Midterm 1 Flashcards
What was the cause of the one-eyed phenotype in the lamb?
- Cyclopamine in corn lillies
- blocks signaling of a gene called sonic hedgehog
What role does sonic hedgehog play in pattern formation?
-prevents the embryonic brain from separating into two lobes
What were the findings of Nusslein and Wieschaus? (one-eyed lamb)
- identified hedgehog in Drosophila
- When mutated, it causes a coat of spines
What were the findings of Beachy and colleagues? (one-eyed lamb)
- observed a similar phenotype in mutant mice as in the sheep
- cyclopamine interferes with the signaling pathway of hedgehog (not the biosynthesis)
How did the one-eyed lamb case lead to anti-cancer treatments?
- uncontrolled hedgehog signaling results in certain cancers
- knockdown signaling pathway by using cyclopamine as a treatment
- derivatives are used instead- less side effects
What are the characteristics of somatic cells?
- diploid
- make up skin, bones, organs
- genetic changes in these cells cannot be passed onto offspring
- divide by mitosis to give rise to diploid somatic cells
What are the characteristics of germline cells?
- diploid
- genetic changes can be passed onto offspring
- divide by meiosis to give rise to haploid gametes
- originate outside the embryo in early development before migrating to the reproductive organs of the organism
What are the functions of fertilization?
- The combining of genes derived from two parental lines -> transmit genes from parents to offspring
- Create new organisms -> initiate reactions in the egg cytoplasm that permits development to proceed
What are the four main steps associated with fertilization?
- Contact and recognition between egg and sperm
- Regulation of sperm entry into the egg: block to polyspermy
- Fusion of sperm and egg genetic material
- Activation of egg metabolism to start the developmental process
How have fish evolved to prevent the union of more than two haploid nuclei?
- Sperm can enter into egg only through the narrow opening (micropyle), while rest of the egg is covered by impermeable chorion
- Sperm can only reach the egg cytoplasm through the micropyle
How have mammals evolved to prevent the union of more than two haploid nuclei?
- Sperm has to migrate the long female reproductive tract to reach the egg
- Structural changes in zona pellucida block polyspermy
How have sea urchins evolved to prevent the union of more than two haploid nuclei?
- A fast reaction that is accomplished by an electric change in the egg plasma membrane
- A slow reaction cause by exocytosis of the cortical granules
What are the advantages of using Sea Urchin eggs to study fertilization?
- They are deuterostomes (like vertebrates)
- Eggs are easily obtained in large numbers
- Eggs are optically clear (easy to observe internal structures)
- Embryo develops in sea water (easily produced in the lab)
What are the structural differences between the mammalian and the sea urchin egg?
Sea Urchin: outer jelly layer, vitelline envelope outside PM
Mammals: outer cumulus cells (follicular cells), thick zona pellucida outside the PM
What are the 5 steps involved in egg and sperm interaction during the fertilization in the sea urchin?
- sperm contacts jelly layer
- acrosomal reaction (formation of acrosomal process)
- digestion of jelly layer
- binding to vitelline envelope
- fusion of acrosomal process membrane and egg membrane
What are the 5 steps involved in egg and sperm interaction during the fertilization in the mouse?
- sperm activated by female reproductive tract
- sperm binds zona pellucida
- acrosomal reaction
- sperm lyses hole in zona
- sperm and egg membranes fuse
What are the key differences between fertilization in the sea urchin and the mouse?
Sea Urchin: fertilization is external, sperm is activated via chemo-attractants, acrosomal reaction takes place in the jelly layer prior to interacting with the vitelline envelope, sea urch forms an acrosomal process, cortical reaction results in the formation of the fertilization membrane
Mouse: fertilization is internal, sperm is activated via capacitance, acrosomal reaction takes place post-binding to zona pellucida, no acrosomal process formed, cortical reaction (zona reaction) results in modification of receptors on zona pellucida, no fertilization membrane is formed
What are the two effects of capacitation?
- increase in flagellar activity
2. destabilization of the sperm head acrosomal membrane via the removal of sterols
What are the two functions associated with resact?
- Species-specific attraction of sperm - attracts sperm cells towards the egg in a dilute environment
- species-specific sperm activation - activates mitochondrial respiration that ultimately lead to an increase in motility of sperm cells
What is resact?
- a species- specific chemoattractant isolated from the atlantic purple sea urchin
What is the function of ZP1?
- crosslink between the two major glycoprotein strands
What is the function of ZP2?
