Development: Animal Development Flashcards
four processes in animal development
fertilization, cleavage, gastrulation, organogenesis
fertilization
union of male/female gametes to restore diploidy
how does the sperm effect the zygote
establishes polarity in the zygote
challenges to fertilization
polyspermy and species recognition (external fertilization)
egg contributes
haploid nucleus, organelles, nutrients, cytoplasmic determinants
cytoplasmic determinants
mRNA, transcription factors, proteins that set up signal/gene expression cascades > lead to differentiation
sperm contributes
haploid nucleus, centriole (form centrosome)
why is the centrosome important
determines location of mitotic spindle which determines plane of cell division
sea urchins have external fertilization, how does gamete species identification occur?
sperm of species displays protein bindin which must bind to species specific receptor on egg plasma membrane
acrosomal process
actin extensions from sperm on which bindin is presented
two mechanisms sea urchins have to prevent polyspermy
fast block and slow block
fast block
sodium channels open up to allows sodium to enter the egg - the change in voltage (membrane potential) prevents additional sperm from entering
slow block
calcium release, cortical reaction and fertilization membrane formation
how does calcium initiate the cortical reaction
cortical granules fuse with cell membrane and exocytose the contents between the membrane and the vitelline layer
what is inside the cortical granules and what happens
enzymes that digest the sperm receptors
how is water involved in the cortical reaction
water rushes into the space between the membrane and the vitelline layer (due to the high solute content) which pushes the fertilization envelope away from the egg
how does sperm entry effect cytoplasmic determinants
causes rearrangement of cytoplasmic determinants - centriole from sperm guides movemennt of cortical (outer layer) cytoplasm
B catenin and GSK3 in frog eggs
both diffuse throughout egg before fertilization (GSK3 targets B catenin for degradation)
where is GSK3 inhibitors found
vesicles in the vegetal pole
what happens upon sperm entry
the cortical cytoplasm shifts, causing vesicles to move along microtubule tracks and release protein
how does the cortical shift in frog eggs rearrange cytoplasmic determinants
B catenin degraded on ventral side (gradient runs dorsal to ventral) and the ventral-dorsal axis is established
cleavage
series of cell divisions where large volume of egg cytoplasm subdivides into smaller cells - no change in size, just number of cells
blastula
ball of small cells after cleavage
blastocoel
fluid filled sac inside blastula
blastomeres
individual cells that make up blastula
blastulation
formation of the blastocoel
what determines the type of cleavage
amount of yolk
complete cleavage
little yolk, cleavage furrows divide egg completely and blastomeres are similar in size
complete cleavage occurs in
echinoderms and mammals
incomplete cleavage
lots of yolk, cleavage furrows can’t penetrate dense yolk mass so embryo forms on top of yolk
incomplete cleavage occurs in
fish, reptiles, birds
superficial cleavage
mitosis without cytokinesis to create a multinucleated embryo
syncytium
multinucleated cell
superficial cleavage occurs in
drosophila
indeterminate cleavage
at the 4 cell stage, a cell can be removed from the embryo and can develop into a new embryo - totipotent
determinate cleavage
if cell is removed from embryo it will die
deuterostomes
echinoderms and chordates - indeterminate cleavage
protostomes
arthropods, annelids, mollusks - determinate cleavage
mammalian cleavage is different because
cell division is slow and asynchronous (can have odd # of cells)
mammalian cleavage at 32 cell stage
separates into inner cell mass and outer sac of cells
blastocyst
mammalian embryo at the 32 cell stage
blastocyst inner cell mass
becomes the embryo
blastocyst outer sac of cells
trophoblast becomes the placenta
functions of blastocoel
prevents cells from interacting too early & allows room for cell movements (gastrulation)
gastrulation
blastula transformed into gastrula by massive cell movements
gastrula
embryo with three germ layers and distinct body axes
three germ layers of gastrula
endoderm, ectoderm, mesoderm
endoderm
innermost layer created by cells that move inward
endoderm becomes what tissues
epithelial lining of digestive tract, respiratory tract, pancreas, thyroid, liver
ectoderm
outermost layer
ectoderm becomes what tissues
