Lecture 3: Gastrulation Flashcards
The formation of the first three tissue layers
Rostral = cranial
head end
caudal
tail end
dorsal
top of the animal
we allocate left and right
ventral
abdominal side
anterior
anterior
side of the face
posterior
opposite of posterior so in animal same as dorsal
proximal and distal
for describing limbs
proximal is close to the body
gastrulation in drosophila
ventral furrow formation = a slit = opening to the blastula
blastopore
gastrulation in sea urchins
deuterstomes
not symmetrical to juveniles
invagination
round blastopore
invagination
where cells are released from and 3 distinct germ layers can separate out = an opening to the inside
will eventually become anus
gastrulation
site is the blastopore/primative streak
formation of first embryonic tissue layers through morphogenetic movements - shape creating from epiblast/primitive ectoderm
- definitive ectoderm = sole source of nervous system
- mesoderm = majority of inner organs + blood, muscle kidney + gonads definitive endoderm
from epiblast
and in aminotes hypoblast = primative endoderm extraembryonic
evolved in ALL bilaterians
gastrulation in xenopus frog
deutrestomes
blastopore
round blastopore with a yolk plug in the middle
gastrulation in chicken
slit blastopore - primitive streak (forms on one side of blastula)
initially short and wide and then extends with cells ingressing at the edges of the slit towards the primative steak = 2mm long under stereo microscope
epiblast - tightly packed cells
or primative ectoderm - cells that undergo EMT and spread underneath
cells leave the epiblast through an EMT
groove - so many cells engaged = end up with.a depression
mesoderm
endoderm
epiblast produces the mesoderm and endoderm and what stays on the outside will become the definitive ectoderm
how do cells in the epiblast move
invagination involution ingression delamination epiboly (growth of cells around the yolk) and a combination towards the blastopore/primitive streak
detach from epiblast and spread underneath to for 2 inner tissue layers mesoderm and endoderm
remainder of the epiblast becomes the ectoderm
gastrulation in humans
implantation:
blastocysts consists of inner cell mass
from which hypoblast forms
amnion
epiblast forms a primitive streak from which cells emigrate
but in mice n rodents developmental anatomy distinct:
primitive streak starts at caudal end
cells detach and spread
endoderm and mesoderm are on the outside
ectoderm on the inside
gastrula inside out initially
the fate of ecto endo and mesoderm
- zygote
- blastula
- gastrula
A = germ cells
B = ectoderm
central nervous system and epiermal layer of skin and pigment cells
vertebrates - cells that can migrate away and form peripheral system
endo
digestive tube gut canal
thyroid cells -pharynx
alveolar cell
mesoderm tubule cells of kidney notocord facial muscle red blood cells bone tissue
time and rostrocaudal (anterior-postrior) (head-tail)position of cells in the streak vs. mediolateral position in the germ layers (close to the node/orsal blastompore vs away from it
cels gasturalting
early = rostral anterior
later - caudual posterior
rostral streak = medial = dorsal once the body wall is closed ventrally
caudal streak = lateral = ventral
medio lateral axis = dorso-ventral axis = back abdomen
left right axis
insitu hybridsation
symmetry is broken
Shh gene
Pitx2
let right as viewd from the top dorsal side
how the germ layers and the longitudinal body axis is formed
conc:
the fate of the dorsal blastopore lip is to make axial mesoderm notochord
the graft induces the formation of the 3 germ layers and organises the formation of the 3 body axis
how does the organiser form
dorsal blasta animal cap cells = ectoderm
middle = mesoderm
ventral blasta vegetal cells = endoderm
when ventral dorsal tissues are co cultured the dorsal tissue is converted to mesoderm
Sox17 endoderm developmental path
vegT - notal genes
endoderm
mRNA for VegT are in the endodermal part of the egg
when translated vgT protein activates TGF beta signalling inform of nodal which signals to the marginal zone
translation of veg1/Gdf1 will raise tgf beta levels
translation of wind components stabilisers beta catenin
activate nodal genes
= nodal and tgf signalling from vegetal pole signals to the marginal cells = induced mesoderm
high = organiser will be induced in marginal zone + expressed inhibitors
high BMP = lateral or ventral mesoderm
absence of BMP
the dorsal
high wnt8 determines caudal or tail end
absence of wnt8 determines rostral or head end of longitudinal body axis
transcription factors:
VegT, B-catenin
secreted = organiser, nodal vg1/Gdf1, BMP, Xwnt8
gastrulation in vertebrates
early cleavage organisation how the embryo deals with the yolk differs
all vertebrates develop an organiser
tail bud
cells gather at tail bud drives formation of sacral and caudal part of body axis
defects in gastrulation are not compatible with life
defects in tail bud development lead to posterior body truncations
defects in gastrulation arise from loss, defects in tail bud formation from the partial loss of function of organiser genes
Niewkoop centre in frogs
in vegetal zone high nodal signalling and beta catenin
the rganiser will be induced in the marginal zone
overlap in the marginal zone and vegetal zone
what is difference between the normal mitotic cell cycle and first zygotic cell cycle
g1 and g2 are omitted
what are structures that are shared between vertebrates
somites
hindbrain consisting of individual rhombomeres segmented
the role of BMP
depending of how much yolk you have
frog = embryo wrapped around yolk rich cells at the vegetal cells
or flat ontop of yollk
midline = primitive streak
the further they are the more lateral or on the side they are
in the middle due to organiser high level of BMP inhibitors expression
could be soluble and travel a distance or can be autonomously and work in the cell
the cells in the midline get the BMP pathway shut off
the cells further away from the midline less and less BMP signalling
cells in the ectoderm through BMP become epidermis cells
mesdoerm = lateral or extraembryonic mesoderm in mice
in frog what was lateral becomes venral
dorsal = midline
ventral= far away
in chicken
once the endoderm closes and forms gut canal - same
midline becomes dorsal
what was out and lateral becomes ventral
