Second Exam Flashcards
For what does cell fate impact
a particular cell and all its descendents
When are cell fates developed
known before the organism has fully developed
What can be made due to the fact that cell fates are known before organism is fully developed
cell fate map
When can cell fate maps be made
particular stages of development
How are fate maps made. What are the two methods
dye injection
time-lapse motion pictures
How does dye injection help develop a fate map
inject dye into a cell and see where the dye is after the organism develops
What are the limitations to these cell fate map methods
they work until the organism is too complicated
Why don’t the cell maps work when the organism is too complicated
there are too many variables, the number and position of cells move around a lot more
Drawing fate maps is complicate by what
variable numbers and positions of primordial cells,
cell migration within the embryo
What is cell potency/potential
how fixed is a cell’s fate
Is fate a complete yes or no
no, cells can have a potential that is in between and cells thus have various fixations
What is the potential of a cell
the total of all the structures a cell or it descendants could form if placed in the proper environment
What is an example of cells having inbetween potential
hematocytoblast vs erythroblast
What potential does a hematocytoblast have
produces a wide variety of cells, wide potential
What potential does a erythroblast have
produces only RBC, narrowed potential
How do we figure out cell potency
Isolation
hetertrophic transplantaion
gene expression pattern
What do we do in isolation to figure out cell potency
isolate the cell, put it in a dish and see how many different cell types you get
What are limitations to isolating cells
They are isolated within a petri, culture dish which is not a normal environment for the cells so their potential observed could be altered
What do we do in heterotopic transplantation to figure out cell fate
take a cell, keep it in a natural environment but move it around within the environment. This enables one to see if the cell produces the same thing or if the fate changes
What do we do in gene expression pattern to figure out cell fate
Take an epithelial cell and transform it into a pluripotentent stem cell
What kind of fate does an epithelial cell have
fixed fate
What kind of fate does a PSC have
not fixed fate, broad potential
How does one transform an epithelial cell to a PSC
give the cell or cause the cell to express transcription factors
What do these transcription factors cause
these are stemness genes, genes that correlate with broad potential
What are the 3 levels of potential
totipotent
pluripotent
unipotent/determined
What is totipotent
the cell has total potential, these cell can produce all cells in an individual
What are examples of totipotent cells
somatic cells, germ cells, trophoblast cells
What is pluripotentent
produces lots of structures
What is unipotent
the cell only produces 1 thing, its fate is determined
At the 2-cell stage cells within mammals are what cell determination level
totipotent
The cells at the 2-cell stage were discovered that they were totipotent how
twins can be produced at this stage, the two cells can create to full organisms
The cell at the 4-cell stage are what determination level
totipotent
How do we know that the 4-cell stage is totipotent
quadruplets are possible
At the mouse 8-cell stage what level of determination are the cells
totipotent
How do we know the morula/8-cell stage is totipotent
when a cell is removed it produces the whole organism, not just a liver, a transplanted cell produces a variety of organisms
In the 16-cell stage, what is the determination of the cells
inside: pluripotent
outside: totipotent
How do we know the determination is different in the 16-cell stage
blastomeres are distinguishable from the inside cells and have different potentials
What do the blastomeres do
develop into anything
What do the inside cells develop into regardless of the environment
the embryo
What is the fate of the inner cell mass cells
totipotent? But they can’t make trophoblasts
People who favor ESC research and transplantation claim what
ESC cells are totipotent
Are ESC cells totipotent
no, they can make any somatic cell but they can’t make trophoblasts
How do cells develop fate. Mechanisms
master control genes
internal signals
external signals
embryonic induction
What are master control genes
genes in heirarchy that dictate certain outcomes
What is an example of the master genes being in control
the eyeless gene within flies
What occurs when the eyeless gene is knocked out
the flies have no eyes. If you switch this gene on in other cells, eyes begin to develop
What specifically makes the master gene in more control
it codes for a transcription factor that then codes for all the other genes and transcription factors
How do internal signals determine cell fate
Within the egg there are internal signals and the cell that inherits the signal develops a specific fate related
How do external signals determine cell fate
Cells that are in contact with the zona pellucida are trophoblasts
What is embryonic induction
the ability of one group of cells to alter the course of development of a neighboring group of cells
What is the name of the cells that alter the course of development for other cells
inducing cells
WHat is the name of the cells that were altered
responding cells
How is embryonic induction done
