BIO 131_ Study guide chapter 43 neural development.pdf

Be able to explain the major steps involved in neurulation; include the role of the neural plate, neural tube, notochord, neural crest cells and somites. Neural development - Development of the brain, spinal cord, and peripheral nerves --- formed from the neural ectoderm --- post-graduation developm...

Be able to explain the major steps involved in neurulation; include the role of the neural plate, neural tube, notochord, neural crest cells and somites. Neural development - Development of the brain, spinal cord, and peripheral nerves --- formed from the neural ectoderm --- post-graduation development stained sea urchin blastula [gastrulation] orange = transcription factors of the mesenchymal cells (mesoderm) Figure 2: flattening of vegetal side; congregating of cells on the vegetal plate Figure 3: movement of mesenchyme cells; can vaguely make out the disruption of cytoskeletons on the animal pole Blastula Fate Map - Note 3 germ layers --- describes all tissue formations that arise from the three layers Notodorm in mesoderm Ectoderm Fate Map zoom in of blastula fate map Important tissues formed from ectoderm: --- neural tube (interior portion becomes the brain, downstream portion becomes the spinal cord and motor nerves) Development of Vertebrate nervous system 1) Formation of Notochord and Neural Plate (neurula) 2) Neurulation [formation of nervous system] 3) Development of the neural tube 4) Migration of Neural Crest Cells 5) Formation of vesicle layers in the brain 3 Mains structures involved in forming nervous system 1) Notochord (mesoderm) 2) Neural tube (between notochord and ectoderm) 3) Ectoderm Formation of Notochord - - A major function of gastrulation of vertebrates is to bring mesoderm underneath the ectoderm on the dorsal side of the embryo and then to form a notochord (important for directing the nervous system.) The notochord then sends a signal to the ectoderm, and causes it to form a neural plate. This is called primary induction. Notochord - Important for directing the nervous system --- located in the mesoderm underneath the neural plate During embryonic development, it directs the neural plate to become the neural tube Understand the term – primary induction. Primary Induction - The method used by the notochord to direct other cells --- when a set of cells send a signal to another set of cells and those cells respond in a specific way to promote a function or development Two Possible Types/Mechanisms 1) Release of Positive Factors 2) Release of Negative Factors Experiments revealed that Release of Positive Factors is the correct way Possible Types of Primary Induction Release of Positive Factor --- notochord instructs the overlying epithelium to become neural (N.B. neural, not neutral) --- aka turned on genes that eventually cause the formation of the neural tube --- particularly, a group of cells in the Spemann organizer part of the notochord was responsible sending signals that result in the formation of the neural tube Release of Negative Factor ---- the signal from the notochord overrides instruction to become epidermal (like the rest of the ectoderm), allowing the default pathways of neural development to proceed --- "neutralize" the instructions to become epidermal Experiments revealed that Release of Positive Factors is the correct way Dorsal side of gastrula where all the precursors of the nervous system are located mostly in the ectoderm The mesoderm underneath the neural plate is the notochord Neurula When the gastrula has reached the point of development where it has formed the neural plate neural plate Part of the ectoderm that becomes the brain and spinal cord --- in frogs, extends from the anterior portion of gastrula to the blastopore --- anterior portion becomes the brain (neural plate of brain) and most of the remainder becomes the spinal cord Part of the ectoderm that becomes the brain and spinal cord --- in frogs, extends from the anterior portion of gastrula to the blastopore --- anterior portion becomes the brain (neural plate of brain) and most of the remainder becomes the spinal cord Neurulation development of the nervous system from neurula --- formation of the neural tube and crest cells from the neural ectoderm --- this specific case is for amphibians, but a similar process occurs in all vertebrate embryos Purple: neural plate in neural ectoderm Yellow: neural folds which contain future neural crest cells (peripheral nerves) Grey: Epidermal ectoderm (ectoderm cells that will eventually cover the neural tube and become the outer layer of skin) Underneath the neural plate is notochord (mesoderm cells that work by using primary induction to send signals to the neural ectoderm Steps Notochord sends signals to the neural plate that causes the cells to move --- neural ectoderm moves inward and forms a circular pattern with hollow space in the middle --- the two neural folds end move inward and eventually make contact with each other and form a layer of neural crest cells --- epidermal ectoderm cells also connect with the opposite end The neural tube will become the brain and spinal cord; the neural crest cells will become the peripheral nerves --- neural crest cells eventually extend and form spinal nerves, peripheral nerves, and connective tissue - Neural Tube an embryonic structure that gives rise to the central nervous system Neural crest cells Cells at the tip of the neural fold; this group of cells gives rise to many components of the peripheral nervous system. - --- spinal nerves, peripheral nerves, and connective tissue - Neural groove in the developing embryo, the groove between the neural folds Landmark Feature of the Developing Neurula - be familiar with all cases Know how the notochord contributes to the formation of the neural tube. How are the molecules Shh, TGF and BMP involved in this process? What type of protein is Shh? What are the major types of neurons that initially develop from the neural tube? Development of the neural tube 1 - The later development of the neural tube depends on further signals from the notochord and from the ectoderm. - --- This sets up gradients of proteins and cells “read” their position in the gradients and respond accordingly Proteins: Sonic hedgehog (Shh) is produced by the notochord and moves into the floor plate of the neural tube, later diffuses further into the neural tube --- direct the formation of additional nerves BMP is a