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CTO 2 > 5. Organogenesis > Flashcards

5. Organogenesis Flashcards

1
Q

Define mature organ

A

Mature organ - carefully organised collection of cells with specialised functions to sustain vital bodily functions

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2
Q

Explain kidney anatomy (organogenesis studied example)

A

Nephron (metanephric mesenchyme MM):
- proximal tubules
- glomerulus
- loop of Henle
- distal convulated tubules
PraGaLaDalsia

Collecting duct (ureteric bud UB)

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3
Q

What germ layer gives rise to kidneys? Which part of the germ layer?

A

From mesoderm - intermediate mesoderm -> kidneys

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4
Q

How kidney differentiation is started from intermediate mesoderm?

A

Early kidney development - by gene expression (TFs): Lim-1, Pax-2, Pax-8:
- paracrine signal (morphogen: bone morphogenetic protein 2 - BMP2) + signal from paraxial mesoderm to intermediate mesoderm - induces TFs transcription (when paraxial and intermediate mesoderm separated - no kidney) - medium level of BMP2 needed for kidney development (Lim-1, Pax-2)

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5
Q

What is the sequence of genetic signalling to induce kidney differentiation in intermediate mesoderm?

A

BMP2 from external sources

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6
Q

Which cell types are the primary source for kidney development?

A

Metanephric mesenchyme (MM) -> nephron
Ureteric bud (UB) -> collecting duct

Local reciprocal inductive interactions between UB and MM drives kidney development (internal communication between tissues)

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7
Q

Explain reciprocal inductive interactions

A

Reciprocal inductive interactions - a two-way dialogue - both cell populations are signalling and targeted (inducers + responders) - responder must be competent to sense the signal - appropriate receptor

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8
Q

What are reciprocal inductive interactions in kidney development?

A
  • Different tissues can grow and develop in coordinated way - development is proportionate - self organisation of the kidney
  • MM and UB use reciproval inductive interactions for growth and branching of UB + mesenchymal-to-epithelial transition (MET) in MM (nephron formation)
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9
Q

Explain transfilter induction assay in kidney development

A
  • Kidney rudiment dissected - MM and UB separated -> in isolation cells did not develop into kidney
  • Kidney rudiment dissected - MM and UB left together - UB branching + nephron formation in vitro
    => close proximity MM and UB needed for kidney development - communicate between each other
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10
Q

Explain what is Ret/GDNF signalling used for

A

Ret/GDNF signalling - outgrowth of UB:

signal: glial cell line-derived neurotrophic factor (GDNF) active in MM
receptor: Ret in nephric duct and tips of UB branches

Signalling induces UB growth into MM - induces branching to produce ureteric tree

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11
Q

How was it determined that GDNF needed for outgrowth of UB? Removal of component experiment

A

GDNF mutant mice / Ret inhibited - no UB branching => GDNF signalling is necessary for budding/branching

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12
Q

How was it determined that GDNF needed for outgrowth of UB? Providing extra ectopic signal

A

Is GDNF sufficient for UB branching - extra GDNF provided -> extra (ectopic) branching => GDNF is both necessary and sufficient for UB budding/branching

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13
Q

Ret/GDNF signalling in UB branching disrupted by Ret mutation

A

Cells with highest Ret activity branch if different activity is induced

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14
Q

How do cells in UB physically branch in kidney development?

A

UB tips swell - bifurcate into two new branches - extend and bifurcate again

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15
Q

What cellular behaviours drive UB branching in kidney development?

A
  • differential cell proliferation
  • cell rearrangement
  • localised remodelling of ECM
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16
Q

What is differential proliferation?

A

Differential proliferation - different potential of cell populations to proliferate under specific conditions

17
Q

Where is differential proliferation observed branching of UB in kidney development?

A

Differential proliferation in branching between tip and trunk of UB:
tip cells proliferate more than trunk - correlation in proliferation and branching - driven by Ret/GDNF signalling

18
Q

How does cell rearangement occur in branching of UB in kidney development?

A

Ret/GDNF signalling mediates rearrangement of epithelial cells before budding to form UB tip

19
Q

Where does ECM remodelling occur in UB branching in kidney development?