inducing cells secrete some protein that stimulates nearby cells if the concentration is high enough
What occurs after the molecule is secreted
cells that are within a certain range and concentration allow the molecule to bind to receptors that then can cause changes that initiate cell fate
The molecule will only bind if what…
if the responding cells are competent, if they have the matching receptors
Responding cells that bind the molecule then have what
certain genes are switched on or off
These genes that are switched on or off correspond with what
certain behaviors and fates
Cells that do not receive signal molecules, don’t receive inducing signals
default pathways of development
What is determination
having a committed cell fate, fate is established and fixed but they are not doing it yet
What is differentiation
acting out the cell determination
What are the two types of cell fate regulation
strict and loos
What type of development is strict regulation
mosaic development
What is mosaic development
cells are unipotent, every cell knows its function since day one
What is the type of development for loose regulation
regulative development
What is regulative development
cells are pluripotent and not determined
In regulative development what occurs
fate can be regulated and is not fixed, cells remain flexible, filling in for each other
What is an example of regulative development
twinning
What are other terms for non-identical twins
fraternal, dizygotic
Why are non-identical twins dizygotic
seperate eggs were fertilized into separate zygotes that implanted separately
What are other terms for identical twins
monozygotic
Why are identical twins monozygotic
because they originated from a single egg, sperm, and zygote but they may originate at different stages of development
What stage do identical twins most commonly develop
post blastocyst stage
What occurs in the post blastocyst stage that causes the development of twins
the inner ccell mass divides or two inner cell masses form, producing two embryos
What do the two embryos share
placentas, trophoblasts
The embryos have how many amniotic sacs
two
What percentage of the time do twins form
66%
In the other 33% of the time, at what stage do identical twins form
blastocyst stage
How do identical twins develop at the blastocyst stage
from the 2 cell stage to the 16 morula stage, the cells separate and escape from the zona pellucida to form 2 separate blastocysts
Twins that were developed in the blastocyst stage have shared and unshared what
each have their own trophoblast layer, own placenta and amniotic fluid, two chorions
What is a rare form of twin formation
separation of part of the embryo within its one amniotic sac
What does the separation of the embryo within one amniotic sac form
conjoined twins that remain attached even after birth
How many births result in conjoined twins
1/100,000
What is shared within conjoined twins birth
shared amniotic sacs, 1 inner cell mass, 1 chorion
When does conjoined twins occur in development
late in development along the primitive streak
What occurs to the primitive streak to develop conjoined twins
cells that line in one streak branch
What system dictates the formation of the rest of the embryo
the nervous system
After the nervous system is developed what occurs
the formation of all the other organs
Do all the other organs split as well
no. Only the nervous system
If the CNS makes two primitive streaks what occurs
monozygotic twins that share one chorion and one amniotic sac
Identical twins sharing one chorion and amniotic sac have what mortality rate
50%
Why is the mortality rate high for this method of twin formation
they become tangled in the umbilical cord
What is the function of amniotic sacs in twin development
keep the embryos and umbilical cords apart, so they don’t get tangled
What can be experimentally done with mice
chimeras
What are chimeras
mixing cells from different morulas or blastocysts into a single, large morula or blastocyst
Do chimeras naturally occur
not typically
What is a chimeric embryo
a mixture of two organisms genomes that are working together to make a human
What type of determination are the cells in chimeric embryos
pluripotent
While the cells are pluripotent, these cells have what that is unique to them
express their own genes
The chimeric offspring have what that is normal
normal size
What does the normal size indicate
the blastocyst cells regulated their development to compensate for the extra cells
How do we get a chimeric human
two sets of genes are used to produce a person
A chimeric person will express what type of gene style
mixed genes
How are chimeric humans developed in the embryonic stage
Cytokinesis in the formation of the polar body was even and these two cells got fertilized each. They were fertilized with different sperm so the eggs have different genes. As the eggs develop in the same zona pellucida its like the embryo is at the 2 cell stage
WHat type of sex cells do chimeric people have
XX and XY
What is the importance of chimerism in research today
create organs in animals that can be transplanted into humans
What animal is used to create human organs
the pig
What is the pig used to create human organs
same size, similar to humans in mass and size
How does a pig create human organs
during embryonic stage of the pig, human cells are added to the embryo
Would the cells of the organ be compatible
human ligands wouldn’t work with animal receptors, therefore, partial compatibiltiy
