Test 2 Flashcards
Stem cell
A cell that retains the ability to divide and re-create itself while also having the ability to generate more progeny capable of specializing into a more differentiated cell type
What does a stem cell divide into
Another stem cell and progeny that can differentiate
Single cell asymmetry
A stem cell and a committed cell is produced at each division
Population asymmetry
Some cells in a population are more prone to produce a differentiated cell
Is population asymmetry symmetrical or not
Symmetrical
Population asymmetry example
One stem cell divides into two stem cells OR two committed cells
Adult stem cell lineage
A cell which goes through many rounds of cell division but eventually will turn into a differentiated cell
Renewal
Continuous division of the stem cell
Totipotent
A stem cell capable of producing all the cell types of a lineage
Pluripotent
Capable of producing all the cells of the embryo. Cannot produce any extra embryonic membranes
Multipotent
Function to generate cell types with restricted specificity for the tissues in which they reside. (Stuck in position. Divides to build up the tissue theyre in)
Progenitor
Can only divide a few times before it differentiates. Works to amplify the number of cells. Will differentiate soon
Precursor
Any ancestoral cell type to the differentiated cell. Lineage may not be known
How are stem cells regulated between these different states in a coordinated way to meet patterning and morphogenic need of the embryo and mature tissue
Regulation is highly influenced by the microenvironment that surrounds a stem cell and is known as the stem cell niche
Where is the stem cell niche found
All tissues possess a unique stem cell niche. Extracellular and intracellular changes regulate stem cell behavior
Extracellular mechanisms
- Physical mechanisms
2. Chemical mechanisms
Physical mechanisms
Structural adhesion factors within the ECM that support architecture of the niche. Differences in cell to cell and cell to matrix adhesions as well as cell density within the niche can alter the mechanical forces that influence cell behavior
Chemical regulation
Secreted proteins from surrounding cells influence stem cell states and progenitor differentiation through endocrine, paracrine and juxtacrine mechanisms. If stem cells are too far from niche, the factors cant reach them and differentiation commences
Interstitial fluid
Fluid not in the bloodstream
Intracellular mechanisms
- Regulation by cytoplasmic determinants
- Transcriptional regulation
- Epigenetic regulation
Regulation of cytoplasmic determinants
Partitioning which occurs at cytokenisis. As a stem cell divides, the factors determining cell fate are either partitioned to one daughter cell (asymmetric) or shared evenly between daughter cells (symmetric)
Transcriptional regulation
Occurs through a network of transcription factors that keep a stem cell in its proliferative state , as well as promoting maturation of daughter cells towards a particular fate
Epigenetic regulation
Occurs at the level of chromatin. Different patterns of chromatin accessibility influence gene expression related to stem cell behavior
Blastocoel
Space in the middle filled with fluid to shift morula cells to one spot (ICM)
Inner cell mass (ICM) creates the _____
Epiblast or embryo proper
Trophoectoderm cells
Create the extraembryonic membrane
What happens if we remove cells from the ICM
We produce embryonic stem cells which retain pluripotency and can generate any cell in the body
Blastocyst
Special name for a mammalian blastula
How does the blastocyst form
After fertilization, cleavage creates the morula. Division continues until it hollows out to become the fluid filled blastocoel. Cells are pushed to one side to become the ICM which retains pluripotency for a while. Trophoblast will become extra embryonic structures
Symmetrical division parallel to apicobasal axis
Trophectoderm expands
Asymmetrical division perpendicular to apicobasal axis
ICM cell created - will not have the same proteins as the original cell and becomes a different cell type
Apicobasal axis
Outer side of the embryo to inner side
When does the asymmetrical localization along the apicobasal axis occur
At the morula stage
What specific factors are localized
- ICM
2. Tropoectoderm
ICM localization
Results in the recruitment of E-cadherin to the basolateral membrane where outer cells contact underlying ICM cells
Trophoectoderm localization
PAR and aPKC families are localized to the outside cells, these factors are called partitioning proteins
Is E-cadherin important in influencing these cell lineages
Yes. E- Cadherin activates Hippo patheay but only in the ICM
Result of E-cadherin influencing cell lineages
- Hippo activated in ICM and the maintenace of pluripotent ICM development through Oct4
- PAR and aPKC inhibit Hippo leading to yap-taz-tead transcription complex which causes an upregulation of cdx2 and the trophoectoderm fate
Hippo on
Oct 4 turned on –> can act as stem cell
Hippo off