- facilitates binding between acrosomal reacted sperm and the egg PM (secondary binding)
What is the function of ZP3?
- facilitates binding of intact sperm with the ZP
- upon binding via GaIT (sperm) and N-acetylglucosamine receptors initiates acrosomal reaction
What are the steps involved in the acrosomal reaction in sea urchins?
- Fucose sulfate rich polysaccharide in the egg jelly coat binds receptors on sperm PM
- Sperm cell becomes depolarized (Na+ influx)
- V-gated calcium channels open- influx in intracellular calcium
a) activation of Na/H increases intracellular pH -> efflux of H (activation of dynein ATPase; increase in sperm motility, extension of acrosomal process)
b) exocytosis of acrosomal vesicle (release of lytic enzymes, exposure of bindin proteins)
What are the functional differences of fast and slow block polyspermy?
Fast Block: immediate signal that one sperm has fused with the egg PM
Slow Block: to avoid sperm fusion with the egg PM after the egg’s membrane potential is restored
What are the mechanism differences between fast and slow block polyspermy?
Fast Block: transient depolarization of the egg PM, triggered by sperm-egg fusion
Slow Block: exocytosis of cortical granules; cortical granule reaction and formation of the fertilization membrane
Why should polyspermy be prevented?
- non-disjunction errors and chromosome aberrations
- ultimate death of the embryo
What are the steps of the fast reaction in sea urchins?
- Sperm fuses with egg PM and triggers a rapid influx of Na+ ions into the egg
- Flow of Na+ into the egg causes a transient depolarization across the egg PM
- Membrane potential changes from -70 mV to about +20mV
- Egg PM is restored to its normal -70mV potential within minutes of fusion as the Na+ channels close
What are the key playes involved in slow block of polyspermy?
- calcium release from ER in the egg cortex (initiated at site of sperm entry)
- corical granules fuse with the egg PM and exocytose their contents into the perivitelline space
- Mucopolysaccharides released by the corical granules form an osmotic gradient, thereby causing water to enter the perivitelline space (vitelline envelope is raised off PM)
- Cortical granule material and vitelline membrane form the fertilization membrane (physical barrier to polyspermy)
- The remaining cortical granule material forms the hyaline layer (jelly like coating between the egg PM and the fertilization membrane)
What does phospholipase C (PLC) do?
- cleaves PIP2 into DAG and IP3
- IP3 causes a release of calcium from the ER
- calcium causes; cortical granule exocytosis, restoration of mitotic cell cycle and membrane biosynthesis, activation of PKC
What does protein kinase c (PKC) do?
- activation of Na/H exchanger
- increase in intracellular pH
- activates the egg metabolism
What is the zona reaction?
- enzymes released from cortical granules modify the zona pellucida sperm receptors such that they can no longer bind sperm
(enzymes released digest sperm receptor glycoproteins ZP2 and ZP3 so that they can no longer bind sperm)
What are the characteristics of monozygotic twins?
- Identical
- develops from a single zygote, which splits and forms two embryos
- genetic clone (share 100% of their genes)
What are the characteristics of dizygotic twins?
- Fraternal
- develop from separate eggs fertilized by their own sperm
- develop independently during the same pregnancy
- share 50% of their genes
- most common (70%)
What is the third type of twin?
Sequizygotic; arise from two sperms fertilizing a single egg
What are the 5 stages of animal development?
- Gametogenesis
- Fertilization
- Cleavage
- Gastrulation
- Organogenesis
What determines the pattern of embryonic cleavage?
- the amount and distribution of yolk (Balfour’s law)
2. the position of the mitotic spindles
What is determinant cleavage?
- cell fate of daughter cell is determined
What is indeterminant cleavage?
- cell fate of daughter cell is undetermined at this stage
What does the ectoderm give rise to?
- outer epithelium
- neural tube (CNS)
- neural crest
What is the “4th” germ layer and what does it give rise to?
- peripheral neurons
- schwann cells
- melanocytes
- some of the bones and connective tissue of the face
What does the mesoderm give rise to?
- somites (muscles, cartilage and bones)
- notochord (degenerates and persists as the nucleus pulposus of the intervertebral discs)
- circulatory system (blood, bone marrow)
- organs of urogenital system (kidney, gonads and reproductive tract)
What does the endoderm give rise to?
-primitive gut (epithelial lining of the digestive and urogenital tract, stomach, colon, liver, pancreas, lungs
What are the characteristics of protostomes?