Would the desired organ be primarily human
no, the organs would be mosaic therefore making it potential that the organs could be rejected by humans
What is an ethical debate about using the pig to create organs
the pig could obtain a human brain
If the pig does not use its cells for organism development, what is an ethical fear
the pig could give birth to a human baby
What is the appeal for using human stem cell transplants
cure many diseases
How do you use human stem cell transplants to cure many diseases
replace dead or defective cells with normal healthy cells of the same type
What are three things that contribute to high healthcare costs
malpractice
cost treatments
bureaucracy
how many patients will be cured by human ESC in the US alone
128,000,000
What could occur with ESC implantation
chimeras
When are the human ESC implanted
blastocyst stage
Where are the sources of stem cells from
adults
human embryos
induced pluripotent stem cells
Where do we get stem cells from adults
bone marrow, fat, muscle, brain, skin, bone, GI tract, placenta, cord blood
Whey are bone marrow stem cells inferior to ESC
they are not totipotent as researchers would claim
What is the plus to using bone marrow stem cells instead of ESC
transplants have been done since 1956, there is lots of experience and proven methodology
When do we get stem cells from human embryos
blastocyst stage
How do we get stem cell from human embryos
take the inner cell mass out, put into a flask, then force the cells to become determined
Once the stem cells fates are determined what do we do
transplant them into a person
Why do researches claim ESC to be better
they are totipotent
Are ESC’s totally totipotent though
no, because they can’t make trophoblast/blastocystes
What are the two attempts that ESCs have been used
spinal cord injury and macular degeneration
What was the result in using ESC to treat a spinal cord injury
the trial was discontinued after 12 months
Why did they discontinue the trial
it is unknown, lab techs were given hush money to not say anything about why it was discontinued
How did they try to treat macular degeneration with ESC
implant SC into eyes so they would replace retina cells
What was the result in using ESC to treat macular degeneration
as of 4yrs ago the person “improved” but it didn’t work because things are too quiet
What are induced pluripotent stem cells
stemness genes are expressed in a patient’s fibroblasts
How do they express these genes in fibroblast cells
virus mediated
RNA mediated
introduction of small molecules
What is the virus mediated method
used viruses that introduced stemness genes
What did ESC researches find as a flaw in using viruses to introduce stemness genes
viruses pose as a danger of inserting mutagenesis, splice into a gene and cause a mutation or cancer
How did RNA mediated introduce the genes
cells would readily pick up the nucleic RNA, the RNA serves as mRNA in the cytoplasm and the stemness genes would be coded for
How does introduction of small molecules introduce stemness genes
drugs that would force the cell to express the stemness genes
What is the source for all the ICM cells
400,000 extra blastocysts resulting from IVF
What is the biggest appeal for using ECM according to researchers
much good could arise from the use of the extra embryos that were going to die anyway
What are 2 problems with the appeal that the researches proposed in using ECM
blastocysts don’t have to die
is it ethical to accelerate their death
What are problems with using ESCs
expensive ($900,000)
Why is stem cells a person a trick question
because the cells themselves are not people but rater they develop the person
What is a more relevant question
are the embryos from which the SC came from humans
What is the humanistic response to whether the embryos from which the SC came from humans
no, they don’t have sentinence, self-awareness or viability
What is the biblical response to whether the embryos from which the SC came from humans
yes, personhood begins at egg activation, persons are made in the image of God, its relationship, not dependent upon us or their characteristics
What is the humanistic response to whether extra embryos have rights
only human people have rights, since the embryo is not a person it has no right
What is the biblical response to whether extra embryos have rights
right to life, Bible doesn’t talk about rights but rather our responsibility to others
What is the humanistic response to people who consent to this responsible for their actions
no, autonomous individuals are not responsible to anyone except themselves
What is the biblical response to people who consent to this responsible for their actions
yes, you are your brother’s keeper, preserve life according to the 6th commandment
What is the humanistic response to good consequences result from the use of embryos
yes, presumably you could cure alot, chief good in culture is happiness convenience
What is the biblical response to good consequences could result from the use of embryos
happiness is not chief end, Micah 6:8 (see justice, love mercy, walk obediently and humble with God), depends on how you define good
What is the humanistic response to does the ends justify the means necessary to achieve goals
yes
What is the biblical response to does the ends justify the means necessary to achieve the goals
the means is killing persons, therefore the results are not equal to the means, they are not balanced. Life is equal for life, not for something less than life.
