Organogenesis

Question 1

What is the definition of a mature organ?

Answer 1

intricately organised collection of cells with specialised activities that function collectively to execute vital bodily functions

Question 2

What is organogenesis?

Answer 2

how organs ovult in development focusing on kidney. from undifferentiated cells to mature organ

Question 3

What is the building block of the kidney?

Answer 3

• nephron and collecting duct

Question 4

Regionalisation of the mesoderm:

• ___mesoderm (will be separated into blocks and make somites – skeletal muscle)
• ___mesoderm generates the kidney and gonads
• ___ mesoderm (generates circulatory system – heart, blood vessels etc.)

Answer 4

paraxial, intermediate, lateral plate

Question 5

First step in kidney differentiation we need 3 genes to be activated. What are they?

Answer 5

Lim-1 (homeodomain TF)
Pax2 & Pax8 (paired box TF)

Question 6

2nd step kidney specification. What is involved?

Answer 6

2 signals
- one from adjacent paraxial mesoderm
- one from lateral side of embryo

Question 7

What type of signalling are these 2 signals?

Answer 7

Paracrine

Question 8

Bone morphogenetic protein 2 (BMP2) is a secreted morphogen that directs different cell fates according to concentration. What level induces kidney tissue?

Answer 8

• Kidney tissue induced at ‘medium level’ of BMP2 activity

Question 9

How cells self-organise to make a kidney? i.e internal conversations between tissues

Answer 9

Local reciprocal inductive interactions between the UB and MM drives kidney development

Within the intermediate mesoderm population of cells – 2 distinct cell types emerge: ureteric bud (UB) and the metanephric mesenchyme (MM)

2 populations of cells communicating between tissues to drive kidney development.

Question 10

What is induction?

Answer 10

• Induction - one cell (inducer) regulates the behaviour of another cell (responder)
• The inducer sends a signal that the responder must be competent to ‘see’ and act on

Question 11

What is reciprocal induction?

Answer 11

a dialogue or two-way conversion between the two different populations of cells

Provides a mechanism by which different tissues that contribute to the same organ can grow and develop in a coordinated way – growth and development is proportionate

Question 12

2 mismatches that forms if UB and MM didn’t have reciprocal induction:

Answer 12

mismatch in ratio/co-ordination

Question 13

How does the transfilter induction assay show the communication between UB and MM?

Answer 13

MM and UB separated and then put together which lead to UB branching and nephron formation.

• they have to be close together to have ‘conversation’ proves the crosstalk
• This suggests the ureteric bud and the metanephric mesenchyme are talking to one another

Question 14

How does the branching of the ureteric tree occur? in relation to Ret/GDNF signalling

Answer 14

GDNF is secreted by MM and is recognised by Ret receptor present in nephrite duct and tips of ureteric branches.

Question 15

What does removing GDNF and no branching show?

Answer 15

GDNF signals is necessary for branching

Question 16

What does ectopic GDNFand extra branching show?

Answer 16

GDNF signalling is sufficient for budding/branching

Question 17

Branching behaviours require Ret receptor activity. relative levels of Ret determines the branching populations. cells with higher ret activity exhibit ____

Answer 17

Stronger branching behaviours

Question 18

What cellular behaviours drive branching?

Answer 18

• differential cell proliferation
• cell rearrangement
• localised remodelling of ECM

Question 19

Describe the differential proliferation in UB

Answer 19

tip cells proliferate more than trunk cells. differential cell proliferation contributes to branching.

Question 19

Describe the cell rearrangement of epithelial cells

Answer 19

ret signalling mediates rearrangement of epithelial ells before budding to form the UB tip domain

Question 20

How does ECM influence branching patterns? In relation to collagen 18

Answer 20

Collagen 18 is expressed in trunk but not tip. GDMP represses collagen 18 at tip

Question 21

Overview of nephron development:
1. ___ cells condense around ___
2. transform into small ___ with epithelial characteristics (renal vesicles) - ______l transition (MET)
3. ______ and ______ fuses with UB
4. blood vessel progenitors invade and construct glomerular capillaries
5. nephron ______ e.g. specialised transporting segments of the nephron

Answer 21

1. metanephric mesenchymal
2. Ureteric bud
3. cysts
4. mesenchymal to epithelial
5. differentiation
6. morphogenesis
7. differentiation

Question 22

Transfilter induction assay shows that isolated MM dies and MM with UB forms nephron after MET. what does this show?

Answer 22

signal from UB is needed for the survival and MET of MM

Question 23

in MET ____ is secreted from ___ which induces MET in ___

Answer 23

1. Wnt (9B)
2. UB
3. MM

Question 24

Renal vesicle size is approximately equal. how is the size measured?

Answer 24

Wnt9B induces Wn4 expression within MM
- acts in autocrine manner to propagate mesenchymal aggregation
- continuous to grow by recruiting more MM until threshold is reached (quorum sensing)

Question 25

During MET how are epithelial characteristics developed?

Answer 25

• tubular shape and form single cell layered lumen
• develop adhesion junctions
• establish apicobasal polarity
• occluding/tight junctions

Question 26

From proximal to distal, how is the pattern formation and regional differentiation in the nephron established?

Answer 26

Distal proximal gradient of gene activity. morphogenic signalling from UB. high conc = distal, low conc = proximal

Question 27

How did the glomerular capillaries develop?

Answer 27

migration of endothelial cells into developing glomerulus

Question 28

How do endothelial cells know where to migrate to?

Answer 28

Podocyte precursor cells secrete a signal to induce endothelial migration into developing glomerulus. Endothelial cells move up the signal gradient (chemotaxis)

Question 29

What is chemoattractant ?

Answer 29

cells move toward a signal source up the conc gradient

Question 30

What is chemorepellent?

Answer 30

cells move away from signal source (down the conc gradient)

Question 31

What is the function of Vascular Endothelial Growth Factor (VEGF)

Answer 31

• expressed n secreted from the inner cup of developing nephron
• Endothelial cells are competent to respond to signal because they express the VEGF receptor on their surface
• VEGF = a chemoattractant

Question 32

How does the polycystic kidney disease lead to kidney failure?

Answer 32

• Progressive formation of large fluid-filled cysts
• Increase in tubular diameter

Question 33

2 ways to shape an organ:

Answer 33

(1) oriented cell division during organ development (anisotropic growth)

(2) cell intercalation = Organ shape is sculpted by cell rearrangement

Question 34

explain the oriented cell division in renal tubules

Answer 34

• ubules increase in length, but not diameter
• Suggests: orientation of cells as they separate at division is aligned with long axis of tubule and not around circumferential axis
• Example of anisotropic growth - divide along one axis

Question 35

What is the mitotic angle in polycystic mutant rodent?

Answer 35

random - abnormal tubule shape

Question 36

Explain cell arrangement in renal tubules

Answer 36

• Rearrangement is driven by cell intercalation
• Highly ordered cell-intercalation increases tubule length and decreases tubule circumference