Flashcards in EXAM2_HE18_LIMB_Development Deck (36):
What expression at primitive node initiates/maintains primitive streak?
Nodal (TGF-B family)
What expression at primitive streak controls cell migration (invagination)?
What expression drives left/right asymmetry later in development?
FGF8 and Nodal expression
Where developed from:
Vasculature of limbs?
long bones of limbs?
Vasculature of limbs- Lateral Plate Visceral
long bones- lateral plate Somatic
Respiratory system- lateral plate visceral
Visceral organs & GI- lateral plate visceral
CT- somatic lateral plate mesoderm
2 divisions. What do each form? what expression for each?
When does myotome differentiation occur?
1. Hypaxial- body wall & limb muscles- anterior primary rami
(MyoD expression-posterolateral origin of paraxial somite)
2. Epaxial- Intrinsic back muscles- post primary rami
(Myf5 expression)- posteromedial origin of paraxial somite)
AT 5 WEEKS!
Signaling for hypaxial and epaxial- what about dermis?
BMP4 & WNT>MYOD> body wall/limb muscles
SHH & WNT >MYF5> intrinsic back muscles
What is special about the epaxial derivatives? hypaxial derivatives?
epaxial ;Myoblasts do not migrate- form intrinsic back muscles
hypaxial- some don't migrate- form intercostal muscles
some Migrate into the limb muscles
Limb buds- when formed? what type of tissue? where tissue from? location of upper/lower buds? what determined by?
- Buds @ 4 weeks
- Paddles @ 6 weeks
- Fingers @ 8 weeks
-Has dermis deep to ectoderm
-mesenchyme from somatic mesoderm form cartilage>bone
-Upper limb bud C4-T2
-Lower limb bud L1-S2
Determined by HOX genes
mesenchyme>dermis>cuboidal ectoderm layers of limbs
What segments of top part of arm? Lower part of arm?
What segments of lateral leg? midline of leg?
Top surface- c4-c7
Under surface T1-T2
lateral leg- L2-L5
midline leg- s1-s3
Apical Ectodermal Ridge (AER)
what causes differentiation?
what does it regulate?
what kind of cells in differentiation zone?
where derived from?
when digits formed?
-AER differentiates response from FGF from mesoderm
-Differentiation zone (chondrocytes & CT) Low FGF is proximal
-Proliferative/progress zone Hi FGF-extends limb
-Mesenchyme from lateral plate somatic mesoderm
-cartilaginous digital rays form in each digit 6-8wks
-apoptosis creates digits by 8 weeks
describe the FGF concentration and its role in limb development. High FGF region? low FGF region? what happens there? What it's called?
Distal End of AER- HIGH FGF= progress zone (proliferative) mitotic
Proximal to AER- LOW FGF = differentiation zone
Nile Blue stain used for?
What is formed at 8 weeks?
6 and 4 weeks?
8- should have apoptosis and digits of CARTILAGE
6- paddles-Hyaline cartilage
Limb development 6 weeks? 8 weeks? 12 weeks? Birth?
what limbs form faster? by how much?
6- limb bones exist as hyaline cartilage models
8- endochondral ossification begins in center of diaphysis
12- primary ossification centers formed
birth- diaphysis is ossified- epiphysis has active secondary ossification centers- branches of intersegmental arteries grow into developing limbs-
Upper limb develop 1-2 days before lower limbs
what is the flow of bone formation?
mesenchyme>cartilage> bv & osteoblasts arrive via blood> ossification
Limb Rotation- When; what rotates how much where?
Begins @ 7 weeks
-Upper limb rotates 90deg laterally
extensors posterior-thumb lateral
-Lower limb rotates 90deg medially
big toe medial
Limb muscle formation and innervation.
-Skeletal myoblasts from HYPAXIAL division of myotome migrate into limb bud by 7 weeks
-CT in the limbs guides myoblast formation of skeletal muscle
problem with CT during limb formation?
if there is a problem with the CT during limb formation the myoblasts will not be patterned correctly
SOMATIC vs SOMITIC
Somatic - referring to lateral plate somatic mesoderm
Somitic- referring to paraxial plate mesoderm somites
What controls the patterns of muscle formation in the limbs? Why is this so important?
Where are occipital/cervical myoblasts derived from?
Where are Body wall/ Limb myoblasts derived from?
