Lecture 29 - Limb Development and Malformations Flashcards
____________ give(s) rise to limb CONNECTIVE tissues including the SKELETON and tendons.
Lateral mesoderm cells
MUSCLE cells of the limb come from the adjacent ________ and migrate into the limb at early limb bud stages.
somites
The _______ is a limb bud signaling center in the region of posterior lateral mesoderm.
zone of polarizing activity (ZPA)
The _______ is a signaling center that presents as a thickening at the tip of each bud.
apical ectodermal ridge (AER)
The critical period for limb development is: A. 2-4 weeks B. 4-7 weeks C. 4-5 weeks D. 3-6 weeks E. 3-8 weeks
E.
“Fused digits” are described as what congenital malformation: A. Syndactyly B. Polydactyly C. Polyamelia D. Brachyamelia E. Septodactyly
A.
“Extra digits” as described as what congenital malformation? A. Syndactyly B. Polydactyly C. Polyamelia D. Brachyamelia E. Septodactyly
B.
“Clubfoot” describes a range of abnormalities in which the foot is turned:
inward and downward
“Missing proximal elements” are described as what congenital malformation:
A. Syndactyly
B. Polydactyly
C. Brachydactyly
D. Brachyamelia
E. Phocoamelia
E.
RA and Wnts are produced by somitic mesoderm and lateral plate mesoderm. What do they help regulate?
transcription factors that define forelimb vs. hindlimb identity
A major function of Tbx genes is to initiate limb bud outgrowth. Tbx4 and Tbx 5 do so by regulating:
expression of FGFs
Which is regulated by Pitx1, which encodes hindlimb identity? A. Tbx1 B. Tbx4 C. Tbx5 D. RA E. Wnts
B.
Which Tbx gene operates at forelimb levels and encodes forelimb identity?
Tbx5
_______ initially promotes the transition of flank mesoderm from an epithelial to a mesenchymal population.
FGFs
Which signaling center of the limb bud is an important source of FGFs?
apical ectodermal ridge (AER)
Which is false regarding the outgrowth of the limb? A. the AER is required for limb outgrowth B. the earlier the AER is removed, the more severe the truncation of the limb. C. Addition of FGFs will not compensate for AER removal. D. FGFs appear to promote cell survival and cell proliferation
C. Addition of FGFs to the region of an ablated AER will correct or compensate for AER removal.
What is the role of Hox proteins in limb formation?
Hox proteins play a role in the definition of proximodistal (PD) limb regions, and are expressed in ‘nested’ patterns within the developing limb buds.
Which protein leads to changes in the expression and function of Gli transcription factors?
Sonic hedgehog
Shh signal transduction takes place in association with _______.
primary cilia
Shh binds to a receptor complex in the membrane that consists of:
Patched and Smoothened proteins. *Note: binding by Shh alleviates the repression of Smoothened by Patched.
Which signaling center of the limb bud is defined by its ability to induce mirror-image duplications of the digits?
The Zone of Polarizing Activity (ZPA)
________ signaling promotes mesenchyme proliferation and expansion of the limb.
Shh
Inactivation of Shh results in the loss of:
all but digit 1
Shh regulates the expression of _____ in most distal limb regions, leading to the establishment of digit identity.
Hox
During early AP patterning, how does Shh act on Gli3?
Shh converts Gli3 from repressor to activator of downstream target genes.
How do BMPs mediate interdigital cell apoptosis in late stages?
via signaling to the AER to decrease FGF expression
Which is responsible for variable upper arm defects? A. Hox genes B. Gli3 C. Pitx1 D. Tbx5
D. Tbx5 is linked to defects such as carpal bone fusion, absent or triphalangeal thumb, syndactyly, etc.
Which is responsible for lower limb defects? A. Hox genes B. Gli3 C. Pitx1 D. Tbx5
C. Pitx1 is responsible for defects such as clubfoot and polydactyly.
Which is responsible for several abnormalities of the hand and foot? A. Hox genes B. Gli3 C. Pitx1 D. Tbx5
A.
Which is NOT primarily responsible for polydactyly? A. Hox genes B. Gli3 C. Pitx1 D. Tbx5
D. Despite several factors being linked to this, the Shh signaling pathway and Gli3 are common causes.
Thalidomide disrupts _______ formation.
blood vessel
Thalidomide exposure reduces limb levels of _____, leading to the death of cells in limb bud mesenchyme and the AER.
FGFs
What are the four components of the atrial septum?
- Septum primum 2. Dorsal mesenchymal protrusion 3. Endocardial cushions 4. Septum secundum
A defect in closure of the ostium primum (i.e. septum primum does not fuse with endocardial cushions) results in: ______.
A. Primum ASD
B. Secundum ASD
C. Common AV Canal
D. Common atrium
A. Primum ASD
Abnormally large ostium due to excessive resorption of septum primum or insufficient septum secundum is what type of defect?
A. Primum ASD
B. Secundum ASD
C. Common AV Canal
D. Common atrium
B.
A _________ is a defect that is a large hole in the center of the heart (i.e. an endocardial cushion defect).
A. Primum ASD
B. Secundum ASD
C. Common AV Canal
D. Common atrium
C.
________ is a complete absence of atrial septa.
A. Primum ASD
B. Secundum ASD
C. Common AV Canal
D. Common atrium
D
What major part of the heart receives contributions from the neural crest cells?
A. AV Canal
B. Atrial septa
C. Ventricular septa
D. Truncal septa
D. Truncal septa, or the outflow tract, arises from the cranial neural crest cells and the SHF cells. These contribute to the truncal cushions and their derivative, the aorticopulmonary septum.
A _____________ is a lack of separation of aortic and pulmonary trunks due to failure of cushion formation, defective cushions, or abnormalities in the neural crest cells.
A. Transposition of the Great Vessels
B. Persistent Truncus arteriosus
C. Ventricular septal defect
D. Tetralogy of Fallot
B.
In one particular defect, the aorta and pulmonary trunks are reversed such that the aorta arises from the right and the pulmonary trunk from the left ventricle.
A. Transposition of the Great Vessels
B. Persistent Truncus arteriosus
C. Ventricular septal defect
D. Tetralogy of Fallot
A. This is thought to reflect failure of truncal cushions and septa to spiral, which in turn may reflet abnormal rotation of the atria.
_______ is the most common cardiac defect and usually an incomplete interventricular septum.
A. Transposition of the Great Vessels
B. Persistent Truncus arteriosus
C. Ventricular septal defect
D. Tetralogy of Fallot
C. VSD is caused by:
a) deficient development of conal cushions
b) failure of fusion of intramembranous and muscular septa
c) failure of AV cushion development and/or fusion
d) insufficient development of the muscular septum
Which is NOT a primary cause of VSD?
A. deficient development of conal cushions
B. failure of fusion of intramembranous and muscular septa
C. failure of the truncal cushions and septa to spiral
D. failure of AV cushion development and/or fusion
E. insufficient development of the muscular septum
C. This is a feature of “Transposition of the Great Vessels”, not VSD.
Problems with Shh signaling at the _________ often result in polydactyly and are linked to Gli3 regions.
Zone of polarizing activity
