Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Development - Seattle Central College
Transcript
Development From gamete to embryo Body plan Digestive tube Nervous System Gastrulation accomplishes 2 tasks 1. Creates and positions the 3 germ layers 2. Creates the gut Three germ layers • During gastrulation – 3 germ layers are formed and repositioned – Ectoderm – Endoderm – Mesoderm • Blastula is rearranged – new neighbors, new positions, and multilayered. • Via INVAGINATION – inward movement of cells • Formation of archenteron – primitive gut The in-pocketing of a layer of cells (http://www.uoguelph.ca/zoology/devobio/210labs/gastrul ation2.html) Detachment of individual cells from the surface epithelium and their moving into the interior of the embryo (http://www.esb.utexas.edu/major/zoo321h/lectures/lecture5.ht ml) Inward migration of the outer layer of cells so that it spreads out under the internal surface of the outer layer of cells (http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation2.html) Other factors Delamination – splitting one cellular sheet into two more or less parallel sheets Epiboly - A thinning and spreading of the surface cells to encompass the yolk or deeper cells (http://www.esb.utexas.edu/major/zoo321h/lectures/lecture5.html) Unit of migration – individual cells or sheets/regions of cells Is the whole tissue spreading? Or is the leading edge dragging the rest? Arthropod Drosophila • Gastrulation begins at MBT • Prospective mesoderm (1000 cells) folds in at the ventral midline to form the ventral furrow – Furrow pinches off to form the ventral tube w/in embryo • Prospective endoderm invaginates as 2 pockets • Pole cells are internalized along w/ endoderm • Embryo bends to form cephalic furrow • Surface ectoderm and mesoderm: converge & extend – Form germ band (future trunk) Drosophila gastrulation http://www.youtube.com/watch?v=1MnwHRURKns &feature=related http://www.youtube.com/watch?v=j87y7EAj8qE&f eature=related Sea Urchin gastrulation • Blastula of about 1000 cells – vegetal pole flattens and thickens • Central cells extend and contract via filopodia – Ingress into blastocoel – Using surface proteoglycans & fibronectin • As blastopore forms – cells migrate w/ convergent extension – cell division too http://www.youtube.com/watch?v=Lgb4wMsZwZA Amphibian gastrulation Starts at 12th cell cycle – MBT – embryonic genome activated Sperm entry = ventral Blastopore = dorsal http://www.youtube.com/watch?v=qisrNX3QjUg Invagination Frog Gastrulation Involution + epiboly Avian Gastrulation • Meroblastic cleavage: yolk gets in the way • Blastula ~ Blastodisc = Epiblast & hypoblast perched atop yolk Avian gastrulation • Primitive streak ~ Blastopore • Invagination + Ingression from epiblast • Migration to form meso & endoderm Avian gastrulation - Yolk sac - Amnion - Chorion - Allantois • Mammalian Gastrulation - holoblastic Blastocyst Forms placenta Neurulation & Organogenesis Making a brain and nervous system…. Neurulation accomplishes three major things (1) Creates the neural tube, which gives rise the central nervous system. (2) It creates the neural crest cells, which migrate away from the dorsal surface of the neural tube; give rise to diverse set of cell types. (3) It creates the bona fide epidermis, which covers the neural tube once it is created. http://worms.zoology.wisc.edu/frogs/neuru/neurul_intro.html Dorsal Ectoderm • Columnar cells • Neural plate – edges thicken and fold • Neural tube – after the neural plate folds together – R and L side of embryo • Neural crest – dorsal-most cells in neural tube http://www.xenbase.org/atlas/movies-neur.html Neural Plate formation From dorsal ectoderm Neural plate folding • Anchored to notochord beneath • Notochord induces ectodermal cells to elongate – become columnar • Plate lengthens along A-P axis via convergent extension Neural plate folding • Anchored to notochord beneath • Notochord induces ectodermal cells to elongate – become columnar • Plate lengthens along A-P axis via convergent extension • cell divisions are rostral & caudal Inducing neurulation • Notochord produces Sonic Hedgehog (SHH) • -> induces dorsal ectoderm to secrete BMP-4. • -> ectoderm cells that bind BMP-4 become epidermis • Cells that do not, due to BMP-4 inhibitors binding to BMP-4 first, become neural plate • Cells from dorsal lip of blastopore initiate these induction events BMP-4 SSH + Vertebrates Neural crest: ectodermal cells that migrate throughout body & form “Vertebrate structures” (teeth, skull bones, gill arches, middle ear bones and associated nerves) Somites: Blocks of mesoderm that form segmented structures (ribs, associated muscles, vertebrae, etc.) • Some Neural Crest cells fates • Craniate structures & associated nerves http://anatomy.med.unsw.edu.au/cbl/embryo/Notes/images/neuron/image_002.gif Human neurulation: Differentiation of the Neural Tube Anterior-Posterior Axis Forebrain – prosencephalon later telencephalon and diencephalon Midbrain – mesencephalon Hindbrain rhombencephalon Nervous System Development http://www.med.unc.edu/embryo_images/unit-nervous/nerv_htms/nervtoc.htm Organogenesis (Table 47.14 text) General Trends • Cell fates narrow during development – Totipotent • Zygotes & often blastomeres – Pluripotent • Late Blastulas & Gastrulas – Multipotent – Terminally differentiated Invagination patterns • Invagination • Ingression • 0 invagination involution epiboly invagination involution ingression
