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MSS > Limb Development > Flashcards

Limb Development Flashcards

1
Q

What are the limb fields?

A

Areas of somatic mesoderm on each side of the embryo at specific axial levels

Axial positioning is regulated by Hox genes

Tbx5 transcription factor for upper limbs

Tbx4 and Pitx-1 transcription factor for lower limbs

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2
Q

What is budding and when does it occur?

A

During week 4: UL 26-27d, LL 28-29d

Small elevations on each side of the embryo at specific axial levels

Formed d/t inherent property of somatic mesoderm, begins producing Fgf-10

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3
Q

What does Fgf-10 induce?

A

Release of Fgf-10 by mesenchyme cells causes the surface ectoderm to form a thickened ridge of ectoderm – Apical Ectodermal Ridge (AER): runs anterior to posterior along the interface between the dorsal and ventral surfaces of the limb bud

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4
Q

What occurs during elongation of the limb?

A

Limb buds change shape

Week 5: flat paddle shaped hand/foot at distal end

Week 6: three segments are visible and digital rays are visible in hand/foot

Week 8: UL digits are complete separate, LL remain partially separated

Devo of upper limb usually precedes that of lower limb by about 1-2 days

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5
Q

When does tissue formation and organization occur?

A

Begins during week 5 in proximal limb – continues in proximal - distal direction

Somatic mesoderm condenses to form cartilage models of limb bones

Somite-derived mesoderm cells migrate to form skeletal muscles

Motor axons of spinal nerves also enter the limb

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6
Q

What are the three sets of linear axes and what develops along them?

A

Proximal-distal: limb outgrowth and elongation

Anterior posterior: develops digits

Dorsal-ventral: muscles and neurovascular structures form and are subdivided

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7
Q
A
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8
Q

What molecules form a gradient for development in the proximal-distal axis?

A

Retinoic acid – high proximally

Fgf, Wnt – high distally

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9
Q

What is the role of the Mesenchyme?

A

Induce the AER (Fgf-10)

Sustains AER (Fgf-10)

Determines limb type UL or LL

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10
Q

What is the role of the AER?

A

Maintain a proliferating pool of mesenchyme cells for linear growth (Fgf-8)

Maintain an A-P axis signaling center - ZPA (zone of proliferating activity)

Interacts with P-D and A-P specific proteins to provide mesenchyme cells with positional information

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11
Q

What is the fate of the Mesenchyme adjacent to teh AER?

A

Forms segment specific skeletal elements

Forms fibrous CT

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12
Q

What happens if the AER is removed during developement of a limb?

A

Limb is truncated

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13
Q

What would cause an amputation along the P-D axis?

A

Problem with the AER and underlying mesoderm communicating with each other

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14
Q

What is micromelia? Amelia?

A

Micromelia: Partial limb devo

Amelia: No limb devo

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15
Q

In what axis do the digits develop?

A

Anterior-posterior axis

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16
Q

What does the zone of polarizing activity (ZPA) influence?

A

Patterning along the anterior-posterior axis of the limb

17
Q

What is a main mediatior in A-P patterning?

A

Sonic Hedgehog (Shh)

Retinoic acid has the same effect

18
Q

How does apoptosis play a role in limb development?

A

Separation of digits

Absence of distal phalanx of large digit

19
Q

What develops along the dorsal – ventral axis?

A

Skeletal muscles: myoblasts organize into dorsal and ventral premuscle masses

Neural and vascular structures

Limb compartmentalization

20
Q

What are some of the main mediators of dorsal-ventral patterning?

A
21
Q

What is oligodacytly?

A

Lobster claw deformity

Causes by longitudinal type absence of limb part along the anterior-posterior axis

22
Q

What is Phocomelia? Which drug commonly caused this before being banned?

A

Distal segment of limb is attached to a more proximal segment with the intervening segment missing or may be directly attached to the girdle

23
Q

What is Syndactyly?

A

Complete or partial fusion of one or more digits

May be due to failure of interdigital apoptosis

24
Q

What is sirenomelia?

A

Fused limb fields or abnormal development of tailbud

25
Q

What is developmental dysplasia of the hip?

A

A condition where the hip joint is easily dislocated, usually after birth

26
Q

What is Cleidocranial dysplasia?

A

Hypoplasia or aplasia of the clavicles

Usually bilateral

Autosomal dominant inheritance

Runx-2 gene

27
Q

What is the Sprengel Deformity?

A

Undescended scapula

Characterized by a scapula that is located at C4-T2 and are dysplastic

MSS (24 decks)

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