- Blastopore become the mouth
- spiral cleavage, which is determinant
- molluscs and annelids
What are characteristics of deuterostomes?
- blastopore become the anus
- radial cleavage, which is indeterminant
- echinoderms and chordates
Why are mammals different than other deuterostomes?
- they have rotational cleavage
What is invagination?
- infolding of cell sheet into embryo
What is involution?
- inturning of cell sheet over the basal surface of an outer layer
What is ingression?
- migration of individual cells into the embryo
What is delamination?
- splitting or migration of one sheet into two sheets
What is epiboly?
- the expansion of on cell sheet over other cells
What is the primitive streak?
- transient structure that arises in the blastula and marks the start of gastrulation
What organisms get a primitive streak?
- mammals, birds, reptiles
What are the functions of the primitive streak?
- initiates germ layer formation
2. establishes bilateral symmetry
What are the steps involved in neurulation?
- Notochord signals part of neighboring ectodermal cells to form neural plate
- Neural plate bends back on itself (or forms a neural groove)
- Neural crest cells found at the borders of the neural plate come together to form neural tube
- The neural tube gives rise to the central nervous system (brain and spinal cord)
How do NTD (neural tube defects) occur?
- result from the neural tube failing to close completely during the first few weeks of embryonic development
How can NTDs be prevented?
- by folate (aka vitamin B9)
What are the two most common forms of NTD?
- spina bifida
- anencephaly
Where is the first point of fusion between the neural folds?
- at the hindbrain/spinal cord junction
What are the characteristics of exencephaly?
- the brain is located outside of the skull
- neuroepithelium appears to protrude from the developing brain
- usually found in embryos as an early stage of anencephaly
What are the characteristics of Anencephaly?
- the absence of a major portion of the brain, skull and scalp that occurs during embryonic development
- exposed neural tissue from exencephaly can gradually degenerate due to exposure to amniotic fluid and trauma
What are the characteristics of Spina Bifida?
- incomplete closer of the spine and the membranes around the spinal cord
- progression of spinal neurulation along body axis is severely delayed or halted
What are the characteristics of Craniorachischisis?
- the entire neural tube from midbrain to the low spine remains open
What are the four main developmental processes of animals?
- Pattern formation
- Morphogenesis
- Cell differentiation
- Growth
How do you make two daughter cells different from one another?
- Cell intrinsic properties (cell fate determinants, unequal segregation of cytoplasm)
- Cell extrinsic properties (inductive signaling)
What happens to cells when they undergo differentiation?
- changes in gene expression occurs as a result of cell-extrinsic and cell-intrinsic properties
- the cell size and shape changes dramatically, as does its ability to respond to signaling molecules
What are three examples from lecture of processes involved in morphogenesis?
- Gastrulation (the dramatic rearrangement of cells in the blastula to create the embryonic tissue layers: ectoderm, mesoderm and endoderm)
- Cell migration (migration of the neural crest cells from the dorsal side of the embryo to the human face)
- Apoptosis ( separation of fingers and toes)
What are three factors that give rise to growth of the embryo?
- Cell proliferation
- Cell enlargement
- Increase in extracellular material (bone and water)
What are the two criteria required for a molecule to be considered a morphogen?
- it must have a concentration-dependent effect on its target cells
- it must exert a direction action at a distance
What experiments could be performed to determine if a molecule functions as a morphogen?
- manipulate gradient and observe if there is a shift in cell fate
- expose cells to different concentrations in a petri dish and observe the cell’s response
What is the significance of the french flag model?
- illustrates how gradients of inductive molecules could subdivide developing tissues into discrete regions of differentiation
What are fate maps?
- territorial diagrams of embryonic development
- used to study cells as they differentiate and gain a specified function
- does not tell you how or when a cell fate is specified and determined
What are the three main experiments used to understand the timing and mechanisms of cell fate specification and determination?
- Cell ablation
- Cell transplantation
- Cell isolation
What is cell ablation?
- selectively destroy one or more cells in an organism of interest and look at the fate of remaining cells
What is cell transplantation?
- the transfer of a cell from one tissue to another - observe the fate of the transferred cell
What is cell isolation?
- separation of individual cells from a solid block of tissues or cell suspension
What are the three general ways a cell can become specified?
- Autonomous specification
- Conditional specification
- Syncytial specification
What organisms go through autonomous specification?
-most invertebrates (molluscs, annelids and tunicate)
What does autonomous specification give rise to?
