2/ vertebrates from egg to embryo Flashcards
what are vertebrates
- endoskeleton (inside)
- axial skeleton runs down length of body, vertebral column
- chordate (phylum) - head, dorsal nerve chord, notochord
closest relative to vertebrate
tunicates (not vertebrate)
vertebrates progression
- hagfish - cartilage and rudimentary vertebrae
- lampreys - proper vertebral column
- Chondrichthyes - jaw
- ray-fined fish - bone
- lung fish - lungs
- amphibians - tetrapods
- snakes, lizards, birds
- mammals
when is there diversity/conservatism (why?) in embryo development
- variation in early embryogenesis
- pharyngula stage conserved. bottle necks during development that are evolutionarily conserved. no embryo if these genes mutate
- variation in late embryogenesis
what do pharyngeal pouches give rise to?
- fish: lower jaw, gills
- land animals: lower jaw, neck, throat
what are metameric structures
- repeated modules that show segmentation
- pharyngeal pouches and somites
what do somites give rise to
skeletal muscles, bone, parts of skin, tendons, cartilage
stages of early development
- zygote
- cleavage. early divisions, divide into blastomeres - all look identical. divisions occur simultaneously, not yet growing
- blastula. with blastoderm on outside and blastocoel inside
how long does it take for cells to divide
30 mins
how do eggs become activated after fertilisation
- after sperm entry, wave of free calcium ions travel across egg
- calcium ions released from intracellular stores like mitochondria
- calcium acts on proteins that control cell cycle to initiate cleavage
- synchronise very rapid cell divisions
- unfertilised eggs start to divide w calcium
cell cycle in early embryo
- S and M phases only, no G phases
- transcription in G1 is suppressed
- maternal stores of RNA and protein allow DNA synthesis
- early division based on mother’s genetics
zygotic genome activation timings and characteristics
- timing vary depending on vertebrate - mice 2 cells, frogs 5000
- cell cycle slows and becomes asynchronous, cell movement begins
what is gastrulation DIAGRAM
- formation of the 3 germ layers
- movement of cells to the inside of embryo to form endoderm and mesoderm
- cells remaining on surface ectoderm
- establish Anterior/Posterior and Dorsal/Ventral axis
ectoderm forms
neurons, glia, epidermis, pigment cells
mesoderm forms
muscle, cartilage, bone, dermis, kidney, heart, blood
endoderm forms
lungs, gut, associated organs
outline gastrulation movement
- blastopore (little hole) forms, endoderm cells stream in and move up
- ectoderm moves around outside to encase embryo
epithelial cells summary
- more structured, tend to be cuboidal
- can migrate but move together - en mass - as sheet or cluster
- due to junctional complexes and anchoring to basement membrane
mesenchymal cells
- move easily
- amorphous - no defined shape
- don’t stick together
- separated by ECM
cell behavior in embryo
- condensation: tissue undergoes coordinated decrease in size and increase in density
- epithelium to mesenchyme
- mesenchyme to epithelium
- involution: creates a gap cells can move into. cells circle back on themselves
- invagination
forces driving cell and tissue rearrangements
- cell shape changes - cytoskeleton
- changes in expression of cell surface proteins - adhesion molecules
- migration
- localised cell proliferation
- cell death - cells destroy themselves to sculpt shape of a structure
what is mprphogenesis
creation of shape
zebrafish early development stages
early cleavage, gastrulation, somitogenesis (form anterior to posterior)
somite formation
- after gastrulation
- form in mesoderm
- mesenchymal cells gather dorsally
- cells on the outside edge epithelialise it to make it distinct from neighboring tissue
- somites dissemble and revert to mesenchymal cells
