W8 Flashcards
What causes the imaginal discs to be formed?
Positional information from the D-V, A-P patterning genes.
What do signaling pathways drive in leg imaginal disc development?
- cell proliferation and 2. pattern formation in the leg imaginal discs during the larval stages. (distalless/Brista inner most of the concentric circles) 3. disc eversion: During pupation, the leg imaginal disc gets “telescoped out”, to generate the extended structures of the adult leg.
What are the important features of the wing pattern?
- The anterior wing margin is equipped with bristles (=microchaete: mechanosensory organs). 2. The first wing vein runs along the anterior wing margin.The other longitudinal wing veins (2nd, 3rd, 4th, 5th) are formed within the blade at defined positions.
What are the posterior and anterior compartments of the imaginal discs?
The en-expressing subregion (en “on”) forms the „posterior compartment“. The other subregion (en “off”) the „anterior compartment“. These compartments are separated by a „border of clonal restriction“.
How was the existence of compartments discovered?
clonal analysis- GFP/en-lacZ marking showed that cells did not cross the clonal boundary.
Clonal analysis Method 1a
35S::Tag1-GUS transgene is used to randomly label cells during Arabidopsis development.
Clonal analysis method 1b
removal of stop cassette from a transgene Act5C>stop>GAL4 > GFP Act5C - constitutive promotr GAL4 - yeast transcription factor As long as the stop cassette is present, there is no transcription. Stop cassette removed by heat shock.
Clonal analysis method 2a
X-ray induced mitotic recombination
Clonal analysis method 2b
Induction by site-specific recombination. For example by FLP recombinase. FLP recombinase can induce mitotic recombination when each of the two homologous chromosomes carry a centromere-proximal FRT site.
Wing pattern formation
engrailed (en) encodes a transcription factor (Posterior). en expression results in hedgehog (hh) expression. The Hedgehog protein (Hh) is a secreted signaling protein which spreads out into the anterior compartment. Only the anterior cells along the compartment boundary are exposed to Hh levels that are sufficiently high to activate a signal transduction pathway (via Patched-Smoothened). As a consequence the expression of decapentaplegic (dpp) is activated in these cells. Another compartment boundary separates the dorsal (apterous expressing) from the ventral side (apterous non-expressing). Similar signalling processes (involving Notch signaling) result in the expression of wingless (wg) along this boundary.
Dpp activates which genes in wing imaginal disk?
Omb at low levels, spalt at high levels.
Dpp acts in a non cell-autonomous way. What is this?
Dpp acts on other cells than the one expressing Dpp.
Which Hox genes determin the identity of the imaginal discs?
HOC-C for example: Antp but not Ubx expression in wing, Ubx but not Antp expression in the haltere.
What are LSDS gradients
localized source and dispersed sink. The exact nature of these morphogen gradients are important for pattern details.
clonal analysis – methods summary
Various genetic strategies (removal of stop cassettes in marker genes, mitotic recombination) can be applied for the induction of a heritable genetic change in single somatic cells. Usually they involve site-specific recombination (for example using induced expression of FLP recombinase recognizing FRT sequences; FRT = FLP recombinase target sequences in Drosophila, or spontaneous excision of the autonomous Tag 1 transposon in Arabidopsis). These genetic strategies produce genetic mosaics/chimaeras: not all cells of an individual are genetically identical. Clonal analyses can also be performed with dye marking instead of genetic marking (for example dye injection into a single cell at t = 0 and analysis at t = x). Past and present clonal analyses in various model organisms have made/are making major contributions to our understanding of developmental processes.