Flashcards
Establishment of body plan - 1 & 2
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- 1Drosophila - key characteristics?rapid life cycle
easy to keep
many accessible embryos for phenotype analysis
relatively cheap - 2Forward genetic screen for genes regulating embryonic development1. induce mutations at random
2. screen for mutants that affect development
3. pattern of denticles (on outer surface of larva) = readout of developmental events
4. genes identified underpin understanding of development of Drosophila body plan - 3Importance of model organisms?1. to understand where genetic control of development started & where most advanced
2. Logic of experimental approach & strategies of genetic control revealed transformed understanding of multicellular development
3. developmental genes & mechanisms highly conserved (basic gene kit for all development)
4. Drosophila model system for pioneering genetic analysis of developmental processes - 4Conceptual tool kitgenes -> proteins -> cell properties -> developmental processes
sequential expression of different sets of genes establishment body plan along A/P axis
- development is progressive
- development proceeds, cells more & more restricted in development potential
- patterns created in fields of cells where there wasn't before
- cells contain same genes, cell properties governed by which genes are expressed - 5Establishment of Drosophila body planA/P & D/V axes set up by maternal genes (develop at right-angles to each other & occur independently)
A/P = head, thorax & abdomen
maternal gene = active in mother during oogenesis (laid down in egg)
anterior, posterior & terminal regions affected by mutations (don't develop specialised structures) - 6Oogenesis1. germ line stem cell (in germanium) divides asymmetrically -> produces cytoplast + other stem cell
2. cytoblast dives 4X = 16 cells
3. 1 becomes oocytes & 15 nurse cells
4. nurse cells = make RNA & protein exported into developing oocyte
*all surrounded by somatic follicle cells - produce materials for vitelline membrane (protection, surrounds egg) - 7Anteiror terminalBicoid gene = necessary for development for anterior structures (key in A/P axis)
bicoid mRNA localised at anterior of newly laid egg
protien transplanted after fertilisation
protein movement & distribution mRNA creates gradient
morphogen = conc dependent regulator
hypothesis = conc dependent regulator - 8French glad modelhow cells develop differently in ordered fashion (pattern formation)
- conc increases, threshold crossed (cells go red to white)
- crosses another threshold = turns into blue - 9Posterior terminalmutation prevents posterior end developing
= abnormal development of abdominal segments
Nanos & caudal = posterior group genes
- also present in gradients
A/P gradient established by inhibition of caudal protein by synthesis of bicoid - 10Nanos - localised maternal mRNA at posterior pole - translated after fertilisation & protein forms gradientTorso - park of RTK signalling
- 2 termini of embryo defined by torso activation (cell surface receptor)
- receptor found all around embryo
- activation ONLY at termini where signal produced - 11what specialises the D/V axis?maternal proteins in egg vitaline membrane
- after fertilisation, spätzle ligand activates Toll receptor
- produces gradient of intra-nuclear dorsal protein along D/V axis
*expression only in follicle cells surrounding ventral region
- two termini of D embryo defined by Torso activation = gradient of intranuclear ventral proteins (found throughout but only responds to signal in ventral region) - 12Toll signalling pathway1. Spatzle ligand activation Toll receptor
- translocation of dorsal TF from cytoplasm into nucleus (stimulated by signal from receptor)
2. bind to dMyD88, which bind to Pelle
3. this bind to Cactus kinase & activates Cactus
4. cactus binds to dorsal protein, cactus phosphorylated & degrades
5. Dorsal protein binds to nucleus
*innate pathway - 13what are the mammalian orthologues of dorsal & cactus?NFKb & IkB
- 14There is localisation of maternal factors during oogenesis, what are the two key features when the egg is laid?1. Bicoid RNA is localised to the anterior
2. machinery to produce processed Spatzle is localised ventrally - 15what are the interactions of the oocyte & follicle cells that spicy the A/P axis of Drosophila?1. oocyte moves from central position of egg chamber to posterior end -> preferential adhesion via E-cadherin between future poster end of oocyte & poster follicle cells, signals = GUrken signal
2. Gurken signal from oocyte via Torpedo receptor (EGF-like) induces posterior follicle cells
3. posterior follicle cells induce polarisation of oocyte cytoskeleton
4. polarised microtubules localise bicoid mRNA to its final anterior site - 16D/V axis formation during Drosophila oogenesis- oocyte nucleus moves along polarised microtubules to dorso-anterior position
- signals to nearby follicle cells (via Gurken)
- follicle cells now different in D/V axis
- end point = localised production of processed Spatzle - 17Anterior-posterior formation1. oocyte localised at posterior end of follicle by cadherin
2. oocyte Gurken protein induces posterior follicle cells via Torpedo
3. posterior signal (from follicle cell) reorganises oocyte cytoskeleton
4. bicoid mRNA localized in anterior, oskar & other mRNAs in posterior
termini = follicle cells at both ends of egg deposit ligand for Torso protein in vitelline envelope - 18what are the main themes in early formation of A/p & D/V axis- egg has crucial asymmetries when laid
- anterior localisation of bicoid mRNA & ventral localisation of machniery to produce processed Spaztle
- result of maternal gene activity
- framework of all later patterning
- gradients of key regulators at fertilisation
A/P = bicoid protein
D/V = intra-nuclear dorsal protein
*gradients interpreted by zygotic genes to subdivide embryo into different areas, produce different cell types & organs - 19mutations affecting segment no. & polarity in Drosophila (mutations in the segmentation genes)1. GAP gene (Kruppel) -> loss of contiguous body segments, resembling gap in body plan
2. Pair-rule gene (even-skipped) -> results in alternating segments (gene expressed as result of differing cons of gap gene)
3. Segment-polarity gene (hedgehog) -> expressed following expression of gap genes & pair-rule genes & establishes antero-posterior axis of each segment - mutation prevent axis formation - 20Syncytium = cytoplasmic mass containing several nuclei = Drosophila embryo in early stages of development1. lots of nuclei in common cytoplasm
2. proteins i.e. TFs can diffuse & influence gene expression in neighbouring nuclei directly - 21How does bicoid control hunchback gene expression?- activates when above certain threshold
- only in anterior end of embryo when bicoid above certain conc
* all development depends on transcriptional circuit of genes whose expression is controlled by combinations of TFs - 22How is Kruppel gene regulated by hunchback protein?- when above certain threshold, activates expression of Kruppel
- can activate or repress
- represses expression at certain conc level
- causes stripe of expression in middle of embryo - 23How does the bicoid gradient sub-divide the embryo along the A/P axis?- egg laid has asymmetries from maternal gene activity
- development proceeds by rounds of patterning
- successive refinements from broad regional differences to small domains
- broad regional differences from series of bands of 'gap' gene expression
*bicoid activates hunchback in anterior
*hunchback regulates other 'gap' genes e.g. Kruppel (all these genes encodes TFs) - 24Steps of Segmentation?1. gap genes, set up boundaries between different segments & regulate pair-rule genes to define 14 parasegments
2. pair-rule genes = TFs, which regulate expression of segment polarity genes
3. SP genes stabilise boundaries between segment by defining polarity of each segment - 25eve gene = pair-rule gene even-skipped - encodes home-domain contains protein 'Eve' - required for development of both odd & even numbered parasegmentscis-regulatory sequences of eve gene comprise series of modules each controlling a particular stripe of expression
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- degree Devleopmental and stem cell biology (Establishment of body plan ) Flashcards on Establishment of body plan - 1 & 2, created by michaela minkin on 01/04/2019.
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