What are the humanistic motivations of the people who demand access to stem cells
selfish, they can die for me, my gain their loss
What are the biblical motivations of the people who demand access to stem cells
we should be selfless, others should live before we are to die
What are some practical problems with HES cell transplants
difficult to grow in dishes
unable to direct their development
cannot control their development
still a transplant
What is the difficulty in growing in dishes
a very unnatural environment for ESC to grow in dish
How many blastocysts does it take to get one stem cell to grow in a dish
100
What percentage of blastocysts fail
99%
What is the success rate to obtain 1 iPSC
0.001%
While it is harder to obtain iPSCs, why is it easier ultimately
easier to get ahold of 1 million fibroblasts than it is to get human
What is the difficulty in being unable to direct their development
to force something into differentiation to grow something specific is difficult, we can observe a cell but it may not totally develop into the cell but rather express only one protein
What does evidence show in supporting differention of one cell into something else
the evidence is skimpy
How would we know for sure if the cell we forced to differentiate differentiated
use dye to mark the cells
What is an example of dye to use
green fluorescent protein
How does green fluorescent protein get into the cell
a virus that has the gene infects cells so they now express the gene
How could green fluorescent protein show differentiation or the lack thereof with the virus
The virus may have spliced in to orginal cell and then cam back out and infected other cells that make it look as though they were differentiated
How could one cell with green fluorescent protein produce other cells without actually differentiating
fuse with a stem cell that has been labeled which produced labeled sperm, cells make bridges with each other and GFP can pass from one cell to another
What is the problem in not being able to control development once the cell is injected
when in a dish you can control factors but once in a person the ESC resume embryonic development
If the ESC resume development after implanted what does this result in
teratoma
What is the problem with the stem cell still being a transplant
without matching every receptor and protein, the cell and organ can ultimately be rejected
What is the solution to stem cell development to prevent rejection
therapeutic cloning and somatic cell nucleur transplantation
How is therapeutic cloning done
get 100 eggs, remove nucleus, put the nucleus of somatic cell in donor egg, TF latch on to the sequences, activate egg development, grows to blastocyst
What is the problem that can occur in removing the nucleus
in metaphase I when the eggs are picked, the chromosomes are not in nucleus but lined up in the middle. You have to get all chromosomes for if you leave one behind you could have a lethal trisomy aneuploidy
Trisomies and aneuploides have a high correlation with what disease
cancer
How do you activate development
let calcium in or caffeine
How does caffeine help activate the egg
holds calcium channels open longer
Once the blastocyst grows in vitro, what two things could be done
implant for reproducting cloning
used for therapy
is reproductive cloning legal
no “thou shalt kill them”
How are blastocysts grown used for therapy
gutted for their ESC
What is the success rate for reproductive cloning
low
WHy is the success rate for cloning low
due to all the mutations
Why would these blastocysts have so many mutations
the DNA used was from somatic cells that have 60+ years of mutations
In cloned animals what percentage of genome was mutated
4%
How many mutations are needed for cancer
6-7
How does mitosis affect the success rate for cloning
mitosis is complete before DNA replication, therefore no checkpoint within the embryonic cycle to fix mutations
Wuppose the cells are not rejected, what oculd the mutations lead to
neoantigens that could cause rejections
What is the good news regarding cell rejection in cloning
the genetic identity with the patient eliminates the risk of rejection
What is the bad news of cloning
requires lots of lost embryos, murder
Do the ends justify the means. Humanistic view of cloning
yes
Do the ends justify the means. Biblical view of cloning
no, never did, ends and means are not equal
What is the proper role of technology to the humanist
a savior
What is the proper role of technology to the Christian
technology is a gift of god, a product of our job to explore the creation to be used within the moral boundaries he has set up
What is required in balance for technology
faith and reason, prayer and technology
Is God opposed to technology
no as long as it is within His boundaries
What makes technology within His boundaries
obedience to Biblical law