Cdx2 turned on –> stops cell from having stem cell ability
What does the hippo pathway prevent
Prevents cdx2 from being transcribed
What must adult stem cells do
- Maintain a long term ability to divide
- Be able to produce some differentiated daughter cells
- Be housed in and controlled by its own stem cell niche which regulates stem cell renewal, survival, and differentiation
Where are neural stem cells found
- Subgranular zone of the hippocampus (SGZ)
2. The ventricular-subventricular zone (V-SVZ)of the lateral ventricles
Germ line
The gametes are the product of the germ line that is separate from the somatic cell lineages
Meiosis
Chromosomal content is halved so the union of two gametes restores the full chromosomal complement of the new organism
How many cells does meiosis produce
4 haploid unidentical cells
Primary sex determination
Determination of the gonads
Secondary sex determination
Determination of the male and female phenotype by the hormones produced by the gonads
Bipotential gonad
Common precursor that male and female gonads diverge from
Gonads
Paired regions of the mesoderm that are adjacent to the kidneys
Male gonadal type
Testes
Female gonadal type
Ovary
Male germ cell location
Inside testes cords (medulla of testes)
Female germ cell location
Inside follicles of ovarian cortex
Remaining duct male
Wolffian
Remaining duct female
Mullerian
Male duct differentiation
Vas deferens, epididymis, seminal vesicle
Female duct differentiation
Oviduct, uterus, cervix, upper portion of the vagina
Male urogenital sinus
Prostate
Female urogenital sinus
Skenes glands
Male labioscrotal folds
Scrotum
Female labioscrotal folds
Labia majora
Male genital tubercle
Penis
Female genital tubercle
Clitoris
Female karyotype
XX
Male karyotype
XY
What is it in the Y chromosome that makes a male a male
Testis-determining factor (SRY gene) which organizes the bipotential gonad into testes
SRY active at the proper time
Male gonads, inhibits ovary formation
SRY gene is not present or fails to act at the appropriate time
Ovary forming genes will function. Female gonads
When do gonadal rudiments appear
Week 4 and remain sexually indifferent until week 7
6 weeks wolffian duct
Indifferent gonad shows expanded epithelium. Mesoderm continues to proliferate
8 week testes development
Developing sertoli cells surround incoming germ cells and organize themselves into testes cord near kidney. Anti mullerian hormone secreted. Seminferous tublues form
16 weeks male
Wolffian duct differentiates to become epididymus and vas deferns. Efferent ducts are the remodeled tubules of the developing kidney
8 weeks ovarian development
Each germ cell gets enveloped by a cluster of sex cord epithelial cells. Germ cells become eggs and surrounding cortical epithelial cells will differentiate into granulosa cells
20 weeks female
Remaining mesanchyme cells differentiate into thecal cells. Thecal and granulosa cells form follicles that envelope germ cells and secrete steroid hormones. Ovary does not connect to the wolffian duct
Cells that surround oocyte
Granulosa closest
Theca on outer layer
Genes expressed in bipotential gonad
Wt1, Lhx9, GATA4, Sf1
Where is Wnt4 expressed
In the bipotential gonad and ovaries, not the testes
____ acts with Wnt4 to produce _____
Rspo1, B-catenin
What is beta catenin important for
Activating further ovarian development and blocking synthesis of Sox9 (a testes determining factor)
What transcription factors for development does B-catenin activate
FoxI2 and follistatin
What is follistatin responsible for
Organizing epithelium in granulosa cells
Evidence that the SRY gene is located on the Y and determines sex
Inserting SRY into genome of a normal XX zygote will make the XX mouse form testes
What gene goes the SRY gene activate to induce testes formation
Sox9
Meiosis vs mitosis
- Meiosis is two cell divisions without an intervening period of DNA replication
- Homologous chromosomes pair together and recombine genetic material
How do homologous chromosomes find eachother
Based on size and sequence
Leptotene
Search
Zygotene
Association of homologous chromosomes -synapse
Pachytene
Homologous chromosomes completely aligned
Diplotene
Recombination
Spermatogenesis
The development pathway from germ cell to mature sperm cell
Spermatogonia
Sperm stem cell
Spermiogenesis
Physical maturation of a sperm cell
Step 1 spermatogenesis
Spermatogonia divide -proliferative phase
Step 2 spermatogenesis
Meiotic phase - meiosis occurs (completes before spermiogenesis)
Step 3 spermatogenesis
Spermiogenesis - sperm is shaped and matured
Spermatogonia division
One stem cell, one cell that will go into meiosis and spermatogenesis
Layers of cells in the seminiferous tubule
- Stem cells outside
- 1 st meiotic division
- 2nd meitoic division
- Meiosis complete
- Mature sperm in center
Low levels of GDNF favor_____
Differentiation of spermatogonium
Oogonia
Stem cell that divides
Primary oocyte
Undergoes one round of meiosis and is stuck in the diplotein stage until puberty
Secondary oocyte
