Lecture 22 Flashcards
What type of gene is Dmef2
Transcription factor
What are the two different tissues contained within the region of the ventral lateral mesoderm that the cardiac cells originate from
Splachnic mesoderm and foregut endoderm
What is the result of a mutation in the earliest gene expressed in the vertebrate heart
No formation of the heart and no looping of the ventricles. Interestingly, upregulation of Mef2B is seen indicating a compensatory mechanism in vertebrates
The bHLH transcription factors dHand and Ehand are involved in the formation of the heart chambers. Outline their localisation
ehand and dHand show specific expression in right and left ventricules. Their restricted expression is complimentary with eHand restricted to the left ventricle and dHand restricted to the right ventricle
Lecture 22 Question 11 - See image
A – axial mesoderm, B – paraxial mesoderm, C – intermediate mesoderm, D – lateral mesoderm (splachnopleura)
What is the result of knockout of this tinman vertebrate homologue specifically expressed in the cardiac crescent
Nkx2.5 mouse mutants do form hearts but show cardiac defects at the heart looping stage.
What is the cardiac jelly
A structure that lies between the endocardial tube and the cushion cells that is rich in extracellular matrix proteins secreted by the myocardium
What is the precise role of tinman in heart development
Tinman is required to specify cells to a cardiac lineage
What is seen in the eHand conditional knockout
Only knockout eHand in the cardiac myocytes. The mice show left ventricule defects, but survive until birth
What approach can be used to stain cells for the marker of a cardiac cell fate
Immunohistochemistry
Once the cells have been specified to a cardiac lineage, what happens in the stages leading to the formation of the heart tube
These cells migrate ventrally under the influence of signals coming from the foregut endoderm and fuse in the midline to form the heart tube
What is the name of the linear structures that form from the cardiac crescent and then fuse to form the looping heart
Heart tubes
What would be used as a control in a gain or loss of function experiment that involves bead implantation into chick/mouse embryos
Implant another bead that is soaked in PBS
What process takes place during heart remodelling
Duplication of chambers
What is the result of mutation in iv
Iv mutant mice have cilia that are immotile
What domain indicative of some transcription factors do the GATA proteins contain
Zinc finger domains
What is the name of the family of tinman homologues found in vertebrates
NK-2 homeobox transcription factors
Like tinman, Dmef2 is also required to form the Drosophila heart, T or F
T
Formation of the septa in heart chamber formation involves the activity of the endocardia, T or F
T
The first stage of cardiogenesis involves the formation of a structure from a mesodermal precursor. What is the name given to this early heart structure
Cardiac crescent
A key factor in the looping of the mammalian heart is the breakage of left-right symmetry which occurs very early in embryogenesis immediately after gastrulation, T or F
T
What two diffusible molecules of the TGF-? family are specifically expressed on the left side of the embryo
Lefty and Nodal
What two processes take place in higher order animals after formation of the heart tube
Looping, chamber subdivision
What is the effects of Dmef2 mutations on cardiogenesis
In the absence of Dmef2 you can still form the precursors of cardiac myocytes. However, these cardiac myocytes are unable to differentiate to form cardiac myocytes
A gain of function experiment was carried out to investigate the role of BMP2 by implantation of a BMP2 soaked bead into the posterior of the embryo. No Nkx2.5 expression was seen. Explain these results and what this indicates about BMP2 role in cardiogenesis
BMP2 needs to be acting in an environment that is favourable for its activity. Posterior implantation of BMP2 soaked beads wouldn’t result in a cardiac specification due to high concentration of BMP antagonists (Noggin, Chordin, Follistatin) released by the notochord. There needs to be a permissive environment to control cardiac specification by BMP2 signalling
What is the role of the iv gene
Inversus viscerum encodes a dynein protein involved in the movement of the cilia
What are the three hypothesised mechanisms of heart looping
Asymmetric cell division, asymmetric cell death or changes in cell shape triggered by asymmetric distribution of microtubules, actin bundles and cell adhesion molecules
What marker can be used to indicate cells that have adopted a cardiac fate
Myosin heavy chain
Why does knockout of Nkx2.5 not cause a failure of the heart to develop
Other members of the family carry some of the function and allow heart development to continue (heart ultimately fails to develop normally)
Cardiac cells originate from a structure of the ventral lateral mesoderm, what is the name given to this region
Splachnopleura
How do inv and iv act to mediate heart looping despite being genes involved in cilia development
Inv and Iv are required for cilia movement, specifically their rotation. Cilia rotation establishes a preferential flow of Nodal and Lefty molecules on the lefts side of the embryo. This rotation prevents the lefty and nodal molecules from diffusing onto the right side of the embryo and allows looping to occur there
What cell adhesion molecule is controlled by GATA expression
N-cadherin
Drosophila can be used to study the earlier development of the heart, however what prevents these models from being used to study the later stages of cardiogenesis
Drosophila have a linear circulatory system and don’t possess a multi-chambered heart
When a gene has multiple vital functions as is common in development, how can we create mice models that specifically look at the later role of these genes if the embryos can’t survive until that stage without it
Create a conditional knockout where the gene can be knocked out at a specific stage in development
Explain a gain of function approach that can be used in mice to investigate the role of the dpp homologue on cardiogenesis
Implantation of a BMP2 soaked bead anterior to the primitive streak in early development.