nervous system, cornea, epidermis and skin accessories, teeth, epithelial lining of mouth and rectum
mesoderm
middle layer
mesoderm becomes what tissues
reproductive organs, blood vessels, dermis, muscles, bones
different cell movements during gastrulation
invagination, involution, ingression, epiboly
invagination
inward movement that forms a cavity
involution
movement of a sheet of cells under another layer of cells
ingression
detachment of cells that migrate elsewhere (mesoderm mostly)
epiboly
thinning and movement of cells over another layer of cells
fate maps
can dye blastomeres to follow them through gastrulation and see where the germ layers form
notochord
part of mesoderm tha torganizes development of the nervous system
blastopore
determines gastrulation pattern, opening of archenteron
sea urchin gastrulation begins with
invagination at vegetal pole and formation of archenteron (primative gut) and endoderm
sea urchin gastrulation formation of blastocoel cavity
mesenchyme cells break off and migrate (form mesoderm)
blastopore in deuterostomes
becomes anus
blastopore in protostomes
becomes mouth
filopodia
extensions of mesenchyme cells that attach to ectoderm and allow the cells to migrate
gastrulation in amphibians initiates when
cells in gray crescent move inwards and form the dorsal lip and involution occurs to form another layer of cells
gastrulation in amphibians after involution
epiboly occurs to surround the yolk cells resulting in three layers
bottle cells
move inward to form the dorsal lip during amphibian gastrulation
what is critical for gastrulation and normal development
cytoplasmic factors (dorsal lip)
spemann organizer
dorsal lip is the primary embryonic organizer (cells of dorsal lip can induce other cells to change developmental fate)
blastodisc
cells on top of yolk that become an embryo in birds and repitles
where is the blastocoel in bird and reptile eggs
between the blastodisc and yolk
blastoderm
the embryo once the blastocoel forms
epiblast
upper layer of the blastoderm
hypoblast
lower layer of blastoderm
hypoblast forms
estraembryonic membranes that nourish the embryo
gastrulation in birds and reptiles begins when
primitive streak (thick ridge) forms on the epiblast (demarcates the ant-post axis)
maturation of the primitive streak
narrowing and lengthening to form the primitive groove
ingression of primitive groove results in
Henson’s node (embryonic organizer)
in mammals, inner cell mass divides into
hypoblast and epiblast
hypoblast
forms amnion
epiblast
forms embryo, gastrulation occurs here
gastrulation in epiblast occurs when
primitive groove forms and eventually forms the node (like Hensen’s node)
organization of embryo after gastrulation
has ant/post axis, dorsal/ventral axis, inside, middle, outside
first event in organogenesis in chordates
formation of notochord from mesoderm, provides structural support during development, eventually replaced by vertebral column in vertebrates
neurulation
formation of neural tube from ectoderm
notochord is organizing center for
neurulation
neural tube forms
brain and spinal chord
notochord and Shh
acts as morphogen to establish dorsal/ventral axis and nerve development
failure of neural tube fusing in posterior region
spina bifida
failure of neural tube fusing in anterior region
anencephaly
what helps prevent NTDs
folic acid
somites
repeating blocks of mesoderm along both sides of neural tube
3 layers of somites become
upper - dermis
middle - muscles
lower - cartilage of ribs and vertebrae
neural crest cells
during neuralation break off (ingress) and become nerves, jaw, skull, face, pigment cells, glands, smooth muscle
what happens when somites break up
migrate to final destination to continue to proliferate and differentiate
hox gene expression in vertebrates
hox genes determine segment identity along ant/post axis and found on chromosome in order of expression
extraembryonic membrane
support embryo by functioning in nutrition and gas and waste movement
amnion
forms fluid filled cavity to protect embryo
chorion
functions in gas exchange between embryo and environment
yolk sac
forms from hypoblast, first extraembryonic membrance
what forms the amnion and chorion
mesoderm and ectoderm extend beyond the embryo
allantoic membrane
produces allantois that stores metabolic waste formed from mesoderm and endoderm
placenta
nutrient and waste exchange, formed from chorion and uterine tissue
in mammals size and importance of allantois depends on
how well the placenta works
