Lecture 10 02 20 2015 Confusing figure legend HLH transcription factors drive neural progenitors to become differentiated neurons Signal cascades activate or repress these HLH factors Astrocytic or pro neural Hes5 astrocyte rather than neuron o Hes 1 proneural gene why does it say this if it takes to astrocytic lineage Just take that out Hes takes to astrocytic lineage Notch New neurons at top layers first set of neruons deep layer 5 6 on top of that layer 4 interneurons on top of that layer 2 3 pyramidal very diverse because the axons have differnet properties and go to different brain areas Take neural stem cell from animal and put in culture dish neurons pop off layer 5 6 first then lyer 4 comes out then wait some more time and layer 2 3 comes out Internal mechanism that regulates what they turn into Cortical cells have at least partial intrinsic mechanism that says what they will turn into alan founder of Microsoft made atlas Saw that every different cortical cell has unique expression pattern that says what they will become where they will go etc Reporter animals trasgenics good way to show expression of certain things are in certain layers A lot of diversity Waddington landscape 1957 Neural cells diverge by the progressive narrowing of potential fates as development progresses See ppt More pluriopotent cell at top goes down hill comes to point where its fate is decided and can t go back up the hill at what point does that take place E19 embryonic day 19 29 days after fertilization P1 postnatal day 1 1 day after birth P1 gives rise to superficial layer 2 3 pyrramidal neuron Neural stem cells from E19 graft into P1 animal turns into layer 2 3 neurons instead of the normal layer 6 neurons it would have made in E29 Therefore it can also respond to extrinsic factors young neurons can be influences by environmental factors Graft P1 into E29 lost ability to be programmed into deep cortical layers Once you make your first decision you can t go back and make a cell that should have been made 3 days ago Intermediate to old E36 normally makes interneurons put into P1 ability to respond to external factors Intermediate to young E36 E29 layer 4 Read slide Lose the ability permanently usually related to cell cycle once you go through cell cycle proliferation post mitotic is when you lose it post mitotic cells are pretty locked down and don t go back Key experiment Study this Retina follows same mechanism of time where the type of neuron born in retina changes over time and becomes restricted to its fate Not all of the nervous system works this way E g spinal cord more dependent on space than time Top left cross section Motor neurons in ventral portion sensory and interneurons on top Ventral root comes down on bottom on ventral side dorsal root comes up on dorsal side Cervical thorassic lumbar top bottom C1 C8 T1 t12 L1 L5 Sacrum S1 S5 Think of it as Sensory on top motor on bottom in vertebrates Lineage labeling see what neuronal subtype they turn into neural crest progenitors give rise to all neural crest derivatives Outside RB cells not found in all animals Dorsal root ganglia sense motion and mechanics when might need to escape from predator RB cells are generated only in embryos send axons to get startle reflex when feel water motion so tadpole can swim away when sense predators RB die off and yo get classic adult sensory system Motor neurons come from dark pink ventral plate More spatial then temporal Great example of morphogen Shh and RA Base floorplate generates Shh along with notochord Basal plate purple motor neurons Alar plate middle Roofplate top How Shh lays down patterning in PNS Dorsal ventral patterning Watch video Highest concentration of Shh motor neurons If you decrease the signaling everything shifts down see video Low concentrations needs Shh but not tat much turns on class 1 HD genes Repress each other class 1 and 2 Break up into sub boundaries that give rise to particular dorsal ventral regions of spinal cord Go over this Each layer of cortex has transcriotionally unique signature laid down by time Here in spinal cord it s laid down by space thanks to concentrations of Shh BMP RA ALtoug end result is very similar the way to get there is very different between spinal cord and cortex Don t need to know al those transcriction factors that gievs rise to different layers this is all to determine ventral dorsal How about the anterior posterior axis LMC innervates forelimb muscles CT innervates sympathetic chain of nervous system Similar to dorsal ventral patterning concentration of morphogens RA generates at spinal cord boundary Later in development after determination of AP spinal cord and brain you still have that region of expression in spinal cord FGF and RA have inhibitory role upon one another FGF turns of RA in posterior RA synthetsis in anterios region of spinal cord FGF lowest at tail and highest at top of spinal cord opposite of RA double check all this FGF turns on posterior hoxC genes RA turns on anterior HoxC genes makes boundaries to turn into different neuronal subtypes go over this Wasn t paying attention Take posterior neuron and place more anteriorally in gradient of anterior cell type sends axons to correct region been re programmed to innervate correct targets CRISPR and brainbows are his favorite things https www youtube com watch feature player detailpage v c NMfp13Uug See video on slide AND youtube video Genetic technique that leabels every neurons a different color like 15 different colors Random different copies of different colors being expressed These new techniques have helped convince Obama that we can map the whole human brain brain initiative Can label all neurons but still a ton of work to track networks see where they go etc Must section neurons etc YOutube video instead of taking sections you can track intact brain makw whole brain transparent Clarity Hydrogel mesh keeps everything in place and then remove fats lipid bilayer Brain becomes transparent to light label different types in different colors Can apply this to any organ have basically made a whole mouse transparent organ by organ Current microscopes only go down to a certain resolution Ed Boyden made polymers that link everything but expand so shape was exactly same but everything was way larger so he could image it Poineer axons first axons to come out of brain Other axons follow pathways laid down by these pioneer axons Might have interactions or crossing over of these axons