- mosaic (determinative) development
What does autonomous specification rely on?
-relies on cell-intrinsic properties inherited (cytoplasmic determinants)
What organisms go through conditional specification?
- all vertebrates; some invertebrates (sea urchin)
What does conditional specification rely on?
- relies on cell-extrinsic cues (interactions between neighbouring cells or from concentration gradients
What does conditional specification give rise to?
- regulative development
What organisms go through syncytial specification?
- most insect classes
What is syncytial specification?
- hybrid of both autonomous and conditional specifications
What does syncytial specification rely on?
- morphogen gradients
What goes on during syncytial specification?
- interactions occur between parts of one cell (the syncytium embryo)
- no cell boundaries; morphogens influence different nuclei in a concentration-dependent manner
- after cellularization, conditional specification is often seen
What is mosaic development?
- cell fate is determined by the components of the cytoplasm found in each blastomere
What is regulative development?
- cell fate depends on its interactions with neighbouring cells, not the cytoplasm it inherits; refers to the ability of an embryo to compensate for the loss of some portions
What do cell extrinsic cues involve?
Inducing signals; growth factors, cytokines, hormones, morphogens, etc.
What are the processes required for a cell to acquire its fate?
- specification
- determination
- differentiation
When is a cell said to be specified?
- a cell or tissue is said to be specified when it has a planned fate, but is able to change that fate given the right cues
How is specification usually assessed?
- via isolation experiments
What is the first form of commitment and is it reversible?
- specification
- yes it is reversible
When is a cell said to be determined?
- a cell or tissue is said to be determined when it is capable of differentiating autonomously, even when placed into another region of the embryo
What is the second form of commitment and is it reversible?
- determination
- not reversible
How is determination usually assessed?
- via transplantation experiments
What is determination generally associated with?
- a change in gene expression
What is differentiation?
- process in which the cell that have their fate determined develop into their specialized shapes and functions
- ie. the developmental pathway at which the cell takes to acquire its fate
What is an inductive signal?
- a signal from one group of cells influences or directs the development of adjacent group cells
What is inductive signaling mediated by?
- paracrine and contact-dependent signaling
What are examples of inducing factors?
- growth factors
- cytokines
- hormone
- morphogens
What are the three main ways inducing signals are transmitted between cells?
- Secreted diffusible molecules
- Direct interaction via surface proteins
- Cell to cell through gap junctions (animals) or plasmodesmata (plants)
What does it mean for a cell to be “competent”?
- the ability of a cell to respond to a specific inductive signal
- competence is an actively acquired condition in response to an inductive signal
What is required for cell competence?
- presence of ligand- specific receptors
- functional signal transduction pathway coupled with the regulation of transcription factors
Inducing signal(s) received by a cell are transmitted in the interior of cell by relays of intracellular signaling molecules.. these signals can result in what?
- changes in gene transcription
- alterations to cytoskeleton (regulates cell division, expansion and movement)
- altered activities of enzymes or other intracellular proteins
What are two types of inductive signals?
- permissive
- instructive
Describe instructive signaling.
- occurs when the responding cell has a choice of fates and will follow one developmental pathway following induction, and an alternative pathway in absence of the inductive signals
Describe permissive signaling.
- occurs when the responding cell is already committed to a certain fate, and requires the inducing signal to proceed in the developmental pathway
What are stem cells?
- precursor cells that have the capacity to divide indefinitely and which can give rise to more specialized cells
What make stem cells unique?
- self-renewal (they are self sustaining by replicating themselves for long periods of time
- they are unspecialized
- they can differentiate into specialized cell types
What kind of division do stem cells undergo?
- asymmetric division (two daughter cells different from one another)
What controls the maintenance and differentiation of stem cells?
- growth factors mainly produced by blood or stromal cells (part of the connective tissue)
- GF’s act in combinations and rely on the history of the cell receiving the signal
What are the two main types of stem cells in mammals?
- Embryonic stem cells (ETC)
2. Adult stem cells
What are characteristics of embryonic stem cells?
- isolated from the inner cell mast of blastocysts that have been fertilized in vitro and donated
- pluripotent (can differentiate into ectoderm, mesoderm and endoderm)
What are the characteristics of adult stem cells?
- AKA somatic stem cell
- found in small numbers in adult tissues, such as bone marrow or fat
- repair and maitain tissue in which they were found
- mainly multipotent (limited to differentiating into different cell types of their tissue of origin)
How do you make embryonic stem cells?
