What is a terratoma?
A germ cell tumor in which the cells have lost their normal developmental control as stem cells and differentiate into all types of cells in the testes. 'tis a monstrous, nasty thing.
When does biological development take place? (5)
1. Embryonic and fetal development
2. Growth and maturation
3. Tissue maintenance and turnover
4. Tissue repair and regeneration
Which type of development is most dynamic and rapid?
Embryonic and fetal development
Which type of development is sporadic?
Tissue repair and regeration
Which type of development is continuous?
Tissue maintenance and turnover (because of the finite lifespan of cells)
Bone vs. Skin: which regenerates and which repairs?
Bone cells regenerate (no scars) while skin repairs and the new cells don't have the same characteristics as the original ones (scarring)
What is aging from a developmental perspective?
cells lose their function, like cartillage in the knees and hips.
What causes arthritis?
Long carbon chains give proteoglycan in cartillage a huge net negative charge, which lets it absorb water into tissue and thus gives cartillage its resiliency. However, these chains become shorter with age, which causes cartillage to resist less and makes bones get closer together.
What is the genomic repertoire of an organism?
The ultimate controlling element to a cell's ability to make developmental decisions. Almost all cells in the oranism have the same genomic repertoire, except some non-DNA cells like red blood cells, gametes, B and T cells.
What causes cells to make developmental decisions, in general?
a temperospatial framework of signals in their local environment. The ability of a cell to make a developmental decision is dependent upon the previous decisions made by the cell.
What are primordial germ cells?
early embryonic cells that acquire developmental potential to develop into the gametes
What is gametogenesis?
The forming of gametes. oogenesis and spermatogenesis.
what is totipotence?
The developmental potential to develop into any cell type of the organism. an egg cell is this.
Characteristics of egg cells (10)
unique haploid genome
abundant stored raw materials and machinery, like proteins, RNAs, nucleic acids, ribosomes, mitochondria
Yolk as the energy supply
outer protective coat (jelly)
What are the three functions of an egg?
1. Contributes 1/2 of unique diploid genome to new organism
2. Provides mechanisms for sperm recognition, binding and fusion, and prevention of polyspermy
3. Provides the raw materials and machinery to carry out early development without any genomic input from zygote
What is formed at the end of egg maturation?
3 polar bodies and only 1 ovum.
There was potential for 4 haploid genomes, but only one ovum formed because all raw materials necessary as investment of energy for the egg.
For most organisms, during what stage of egg development does fertilization occur?
2nd oocyte stage, before maturation of ovum
(before for dogs and drosophila, after for sea urchins)
What are the two parallel parts of gametogenesis?
genomic (mitosis and meiosis) and specialization events
(5) characteristics of sperm
unique haploid genome
motile through flagella
a few organelles: mitochondria and centrioles
What are the three functions of sperm cells?
Get to and fuse with the egg
Contribute 1/2 of unique haploid genome of new organism
Activate the egg
What is resact?
a soluble GLYCOPROTEIN from the jelly layer of egg. It is released into surrounding seawater for sperm to recognize and bind to. It activates at least three receptors on sperm plasma membrane
What is chemotaxis?
The migration of cells towards a soluble concentration gradient of a stimulant
What is sperm's reaction to resact? (4)
1. Increased intracellular Calcium (which leads to...)
2. Directional sperm migration
3. Increased mitochondrial respiration (through ATP production)
4. Activation of dynein ATPase activity (stimulates flagellar movement)
Sperm membrane proteins activated by sulfated polysaccharides in sea urchin egg coat
calcium transport channel
Na/H ion exchanger
What is the next step after recognition at a distance?
contact recognition & the acrosomal reaction
How does the acrosomal process form?
forms through polymerization of actin monomers to form an actin filament.
This is controlled by increase in intracellular pH and calcium activation of RhoB
What happens, generally, in acrosomal reaction?
The formation of the acrosomal process pushes the acrosomal vesicle inside out. The acrosomal vesicle fuses with the plasma membrane of the egg, causing an extracellular release of digestive enzymes.
What is Bindin?
a PROTEIN molecule on acrosomal membrane of sea urchin sperm that binds with species-specificity to EBR1 receptors on vitelline layer of egg
3 Layers of species specificity in fertilization
recognition at a distance
Bindin at vitelline layer (after dissolving jelly layer)
In egg and sperm fusion, where is actin polymerized?
