Embryology: Mesoderm Flashcards
Where does skeletal muslce develop from?
Paraxial mesoderm
Where does smooth muslce develop from?
Visceral plate of lateral plate
Where does cardiac muslce develop from?
Visceral plate of lateral plate
When do somites start to form?
Day 20
What is the clock gene, involved in the clock and wave front mechanism?
Notch
What is the wave gene, involved in the clock and wave front mechanism?
FGF8
What is a somite?
Block of paraxial mesoderm that gives rise to skeletal muslce
Once somites are formed, what do they differentiation into?
The ventral and medial part forms the Sclerotome and the dorsal part forms the dermomyotome.
What does the dermomyotome split into?
Dermatome and myotome
What does the Sclerotome from?
vertebrae and ribs
What does the myotome split into?
Primaxial and Abaxial muscles
Where are tendons derived from?
Sclerotome
What gene influences tendon formation?
Scleroaxis
What are the function of the transcription factors, MYOD and MYF5?
These activate muslce-specific genes and allow myoblast formation in the dermomyotome.
What is the function of Myogenin?
This allows the myoblast cells to align and fuse to from primary myotubes
How is MYOD activated?
WNT (activating) and BMP (inhibiting) are released from the neural tube. These work together to activate MYOD.
What creates MYF5?
MYOD
What forms the lateral body wall?
Somatic layer of lateral plate
What is responsible from smooth muscle differentiation?
Serum response factor
What does the intermediate mesoderm form?
Urogenital structures
What does the dermatome form?
Dermis and connective tissue
What does the parietal layer of the lateral plate form?
The Body wall and bones
What does the visceral layer of the lateral plate form?
Wall of the gut tube and serous membranes
What forms the wall of the gut tube?
Visceral layer
What forms the serous membranes?
Visceral layer
What forms the ribs and the vertebrae?
The Sclerotome
How many pairs of somites form from day 20 until week 5?
3 pairs a day
What are MOD and MYF5?
Transcription factors
When myoblast cells fuse, what do they form?
Primary myotubes
Where is WNT produced?
Neural tube
Where is BMP produced?
Neural tube
What type of muslce does the visceral layer of the lateral plate form?
The smooth muslce and cardiac muscle
What type of muslce does the paraxial muslce form?
Skeletal muscle
What forms the dermis?
The dermatome
What does the visceral layer of the lateral plate form?
Serous membranes and the wall of the gut tube
What does the parietal layer of the lateral plate form?
The body wall and bones
What does the Sclerotome form?
The vertebrae and ribs
What is the function of neurotrophin-3?
Directs the dermatome to become the dermis. It is secreted by the dorsal neural tube.
Neurotrophin-3 functions to direct the dermatome to become the dermis. Where is it secreted?
The dorsal tube.
What activates MYOD and subsequently MYF5?
Wnt (activating) and BMP (inhibiting) combine to MYOD and. MYOD creates a group of muslce cell precursors which express MYF5.
What is the function of MYOD and MYF5?
These are myogenic regulatory factors. These activate muscle-specific genes and can convert non-muslce cells to other muscle cells.
Name two myogenic regulatory factors
MYOD and MYF5
What affect does Sonic Hedgehog and Noggin have on Sclerotome formation?
They induce it
What is the lateral plate mesoderm?
This is the border between each somite and the lateral plate mesoderm. It separates the two mesodermal domains.
What are the two mesodermal domains?
Primaxial: region around the neural tube that is somite derived mesoderm
Abaxial: parietals layer of the lateral plate mesoderm and some migratory somatic cells
Where do the signals for the primaxial mesoderm come from?
Neural tube and notochord
Where do the signals for the abaxial region come from?
Lateral plate mesoderm
Where do the scalene muslces originate from?
Primaxial
What is the origin of the Intercostal muslces?
Primaxial
What is the origin of the Rhomboids?
Primaxial
What is the origin of the Levator scapulae?
