Fertilizaton To Gastrulation Flashcards
(37 cards)
1
Q
Advantages of mouse as model organism
A
- easy to maintain
- mammal
- high reproductive rate
- genetic knockouts - has very powerful gene tics and or many years was the only vertebrate in which genetic mutations could be targeted to a specific gene of interest (knockouts)
All in all it should be a good model for human development
2
Q
Nobel prizes won for research in mice
A
2007 Capecchi, Evans, Smithies ‘for their discoveries of principles for introducing specific gene modification in mice by the use of embryonic stem cells’
3
Q
Disadvantages of using mice in the lab
A
- relatively long life cycle
- expensive to maintain
- since mammalian development occurs inside the uterus the mouse embryo is inaccessible and its small size makes micro manipulation very difficult
4
Q
Advantages of using chickens (Gallus gallus) in the lab
A
- easy to obtain
- large eggs
- easily observable embryos
- excellent for micromanipulation (as they are accessible at most developmental stages)
- is an amniote and shares many developmental features with humans
5
Q
Historical models of using chickens in the lab
A
- Aristotle (384-322 BCE) - observed embryos with naked eye (cracked open eggs on each day of 3 week incubation and recorded the changes with is naked eye
- Marcello Malpighi (1628-1294) - first microscopic study of embryonic development of chickens
6
Q
Disadvantages of using chickens in the lab
A
- not very amenable to genetic/transgenic analysis
7
Q
Advantages of using frogs (Xenopus laevis) in the lab
A
- easy to maintain
- egg laying can be induced by injecting females with gonadotrophin (pregnancy hormone)
- large eggs - excellent for observation and micro manipulation
- large numbers of eggs
- it is very easy to inject reagents into its membranes
8
Q
Nobel prizes using frogs in the lab
A
2012 Sir Joseph Gurdon “for the discovery that mature cells can be reprogrammed to become pluripotent
- used the frogs for his pioneer studies on a single cell nuclear transfer (animal cloning) for which he was awarded the Nobel price
9
Q
Disadvantages of using frogs in the lab
A
- Not very amenable to genetic/transgenic analysis
- not suitable for classical genetics due to its long life cycle and largely tetraploid genome
A related diploid species - Xenopus tropicalis - has a shorter life cycle and is being used for both embrylogical and genetic studies
10
Q
Advantages of using zebrafish (Danio rerio) in the lab
A
- easy to maintain
- high reproductive rate
- transparent embryo
- genetically amenable
- embryos that are that are accessible at all stages in the development
11
Q
Disadvantages of using zebrafish in the lab
A
- expensive to maintain
- relatively long life cycle
Micromanipulation is difficult
12
Q
Advantages of using fruits flies (Drosophila melanogaster) in the lab
A
- easy to maintain
- high reproductive rate
- very amenable to genetics
13
Q
Nobel prizes in fruit fly research
A
- 1995 Lewis, Nusslen-Volhard, and Wiechaus “for their discoveries concerning the genetic control of early embryonic development”
- 2017 Hall, Rosbah and Young “for their discoveries of the molecular mechanisms controlling the circadian rhythm”
14
Q
Disadvantages of using fruit flies in the lab
A
- not a vertebrate
15
Q
Advantages of using nematode (Caenorhabditis elegans) in the lab
A
- Easy to maintain
- Short life cycle (~3 days)
- transparent
- first animal with sequenced genome
- first animal to have its connect one fully described
16
Q
Nobel prizes won using nematodes in the lab
A
- 2002 Brenner, Sulston, Horvitz “for their discoveries concerning genetic regulation of organ development and programmed cell death”
- 2006 Fire and Mellow “for their discovery of RNA interference”
- 2008 Chalfie “for his work on green fluorescent protein”
17
Q
Disadvantages of using nematodes in the lab
A
- not a vertebrate
18
Q
Gametogenesis
A
Sperm and eggs are haploid cells produced in the gonads (testes and ovaries respectively) by a process called gametogenesis - which requires meiosis
In males meiotic divisions are usually equal and produce 4 sperms while in females they are usually unequal and produce a single ovum and two polar bodies
19
Q
Oogenesis
A
- begins in fetal ovary but meiosis not completed until fertilisation
- Oocytes are held in prophase I until a few are activated each menstrual cycle
- once activated held at metaphase II until fertilisation
- the polar bodies contain the nuclear material of the first and second meiotic divisions are
20
Q
Spermatogenesis
A
- begins at puberty
- huge numbers produced
21
Q
Eggs vary greatly in size
A
- eggs vary enormously in size (50 micrometers worm, 100 micrometers mouse, 180 micrometers fly, 700 micrometers fish, 1.3mm frog, 5cm chick)
- size depends on nutrition required (i.e. on the side of larval organism)
- mammals are an exception as they receive nutrients via the placenta
22
Q
Eggs are stockpiles with maternal goodies
A
- yolk proteins (Vitellogenin) is 90% of protein content
- proteins required for ‘household’ functions (metabolism, cell division, DNA replication, transcription, etc.)