motivated by Biblical love
With a concern for Biblical justice
respecting God’s sovereignty over all things
What is Biblical love
selflessness not selfishness
What is Biblical justice
you get what you deserve
you take responsibility for the consequences of your actions
The cell begins gastrulation as what
disorganized cluster of cells
What is this disorganized cluster of cells
the inner cell mass within the blastocyst
What does gastrulation end with
the basics of a body plan
What is the basics of a body plan called
gastrula
What produces the changes in shape of the embryo
basic cell activities by different places at different times
What types of cell activities occur
migration intercalation ingression change of cell shape division adhesion and detachment cell suicide
What is migration
movement
What is intercalation
wedging of cells between their neighbors, adding themselves to a layer or group
What is ingression
cells leaving a group to enter a cavity or space in the embryo
What is division
proliferation by mitosis and cytokinesis
What does division lead to
growth
What types of cell shape changes occur
cuboidal to bottle flask shaped
How does adhesion and detachment of cells change
expressing or ceasing expression of adhesion proteins within the PM
What is cell suicide
programmed cell death, apoptosis
Can cell suicide be good
yes, it occurs in specific places for the good of the embryo
What is epithelial movements
movements of sheets of cells due to coordinated cell activities
What types of epithelial movements occur
invagination involution convergent extension epiboly delamination
What is invagination
inward buckling of a sheet of cells to form a pit or pocket, depression, groove
What is involution
migration of a layer of cells around a corner toward the inside, mass migration
What is convergent extension
converging to extend, merging to elongate
what is epiboly
surrounding a mass of yolk or of cells
What is delamination
splitting of a group of cells into two layers
Where does gastrulation start in fish
fish blastocyst
What does a fish blastocyst consist of
a mound of three groups of cells on top of uncleaved
What type of yolk do fish blastocysts consist of
telolecithal
What type of movement does gastrulation begin with
epiboly by all three layers
Shortly after epiboly begins, what occurs
the deep cells undergo involtuion to produce two layers
What is the outer layer called
epiblast
What is the inner layer called
hypoblast
What occurs to the outer epiblast
continues to surround the yolk
What occurs to the inner hypoblast
moved back toward the “north” animal pole
What is the crease where involution beings called
germ ring
Where is the germ ring found
bottom edge of the growing cap of cells
What does the germ ring do
moves as epiboly continues and cells proliferate
While epiboly and involution are going on, what occurs to the epiblast and hypoblast cells
convergent extension
How long does the zona pellucida last in fish
up until the fish swims away, removal is the last step
In the fish blastocyst, what are the three groups of cells
two layers of individual cells and one layer of undivided cells
What is the undivided layer known as
syncytial
What is the top layer of individual cells
enveloping layer
WHat is the function of the enveloping layer
functions as protection, boundary layer
Does the enveloping layer produce and embryo
no
What is the middle layer of individual cells called
deep cells
What is the function of the deep cells
produces embryo proper, all tissue types come from this
What is the last layer of syncytial cells known as
yolk syncytial layer
WIth distinguished layers of cells, what does this do to the cells
determines their fate
The cells that are undergoing convergent extension results in what
layers of cell are drawn to animal pole, extend toward opposite poles and then accumulate, drawn to the center and the forcing the group to elongate
Elongation of the cells creates what
the embryonic shield
With time, what has happened to the epiblast
it has thickened
What does the thickened epiblast create
the ectoderm
What does the ectoderm form
skin and nervous system
In adults what is the ectoderm
the outermost layers
What occurs to the thickened hypoblast
delaminates
What causes the hypoblast to delaminate
changes in adhesion
When the hypoblast delaminates what forms
two layers
The one closes to the yolk syncytial layer is what
endoderm
What will the endoderm form
digestive system
What layer digests the yolk
endoderm layer
What is the layer between the endoderm and the ectoderm
the mesoderm
What does the mesoderm form
organs between the GI tract and the skin, bones, muscles, blood vessels ect
What is the result of gastrulation in fish
the basic body plan, organization of the three primary germ layers are laid out
What are the major axes established from a mound of cells
