Body plan Flashcards
what happens to the spätzle ligand after fertilisation
the toll receptor is activated to produce a gradient of the dorsal transcription factor protein along the dorsal/ventral axis
where is the spätzle ligand localised and what protein is expressed in the nuclei of this area
in the ventral region, expresses the dorsal protein in these cells
describe how the toll signalling pathway means that a spätzle signal can result in the transcription of dorsal proteins
spätzle signal binds to the toll receptor, causes a transduction mechanism that results in dorsal protein being translocated to the nucleus where gene expression can be altered.
how is the dorsal protein kept in the cytoplasm
through an interaction with the cactus protein
what are the two key features of the egg when it is laid
bicoid RNA is localised at the anterior + machinery to produce the spätzle ligand is localised ventrally
explain how bicoid mRNA becomes localised to its final anterior site in the drosophila egg
oocyte becomes localised at posterior end and the posterior end of the oocyte sticks to the posterior follicle cells. EGF-like signal from oocyte induces posterior follicle cells with then induce polarisation of oocyte cytoskeleton. polarised microtubules localised bicoid mRNA to its anterior site
how is the D/V axis formed in drosophila oogenesis
oocyte nucleus moves along polarised microtubules to a dorso-anterior position, signals to follicle cells which mean they become different, the ventral follicle cells can not produce spätzle and the dorsal cannot
what are ‘gap’ genes responsible for
coding for transcription factors, result in broad regional differences. regulate ‘pair-rule’ genes to define 14 parasegments
why is it useful that the drosophila embryo is a syncytium
there are a lot of nuclei in a common cytoplasm, means that transcription factors and other proteins can diffuse and influence gene expression in neighbouring nuclei directly
list 5 gap genes in drosophila embryo
hunchback, giant, kruppel, knirps, tailless
describe what the bicoid protein is responsible for
in high concentration at the anterior end, is a direct regulator of hunchback
explain how the kruppel gene is regulated
there is a threshold level of hunchback protein which when reached will result in kruppel expression. expression is stopped when the repression level of hunchback is reached. results in a central line of kruppel. with lower hunchback levels, threshold for kruppel is lower so will be produced more and have no repression stage -> therefore is expressed more anteriorly like hunchback is
what is the purpose of ‘segment polarity’ genes
stabilises boundaries between parasegments so that they can go down different developmental pathways
give an example of two ‘pair-rule’ genes
eve and ftz proteins, result in 7 clear stripes along the drosophila
how does the eve gene code for 7 unique stripes
the DNA contains 7 regulatory sequences, each transcribed to form a separate line and each regulated by their own activators and repressor
what can pair-rule expression genes be impacted by
the concentration of gap gene transcription factors
What establishes the body plan along the anterior/ posterior axis?
Sequential expression- makes differences in embryos- Starts broad and progressively subdivides
Does maternal or paternal genes set up A/P and D/V axes?
Maternal
Do the A/P and D/V axes develop at different times or simultaneously?
Simultaneously
What are the steps if drosophila Oogenesis?
- Germ line stem cell in germanium, divides asymmetrically to produce a cyst oblast and another stem cell
- Cystoblast divides 4X to give 16 cells
- One becomes oocyte, other 15 are nurse cells
- The nurse cells make RNA and protein that is exported into developing oocyte
- All surrounded by somatic follicle cells- produce materials from the protective membrane ( the viteline membrane) that surrounds the egg
What are the three maternal gene mutations in drosophila? What regions do these mutations affect?
Biccoid mutation - affects anterior
Nanos mutant- affects posterior
Torso mutant- affects terminal regions
What is the biocoid gene needed for?
The development of anterior structures
What happens if bicoid gene from the wild type egg is taken and inserted into the bicoid mutant egg?
Some anterior structures develop - restores some normal development
What happens if you move the bicoid gene from the wild type egg into the centre of a bicoid mutant egg?
Head structures developed at the site of injection and the adjacent segments became thoracic segments, setting up a mirror image body pattern at h the site injection.
Where is bicoid mRNA localised to in a newly laid egg? What happens to this mRNA once it has been translated?
mRNA is localised at anterior of newly laid egg.
The bicoid mRNA is translated after fertilisation into bicoid protein and is present in a gradient.
How is the gradient of bicoid protein produced?
Bicoid protein movement and distribution of bicoid mRNA
What is the french flag model for how cell can develop differently in an order formation? (Pattern formation)?
Each cell in a line of cells has the potential to develop as bile, white or red. The line of cells is exposed to a concentration gradient of some substance and each acquires a positional valve it has acquired and differentiates into blue, white or red.
What is a morphogen?
Substances that can direct the development of cells according to concentration gradients within a group of cells, influencing their positional value and subsequent developmental fates.
