vertebrates from egg to embryo Flashcards
What makes an animal a vertebrate?
-Chordate – head, dorsal nerve chord, notochord
-tunicates- closest relative to vertebrates:
=larval stage:
=sensory organs and have a clearly defined head region (concentration of nerves
=neural tube which runs down dorsal part f body down tail
=precursor of vertebrates column called notochord- early form of spinal chord
-tunicates sit at bottom of ocean in larval stage and looks like a tadpole
example of vertebrates
-tunicates
-hagfish – cartilage and
-rudimentary vertebrae
-lampreys - vertebral column
-chondricthyes - jaw
-ray-fined fish - bone
-lung-fish - lungs
-amphibians - tetrapods
-mammals
-snakes, lizards, birds
whats Ernst Haeckel
-Pharyngula stage: we don’t know why its so conserved, classic development
-pharyngeal pouches- gives rise to gills and lower jaw
-somites
-Metameric structures (lots of similarities)– repeated modules- segmentatation (process)
-These similarities are probably due to “bottle-necks” during development that are evolutionarily conserved.
-look at slide 5
whats Idealised early development
-oocyte and sperm= zygote
-cleavage- because cells are large to start with
-blastomeres- all identical
-blastula- contains blastoderm ( outside) and blastocoel (inside cavity)
equations showing Early cell proliferation is exponential
-Nstart X 2(tXf) = Nfinish
-N = number of cells
t = time
f = frequency of division
what occurs during Fertilisation: egg activation
-After sperm entry a wave of free Ca2+ ions travels across the egg (red dye which fluoresces in contact with Ca2+)
-Now development can proceed
-Calcium acts on proteins that control the cell cycle to initiate cleavage (cell division)
-Oscillations in Ca2+ levels during early development synchronise cell division. Cell divisions are very rapid.
what happens in the cell cycle in the early embryo
-Rapid, synchronous cleavages
-S and M phases only; no G phases
-G1 transcription is suppressed*
-Maternal stores (RNA and protein) provide building blocks for DNA synthesis and growth
-rely on maternal stores of RNA of a protein-contains genome and special RNA
what happens in Zygotic genome activation
-Timing:
2-cell stage (mouse)
5,000-cell (frog)
-Characteristics:
Cell cycle slows
Cell cycle becomes asynchronous
Cell movement begins
-look a slide 10
whats Gastrulation: formation of the three germ layers
-Movement of cells to the inside of the embryo to form the endoderm and mesoderm.
- The cells that remain on the surface form the ectoderm.
- Establishment of the A/P and D/V axes (anterior/posterior and dorsal/ventral)
what are the different types of Germ layer derivatives
-ectoderm: Neurons, Glia, Epidermis, Pigment cells
-mesoderm: Muscle, Cartilage, bone, Dermis, Kidney, Heart, Blood
-endoderm: lungs, gut and associated organs
what does gastrulation involve
-the complex rearrangement of tissues
what are Epithelium and mesenchyme
-the first tissues
-Epithelial cells (move on mass) are more structured and tend to be cuboidal- joined together by junction complexes which keeps bacteria from getting inside of us
-They can migrate but usually move en masse (together) as a sheet or cluster
-Mesenchymal cells (random shape) move easily and are amorphous (no defined shape) so they separate by extracellular proteins/matrix therefore they easily move around
whats Cell behaviour in the embryo like
-epithelia can from mesenchymal cells by condensation
-mesenchyme can form epithelium by involution and invagination (cavity formed)
zebrafish
-Early cleavage -> Gastrulation -> Somitogenesis
neural tube formed in the middle with somites on either side
-notochord formed at the base
whats are the Forces that drive cell and tissue rearrangements
-Cell shape changes (cytoskeletal rearrangements)
-Changes in the expression of cell surface proteins (cell adhesion molecules)- holds cells together or rips them apart
-Migration
-Localised cell proliferation Cell death- gives rise to change I tissue shape
-MORPHOGENESIS =(change shape of the embryo) the creation of shape
whats is The vertebrate body
segmental
-Somites are a transient structures that form following gastrulation in the mesoderm- temporary structure formed in the embryo that become segmented and disintegrate
-at the end of gastrulation, mesenchymal cells gather dorsally
-cells on the outside edge of
the somite epithelialize to make it distinct from neighbouring tissue
-The somites then disassemble and revert to mesenchymal cells
what are Mesodermal progenitors in the somite like
-Dermomyotomem -> dermis and skeletal muscles
-Sclerotome -> vertebrae and ribs
-The segmentation of these structures in the adult is a result of the segmentation during somitogenesis. However one somite does not give rise to one vertebrae. It gives rise to two halves of a vertebrae
an example of segmented muscles
-trunk muscles
-formation of neural tube happens after gastrulation
what does the neural tube in the brain and spinal chord arise from
-ectoderm
-Morphogenesis takes place by cell shape changes
