Pathway Q's Flashcards
Dorsal-Ventral polarity in Drosophila Pathway - 10 steps
- Oocyte nucleus travels to anterior dorsal side of oocyte where it localized gurken mRNA
- transplanted turkmen is received by torpedo proteins
3a. torpedo signal causes follicle cells to differentiate to a dorsal morphology
3b. pipe synthesis is inhibited in dorsal follicle cells - turkmen does not diffuse to ventral follicle cells
5a. ventral follicle cells synthesis pipe.
5b. pipe signals sulfate ventral vitelline proteions - sulfated viteline membrane proteions bind gastrulation- defective (GD)
7a. GD cleaves snake to its active form and forms a complex with snake and uncleaved easter proteins
7b. easter protein is cleaved into its active form - clever easter binds to and cleaves Spatzle activated spatzle binds to Toll receptor protein
- Toll activation activates Tube and Pelle which phosphorylate the Cactus protein. Cactus is degraded, releasing it from Dorsal
- Dorsal protein enters the nucleus and centralizes the cell.
Hedgehog signaling: Drosophila early development
NO HH
•in absence of Hh binding to patched, Ci is tethered to m.tubules by Cos2 and fused proteins.
•The binding allows PKA and Slimb proteins cleave Ci into a transcriptional repressor that blocks transcription of particular genes
HH
•when Hh binds to patched, conformational changes releasing inhibition of smoothened protein.
•Smoothened then releases Ci from m.tubules (add more P to Cos2 and Fused)
•Inactivates cleavage proteins PKA and Slimb
•Ci protein enters nucleus binds CBP proteins and acts as a transcriptional activator of a particular gene.
Paracrine regulation of wingless and hedgehog transcription
- Reciprocal interactions between neighboring cells:
- Cells secreting hedgehog activate the transcription of wg.
- wg binds to frizzled, activates Dsh inhibts GSK which activates B-cat which activated Hh
- Cells secreting wg activate the transcription of en and hedgehog.
4 Steps in Cell Migration
- Cells become polarized (form a front and rear end):
• The process involves the reorganization of actin cytoskeleton.
• Polarisation is directed by signals (eg. chemotactic or extracellular matrix) - Protrusion of cells leading edge: • Polymerization of G-actin to F-actin
• Formation of filopodia.
• Signaling Rho-GTPase activated - Adhesion of the cell to the extracellular matrix (ECM):
• Integrins on cell membrane attaches to ECM (focal adhesion) and to actins within the cell. - Release of the adhesion in the rear end
Molecular mechanisms of primitive streak formation how does it go straight in the center
- Epiblast cells next to Koller’s sickle activate the Wnt-planar cell polarity pathway.
- If blocked then the mesoderm and endoderm form peripherally rather than centrally.
- Wnt pathway inturn is activated by the fibroblast growth factors (FGFs) synthesized by the hypoblasts.
- If the position of hypoblast is altered so is the orientation of primitive streak.
Wnt Signalling Pathway: Canonical Pathway (A)
- wnt binds to frizzled which activates Dsh
- Dsh inhibits GSK
- therefore B-cat is acivated
- B-Cat enter nuc binds to gene and trasciption
Planar Cell polarity (PCP) Wnt Signaling pathway: Non-Canonical (B and C)
- Belongs to the category of non-canonical pathway.
- Wnt binds to Frizzled and ROR activate DSH
- DSH activates RhoA-GTPase and Rac.
- Rho-GTPase activates the kinases that phosphorylate the cytoskeletal proteins that alter cell shape and movements.
STEM CELLS: iPS derived HSC correct sickle cell anemia
1) harvest tail tip fibroblasts
2) infect with Oct 4, Sox2
3) correct sickle cell mutation in iPS cells by specific gene targeting
4) differentiate into embryo bodies
5) transplant corrected hematopoietic progenitors back into irradiated mice
Polarity in Planaria regeneration: DV and Ant-Post
DV Axis:
•BMP defines the dorsal region in flat worms.
•Noggin in the Ventral
Anterior Posterior:
•Anterior posterior polarity is regulated by Wnt and β-catenins.
•β-catenin is activated by Wnt in the posterior regions (generating tail).
•Repressors of Wnt prevent β- catenin production in the anterior– facing regenerating neoblast cells.
•If Wnt pathway is blocked in the posterior blastema then the result is a worm with heads at both the ends.
Regeneragtion: Upon amputation of salamander limb
- plasma clot forms at the site of injury.
- epidermis from the stump migrate and form wound epidermis.
- Nerves innervating the limb degenererate for a short distance proximal to the plane of amputation.
- Extracellular matrices are degenerated by protease and single cells that undergo dedifferentiation are formed.
- These cells redifferentiate to form new structures of the limb.
- Wound epidermis thickens to form AER equivalent structure called apical ectodermal cap (AEC).
- cut wait 72 days whole limb regrown •AEC much bigger than AER
- accumulation of blaster under AEC
Regeneration: Blastema is similar to progress zone of developing limb
- The anterior-posterior axis is established by sonic hedgehog activation and HoxD gene activation, just as in limb buds
- Proximal-distal axis is established by interactions between HoxA gene activation and retinoic acid (RA)
- The most distal cells are fated to become autopod structures
- A transplanted limb blastema can substitute for an AER on a developing limb
- The full ‘nested’ Hox gene pattern is restored during regeneration and is influenced by RA which PROXIMALIZES blastema cells
Early interactions between AER and limb-bud: SHH
- As limb bud grows, the ZPA region is induced.
- ZPA region is where SHH is active.
- SHH turns on activation of Grem1 which is inhibitor of BMP pathway.
- Once Bmp is inhibited, Fgf8 can be expressed and that’s where we have AER secluded to small region of ectoderm. •Posterior is En1 and anterior is Wnt7a expressed. That’s how you get borders of AER. Dorsal has Wnt7a but not ventral side.
- First is proximal-distal established, then anterior posterior, then dorsal ventral.
AER and limb-bud mesenchyme interactions: Wnt
- Fgf10 from mesenchyme generated by the lateral plate mesoderm activates Wnt.
- Wnt activates β-catenin that induces the synthesis of Fgf8 in AER.
- Fgf8 activates Fgf10 in positve feedback loop.
- BMP expressed in the ventral region causes the expression of engrailed-1, which represses Wnt signaling.
Notch-Delta Signaling Pathway
Before:
•CSL TF is on the enhancer of Notch regulatory genes and binds the repressors
Activation: Injured muscle fiber
•ligand (ex. delta) binds to extracellular domain of Notch on an adjacent cell
•causes shape change in intracellular domain of notch •activates protease
•protease cleaves notch •intracellular region of notch enters nucleus and binds to CSL
•intracellular notch region displaces repressor and binds activators of transcription (ex.p300)
•activates CSL can transcribe target gene
Induction of aging process
-The p53 induced by telomere dysfunction binds to and represses the expression of PGC-1å and PGC-1ß
•repression of both blocks mito production of reactive oxygen species (ROS)
•leads to functional decline of post-mitotic tissues and stem cells
•therefore aging
