Lecture 1- Limb Development

Question 1

what makes up the cingulum in thoracic and pelvic limbs

Answer 1

Thoracic- scapula and clavicle
Pelvic- pelvis- ilium, ischium, and pubis

Question 2

What makes up the stylopod in pelvic and thoracic limbs

Answer 2

Thoracic- humerus
Pelvic- femur

Question 3

What makes up zeugopod in pelvic and thoracic limbs

Answer 3

Thoracic- radius and ulna
Pelvic- tibia and tibia

Question 4

What makes up autopod in thoracic and pelvic limbs

Answer 4

Thoracic- carpus, metacarpus, and phalanges
Pelvic- tarsus, metatarsus, and phalanges

Question 5

Where do cells derive from to make fore and hind limbs

Answer 5

Cells of the ectoderm derived from dermatology and hypaxial portion of myotome mix with somatic component of lateral plate mesoderm to give rise to fore and hind limbs

Question 6

What is the mesenchyme core

Answer 6

Undifferentiated tissue from mesoderm

Question 7

What does the lateral plate mesoderm form

Answer 7

Cartilage, bones, and general CT

Question 8

What does the paraxial mesoderm form

Answer 8

Somites, skeletal muscle

Question 9

What is the ectoderm

Answer 9

Outpocketing of ventral body wall- epidermis of skin, nails, hair
Spinal nerves- form nervous plexuses

Question 10

What controls the timing of development of the limb

Answer 10

How genes expressed at different times

Question 11

What direction do limbs develop

Answer 11

Proximal to distal

Question 12

what determines limb identity

Answer 12

T box genes

Question 13

What determines where limb buds form and what limb develops at specific location

Answer 13

Hox genes

Question 14

What occurs in the limb field

Answer 14

Induction of limb development and establishment of AER and ZPA signaling centers

Question 15

What occurs in limb bud

Answer 15

Promotion of outgrowth and patterning

Question 16

What transcription factors induce epithelium to mesenchyme formation that induces formation of limb bud

Answer 16

Fibroblast growth factors and T-box genes

Question 17

Which limb bud ridge appears first

Answer 17

Forebud ridge appears first then 1-2 days later hindbud ridge

Question 18

What are the three axes limb buds development on simultaneously

Answer 18

1. Proximodistal
2. Dorsal ventral
3. Craniocaudal

Question 19

What determines pattern formation in proximo-distal axis

Answer 19

Apical Ectodermal ridge

Question 20

What is the apical ectodermal ridge

Answer 20

Thickened, specialized epithelium located at the dorsoventral border of tip of bud

Question 21

what is the progress zone

Answer 21

Area of mesenchyme just proximal to AER

Question 22

What induces proliferation of limb bud mesenchyme

Answer 22

AER

Question 23

Limb bud development depends on the interaction between….

Answer 23

Limb bud mesenchyme and apical ectodermal ridge, communicate via positive feedback loop

Question 24

Describe positive feedback loop between lateral plate mesoderm and AER

Answer 24

Lateral plate mesoderm expressed Fgf10 to initiate AER. AER then expresses Fgf8 and Fgf4 to maintained Fgf10 expression

Question 25

What happens once the limb bud reaches its terminal length in proximodistal development

Answer 25

Terminal portion of limb bud flattens to become hand and foot plates and then two constrictions occur to create 3 segments- stylopod, zeugopod, autopod

Question 26

What does mesenchyme condense into once limb bud acquires terminal length

Answer 26

Cartilage models for future long bones

Question 27

What is the dorsal ventral axis

Answer 27

Pattern formation that follows lateral folding of embryo

Question 28

Where does dorsal ventral signaling center reside and what does it express

Answer 28

Resides in dorsal ectoderm and expresses Wnt7a

Question 29

Describe muscle and innervation compartments in dorsal ventral development

Answer 29

Precursor muscle cells from ventrolateral myotome of somite migrate to limb bud, bring ventral and dorsal muscle groups, ventral and dorsal rami branches

Question 30

What is the cranial-caudal axis

Answer 30

Zone of polarizing activity that directs pattern formation

Question 31

What is the zone of polarizing activity

Answer 31

Area of mesenchyme on caudal border. Gives cranial-caudal identity to differentiating cells

Question 32

What does ZPA express

Answer 32

Retinoic acid and sonic hedgehog

Question 33

What does the shh gradient induce

Answer 33

Expressed of mesenchymal hox genes

Question 34

Limb morphology is a product of ____

Answer 34

Apoptosis

Question 35

Describe how apoptosis shapes final limb morphology

Answer 35

1. As limbs development progresses AER breaks up and only covers emerging digital rays
2. Interdigital spaces no longer have AER and can be sculpted by apoptosis

Question 36

Describe horse digit reduction

Answer 36

Post patterning changes
Initial limb segments are laid into cartilage
Digits I and V lost first- not known why
Digits II and IV lost as a result of apoptosis

Question 37

Describe cattle and swine digit loss

Answer 37

Patterning changes
Digit loss and shift of central axis of foot between digits III and IV

Question 38

What is the order of digit loss

Answer 38

I, V, II, IV

Question 39

What direction does forelimb rotate

Answer 39

Dorsally

Question 40

What direction does the hindlimb rotate

Answer 40

Ventrally

Question 41

What does limb rotation shape

Answer 41

1. Joint movement- stifle and elbow face opposing directions
2. Shapes position of muscle compartments and constrains neurovasculature to compartments
3. Shapes distribution of dermatome