Both in sperm to make acrosomal process (for acrosomal reaction) and in egg to form microvilli (to facilitate egg and sperm fusion)
What are the two blocks to polyspermy in sea urchins?
1. The fast transient block, for which the egg plasma membrane depolarizes because of an increase in Sodium. This takes 1-3 seconds and lasts about 1 minute (until egg gets repolarized)
2. The slow permanent block through the cortical reaction. Cortical granules fuse with egg plasma membrane, resulting in release of molecules into extracellular space
Molecules released by Cortical Reaction
Proteinases and Glycosidases, which separate vitelline layer from plasma membrane
Mucopolysaccharides (Glycosaminogycans), which are negatively charged sugars that create an osmotic gradient
Peroxidases: Ovoperoxidase (soluble) and Udx (membrane-bound)
Hyalin protein, which coats outer surface of egg and is used during early development
This mechanism is not species-specific
membrane fusion between egg and sperm, which is mediated through fusogenic proteins and plasma membrane
What is Src?
a type of tyrosine kinase in sea urchins that is activated by G protein and activated PLCy.
What are the early events of egg activation?
increase in cell metabolism through activation of metabolic enzymes (NAD+ kinase). This is regulated by increase in intracellular Calcium
What are the late events of egg activation?
initiation of protein and DNA synthesis in preparation of first cleavage division, regulated by calcium ions and increased intracellular pH caused by DAG activity
What is translocation?
mechanism whereby sperm are transported by uterine contractions in mammalian fertilization
What is capacitation?
sperm interaction with secretions in female reproductive tract (of mammals) that increases sperm metabolism and motibility. This is required for future sperm and egg binding and fertilization. Decreases sperm affinity for oviduct membrane, so they begin swimming up
What are the major molecular components of the mammalian egg used for sperm binding?
Peripheral Zona Protein: weak binding
SED1 - moderatly strong binding
ZP3: initiation of acrosomal reaction
ZP2 and Proacrosin: binds to acrosomal membrane
Order of mammalian fertilization
sperm is translocated
sperm migrate in response to thermotaxis
sperm GA1T receptors bind to ZP3
second meiotic division completed
single cell fertilized egg
study of animal development
6 fundamental parts of embryogenesis
Four major events of fertilization
Contact and Recognition (species-specific most of the time)
Regulation of Sperm entry ino egg (polyspermic blocks)
Fusion of genetic material
Activation of egg metabolism to start devt.
What makes up sperm axoneme?
This is the flagellum. Made of microtubules and tubulin
(2 + 9)
Cytoplasmic storehouse contents of the egg (5)
Nutritive proteins (yolk proteins)
Ribosomes and tRNA for protein synthesis after fertilization
mRNA - accumulated and represed until after fertilization
Morphogenic factors: molecules hat direct differentiation of cells into certain cell types, like transcription facotrs and paracrine factors
Protective chemicals: UV filters, antibodies, DNA repair enzymes
Cell membrane in mammals
in mammals, substance made of ovarian follicular cells that nurture egg when released from ovary. Surrounds the zona pellucida
What is the cortex
Thin layer beneath cell membrane of stiff cytoplasm with high concentration of globular actin.
During fertilization, they polymerize to form long cables (microfilaments).
Necessary for cell division and used to extend egg surface into microvilli, which aid sperm entry into cell
contains cortical granules
have proteolytic enzymes and mucopolysaccharides,
adheside glycoproteins and hyalin protein (provide support for cleave-stage blastomeres)
extracellular matrix that forms fibrous mat around egg. involved in sperm-egg recognition and contains glycoproteins
5 steps of recognition of egg and sperm
Chemoattraction by soluble molecules secreted by egg (resact ->calcium)
exocytosis of sperm acrosomal vesicle to release its enzymes
Binding of sperm to ETC matrix (vitelline envelope or zona pellucida of egg) - step #2 in mammals
Passage of sperm through ETC matrix
Fusion of egg and sperm
What cuases sea urchin sperm to move toward egg?
Elevated pH makes sperm mvoe by activation of Dynein ATP-ase
How does influx of calcium into sperm provide a directional cue?
Activates ATP-generating apparatus and Dynenin ATPase that stimulates flagellar movement
Two things resact does for sperm in sea urchins
Provides instruction on where to go
- Activates Calcium channels and calcium increases motility
What is acrosome reaction initiated by?
