Part 3 Flashcards
Cardiovascular disease
Main cause of death in UK and world wide, over 1 in 4
Myocardial infarction
Heart attack
Leading cause of death in developing countries, one person has a heart attack every 3 min in uk
Congenital heart diease
800 deaths per year
1/3 babies
Health care cost
around £11 billion per year in UK
Why do we study Drosophilla (lower organisms)?
Help understand human organogenesis
Drosophilla genome sequenced- March 2000
929 genes in humans- 548 have homologues in drosophila
Discovered- Hh, Notch, Wg, Dpp
Timings of cardiac development in different organisms
Drosophila (24h), mouse (19.5 dpc) and human (40 hrs) all have same steps different timings
Straight after gastrulation:
- fusion and formation of heart tube/looping
- Chamber form
- Heart functions
Where do cardiac cells originate from?
Ventral latera mesoderm called splanchnopleura
Somatopleura= Splanchic mesoderm and ectoderm Splancnopleura= Splanchnic mesoderm and foregut endoderm (lateral)
Heart precursor cells have 2 origins
First heart field
second heart field
Fate cells- identify in early development and follow to late to see what they make
What does the first heart field consist of?
- left ventricle
- right ventricle
- atrio-ventricular canal
What does the second heart field consist of?
- right ventricle
- outflow tract
- inflow tract
Cardiac specification
Production of angiognetic cell clusters
Above neural plate
- Arise immediately after gastrulation
- Crescent mannor is the anterior part of the embryo
Steps in heart formation for vertebrate and drosophila
Step 1
Precursor to cardioblast
(specification)
Drosophila- Tinman
Vertebrate- Nkx2.5
Heart formation
Step 2
Cardioblast to cardiomyocyte
(Differentiation)
Drosophila- Dmef2
Vertebrate- Mef2
Heart formation
Step 3
Cardiomyocyte to linear heart tube
Drosophila- Pannier
Vertebrate- GATA4
Heart formation
Step 4
This stage is where there is a difference between drosophila and vertebrate
Drosophila is linear heart tube to dorsal vessel
Vertebrate is linear heart tube to looping heart tube (InV)
Heart formation
Step 5
Only in vertebrates
Looped heart tube to multichambered heat
dhand and ehand
What drives the specification of cells in heart formation?
Drosophila
- Uses expression of tinman using dpp
- Tinmnan= protein code for TF homeobox
- Expressed through mesoderm however it becomes restricted as the embryo develops only being expressed in the dorsal vessel
Trunk mesoderm - dorsal mesoderm - dorsal vessel
Vertebrate
- Homologues of tinman= Nkx-2
- Nkx2.5 is the earliest to be expressed and specifically in cardiac crescent- restricted to angiogenetic cells
What happens when you have a mutant mice of Nkx 2.5?
Do not form a heart and show cardiac defects at looping stage- compensatory mechanism
Mutant humans- congenital heart defects
What regulates the expression of a gene?
- Onset
2. spatial mannor
What induces Nkx2.5 expression?
BMP
Express ectopically in gain or loss of function approach
1- electrooporate the BMP genes in the chick timing either immediately prior or same time as you would expect the genes to be expressed.
2-grafting cells expressing Bmp
3- adding beads (BMP bead soaked and control bead), allow chick embryo to develop, carry out in-situ hybridisation,
-Bmp bead expresses Nkx2.5 but at the paraxial mesoderm
-control expresses Nkx2.5 where it would normally be expressed
What signal is produced in the anterior mesoderm and neural plate?
Wnt so block BMP -Create an evironment which is favourable for induction -Block inhibitory factors - array of genes +proteins required
Endocardium
Contains precursors of endothelial lining of the heart and cushions cells that form valves
Myocardium
Contains myocytes of atria and ventricles and purkinjie fibres
What is used for cardiac muscle differentiation on drosophila and vertebrate?
Drosophila- Dmef2
- Induced by Tinman
- Protein expressed in all muscles of developing embryo
- Mutant= lose differentiation of muscle function but still see tinman expression
Vertebrates- Mef2A, Mef2B, Mef2C
- Earliest gene expressed in heart mef2C
- Mutant- no heart looping and no right ventricle up-regulation of ef2B