Broccoli: Lecture XVII Flashcards
Human Embryo Development
What is a zygote?
the cell we derive from
How does the zygote form?
fusion of the sperm and ovum along the oviducts
What kind of single cell forms after the fusion of the sperm and ovum?
diploid cell
What is the membrane of the diploid cell?
membrane pellucida
What doe the membrane pellucida protecting the embryo from?
maternal tissue
When does the embryo break maternal tissue?
when it arrive in the uterus, it breaks the maternal tissue to attach to the maternal endometrium
How long does it take an embryo to travel from the oviduct to a uterus?
5 day in humans
How many times does the embryo divide during its journey to the uterus?
into 32 blastomeres
When does the morula stage of the embryo occur?
when it has divided into 32 blastomeres
What kind of cells are the 32 embryonic cells called?
totipotent cells
What happens when the embryo forms an internal cavity?
it becomes a blastocyst
What are the “flat cells” of the blastocyst?
trophoblast cells that generate the walls of the blastocyte
they protect a mass of 50 internal cells called inner cell mass (ICM)
What does the ICM do?
give rise to an entire individual
pluripotent stem cells that form organs
What do the trophoblast cells do?
give rise to the embryonic part of the placenta
What is the Leukemia Inhibitor Factor (LIF)?
molecule that maintains pluripotency
What is pluropotency a unique property of?
ICM at the blastocyst stage
When do adult stem cells form?
once the embryo forms the fetus
What are adult stem cells?
organ-specific stem cells, which are organ specific meaning they cannot be differentiated
Where are totipotent stem cells found?
only in the zygote in the morula stage (1-5 days)
When are pluripotent stem cells found?
when blastocyst is formed (5-10 days)
Adult stem cells are ___.
multipotent
What does it mean is adult stem cells are multipotent?
they can differentiate into some cell types, but very few
How are neuronal cells created?
ectoderm → neural plate (brain, spinal cord, and neural projections) & epidermal tissue (epidermis and epidermis sheets) → neural progenitors → neural tube
What are BMP factors?
bone morphogenetic factors, which are expressed by the epidermis and specify the epidermal tissue
What are fibroblast growth factors (FGF-2)?
the signal of BMPs protect neural progenitors by the FGF-2
FGF-2 are proteins that block the action of BMPs and specify the ectodermal cell to become neural progenitors
How can we be use that the cultured cells are pluripotent?
we inject them into a blastocyst host in the blastocele cavity, which can the be replanted into a surogate mother
What is a chimeric animal?
when an inoculated blastocyst attaches tot he endometrium and generates an embryo or fetus
they are animals that are generated by 2 different cell types (1 with an ICM of the host blastocyst and the other from ESCs cultured in vitro and injected in the blastocyst)
If ESCs are injected, as they are in vitro, into an adult animal, what would they give rise to?
tumor of embryonic origin because the cells will not have a signal to be able to differentiate and cause them to stop proliferating
What is the tumor called that is produced when ESC are implanted into adult tissue?
teratoma
What is a hypotoxic environment?
environment that does not have much metabolic supprt
What are the minimal molecular signals that are sufficient to maintain cells in a pluripotent state?
culture condition in which there are fibroblasts and animal serum
the 2 molecules found in these that are necessary for the pluropotency of the cells are PD0325901 and CHIR99021
What is PD0325901?
small inhibitor of the FGF pathway
What is CHIR99021?
inhibits the GSK3 pathway
What do pluripotent cells express?
FGF4 receptor
If FGF4 is expressed, what is caused?
iPS cells start to differentiate
What are the 2 signals that activate the network of TFs that stimulate pluripotency?
β-catenin and STAT1/3
What are the 3 pluripotency TFs?
Oct4
Sox2
Nanog
What happens if Oct4, Sox2, and Nanog are not activated?
they do not specify inner cell mass and they lose their pluripotency
Why is the ICM important in vivo and in vitro?
it creates a feed forward-loop that is essential to maintain the stable expression of proteins, which is required for the pluripotency state of the ESCs
What is required to culture human embryonic stem cells?
FGF2 and activin without serum
Describe the difference between human ESC and mouse ESC:
mice colonies have a dome shape, and human colonies are flat
trypsin is used for mice for single cell suspension and humans cannot grow from a single cell
What are epiblast stem cells?
made from the epiblast, which is a late stage where the blastocyst starts to generate an ectoderm and are found in mice
In the 1st experiment, what were the 4 factors found to be necessary to start the conversion of adult fibroblasts into mouse embryonic stem cells?
Oct4
Sox2
Klf4
c-Myc
In the 2nd experiment, what was found?
fully mature hepatocyte can be reprogrammed into iPScell through the TFs Oct4, Sox2, Klf4, and c-Myc
What is cell reprogramming?
the idea that we can reprogram the identity of cells altogether
What is a limitation in cell reprogramming?
it is not very efficient: the pluripotency switch occurs in 1 of 100,000 cells
Why is efficiency so low?
it is not known
What are the Yamanaka factors?
Oct4
Sox2
Klf4
c-Myc
they can reprogram iPS cells into any type of cell
What cells have a higher percentage of reprogramming?
progenitors of mature T & B cells
Fibroblast-derived iPS cells have a ___ percentage to differentiate in blood stem cells compared to blood-derived iPS cells.
low
this infers the cells have memory
