bilaterian animal species, including mice, chickens, humans, insects, nematode worms and planarians. [3] It also prevents the recrossing of commissural axons.
President-elect Donald Trump said Tuesday that NATO member countries “were taking advantage” of the U.S. and should be paying more than double what they currently are required to pay for their ...
The oculomotor nerve crosses the midline before leaving the central nervous system. The trochlear nerve crosses the midline in a chiasma on the dorsal side and the abducens innervates an eye muscle on the same side. [29]: Fig. 17.8 In the light of the axial twist theory, this complicated pattern can be understood.