Developmental Biology Flashcards
What are the advantages & disadvantages of using mice as a model organism?
Chicken?
Frog?
Zebrafish?
Fruit fly?
Nematode? (worm)
- easy maintenance, high reproductive rate, mammal, genetic knockout
- expensive to maintain, long life cycle
- easy maintenance, high reproductive rate, mammal, genetic knockout
- large eggs (embryos), easy obtain & observe embryos, great for micromanipulation
- not emenable for genetic/transgenic analysis
- large eggs (embryos), easy obtain & observe embryos, great for micromanipulation
- easy maintain, induce egg laying by injecting females with gonadotrophin, large eggs (observation & micromanipulation)
- not amenable to genetic/transgenic analysis
- easy maintain, induce egg laying by injecting females with gonadotrophin, large eggs (observation & micromanipulation)
- easy maintain, high reproductive rate, transparent embryos, genetically amenable, vertebrates
- expensive to maintain, long life cycle
- easy maintain, high reproductive rate, transparent embryos, genetically amenable, vertebrates
- easy maintain, high repro rate, amenable genetics
- not a vertebrate
- easy maintain, high repro rate, amenable genetics
- easy maintain, 3 day life cycle, transparent, first animal with fully sequenced genome
- not a vertebrate
- easy maintain, 3 day life cycle, transparent, first animal with fully sequenced genome
How are oocytes (immature eggs) held/what is the first step of Oogenesis?
What happens once they have been activated?
Fertilised?
What do polar bodies contain?
Primary oocyte in foetal ovary- held in prophase I until activated in menstruation (2n)
Secondary oocyte (oocyte II) formed at metaphase II (n due to meiosis- first polar body formed n)
Forms 2n Ootid which undergoes meiosis again (2nd polar body formed) to form n ovum which eventually goes into zygote 2n
Nuclear material of 1st & 2nd meiotic division
When does spermatogenesis begin?
What happens?
Why are mouse eggs significantly smaller than others?
What are eggs stockpiled with?
Puberty
Primary spermatocyte 2n undergoes 2 rounds of meiosis
meiosis I = secondary spermatocyte n formed
meiosis II = spermatid n formed
Mammals receive nutrients via placenta (externally) & other animals can’t- other eggs are big as need nutrients in them
Maternal goodies: yolk protein 90%, proteins for household functions (metabolism, cell division etc), RNA, lipids, glycogen etc
How do mammalian eggs differ? 5 ways
To what does egg size depend?
What specialised structures do sperm have? 5
What happens on fertilisation with the egg & sperm in humans?
How is polyspermy prevented?
- Small- 100 micrometre diameter
- Lack lots yolk
- Held in metaphase II after ovulation
- Contain cortical granules below membrane
- Zone pellucida = layer follicle cells from ovary (outside layer)
Yolk content
Cytoplasm = lots of it is lost
Acrosome = enzymes at tip of head to break down zone pellucida
Mitochondria = in midpiece for moving flagella
Centriole (base of head)
Flagella
- Contact with sperm & zona pellucida = acrosome bursts releasing enzymes to digest a hole
- Sperm pass through & fuse
- Calcium waves activate end of meiosis
Enzymes released by acrosome modify zona pellucinda to prevent sperm getting through
What happens to the embryo after fertilisation has occurred?
How does this occur?
What 4 things does a fertilised egg must do?
What are the 2 types of cleavage of embryos?
What are cleavages not accompanied by?
Cytokinesis (completes mitosis)
Contractile ring of actin & myosin forms beneath plasma membrane on same plane that used to be the metaphase plate. Actin & myosin slide past eachother = ring contracts & pinches cell apart
- Produce trillions cells mitosis
- Instruct cells on cell-type = specification & determination
- Organise these into tissues & organs = morphogenesis
- Give cells characteristics for their function = differentiation
Holoblastic = entire cell cleaved during each division Meroblastic = only part of the egg is cleaved
Growth
What type of cleavage do mammalian cells undergo?
What are the 2 sub-types of meroblastic cleavage? What organisms undergo these?
How do cleavage divisions occur? 2
What modifications are made to the cell cycle in synchronous/early embryos? Why?
What changes to the cycle in the blastula stage of embryos?
What is the transition called between the 2 changes? What happens at this stage?
What occurs to the maternal gene products & zygotic gene products after this point?
Holoblastic (due to lack of yolk)
- Discoidal: restricted to disc of yolk-free cytoplasm at the animal pole (top)- only cells on top cleave. Zebrafish
- Superficial: yolk free cytoplasm covering the egg surface. Eggs have concentrated yolk in centre with yolk free periplasm- nuclei migrate to the egg’s periplasm & undergo nuclear division & cleave outside of egg
Synchronous & rapidly
Remove G1 & G2 (gap phases), shorten S-phase (DNA replication is faster), & in some remove cytokinesis (only nuclei divide)
- so only M & S
To make cell division faster in early embryos
Gaps re-introduced & becomes asynchronous divisions = blastula stage & transcribes own zygotic genes
Mid-blastula transition- embryo undergoes its own zygotic transcription (turns on genes & direct to cell types)
Levels of maternal gene products decrease (transcribed from mother’s genome & stockpiled in egg) and levels of zygotic gene products increases (from maternal & paternal)
What are the 2 poles in embryos and how are they different?
