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What is the difficulty with repressors and activators?
you can't accurately label proteins repressors and activators because different proteins can act as either one under different circumstances.
For example, some can act as repressors when combined with one specific type of protein and can act as an activator in another circumstance.
Explain egg development of a fruit fly.
the egg cell doesn't grow early in development. it gets divided into one cell with several nuclei called a syncytium.
The nuclei migrate to the periphery, and cell boundaries start to form.
Primordial germ cells and somatic cells form as the egg becomes a hollow ball of cells with cytoplasm
What is patterning?
It is based on relative locations, cell figure out what they are near
This is due to morphogens= signaling molecules that can impose a pattern on a field of cells by causing cells in different places to adopt different fates
Explain the egg cell when it contains differentiated cells.
It has follicle cells, which produce molecules and insert them into the membrane.
Cells look homogeneous, but they are not. Nurse cells are present and some follicle cells provide terminal signals, while others provide ventral signals.
Explain dorsal-ventral patterning.
It starts out before fertiliation when the egg is in the follicle in the mom. The follicle divides into 16 cells. 1 becomes an oocyte, the other 15 become nurse cells, synthesizig proteins and RNAs needed by oocytes.
Nurse cells pump protiens and RNA, unevenly distributing them.
What are the dorsal ventral proteins?
Toll and Dorsal and Cactus
- Toll: produced by the follicle cells while the oocyte develops; inserted in membrane in one particular membrane
- transmembrane protein activated by follicle cells; sends signals into large cytoplasm. The signal is strong close to the follicle but diffuses outward
A combo of proteins that is evenly distributed throughout is __, which __ binds to.
- transcription factor= activator and repressor
- --> can't act as either unless out of cell and into the other
Toll sends a signal, which is amplified by phosphorylation of kinase to Dorsal. Dorsal lets go of Cactus, allowing P-Dorsal to get into the nucleus
What occurs when Dorsal is in the nucleus?
it binds to promoters, activating a gene called Twist, which activates other genes associated with the ventral side
Explain Dorsal as a repressor.
It represses DPP, which, if active, acts as a TF that turns on genes for Dorsal
What happens far away from the Toll signal?
Dorsal attached to Cactus and not into nucleus of cells--> dorsal features occur because DPP is active
In summary, explain Dorsal.
active: allowed to get into the nucleus to turn of DPP, allowing formation of ventral characteristics
inactive: restricted from getting into the nucleus, keeping DPP on, and thus causing dorsal features
Explain anterior-posterior segmentation.
Pump different amounts of proteins at different times: cytoskeleton can get tangled up and be present in gradients
What does the first level signaled by GAP gene (Kruppel) do?
Allows developing fruit fly to form. if not present, the developing fruit fly is cut in half
What does Pair Rule Gene (even-skipped gene) do?
Even segments and odd segments
Without it, even segments don't go through
What happens if the segment polarity gene, gooseberry, is absent?
Half of each segment will be missing
In regards to the anterior and posterior segmentation, what are the proteins required; and, what is important?
Bicoid and Hunchback
Giant and Kruppel
Some activate; some repress. They are not evenly distributed throughout the embryo. All act as TFs
Explain the promoter region of even-skipped gene.
Turned on when activator is present or the repressor is absent.
There are little segments of modules. Within over all promoter, there are subsections that deal with individual stripes.
What was done to examine stripe 2 module?
Took it out and put it into a gene reporter gene and back into the embryo to detect the stripe.
Once the gene reacts with a substrate, it will cause a colored product
Explain stripe 2.
Multiple binding sites
480 nucleotide pairs
- Bicoid and Hunchback are activators
- Giant and Kruppel are repressors
What must be the condition for anterior posterior segmentation?
Both Hunchback and Bicoid must be present and Giant and Kruppel absent