zygote neurula Flashcards
Name stages of early embryogenesis
- zygote
- cleavage (mitosis)
- morula
- blastula (first embryonic cavity)
- gastrulation (forms germ layers)
- gastrula (new cavity)
- organogenesis (neurulation, forms chorda dorsalis, then systems + organs) (vertebrates)
what kind of cells made during cleavage
during cleavage, volume of egg cytoplasm is divided into smaller cells called BLASTOMERES
what triggers blastomere division. (cleavage)
what is the role of cylin dependant kinases
. activation of mitosis promoting factor (MPF) which is a type of CDK
. regulates the cell cycle of early blastomeres
what does initial activation of MPF do
causes alternating M + S phases, no gap phases (G1+G2)
is yolk concentration high in the animal pole?
what is yolk rich pole known as
. quite low. cellular divisions faster at animal pole
. vegetal pole
what is the purpose of the blastula
. provides first cell layer + cavity (blastocoel) in embryo
what is a blastoderm
the wall of the blastula formed from blastomeres
role of blastocoel
. provides space for gastrulation cell movements
. prevents premature interactions btw cells with different future development
what determines the look of the blastula
pattern of yolk distribution + gradient of some molecules in ooplasm
brief expl blastula formation in mammals
. first 2 days, division of cells = 24 hours
. division of mammalian blastomeres = asynchronous (dont happen at same time)
. embryo 16 cells = morula
. in mammals the blastula is called BLASTOCYST
why after blastocoel formation in mammals its called blastocyst not blastula
blastula - all of it is part if the embryo
in mammlas, only some cells form embryo, others form foetal part of placenta + envelopes?
Blastocyst is what implants into uterus
It also has other struxtures like trophoblasts
types of cell movement during gastrulation
.Invagination - epithelial cells bends inwards
.Ingression - individual cells leave epithelial sheet + become migrating mesenchyme cells
.Involution - epithelial sheet rolls inward + forms underlying layer
.Epiboly - sheet of cells spread by thinning
.Delamination - one cell layer migrates + develops second layer.
** pg 10 look ppt for pics :)
explain diploblastic + triploblastic animals
Diploblastic (radiata) - forms ecto and endoderm
Triploblastic (animals with bilateral body symmetry) - ecto, meso, endoderm
protostomes vs deuterostomes
P. mouth then anus, coelom forms from splitting of mesoderm.
D. anus then mouth, coelom forms from mesodermal budding of archenteron (cavity wth 2 openings)
what does the neural tube + crest do
gives rise to spinal cord + brain
neural crest cells migrate form tube + forms different cells
Neuralation brief expl
*cuboidal cells turn columnar, = thickens ectoderm
*cell adhesion causes edges of the plate fold+ rise to form a tube
*cells at tips of neural folds become neural crest cells (epidermis + n plate can give rise to this)
*somites form pairs flanking neural tube + form segmental pattern in vertebrate embryo
explain mosaic development
. fertilised ovum undergoes determinate cleavage
. each blastomere has limited development potency
. blastomere is precursor of specific part of embryo.
. blastomere damage/detruction = defective organism
. this due to ooplasmic segregation of morphogens
* not valid for mammalian eggs
what are morphogens
. they direst cell/tissue development
. theyre conc gradients in oocytes = ooplasmic segregation
. blasmomeres get a specific set of them during cleavage
. in early devlpmnt the gradients cause diff cells types in distinct spatial order
.*they act by inducing/maintaining expression of diff tagrget genes
* M are secreted proteins that signal btw cells, TF or small molecules
when does ooplasmic segregation finish and what happens next
after sperm egg contact.. provokes movement cortical ooplasm
first cleavage furrow goes through middle of grey crescent therefore first 2 blastomeres equal.
next divisions, blastomeres takes diff cytoplasm (depends on location)
* final ooplasmic segregation forms ant/post + ventral/dorsal axis of symmetry
what are presumptive regions
cell groups predetermined for certain cell fate (before differention). determinations of these regions increase during early gastrulation
why can amphibian embryos be used to revel things in early embryogenesis
they develop in water so can be experimented at all stages. jelly coat can be removed and microsurgeries easily performed on the eggs so no complicated/expensive tools needed
stages of the amphibian embryo
- first cleavage divides zygote into 2 equal blastomeres ( each takes half whats needed morphogens in correct gradient)
- if first 2 blastomeres split, they’ll become 2 genetically identical normal larvae
- if grey crescent stays in only 1 of them, only that blast becomes normal larva
how do you get conjoined twins (gastrula)
if you split the presumptive region into 2, you create 2 organizers in same embryo: 2 sets of neural tubes + notochord created.
Why do mammals not need egg yolk
Bc They have placenta
Birds and frogs need lots of yolk since their eggs develop outside body
Do fish or amphibians have more yolk?
Fish has more yolk bc they have no larval stage-no metapmorphasis (when egg hatches tiny fish comes out no tadpole etc)
What is the result of yolk being evenly distributed in mammals
Mammalian cleavage complete and blastomeres equal size
How is a frogs have asymmetrical blastomeres
3rd cleavage furrow =equatorial cleavage delayed in vegetal part of the egg
What is the grey crescent
Is a structure of AMPHIBIANS that determines body symmetry
How is grey crescent formed in external fertilization of amphibians
- Sperm has to penetrate animal pole as vegetal pole full of yolk
- Sperm carries centrioles which contains microtubules to allow rotation of cortical layer of egg
- Mixes dark and light cytoplasm= grey crescent
Grey crescent is the future dorsal part of embryo, notochord formed. When crescent bisected-we get left+right
What chromosomes produce molecules for early embryonic development of amphibian
Lampbrush chromosomes (found in oocytes of animals except mammals)