Primaxial
What is the origin of the latissimi dorsi?
Primaxial
What is the origin of the Infrahyoid muslces?
Abaxial
What is the origin of the Geniohyoid muslces?
Primaxial
What is the origin of the pectoralis major and minor?
Abaxial
What is the origin of the external and internal oblique muscles?
Abaxial
What is the origin of the transverses and rectus abdominus muslces?
Abaxial
What is the origin of the distal limb muslces?
Abaxial
What is the origin of the pelvis diaphragm?
Abaxial
What are the epaxial and hypaxial regions supplied by?
Epaxial (true back muslces): dorsal primary rami
Hypaxial (limb and body wall): ventral primary rami
What are limb buds?
Small buds of undifferentiated mesoderm cells that are covered with cuboidal ectoderm
What shape is the ectoderm covering the limb buds?
Cuboidal
At what day do the limb buds first become visible?
Day 24
What is the time period of limb morphogenesis?
Weeks 4-8
Where is mesenchyme derived from?
Dorsolateral mesoderm of the somites and parietal layer of the lateral plate mesoderm
When the ectoderm at the distal border thickens, what does it form?
The apical ectodermal ridge
The apical ectodermal ridge always remains undifferentiated. true or False?
True
What is limb outgrowth initiated by?
FGF10
What is the function of FGF10 during limb development?
Initiate limb outgrowth
What does the dorsal ectodermal ridge express?
Radical fringe
What does the ventral ectodermal ridge express?
Engrailed-1
Where is Engrailed-1 expressed?
Engrailed-1 is expressed in the ventral ectodermal ridge
Where is radical fringe expressed?
Dorsal ectodermal ridge
Once the AER (apical ectodermal ridge) is established, what does it express?
FGF4 and FGF8
What is the function of FGF4 and FGF8?
Essential for maintenance of an undifferentiated zone
Where is FGF10 secreted?
Lateral plate mesoderm. This is responsible for limb outgrowth.
What is the function of retinoic acid in limb development?
This is present on the proximal ends of the limbs and starts differentiation into the proximal compartments.
What is the function of Radical fringe?
This restricts the AER to dorsal tip
What is the function of Engrailed?
This restricts the AER to the ventral tip
What does the AER promote and prevent?
The AER promotes mitosis and prevents differentiation.
What is polydactyly?
This is the presence of extra digits
What the three possible genes that can be mutated in polydactyly?
Hox, Shh or Wnt
Is Polydactyly recessive or dominant?
Recessive
When do the terminal portions of limb buds become flattened and what do they form?
Week 6: handplates and footplate
Development of limb buds occurs in what direction?
Proximodistally
What are the three comparts of the limb development, proximal to distal?
Stylopod, Zeugopod, Autopod
What is positioning of limbs along the craiocaudal axis regulated by?
HOX genes
What how gene is only present in the hands?
Hox-13
What gene family is responsible for designating upper and lower limbs?
T-box transcription factors
What T-box transcription factor is expressed in upper limbs?
TBX-5
What T-box transcription factor is expressed in the hind-limbs?
TBX-4 and PITX1
Briefly describe the formation of the digits?
There is cell death in the AER and this separates the ridges into 5 parts. The five fingers will then grow out. Digit separation is complete by day 56.
When is digit separation complete?
Day 56
When does limb rotation occur?
Week 7
What is the direction of rotation that occurs with limbs?
Coronal to Parasagittal, then along the long axis
What way does the upper limb rotate?
90 degrees laterally
What way does the lower limb rotate?
90 degrees medially
Where do the extensor muslces of the upper limb lie?
Lateral and posterior side
Where do the extensor muslces of the lower limb lie?
Anterior surface
When can cartilage models be seen?
Week 6
What is the function of WNT 14?
Cell proliferation, increased density, cell differentiation and cell death
When does ossification begin?
Week 8
When are all primary centres of ossification present in long bones?
Week 12