anterior and posterior
dorsal and ventral
proximal and distal
left and right
What do the anterior and posterior axes equal
head and tail
What do the dorsal and ventral axes equal
back and front
What do the proximal and distal axes equal
nearest embryonic shield to distant from shield
In gastrulation of birds, where is the chicken blastocyst
sits atop the yolk at the animal pole of the embryo
What occurs first to the blastocyst
delamination
Delamination causes what
creation of two layers
What are the two layers created
upper epiblast
lower hypoblast
What is between the layers
hollow blastocoel in between
What occurs after delamination
convergent extension
What happens during convergent extension
cells from posterior section of epiblast move toward their midline=converging
What happens after the cells move toward their midline
they move forward toward the head of the embryo=extension
What does converging extension form
primitive streak
What occurs after the primitive streak is formed
Invagination
What occurs during invagination
the entire primitive streak buckles inward
What is formed from invagination
the primitive groove
What causes invagination
simultaneous shape changes by all cells along the groove
What shape changes occur
cells go from cuboidal to bottle shaped
Along the primitive groove, what forms
a dimple
Where does the dimple form along the primitive groove
at the anterior end
What is the name for this dimple
primitive pit
What surrounds the primitive pit
mound of cells
What is the mound of cells known as
Hensen’s node
What occurs after invagination
involution
What occurs during involution
epiblast cells move toward the primitive groove and pit, turning the corner to enter the depression
What occurs after involution
ingression
What cellular changes occur during ingression
the epiblast cells leave their layer and migrate into the blastocoel
Are the cells that migrate into the blastocoel connected to other cells
no
What is another term for the “free floating” cells
mesenchyme
As a result of the epiblast cells leaving what occurs
new cells move toward the groove and pit to take their places
What happens to the cells within the blastocoel
initially loose but ultimately group together into layers
The first layer formed is what
endoderm layer
What does the endoderm layer do
pushes the hypoblast cells out of the way to contact the yolk
What is the second layer formed
mesoderm layer
What is the final layer formed
epiblast layer is now called the ectoderm
In what direction of axes does ingression proceed
anterior to posterior
After the three primary germ layers are formed, what occurs
epiboly
What happens in epiboly
the yolk begins to be surrounded by all three primary germ layers
Where does the ectoderm spread
just beneath the vitellin membrane around the yolk
What is the vitelline membrane
zona pellucida in birds
Where does the endoderm spread
directly on top of the yolk, displacing the hypoblast, breaking down yolk molecules for energy and subunits
Where does the mesoderm spread
between the other two, to form blood vessels to distribute absorbed subunits
What is the final step of gastrulation in chickens
ventral closure
Where does ventral closure first start
at the anterior end, then at the posterior end
What occurs to the germ layers during ventral closure
they change shape, producing invagination above the yolk
What is formed due to ventral closure
a tube-shaped body, the head lifts off the yolk
What occurs to the yolk during ventral closure
remains bound in a sac, connected to the embryos gut by a tube
What occurs to the yolk sac as the embryo grows
the sac gets smaller
Why does the sac get smaller
contents are used up and eventually disappear
What is the final step of gastrulation in a chicken
chick hatches out of zona pellucida before hatching out of a shell
What has resulted to the embryo due to gastrulation
axes have been formed
Why is gastrulation in humans somewhat different
due to the need to implant and uses isolectithal egg yolks
After implantation what is the very first step
three rounds of delamination occur
What is the first round of delamination
hypoblast layer delaminates from the side of the inner cell mass facing the blastocoel
What is formed due to the first round of delamination
an epiblast
What undergoes in the second round of delamination
the epiblast
On what side does the epiblast delaminate
on the opposite side
What is formed via this delamination
amniotic ectoderm
What is between the amniotic ectoderm and the epiblast
amniotic cavity
What will happen to the amniotic cavity during development
expand to surround the entire embryo
What is the third round of delamination
The trophoblast splits into two layers
What are the two layers
cytotrophoblast and the syncytiotrophoblast
Which way does the cytotrophoblast face
the yolk sac