A

Remodelling of ECM:
different components of ECM between UB tip/trunk - collagen 18 in trunk but not tip - because GDNF represses collagen 18 in tips
=> collagen 18 pattern influences trunk branching

20
Q

Explain how mesenchymal-to-epithelial transition (MET) is induced and occurs in kidney development

A
  • MM induced for MET by Wnt morphogens (family of genes) - Wnt9B secreted from UB (paracrine signal) - induce MET to form nephrons
  • Wnt9B induces Wnt4 expression - autocrine signalling - propagates mesenchymal aggregation: renal vesicle grows by recruiting more MM until Wnt4 threshold reached - renal vesicle begins to differentiate
    => ensured that renal vesicle is of appropriate size
21
Q

What experiment could be used to determine if WntB9 is needed for kidney development?

A

Wnt9B mutants - failed to undergo MET in MM - no kidney formed => Wnt9B crucial for kidney development

22
Q

What is quorum sensing?

A

Quorum sensing - for of cell communication which allows cells to share info about cell density - regulate of gene expression responding to fluctuations in cell density

23
Q

What is the evidence for quorum sensing in kidney development?

A
24
Q

Explain what epithelial character is developed in MET in nephron development in the kidneys

A
  • tubular shape is developed - lumen formed (single-cell layer, non-startified tubular epithelium)
  • adhesion junctions developed (ex cadherins)
  • apicobasal polarity established (different transport proteins on membranes)
  • occluding junctions developed (to ensure tubes are not leaky + stops passing unwanted solutes)
25
Q

What are the functions of nephron parts?

A
26
Q

Explain th patterning process in the nephron

A

Patterning process:
- patterning starts in renal vesicle (proximo-distal axis): initial RV -> comma shaped RV -> S shaped RV -> mature nephron
- patterning controlled by morphogens

27
Q

What kind of differentiation events occur after patterning in nephron?

A

Differential gene expression:
- ion channels, transporters, specialised cell architectures

28
Q

Explain Bartter syndrome

A

Bartter syndrome:
- ascending limb of loop of Henle doesn’t differentiate properly - dysfunction in Na-K-Cl ion transporters
=> low K levels, increased blood pH

29
Q

Explain how the glomerulus capillaries develop in kidney development

A

Endothelial cells migrate into the developing glomerulus - migrate into cleft of S shaped body - sit **on top **of podocyte precursors -> development -> glomerular capillary surrounded by podocytes inside Bowmann’s capsule

30
Q

What is the function of glomerulus?

A

Glomerulus filters blood - mostly small molecules like water

31
Q

What is chemotaxis?

A

Chemotaxis - movement of cell in response to a increasing / decreasing gradient of a chemical signal

Chemoattractants / chemorepellents

32
Q

How do endothelial cells know that they have to migrate into the S shaped body cleft in kidney development?

A

Endothelial cells respond to a signal - chemotaxis - chemoattractant vascular endothelial growth factor VEGF - cells move towards the higher conc of signal in S shaped body

33
Q

How was is the importance of VEGF in kidney development tested?

A

VEGF mutants - no endothelial cell migration - capillaries did not develop

34
Q

How is blood delivery and filtration matched?

A

Blood delivery (capillaries)
Blood filtration (podocytes)

Capillaries and podocytes grow and develop proportionately -> proportionate development

35
Q

Explain polycystic kidney disease

A

Polycystic kidney disease (PKD):
- autosomal dominant (ADPKD)
- autosomal recessive (ARPKD)

Progressive formation of large fluid-filled cysts - increase tubular diameter, nephron loss, kidney failure

36
Q

How is a tubule formed in organogenesis?

A
  • regulated orientation of cell divisions (anisotropic growth)
  • organ shape sculted by cell rearrangement
37
Q

Explain how the cell divisions are oriented in renal tube formation

A

Tubules only increase in length but not diameter - oriented cell division - anisotropic growth - measured mitotic angle (mitosis orientation 95% along long axis)
BUT in polycystic mutant - mitotic alignment is random

38
Q

Explain how the cells are rearranged in renal tube formation

A

Renal tubes sculpted by cell rearrangement - renal tube diameter reduces in embryonic development - rearrangement driven by cell intercalation - increase tubule length - decrease diameter => convergent extension

CTO 2 (8 decks)

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