Organogenesis (Heart, Kidney and lungs)

Question 1

describe the 6 stages of cardiogenesis

Answer 1

1. specification of cardioblasts
2. differentation of cardioblasts to form cardiomyocytes
3. formation of the ventral heart tube
4. looping of the heart tube
5. extensive remodelling to form a 4 chambered heart
6. maturation of cardiomyocytes to form conductive fibres

Question 2

1. what is the name given to the area of ventral lateral mesoderm from which the heart develops?
2. what does the 1st heart field give rise to?
3. what does the 2nd heart field give rise to?

Answer 2

1. splanchnopleura
2. LV, part of RV, and both atria
3. RV, inflow tracts and outflow tracts.

Question 3

Cardiac Specification

1. which gene is required for drosophila heart specification?
2. what is this gene induced by?
3. what is the phenotype of mutants?
4. where is it expressed?

Answer 3

1. tinman
2. dpp
3. fail to form a heart
4. dorsal vessel (drosophilla heart)

Question 4

Cardiac Specification

1. what family are the vertebrate homologues of tinman. Name 1 specific example
2. where is Q1 expressed?
3. Q1 mutants have what phenotype?
4. What is the vertebrate homologue of dpp? What does its ectopic expression lead to? What is also required?

Answer 4

1. Nk-2 family, eg. Nk2.5
2. in the cardiac crescent
3. heart defects at the looping stage (compensatory mechanisms prevent earlier disruption)
4. BMP2. An ectopically expressed BMP2 soaked bead induces ectopic Nk2.5 expression. A favourable/permissive environment of anterior specific factors (FGFs and Wnt antagonists) are also required

Question 5

Cardiac Differentiation

1. what drosophila gene is essential for cardiomyocyte differentiation?
2. what is the expression of this gene induced by?
3. what is the phenotype of mutants?
4. name 3 vertebrate homologues of this gene

Answer 5

1. Dmef
2. tinman
3. lack differentiated muscle cells, but have cardioblasts
4. Mef2A, Mef2B and Mef2C

Question 6

1. What TFs are required for heart tube formation?
2. describe the morphogenetic changes that result in the formation of the heart tube
3. which gene is mutated in organisms that have 2 lateral heart tubes? What human disease is this similar to?

Answer 6

1. GATA
2. differentiating cells migrate towards the midline and form 2 endocardial tubes which fuse forming the heart tube
3. GATA4 | cardia bifida

Question 7

1. where are inflow and outflow tubes located before looping?
2. what does looping result in?
3. name 3 hypotheses for looping mechanisms.

Answer 7

1. anterior inflow, posterior outflow
2. outflow being positioned anteriorly and to the right
3. asymmetrical cell deathasymmetrical cell divisionchanges in cell shape as a result of asymmetrical distribution of microtubules and actin bundles

Question 8

1. which genes are expressed on the right of the heart tube?
2. which genes are expressed in the left of the heart tube?
3. how is this asymmetry set up?
4. mutations in which genes can cause sinus inversus? What are the characteristics of this disease?
5. what do each of these genes encode and what are they required for?

Answer 8

1. activin
2. nodal, Shh, Lefty and Pitx
3. nodal is expressed on the left due to the leftward flow of fluid across the midlineactivin that is expressed on the right represses Shh, so that its expression is confined to the left. Shh induces nodal. Activin also represses lefty so that is its confined to the left. Lefty induces Pitx
4. Iv and Inv. the arrangement of visceral organs are reversed about the midline
5. Iv encodes dyenin which is required for cillia rotationsInv encodes inversin which encodes the ankryn repeats of cilliathey are required for cillia rotation which establishes the preferential flow of nodal and lefty to the left.

Question 9

chamber formation

1. where is dHand restricted?
2. what is the phenotype of dHand KO?
3. where is eHand restricted?
4. what is the phenotype of eHand KO?

Answer 9

1. RV
2. hypoplasia/underdevelopment of RV
3. LV
4. death due to placental defects; conditional KO results in LV defects/hypoplasia

Question 10

1. name the 3 layers of the kidney
2. in which layers are the nephrons found?
3. name the parts of the nephron (4)
4. describe the path of urine from the end of the nephron to the bladder

Answer 10

1. capsule (outer layer), cortex (peripheral layer) and medulla (inner layer)
2. cortex and medulla
3. glomerulus, proximal tubule, intermediate tubule, distal tubule
4. collecting tubule > minor calyx > major calyx > renal pelvis > ureter

Question 11

1. what do the kidneys develop from? What is this derived from?
2. how does kidney development differ from the formation of the somites?
3. what forms from Q1? In which direction does it extend and towards what?
4. What does Q3 induce in what? What do these structures join to?
5. What type of interractions occur between the metanephric mesenchyme and the uteric bud?