Fucose sulfate in sea urchins.
What is Bindin?
the acrosomal protein mediating recognition in sea urchins
What is ERB1?
Bindin receptor glycoprotein on egg vitelline envelope (species-specific)
Why does the fast block to polyspermy work? (sea urchins)
It changes the electric potential of the egg cell membrane, causing a selective barrier.
Usually, seawater has high [Na+], low [K+]; egg has low [Na+], high [K+]. Egg is usually negatively charged compared to water.
However, fast block shifts it to positive charge by small influx of Na+ into egg
What happens in sea urchin slow permanent block to polyspermy?
cortical granule reaction (mechanical block)
Cortical granules fuse with egg cell membrane and release contents between it and vitelline envelope.
Releases some proteins, like serine protease, which separates vitelline layer and cell membrane
clips off bindin receptors and the sperm attached to them
Fertilization envelop forms starting at point of sperm entry by absorbing water, expands around egg
What forms coating around egg after slow block to polyspermy?
hyalin cortical granule proteins. this layer provides support during cleavage for blastomeres
What is responsible for the cortical reaction?
Calcium increase in the egg due to fertilization. This Calcium comes from within the egg starting at the point of sperm entry & moves across the egg.
(This Calcium is stored in ER of egg)
What does release of calcium from egg's ER do?
starts the slow block
activates egg's metabolism to initiate development
What is the primary mechanism for releasing Calcium from ER?
What activates IP3?
What is Src?
Proteins found in cortical cytoplasm that help release Calcium. Activated by G proteins in cortex of egg
What does PLC do?
Activates IP3, which releases Calcium by opening Calcium channels of ER
What are the early responses to Calcium? (4)
Cortical granule reaction
re-entry of egg into cell cycle
reactivation of egg protein synthesis
activation of enzyme NAD+ kinase, which converts to NADP+
What are the late responses to Calcium? (3)
Resumption of protein and DNA synthesis
New burst of DNA and protein synthesis
Fusion of egg and sperm, which leads to increase in pH
When does fertilization happen in sea urchins?
AFTER second meiotic division
Where does fertilization occur for mammals?
What is the ampulla?
region of oviduct where fertilization takes place
How does sperm get to oviduct?
primarily moves by muscular contraction of uterus
5 steps of sperm translocation
Uterine muscle contractions get sperm to oviduct
Region before ampulla may slow sperm down and release them slowly
Flagellar motility important once sperm arrives within oviduct and sperm becomes hyperactive in vicinity of oocyte
Sperm may receive directional cues from temperature gradients and some chemical cues
Sperm matures (capacitates) during trek so can fertilize egg
What is capacitation?
set of physical changes by which sperm become competent to fertilize the egg
What happens if sperm are not capacitated?
Are held up in cumulus matrix and unable to reach the egg to fertilize it
Time frame for mammalian fertilization
fertilizing sperm could take up to 6 days to reach the egg; shortest journey takes maybe 30 minutes, but many have little chance of fertilizing that soon because have not yet undergone capacitation.
Sperm also lose competence if stay around too long
5 molecular changes during capacitation
Albumin proteins in female reproductive tract remove cholesterol from sperm cell membrane
Some proteins and carbs on sperm surface lost
K+ ions leave sperm, making membrane potential more negative
Outer acrosomal membrane changes and comes into contact with sperm cell membrane
Role of albumin proteins
in female reproductive tract
remove cholesterol from sperm cell membrane, which changes location of lipid rafts (receptors) to front of sperm head to allow them to participate in acrosomal reaction
What are lipid rafts?
Isolated regions of sperm cell membrane that contain receptor proteins for binding to zona pellucida
Makeup of mammal zona pellucida
ZP1, ZP2, ZP3
What is SED1
Sperm surface protein that binds to zona pellucida complex
What is GalT?
Sperm protein that crosslinks tightly and specifically to ZP3 to activate G proteins
What do G proteins do?
initiate acrosomal reaction (in mammals)
What happens when sperm binds to ZP3?
Causes Calcium-mediated exocytosis of acrosomal vesicle
How does DNA synthesis in mammals occur?
Occurs separately in male and female pronuclei, then they migrate towards each other because of microtubules. true diploid zygote not seen in zygote (not until 2-cell stage)
Where does PLC come from in mammals?
comes from sperm probably.