Organogenesis Flashcards
What are the basic units of the kidney?
Nephron (metanephric mesenchyme) and collecting duct (uteric bud)
What does the paraxial mesoderm give rise to?
somites-> skeletal muscle
What does the intermediate mesoderm give rise to?
Kidney
What does the lateral plate mesoderm give rise to?
circulatory system
What TF control gene expression in kidney differentiation?
Pax2/8 (paired box) and Lim-1 (homeodomain), if remove Lim-1 then no kidneys form (master regulator)
What kinds of sigalling are in kidney differentiation? From what tissues?
- Paraxial to intermediate paracrine signalling (if seperate paraxial and intermediate then genes stay off so they need to be adjacent)
- Lateral to intermediate paracrine signalling (at a medium level of BMP2)
BMP2 is a morphogen
What are reciprocal inductive interactions?
Two cells capable of changeing each other via signalling (both are inducers and responders of each other) Eg MM and UB
This is why different tissues can contribute to the same organ and grow in a porportionate way
Grobsteins transfilter assay
- Kidney rudiement disected
- MM seperated from UB
- cultured seperately or togetheron polycarbonate filter
Result: shriveled and died if seperate, UB branchinng and nephrons if together
Meant that UB and MM were influencing each other
How does UB and MM start uteric branching?
Signalling tells UB to start growing into the MM, then the UB starts branching. The tip of the UB swells and then splits in 2, and repeats
What signals do the UB and MM use to promote each other?
Ret/GDNF signalling. Ret expressed in nephric duct and tips of uteric branches. GDNF expressed in MM.
Ret is the receptor and GDNF is the signal
GDNF = glilal cell line derived neurotrophic factor
What experiments were done to show how Ret/GDNF signaling works?
Experiement 1: remove Ret or GDNF via genetic manipulation or pharmological inhibition results in no nephric branching
Experiement 2: add GDNF soaked bead results in extra branching
Experiement 3: low Ret and normal Ret cells combined= the normal Ret made the branching. High Ret and normal combined= high Ret formed branches.
Relative levels of Ret determine branching activity, GDNF is suffiecent to grow branches
What behaviors drive UB branching?
- differential cell proliferation
- cell rearrangement
- localised remodelling of the ECM
What is differential cell proliferation?
Eg. The tip of the branch divides more than the trunk does, likely theres increased Ret/GDNF in the tips rather than trunk–(soaked GDNF bead resulted in extra proliferation of the tips)
In regards to cell behaviors that drive UB branching
What is cell rearrangement?
Eg. cells move bc of Ret signalling, cells with the most Ret will migrate towards the tips of the buds
In regards to cell behaviours that drive UB branching
What is localized remodelling of the ECM?
Kidney mesenchyme represses (secretes GDNF) collagen 18 from forming in the tips of the UB.
If you get rid of the mesenchyme and replace with lung mesenchyme which secretes Wnt2 then you get collagen18 forming in the tips
MET
Mesenchymal to epithelial transition
The formation of renal vesicles from the MM. Renal vesicles= formation of the nephron
What signals are involved in MET?
- Wnt9b, paracrine (Wnt9b -/- mouse doesnt do MET and no kidneys formed)
- Wnt4, autocrine (induced by Wnt9b and secreted from MM. UB recruits MM until Wnt4 reaches a threshold via quorum sensing)
Example of quorum sensing in the kidney:
Wnt4 expression weak in loose MM, and strong in the aggregate.
Characteristics of a MET epithelilal tube
- Single cell, non-stratified layered epithelial tubulum (has a lumen)
- Has cadheren and occluding junctions
- ## Apicobasal polarity (diff transport proteins on either side)
What axis does the nephron form along and why?
The proximo-distal axis. Important because morphogenic signalling sectioned UB into 3 layers at the renal vessicle stage. Patterning is important bc leads to cell differentiation, if goes wrong its bad eg Barter syndrome
renal vescile-> comma shape-> s shaped body-> nephron
What is barter syndrome?
Excessive loss of NaCl & K bc of a bad ion transporter in thick loop of henle.
Delevoping glomerular capillaries
Podocyte precursor cells secrete VEGF (chemoattractant) and endothelial cells sit on top of them, eventually develop into glomerulus. Mutant: no VEGF no capillary formation
Vascular endothelial growth factor= VEGF
endothelial cells end up being the glomular capillary. Podocytes are the blood filtration
What is chemotaxis?
Responding to signals based on their gradient. Chemattractant= towards the source/up the gradient. Chemorepellant= away from source/down gradient
What shapes the nephron?
- Regulate orientated cell division during embryonic development (anisotropic growth)
- Cell rearangement/ intercalation (convergent-extension)
anisotrophy= growth rate different in different directions
- Theres lots of proliferation after birth, and cells grow along the long axis not the circumference, so theres unequal growth rates. The mitotic angle is always less than 30, influencing the direction of growth
- renal tube diameter decreases from 11-12 cells to 3-4 during embryonic development- this would inc tube length while decreasing diameter.