- RNA
- Lipids, glycogen etc
23
Q
Mammalian eggs
A
- 100 micrometers in diameter
- lack large amounts of yolk (don’t really need a lot as nutrients and stuff supplied by placenta???)
- held in metaphase II after ovulation
- cortical granules just beneath the plasma membrane
- surrounded by a layer of follicle cells derived from the ovary and a membrane known as the zona pellucida
24
Q
Sperms: highly specialised cells
A
- lost most of cytoplasm
- head contains haploid nucleus, centriole and acrosome
- midpiece contains mitochondria and base of flagellum
Check structure diagram and memorise the parts
25
Fertilisation
- contact between sperm and Zona pellucida causes acrosome to burst
- acrosome releases enzymes that digest a hole
- sperm pass through and fuse
- calcium wave activates end of meiosis
- enzymes released to modify zona pellucida to prevent polyspermy
26
Mammalian fertilisation
Check diagram in the slides
27
Cytokinesis
- cytokinesis completes mitosis and divides the cytoplasm between both daughter cells
- a contractile ring forms beneath the plasma membrane, containing a band of actin and myosin filaments. It always forms in the same plane that was previously occupied by the metaphase plate
- as the actin and myosin filaments slide by one another, the ring contracts and pinches the 2 cells apart
28
The fertilised egg must
- produce hundreds to trillions of cells through the process of mitosis
- instruct these cells on what cell type they must become (specification and determination)
- organise them into tissues and organs
- give cells characteristics required for their function (differentiation)
29
Cleavage divisions
First mitotic divisions are not accompanied by growth
Daughter cells (blastomeres) are half the volume of the parent cell
There are types of cleavage
- Holoblastic and Meroblastic
30
Holoblastic cleavage
Entire egg is cleaved during each division (mouse, frog, worm)
31
Meroblastic cleavage
Only part of the egg is cleaved during
- discoidal - restricted to disc of yolk free cytoplasm at animal pole (zebrafish, chick)
- superficial - restricted to yolk free cytoplasm covering egg surface (drosophila)
32
Holoblastic cleavage: mouse (check diagram on slides)
Most mammals have small eggs containing very little yolk that is equally distributed in the egg
These fertilised eggs almost always use Holoblastic cleavage
Cleavage divisions are not synchronous and the embryo soon has an odd number of blastomeres
At the 16-32 cell stage blastomeres undergo compaction whereby they maximize contacts with each other
They then form a fluid filled cavity called the blastocoele and the embryo is now known as the blastocyst
33
Holoblastic cleavage: Xenopus
Drosophila eggs have a lot of yolk that is concentrated within the center with a peripheral yolk free periplasm.
The first 8 nuclear divisions occur centrally and are not accompanied by cytokinesis.
Most nuclei then migrate to the egg periplasm to form the syncytial blastoderm, where they undergo a further 4 nuclear divisions.
Plasma membrane then folds inwards and
partitions each nucleus into a single cell, to form the cellular blastoderm
34
Cleavage divisions can be very rapid
Drosophila melanogaster (fruitfly) 8 minutes
Caenorhabditis elegans (nematode) 20 minutes
Danio rerio (zebrafish) 20 minutes
Xenopus laevis (frog) 25 minutes
Gallus gallus (chick) 1.5 hours
Mus musculus (mouse) 20 hours
35
Modifying the cell cycle
Remove GTP phases (G1 and G2)
Shorten S-phase (DNA replication)
Remove cytokinesis (only nuclei divide)
36
Mid- blastula transition
Rapidly dividing cleavage stage blastomeres modify the cell cycle, eliminating gap phases (G1
and G2) and shortening S-phase (by increasing the number of sites at which DNA replication is
initiated).
After 12 cell divisions (in Xenopus) the normal cell cycle is introduced and and cell division becomes asynchronous. This point is known as the mid-blastula transition (MBT).
MBT is also found in zebrafish and Drosophila embryos
37
The maternal/zygotic transition
- Maternal Gene Products: transcribed from the mother’s genome during oogenesis and stockpiled in the egg
- Zygotic Gene Products: transcribed from the embryo’s genome, both maternal and paternal chromosomes.
The cell cycle is so rapid before MBT that there is very little time for transcription.
As a consequence the oocyte must stockpile the RNA that it needs during the cleavage divisions.
Since only the maternal genome contributes to this stockpile the RNA is known as maternal RNA.
Zygotic RNA synthesis increases significantly at the MBT, while maternal RNA is degraded