How is Dmef2 expression induced
By the expression of tinman
Explain a loss of function approach used in Drosophila to investigate the role of tinman in cardiogenesis
Introduce deletions into the tinman gene and stain cells for a marker of cardiac cells
Once the heart tube has formed it contains two main tissues, the endocardium and the (epi)myocardium. What are the derivatives of these two tissues
Endocardium contains precursors of endothelial lining of heart and cushion cells that form valves. Myocardium contains myocytes of atria and ventricles, and Purkinje fibres
What is the role of the second heart field and where is it located
The second heart field is located immediately behind the first heart field. It give rise to part of the right ventricles, inflow and outflow tracts as well as plating an important role in the growth of the heart
Explain how left-right symmetry is broken in the chick embryo
In chicks, this symmetry is broken at the level of the (Hensen’s) node due to the asymmetric expression of sonic hedgehog in the left and right. Sonic hedgehog is inhibited by activin receptors on the right of the embryo leading to higher expression on the left of the embryo with low sonic hedgehog levels on the right
Following the formation of the heart tube, Drosophila cardiogenesis is complete as they possess a linear heart. What other embryo also has a neoheart tube with a single atrium and ventricle
Zebrafish embryo
What is the result of knockout for the GATA genes involved in cardiogenesis
Knockout of GATA4 in mice results in a failure of the heart tube primordia to migrate and fuse to form the heart tube. This is known as cardiac bifida
What is the role of the GATA transcription factor family of gene in cardiogenesis
The GATA genes drives the fusion of the primordium into the early heart tube
Which specific BMPs is decapentaplegic a invertebrate homologue of
BMP2 and BMP4
Dmef2 mutants still show expression of tinman. What can be inferred by this observation
Tinman acts upstream of Dmef2
Which side does normal heart looping occur
To the right
Heart precursor cells have two origins, the first and second heart fields, what structures are derived from the first heart field
Cardiac crescent, left and right ventricles, AV canal and the atria
Which is the gene that is expressed earliest in the vertebrate heart
Mef2C
Endocardial tube in the inner part of the heart tube eventually contributes to the endothelial lining of the heart, T or F
T
What are the results of mutations in Dmef2 in Drosophila
Mutations in Dmef2 result in no formation of the dorsal vessel in Drosophila
Whilst dHand knockout mice die at E10.5 with ventricule hypoplasia, eHand knockout mice die at E8.5 with placental defects. Why is this
The embryos don’t survive long enough to look at effects on heart development. dHand must be acting earlier in development in another vital process
What are the three homologues of Dmef2 in vertebrates
Mef2A, Mef2B and Mef2C
What is the role of the inv gene
Inversion of embryonic turning encodes for Inversin, a protein containing ankyrin repeats found in cilia
What signalling mechanism is responsible for the regulation of tinman expression in Drosophila. Also list the vertebrate homologue
Decapentaplegic (BMP in vertebrates)
Tinman expression is initially induced very broadly in the tract mesoderm, however what is the name of the structure that its expression becomes restricted to later in the development of the fruit fly heart
Dorsal vessel
Lecture 22 Question 27 - See image
A – BMPs, B – Nkx2.5, C – Mef2C, D – GATA4, E – inv and iv, F – eHand and dHand
Lecture 22 Question 12 - See image
A – notochord and prechordal mesoderm, B – somites, C – urogenital structure such as the kidneys, D – cardiac and circulatory system
Which specific tinman vertebrate homologue is specifically expressed in the cardiac crescent
Nkx2.5
Dmef2 is also required to specify cells to a cardiac lineage, T or F
F – Dmef2 is required to differentiate cells into cardiac myocytes
Dmef2 is present is all differentiated cardiac muscle cells, T or F
F – is it present in all differentiation muscle cells (skeletal and smooth muscle too)
What is the result of gain of function experimentation with BMPs involved in cardiogenesis
Bead soaked in BMP2 induces the expression of Nkx2.5 in cells that wouldn’t normally express it. This indicates that BMP2 is sufficient to induce expression of Nkx2.5 in cells that wouldn’t normally
The timing of heart development across the species is relatively conserved, when does this tend to occur
Immediately after gastrulation
Outline the role of the iv and inv genes in heart looping
Iv and inv involved in the development of motile cilia
What would be the effects of tinman mutations on Dmef2 expression
Tinman mutants would not show Dmef2 expression
Tinman was a gene determined to be involved in the development of the heart. What type of gene is tinman
Homeobox domain containing transcription factor
Which specific members of the GATA family are involved in cardiogenesis
GATA 4-6
Explain the results of tinman loss of function analyses on cardiac development and what this tells us about its function
Deletions inserted into Drosophila genome in the tinman gene results in mutations that show a loss of myosin heavy chain expression. This indicates that tinman is required for the formation of cardiac cells