CT Fibroblasts (somatic lateral plate)- in buds will direct the myoblasts migration and massing
-Myoblasts migrate within CT in limb buds and develop into specific muscle divisions
Occipital/Cervical muscles- from SOMITIC mesoderm of paraxial mesoderm
Body wall/limbs- SOMATIC mesoderm from lateral plate mesoderm
Where can Connective tissue be derived from?
Head, Cervical/Occipital, Limbs.
Lateral Plate- somatic MAINLY- limb ct for myo formation
Paraxial mesoderm- cervical/occipital ct for myo formation
Neural crest- CT for myo formation of head muscles
Innervation of muscles- What RAMI? 2 divisions of that rami? Functions of each division?
Why is nerve/muscle contact so important?
ANTERIOR PRIMARY RAMI forms appropriate spinal nerves that enter limb buds and has TWO DIVISIONS:
1. Anterior division- innervates flexors of limbs
2. Posterior division- innervates extensors of limbs
nerve/muscle contact required for complete differentiation
-if muscle develops without innervation- they malfunction
What nerves innervate extensor muscles of the arm and forearm?
Posterior division of the ANTERIOR PRIMARY RAMI forms a posterior nerve:
1. RADIAL NERVE- extensor muscles of the arm and forearm
What nerves innervate Flexor muscles of the arm? flexor muscles of the forearm?
Anterior division of the ANTERIOR PRIMARY RAMI forms 3 anterior nerves:
1. MUSCULOCUTANEOUS NERVE- flexor muscles of ARM
2. ULNAR & MEDIAN NERVES- flexors of FOREARM
Clinical aspects of limb development- AER/ZPA
What is AER- where derived from? what expressed? why?
What is ZPA- where derived from? what expressed? why?
What affects proper limb growth/digit order/ etc?
AER- apical ectodermal ridge expresses FGF to maintain progress zone.
ZPA- zone of polarizing activity derived from mesoderm
-located posterior margin of limb bud- expresses SSH (sonic hedgehog).
-SSH controls anterior-posterior patterning
AER + ZPA req. for proper limb bud outgrowth, digit order, etc.
Where does ZPA form? why is this important? What is expressed? what gradient?
ZPA forms anterior/posterior axis
- forms initially on posterior side of limb and produces SSH.
-SSH gradient higher posterior and less SSH anterior
What determines the final length and size of limb?
What happens if you remove SHH from AER?
Breakdown feedback between AER (FGF) and ZPA (SHH)-
-ectopic digit formed if SHH removed from AER (SHH removed from ectoderm not from mesoderm).
How does AER and ZPA regulate signaling and limb development?
Feedback loop between AER/ZPA establishes proper amount of SHH and FGF for limb development
If you take out SHH of ectoderm only?
If SHH removed completely?
How does morphology fingers relate to SHH?
extra digit if SHH removed from ectoderm
only thumb develops if SHH removed entirely
-thumb is independent of SHH:
-SHH Gradient (HIGH pinky 5, 4, 3, 2 LOW)
-NO SHH creates the thumb
AER/ZPA- ZPA transplanted to ANTERIOR margin of limb bud. What was result?
Limb developed with TWO POSTERIOR IDENTITIES
-No thumbs developed
-Fingers 5,4,3,3,4,5 with no 1 or 2 digits
Patterns of limb development:
Ablation of FORELIMB PARAXIAL MESODERM:
Ablation of TRUNK PARAXIAL MESODERM:
Why is this experiment important?
Forelimb ablation- decreases limb bud outgrowth
Trunk ablation- increases limb bud outgrowth
-Limb buds form from somatic lateral plate mesoderm
--Important discovery that a relationship exists between Paraxial mesoderm (seemingly unrelated to limb bud growth) and limb bud growth.
3 experiments done to confirm relationship of paraxial mesoderm to limb development
What was result of Last experiment?
1. ablation of forelimb/trunk paraxial mesoderm
2. Counted cell proliferation resulting from ablation
3. transplant excess forelimb/trunk paraxial mesoderm
Extra forelimb mesoderm> bigger growth
Extra trunk mesoderm> smaller growth
OVERALL results of experiments for limb bud development?
Forelimb Paraxial mesoderm stimulates limb growth
Trunk paraxial mesoderm inhibits limb growth
What genes regulate morphology? How many do we have?
- Humans have 4 sets of HOX genes
- HOX genes regulate types and shapes of bones (morphology)
4 Digital Defects:
1. brachydactyly- short digits
2. Polydactyly- extra digits
3. Syndactyly- fused digits
4. Cleft foot- extreme syndactyly (all merged to 2 digits)