Answer 11

1. nephrogenic chord derived from intermediate mesoderm
2. they bud off in the same way as somites, however anterior buds are lost and only posterior buds are maintained to form the mature kidney
3. nephric duct. It extends posteriorly towards the cloaca
4. it induces the nephric tubules in the adjacent nephrogenic cord. These tubules join laterally to the nephric duct.
5. reciprocal interractions

Question 12

1. in which vertebral region does the pronephros arise?
2. what is the name of the tubules that are induced?
3. why is the pronephros considered non-functional?
4. what does the most posterior portion that persists form?
5. what is the function of the pronephros?

Answer 12

1. cervical
2. pronephric tubules
3. because it is fully contained within the embryo (no path for filtrate to be excreted)
4. nephric duct
5. to induce the mesonephros

Question 13

1. what does each mesonephros tubule attract and what does this form? What is this structure allow?
2. name 3 functions of the mesonephros

Answer 13

1. attracts a blood supply from the nearby aorta forming a capillary tuft surrounded by the tubule. It allows for blood filtration
2. it persists in males forming the vas deferens and the epidiymisit is a souce of haemopoetic stem cells requrired for blood cell developmenttriggers the formation of the uteric bud as the mesonephric ducts breaks through into the cloaca.

Question 14

1. what is the metanephros
2. from what is the metanephric mesenchyme induced from?
3. what does the metanephric mesenchyme tell the uteric bud to do?
4. describe the following reciprocal interractions
5. what structures does the uteric bud form? (2)
6. what structures does the metanephric mesenchyme form? (1)
7. name 6 molecules which mediate the reciprocal interractions.

Answer 14

1. the permenant kidney
2. the intermediate mesoderm/nephrogenic cord
3. induces the uteric bud
4. the uteric bud tells the metanephric mesenchyme to condense around it and differentiate into the nephron.

the metanephric mesenchyme signals for the uteric bud to branch. it also breaks down the basal lamina of the uteric bud so that the 2 tubes can fuse

5. collecting ducts and ureters
6. nephron
7. growth factors | adhesion molecules | integrins | c-met, c-ros and c-ret

Question 15

1. name a molecule which governs branching morphogenesis
2. name the 2 hypotheses for renal vascular development

Answer 15

1. sprouty
2. angiogenic - vessels are derived from the nearby aorta and other pre-existing extrarenal vessels
   
   • *vasculogenic** - vessels originate from vascular progenitors

Question 16

1. which gene expression identifies and maintains nephron stem/progenitor cells?
2. what does the overexpression of this gene lead to?
3. what doe the conditional loss of this gene lead to?
4. mutations in this gene can lead to what?
5. Signals from where induce branching morphogenesis? Give 2 examples.

Answer 16

1. Six2
2. lack of differentiation (cells keep proliferating)
3. depletion of the progenitor pool
4. cancer/polycystic kidney disease.
5. from the metanephric mesenchyme. GDNF and Ret.

Question 17

1. what are the lungs a derivative of?
2. what signalling pathway specifies the region of the gut tube that will form the trachea and lungs?
3. what is tracheal-oesophageal fistula?

Answer 17

1. digestive tube
2. wnt signalling and beta-catenin accumulation
3. a condition whereby the separation of the trachea and oesophagus is incomplete.

Question 18

1. what do cells of the tracheal bud express?
2. what do the surrounding mesenchymal cells express? How does this protein act?
3. What does the highest concentration of Q2 induce? (3) Which cells receive this concentration
4. What do each of the Q3 proteins do?

Answer 18

1. FGFR
2. FGF10
3. cells at the tip of the tracheal bud receive this concentration. It induces the expression of BMP4, Shh and Sprouty2
4. BMP4 inhibits epithelial cell proliferation to limit branch extension at the tipShh inhibits FGF10 expression in the cells closest to the tip of the bud, consequently splitting the FGF10 expression pattern in 2

sprouty 2 restricts branching to the tip of the branch.