4 3 12 Lecture 1 4 16 13 9 50 PM Issues at hand 1 Fertilized egg a region becomes NS what s the mechanism and mapping of where NS will be Specifying the region of the embryo that gives rise to the NS Region called neuro ectoderm Three germ layers Inner layer endoderm gut intestinal tubes Middle layer mesoderm muscle fat blood Outer layer ectoderm two components o Epidermis skin o Neuroectoderm NS The mechanism by which you establish the dorsal ventral axis for the embryo determines the tissue partitioning anterior posterior axis gets separated into various segments Maternal vs zygotic gene functions Maternal completely from maternal genes Ex dorsal region of embryo is from the egg mother Mother s dorsal ventral axis can be through transferred to the egg to have dorsal ventral axis Zygotic genes provided by both parents Activated at a certain point and the zygotic genes then take over development 2 Pathfinding how cells wire together Axon s follow a few critical choice points at which there are several independent cues that are informative 3 Learning experience based rewiring overlap between developmental and learning pathways and associative mechanism by which coincidences are registered brain is designed to remember coincidences as the essence of how you learn Model Systems Humans o Advantages many diseases are self reported so information comes from there Genome sequence is complete and can identify many defects in the genome Genetics comparison in animal studies vs human models is different b c in order to detect subtle mutations in animals is harder than subtle relations in humans because the subtle abnormalities in humans such as the leg tripping ex are self reported o Can record behavior and can ask subjects about state of minds and record self reported mutants 7X10 9 humans in the world Thought that around 5000 genes that can be mutants o No experimental access and fetal material hard to get Disadvantages Non Human Primates Advantages o Most like human in terms of physiological and some behavioral aspects o Can show theory of mind can estimate what other animals are thinking and what they want them to do or not to do Disadvantages o Fetal experiments difficult and expensive o No genetics there s no systematic genetic analysis available Carnivores dogs cats ferrets Advantages o Humanlike brains visual systems are born immature so NS develops much more after birth o Advanced mammals o Fetal work is easier o Dog genome including for diseases such as epilepsy and behaviors such as sheep eye and well established breeds o Some behaviors are determined purely by single genes Disadvantages o No genome sequenced for cats and ferrets 4 5 12 Rats and Mice Advantages Mice o still somewhat similar to humanlike brains o Reverse genetics many mutants exists and possible to do targeted gene knockouts introduce into embryonic stem cell of mouse and knockout gene of interest upto a single AA change and use the mouse may carry a single or even two copies of the gene Can even introduce a human gene mutation in the mouse to study effects o Genetic mosaics trimeric mice Ex mouse that trembles may be a defect in the nerve or a defect in the muscles Take a wild type and mix with cells of a mutant can tell them apart by using gfp or some other bacteria to detect gene If knockout in NS and still trembles then it s probably a muscle defect Rats experiments o Advantages Rats are smarter than mice so better for maze o Disadvantages difficult to do embryonic studies because if a mutant is severely deformed then mother will resorb it Harder to do knockout and development is relatively slow Chicks Quails Advantages The genome for chickens is known Genes can be crossed between chicks and quails to see which regions control which behavior ex quail can be transgenic to make chicken sounds Chicken embryos are accessible outside of mother in eggs cut a hole in the egg and can cut out regions of the embryo and place that region in an egg of a quail Grafting experiment Disadvantages 300 million years of separation difference between birds and mammals There s little systematic genetics available Amphibia Frogs and Newts Advantages The best for grafting experiments Still vertebrate Accessibility of embryo tadpoles develop outside of mother and there s not shell Can do gene knock down by suppressing it s function but not completely knocking it out Disadvantages Not so good for genetic studies because harder to knock genes out and make transgenic frogs Frogs are tetraploid so it s harder to control genetics Zebrafish Advantages excellent genetics many mutants exist because they are transparent and can find mutants much more easily Embryos are easy to work with to make knockout fish gene knock down from RNAi and morpholinos Easier to do grafting Disadvantages Gene knockouts are hard Invertebrates dorsal ventral axis is also inverted in embryo Drosophila Advantages Genetics are very well known Can actually knockout knockdown mis regulate take a gene and make it active only in certain areas Transgenesis is very easy Can add a peptide tag to a fruit fly gene so that they glow Gene manipulation is very flexible Fast generation time 2 weeks Disadvantages neurons are small so hard to do physiological experiments i e sticking electrodes in not a vertebrate 550 million years of separation C Elegans Advantages excellent genetic known RNAi knockdown is possible for every gene 959 cells 302 neurons 56 glial Less neurons so can see experimental effects of individual neurons laser ablations of specific cells that have defined lineage Cell cell communication known entire wiring diagram of neural circuits is known faster life cycle Disadvantages can t do physiological experiments even more separation from humans Gurdon Exp frog embryo removed of nucleus and inserted another frog nucleus in its cytoplasm Could do this with any organ system such as a nucleus from a skin cell the skin cell nucleus had all the genes necessary to make the fully developed frog in the irradiated egg development is due to the selective activation of specific genes in the cell but the all the genes have all the necessary DNA 4 10 12 cytoplasm central dogma of biology Double stranded DNA in the nucleus transcribed by RNA polymerase into single stranded mRNA translated into protein in DNA has 2 parts coding region actual codes for mRNA regulatory region can be on or off and allows RNA polymerase to bind controls whether the gene will be transcribed or not