Which way does the syncytiotrophoblast face
the endometrium
How do nutrients get into the gastrula
maternal blood supply feeds the syncytiotrophoblast cells
What is the space between the hypoblast and the cytotrophoblast that surrounds the entire yolk sac, amniotic cavity, and germ disc
extraembryonic coelom
What happens after 3 rounds of delamination
convergent extension
What is formed due to convergent extension
primitive streak from the epiblast
What happens after convergent extension
invagination
What is formed due to invagination
a primitive pit, primitive groove, hensens node
What happens after invagination
involution
What occurs during involution
epiblast cells move toward the primitive groove and pit, turning the corner to fill the depression
What happens after involution
ingression
What occurs during ingression
the cells move forward and laterally
What is formed due to ingression
endoderm and mesoderm are formed
Where does the ectoderm come from
epiblast layer is renamed
What occurs after ingression
epiboly and ventral closure
What has been considered proof of evolution
the similarity of gastrulation in humans and birds
What does the phrase ontogeny recapitulates phylogeny mean
as an organism develops, it replays the development of its phylum, evolution sees that we all started one organsim that branched off
Life began as what
a single cell
What in the human embryo life is one cell
zygote
What is the believe as to where the one cell began
in a liquid lake
Where does a zygote begin its life
in a “liquid lake”
How were the stages of gastrulation studied in 1956
someone studied uteruses due to hysterectomies. Some of the women were pregnant=embryos in the uteruses
Most of what we know about gastrulation comes from what
mice
What is the problem with using mice
mice do not equal humans so its an assumption that humans develop the same way
What occurred in 1979 to make human gastrulation studies different
IVF so we could study in a dish
What was studied
blastocysts
What were the rules though for studying
all had to be discarded by 14 days
What was specific about ridding the embryos by the 14th day
that is when the primitive streak arose from the circle of cells
What is the last stage that twins can be formed
the primitive streak
If two primitive streaks were formed then what could happen
twins
What was their ethical reason for discarding after 14 days
until you know one or two persons you can kill it, at 14 days it is hands off cause you know how many individuals it will be
What is the Christian argument in response to hands off after 14 days
the 14 day rule is bogus because it is always atleast one human
What was also a practical reason as to why14 days was the limit
they struggeled to keep cells alive past 14 days
With the technology today, what is the rule for how long one can keep an embryo
28 days
What are the goals for being able to study embryos for 28 days
understand causes of birth deffects
study effects of teratogens
study causes of miscarriages
In a christian argument is studying gastrulation in vitro ethical
no, the means require do not equal the end
Why do the means not justify the ends
lots of human embryos are killed and sacrificing them, those are persons
What do people say to view this research as ethical
embryos are subhuman species
What is the importance of cell adhesion in embryogenesis
many of the cell movements involve changes in cell adhesion
What are the movements that require cell adhesion
ingression
delamination
endoderm formation
migration
What is migration
coordinated loss and gain of adhesion
What are the two mechanisms of adhesion
CAMs and SAMs
What are CAMs
cell adhesion molecules
What are SAMs
substrate adhesion molecules
What are cell adhesion molecules
transmembrane proteins that attach to corresponding transmembrane proteins in neighboring cells
How selective is CAM adhesion
quite selective, enables only certain kinds of cells to attach to each other, not other kinds of cells
Is CAM adhesion week or stron
weak, allowing cells to migrate when necessary
CAM precedes formation of what
permanent junctions between cells
What are just like CAMs but in a different family
cadherins
How are cadherins different
structurally different and require calcium to seperate cells
What are SAMs
transmembrane proteins which attach to long, fibrous extracellular matrix proteins around and between cells, their “substrate”
What types of molecules do they bind to
collagen
What is the actual name for SAMs
integrins
How many substrate receptors are there
as many as there are substrate molecules
HOw is adhesion regulated
synthesis of CAM or SAM requires the proper gene to get switched on, the cell will adhere then
What can cell adhesion provide to a cell
the signal for a cell to switch certain genes on or off
How do adhesion patterns differ
they change as embryogenesis proceeds