- DNA from adult cell is injected into a fertilized human egg with no nucleus
- Egg begins dividing forming a mass of cells
- At the end of cleavage a blastocyst forms, containing a trophoblast and an inner cell mass
- Stem cells are harvested and embryo is destroyed
What are three examples of adult stem cells?
- Hematopoietic
- Mesenchymal
- Neural
What are hematopoietic stem cells?
- blood cells; RBCs, B lymphocytes, natural killer cells etc.
What are mesenchymal stem cells?
- bone marrow (bone marrow stroma stem cells and skeletal stem cells)
- gives rise: bone cells, cartilage cells, fat cells, stromal cells that support blood formation
What are the neural stem cells?
- brain; neurons, astrocytes, oligodendrocytes
What type of adult stem cells are used in transplantation experiments?
- Adult hematopoietic, or blood-forming, stem cells from bone marrow have been used in transplants for more than40 years
How do embryonic stem cells and adult stem cells differ in their ability to be grown/divide?
- Adult: removal from the body limits their capacity to divide (isolating and harvesting is a challenge)(can not be easily grown in vitro)
- Embryonic: can be grown in large numbers relatively easily in culture
Why is it believed that adult stem cells, and tissues derived from them, are currently believed less likely to initiate immune rejection after transplantation compared to embryonic stem cells?
- this would involve the patient’s own cells being expanded in culture, coaxed into assuming a specific cell type, then reintroduced into the patient
What are the 5 different types of stem cells in order from most potent to least potent?
- Totipotent
- Pluripotent
- Multipotent
- Oligopotent
- Unipotent
What are the two types of potency observed in embryonic stem cells?
- totipotent
- pluripotent
What are the characteristics of totipotent stem cells?
- most powerful
- can differentiate into embryonic as well as extra-embryonic tissues
- can generate a fully-functional, living organism
- zygotes*
What are the characteristics of pluripotent stem cells?
- second most powerful
- derived from the inner mass of the blastocyst
- can self-renew and differentiate into any of the three germ layers
- two types; natural (ESC), human-made (induced pluripotent)
What are the three types of potency found in adult stem cells?
- multipotent
- oligopotent
- unipotent
What are characteristics of multipotency?
- can self-renew and differentiate into a specific range of cell types
- hematopoietic and mesenchymal cells
What are the characteristics of oligopotency?
- can self-renew and differentiate into a limited number of cell types, of which are closely related
- lymphoid, myeloid
What are the characteristics of unipotency?
- can differentiate along a single lineage
- muscle, epidermal, satellite
What are iPSCs?
Induced pluripotent stem cells
- adult cells that have been genetically reprogrammed to an embryonic stem cell-like state (epithelial cells)
- involves the induced expression of genes and transcription factors important for maintaining embryonic stem cell properties (pluripotency)
What are some examples from lecture of how stem cells can potentially be used for treatments?
- regenerating bone using cells derived from bone marrow stroma
- developing insulin-producing cells for type 1 diabetes
- repairing damaged heart muscle following a heart attack with cardiac muscle cells
- nuerogenerative diseases: parkinson’s, alzheimer’s, huntington’s, MS
- spinal cord injury
- rheumatoid arthritis and osteoarthritis
What are two approaches stem cells can be used for therapy?
- Transplant: stem cells are harvested either from the patient or a donor and refined or modified in some way before being injected or grafted into the patient
- Target for a drug: drug is intended to activate a desired response from stem cells that already exist in patient
What are the types of stem cell transplants?
- Autologous (stem cells come from patient)
- Allogeneic (stem cells come from a donor)
- Syngeneic (stem cells come from your identical twin)
Who is Anton van Leeuwenhoek?
- the dutch microscopist who co-discovered sperm in 1678 (first believed sperm were parasitic animals living within the seminal fluid)
What did Oscar Hertwig and Herman Fol do?
- in 1876 they demonstrated sperm entry into the egg and the union of the two cell’s nuclei
What did Moy and Vacquier do?
- in 1979, using immunological techniques, they demonstrated that bindin is located specifically on the acrosomal process exactly where it should be for sperm-egg recognition
What did Vacquier and colleagues do in 1977?
- isolated bindin from the acrosome of the purple and red sea urchins and found that each was capable of binding to dejellied eggs of the same species
What is convergent extension?
- tissue of embryo narrows along one axis while elongating along a perpendicular axis
- this can occur when rows of cells intercalate or by directed migration of two population of cells toward each other