protein that accumulates in the endoderm and is released into the roof plate (dorsal part of the neural tube), later diffuses across the neural tube - The release of Shh from the notochord and BMP from the ectoderm leads to gradients of growth factors in the developing neural tube - Cells within the neural tube read their positions within the gradients and differentiate accordingly --- see all the different type of interneurons (neurons that connect to other neurons) that form [see "Development of the neural tube 2"] --- Shh is influential in forming motor neurons Sonic hedgehog (Shh) - protein secreted from notochord cells that activate a receptor in neural tube cells and directs motor neuron formation. --- moves into the floor plate of the neural tube, later diffuse further into the neural tube --- name comes from scientist's son --- Shh is influential in forming motor neurons Sonic hedgehog (Shh) Activation and Activity [in notochord] - When the Shh gene is activated in notochord cells, the Shh precursor is transcribed. Shh precursor has two ends: the N terminus is for signaling and the C terminus is a catalyst (enzymatic activity.) - The precursor is modified into active Shh and secreted out of the notochord and heads toward the floor plate of the neural tube. - [at the floor plate of the nerual tube] - At the membrane of the neural tube, it interacts with the receptor. - The receptor for Shh is two proteins Smo (smoothened) and Ptc (patched). These need to come together to form the correct 3D shape to interact with Shh. - Once Shh interacts with the receptors, it stimulates the signaling of activators and repressors that can manipulate gene expression. --- Shh gets into the cell through vesicles BMP - Influential in neural tube development - protein part of TGF-beta family [transforming growth factor] (incl. BMP4, BMP7, BMP5, Dorsalin, Activin) Stain of developing notochord - Blue marks a protein induced by a signal from the ectoderm Sonic hedgehog (Shh, stained green) in the notochord and floor plate of the neural tube. Motor neurons are seen in orange/yellow Somite - series of segmented blocks of mesoderm that exist in pairs just lateral to the notochord in a vertebrate embryo. --- common in segmented animals; landmark feature of the progression of development --- eventually become muscle cells that support the spinal chord --- important for development and progression of the spinal cord in vertebrates Myotomes - tissue derived from somites that will become muscle tissue Migration of Neural Crest Cells - Neural crest cells migrate from the dorsal side (top)of the neural tube and travel throughout the developing embryo. - The migration begins at the anterior end of the neural tube with the more posterior neural crest cells migrating later. Cross-section of developing vertebrate - note ecto/meso/endoderm - Can see that the neural tube has formed the spinal cord and brain (blue w/ hollow middle) - --- brain section is no longer a round circle; has formed indentations called vesicles that will form different parts of the brain and head - somites are muscle tissue supporting spinal cord - Notochord underneath spinal cord - can see that the neural crest cells have migrated out from original period; innervate other parts of the body What do crest cells actually become? - Two major groups of crest cells: - Cranial Crest (come from head region) become In sensory nervous system --- cranial nerves In Parasympathetic nervous system (part of the automatic nervous system) --- parasympathetic ganglia of head and neck Trunk (lower back) and Cervical (upper back) Crest (come from spinal area) make In pigment cells --- melanocytes (Create pigments for skin color) In the sensory nervous system --- spinal ganglia (cells that transfer sensory info from different parts of your body) In sympatric NS (part of the automatic nervous system) --- cervical ganglia --- vertebral ganglia --- visceral and enteric ganglia automatic nervous system - the part of the peripheral nervous system that controls things that happen automatically - made up of sympathetic (stress, flight/fight) and parasympathetic (calms body) Be able to convey how the neural tube results in the formation of the brain. Structure of Developing Brain - - The vertebrate brain develops at the anterior (front) end of the neural tube. Initially, three primary vesicles of the neural tube are the Forebrain, Midbrain and Hindbrain. The forebrain (aka prosencephalon) controls body temperature, reproductive functions, eating, sleeping, emotions. It separates into the diencephalon [internal part of the brain; controls those functions] and telencephalon [most recently evolved part of the brain which develops into the cerebrum] The midbrain (mesencephalon) controls vision, hearing, motor control. Hindbrain (rhombencephalon) develops into medulla, pons and cerebellum and supports vital autonomic processes After the hindbrain, the neural tube decreases in width and continues as the spinal cord. Forebrain aka prosencephalon - controls body temperature, reproductive functions, eating, sleeping, emotions. It separates into the diencephalon [internal part of brain; controls those functions] and telencephalon [most recently evolved part of the brain which develops into the cerebrum] midbrain - aka mesencephalon - controls vision, hearing, motor control. hindbrain aka rhombencephalon develops into medulla, pons and cerebellum and supports vital autonomic processes tadpole overview (for following cross sections) Cross-section of Hindbrain Area (tadpole) spinal cord notochord somite epidermal ectoderm underneath notochord is midgut (aka just the gut) dorsal aorta (major blood vessel that distributes blood to the entire body) nephrotome (Eventually become kidneys Cross-section of Midbrain (tadpole) midbrain = mesencephalon notochord (less pronounced than in hindbrain) pharynx (becomes the pathways which food travels from mouth to digestive system) dorsal aorta aortic arch (idk??) epidermal ectoderm head mesenchyme (mesoderm that remains which eventually becomes different parts of the head) Cross-section of Forebrain (tadpole) forebrain = prosencephalon neural tube has definitive curves and physical features (vesicles) epidermal ectoderm neural crest optic vesicle (becomes eyes) lens placode (ectoderm that becomes lens; like neural plate for eyes; affected by primary induction) infundibulum (connects with developing pituitary; discrete different hormones)