What is gastrulation?
What does it result in?
What are the 3 types of gastrulation movements?
How are the poles of the embryo established in gastrulation?
Animal pole (small rapidly dividing cells) & vegetal pole (large yolky slowly dividing cells)
Movements where single layers of blastula is reorganised into multilayered gastrula
Formation of 3 germ layers: ectoderm, mesoderm, endoderm
Ingression, invagination, involution
What is ingression?
What is invagination?- where does it originate & what does it form?
In what cells does it happen?
What does buckling of the vegetal plate depend on?
What does elongation/forming the tube require? How does it form the tube?
What cells form at the tip of the archenteron & what do they do?
What does the archenteron & blastophore become?
What happens to the outside of the cell where invagination occurred?
Cells in the thickening vegetal pole migrate individually from surface/plate into the cell
Cells from thickening vegetal pole folds/’buckles’ inwards from the blastophore to form the archenteron (tube)
Sea urchins & c elegans
Convergent extension-
lamellipodia converge: perpendicular to invagination & intercalculate with eachother (form sheets side on)
extend: elongated parallel (stretched up) to form long & narrow archenetron
Apical contraction of actin-myosin complex relative to the basal surface (shortens the apical surface)
Archenteron = gut, blastophore = anus
Secondary mesenchyme cells- produce pseudopodia to pull the archenteron to the animal pole and fuse to it
cells patch it up
What is involution?
In what cells does it occur?
How does it occur?
In what sequence do the different germ layers move & what do they form?
In-turning of expanding outer layer of cells
Fish & frogs
Blastoderm sits on the yolk- cells on the outside involute inside & migrate up
- Endoderm (inmost): gut/digestive tract, liver, lungs, pancreas, gall bladder
- Mesoderm: muscle, blood, heart, kidney, gonads
- Ectoderm (outside): skin & nervous system
How does a mammalian blastocyst form?
What is special about the inner cells?
What are the inner cells subtypes & what can these go on to form?
What does the trophoblast form?
- Fertilised egg undergoes holoblastic cleavage
- At ~16 cells/morula stage cells undergo compaction & minimise contact (cells in centre = inner cells, peripheral cells = trophoblast)
- Cavity forms blastocoel forms in centre of embryo = blastocyst
Pluripotent (form any cell type)
Epiblast = 3 germ layers, amniotic membrane, extraembryonic mesoderm (forms placental vasculature) Hypoblast = extraembryonic endoderm (Heuser's membrane/yolk sac)
Placenta
Implantation:
How does a blastocyst penetrate the uterine wall?
What happens to the membranes?
Attaches & trophoblast divides/proliferates to form syncytiotrophoblast which penetrates the uterine wall
Membrane divides & forms epiblast & hypoblast layers- epiblast forms amniotic membrane & hypoblast forms Heuser’s membrane
What is the most common gastrulation method in mammals?
What occurs during gastrulation in mammals?
What cells are responsible in forming the 3 germ layers in mammals?
What do the cells migrating through the node form?
What do the cells ingressing through the primitive streak form?
Ingression
Epiblast cells
- Ingression occurs first by the epiblast cells entering via primitive streak individually
- The endoderm ingresses & displace hypoblast = embryonic endoderm (gut)
- Then mesoderm = embryonic mesoderm
- Remaining cells in epiblast make up ectoderm
Axial mesoderm, prechordal mesoderm & notochord
Form paraxial by condensing either side of notochord
What is a somite?
What process is this?
How are they formed?
In response to signals, what do somites divide into & what do they each form?
How quickly do somites form in zebrafish, chicks & humans?
When paraxial mesoderm either side of the neural tube divides
Morphogenesis
In pairs & from rostral to caudal (top to bottom)
Sclerotome = axial skeleton Myotone = skeletal muscle Dermatome = connective tissue of dermal layer of dorsal skin
30 min, 90 min, 5 hours
Which cells are responsible for forming the neural plate in neurulation?
How does this occur?
What does this go on to form?
How does the neural tube close?
What can often occur in this?
Ectoderm (exterior)
Cells on neural plate elongate from rostral to caudal & form pseudostratified columnar epithelium/neural tube
Spinal cord & brain of central nervous system
Apical (exterior side of layer of ectoderm/neural plate) constriction of the neural plate like invagination- layer is rich in actin & myosin
neural tube closure defects- lead to open spines & congenital conformations
In vertebrates, what forms on the dorsal roof of the neural tube?
What process is this?
What type of cells are these and what can they form?
What stage in vertebrates is reached after neurulation?
What is shared between vertebrates at this stage?
Neural crest cells
Morphogenesis
migratory multipotent stem cells- form mesoderm & ectoderm tissues (key role in vertebrate evolution)
Phylotopic stage- display basic vertebrate body plan & all quite similar
Common molecular anatomy