Released by the ovary in the stage of metaphase II. Meiosis is completed upon fertilization
Meiosis in oocyte
oogonia –> primary oocyte (meiosis round 1, stops in diplotein phase) –> secondary oocyte (stops at metaphase 2 until fertilization) –> meiosis is complete
What does an oogonia split into
Primary oocyte and stem cell to replace itself
Why do older women have a higher chance of giving birth to a fetus with an extra chromosome
Break down of cohesion proteins needed during meiosis which causes aneuploidy
How long is meiosis
16 hours to assemble meiosis spindle, 4 hours in mice
Why are more downs syndrome babies born to younger women if older women have a higher chance of having them
Younger women have more babies in general
Four major events of fertilization
- Contact and recognition between sperm and egg
- Regulation of sperm entry into the egg
- Fusion of genetic material of the sperm and egg
- Activation of egg metabolism to start development
What is the sperm tail made of
Centrioles, made of microtubules
What powers the tail of the sperm
Mitochondria
What does the golgi form in the sperm
Acrosomal vesicle
What happens to the remaining cytoplasm in the sperm
It is expelled to get rid of extra weight
What enters the egg from the sperm during fertilization
The nucelus and centriole
Structure of sea urchin egg
Plasma membrane (inner), Vitelline envelope (middle), Jelly coat (outer)
How is polyspermy prevented in the sea urchin egg
The vitelline envelope condenses to prevent more than one sperm from fertilizing the egg
Germinal vesicle
Name given to the large diploid nucelus of the primary oocyte
When does the sperm enter the egg in most mammals
Second metaphase
When does the sperm enter the egg in sea urchins
Meiosis complete
Structure of mammalian eggs
Plasma membrane (inner), zona pelicuida (middle), cumulus (outer)
What is the vitilline analogous to in the mammal
Zona pelucida
What is the jelly layer analogous to in the mammal
Cumulus
Steps of fertilization in sea urchin
- Sperm contacts jelly layer
- Acrosome reaction
- Digestion of jelly layer
- Binding to vitelling envelope
- Fusion of acrosomal process membrane and egg membrane
Steps of fertilization in mammals
- Sperm activated by female reproductive tract
- Sperm binds to zona pelucida
- Acrosome reaction
- Sperm lyses hole in zona
- Sperm and egg membrane fuse
How does sperm travel through the female
Chemotaxis, sperm goes towards higher concentration of chemotaxis faster
Chemotaxis pathway in sea urchin
Resact from egg binds to RGC –> GTP –> cGMP–> Ca2+ –> sperm swim towards egg
Protein for sperm egg recognition
Bindin
Why cant different species have offspring
Bindin is species specific
How do sperm know where to bind to the egg
Sperm only bind where bindin receptors are on egg
Dispermic sea urchin process
- Fusion of three haploid nuclei (18 chromosomes each)
- 54 chromosomes randomly assort on the four spindles
- Duplicated chromosomes pulled to four poles during anaphase I
- Four cells contain different numbers and types of chromosomes
- Early death of embryo
Potential of egg membrane before sperm
-70 mV
Slow block to polyspermy
- Sperm surround egg 10 seconds after addition
- 25 and 35 seconds after, fertilization envelope is formed around the egg starting at point of sperm entry
- Fertilization envelope is complete and excess sperm are removed
Fast block to polyspermy
-70 mV to +120 mV
Formation of sea urchin fertilization envelope
Corticle granules fuse with plasma membrane, H20 breaks connection
Where are calcium ions released from
The ER
Where is the bindin protein on the sperm
In the acrosomal process
Mucopolysaccharides
Produce the osmotic gradient for the fertilization envelope
Peroxidase enzyme
Crosslinking tyrosine residues. Hardens envelope
Hyalin
Coating around the egg
What surrounds the cortical granules in sea urchin eggs
Endoplasmic reticulum
Formation of fertilization envelope pathway (mechanism of egg activation)
PIP2 –> IP3 –> Ca released from ER –> cortical granule exocytosis (fertilization envelope develops)
What else does PIP2 activate
DAG
G protein involvement in Ca entry into sea urchin eggs
Sperm contact and fusion –> G protein activation –> Src activation –> PLCy activation –> PIP2 –> IP3/DAG –> Ca release –> cortical granule exocytosis (slow block) OR inactivation of MAP kinase (reinitiation of cell cycle)
Sperm capacitation
Removal of cholesterol by albumin –> influx of ca and bicarbonate –> promote AC activity –> make cAMP from AMP –> protein kinase A (inhibit PTP) –> PTK –> phosphorylate capacitation proteins
What must a sperm go through in order to fertilize
Capacitation
Why doesn’t the first sperm to reach the egg fertilize it
It probably did not go through capacitation. Capacitation is a long process
Where does the acrosomal reaction occur in mammals
Cumulus
What is the zona pellucida made of
Four glycoproteins: ZP1, ZP2, ZP3, ZP4
Which glycoprotein blocks polyspermy in mammals
ZP2
How does the nuclei of the egg and sperm migrate to eachother
Migrate following microtubules
