The secretor proteins are further processed in the Golgi. So in Golgi, as we learned before, the proteins there are some process in the Golgi apparatus one is coagulation. And the other one is phosphorylation and sulfation can be done in the Golgi apparatus. And besides this there are some other protein modification happening in Golgi apparatus, is acylation. The thioacylation and isoprenylation, these modifications also happen in Golgi. So after synthesize and multiplication, the protein needs to be transported or trafficked to the target region. So, there are some way for protein trafficking, one exportation, endocytosis, and exocytosis. So, the transport of a protein from cell body to different part, the speed to different part, the speed of transport can be different from region to region. And then we can track the protein trafficking, we can take use of this protein trafficking to track either the protein localization or the connections of two brain regions. So, for example, we can inject some dye or some protein synthesis marker into one brain region and, after a while, we can track. Where this dye appears in another brain region so that we can know these two brain region has synaptic connections. So basically we can inject some dye in a brain region, and then after some time we cut the brain and we see where we can see this dye up here. Sometimes there could be here in the region be, or sometimes it can in the region very far away from the original region. The tracking required a connection, the tracking technique. Recently, there is a technique developed by Edward Callaway group called monosynaptic tracking technique. So the pretty simple of this technique is to use a rapid virus. They construct a pseudo rapid virus that can be a neuron in the brain and it can cross the synapse and then can in fact be neuron upstream of the original neurons. So the construct is rapid virus, make the virus can only cross one synapse but not multiple synapse. So in the print slice, the original neurons is labeled as red. And then all the neurons have monosynaptic connections with this original neurons are labelled green. So in this network, you can recognize in this complicated neuronal cultures, this neuronal system which neurons has one synapse connected to the original labeled neurons. So, the proteins and organelles are transported along the axons. The speed of axonal transport are different. There are fast and slow axonal transport happening in axons. The fast one can transport organelles faster than 400 mm per day. And then in this fast axonal transport, it has two directions. One is the anterograde. The other is retrograde. The anterograde meaning move toward the end. The distal area of the axon move towards the nerve terminals. And the retrograde moves back to the cell body. And the slow transport. Slow transport. The cytosol and cytoskelton proteins can be transported in the axon with this slow speed. With this low speed can only be anterograde to transport is around 0.2 to 2.5 millimeter per day. So the organelles, this is a actual picture in the yam. So the transport happening in the axon is along the microtubule. So we mentioned before the cytoskeleton, one important function for the cytoskeleton, is as a transport highway for materials and vesicles. So in this picture here, this big thing is microtubule structure. And on the top of this microtubule is kinesin, is the motor protein. So motor protein carry the cargo, this is organelle or vesicle. This motor protein can carry this organelle and then go along the micro tubal. And there are several types of motor protein kinesins. Some kinesins, some motor protein only move neurons to the plus end. Some motor protein only move towards the minus end of microtubule, some kinesin can move both ways, either to plus end and minus end. And then the cargo specific, there are cargo specific cages for each kinesin. So, that means the kinesin can only carry certain cargoes, not everything that every kinesin can carry. So, it's highly regulated transport pathway within the axon. So the materials of vesicles on your chest meters can be transported from the cell body to the distal area of exempt. So, for neurotransmitters, the neurotransmitters are wrapped within the synthesized in the cell body, and then the vesicles are transported. From cell body down to the axon terminal and that release there, at the axon terminal.
