Lecture 1: Limb Development

Question 1

limb field definition

Answer 1

hox genes determine in which position each of the 4 limb buds will form in vertebrates

Question 2

what substance plays an important role in initiating limb bud outgrowth

Answer 2

retinoic acid

Question 3

what 4 developmental tissues/cells give rise to forelimb and hindlimb

Answer 3

ectoderm
dermatome
myotome
somatic lateral plate mesoderm

Question 4

what determines the timing of limb development

Answer 4

different hox genes expressed at different times

Question 5

how do limb elements develop (in what direction)

Answer 5

proximal to distal

Question 6

T box genes determine

Answer 6

limb identity (pectoral vs thoracic)

Question 7

what do hox genes determine (2)

Answer 7

where limb buds will form
what limb will develop at specific location

Question 8

what forms the core of the limb field

Answer 8

mesenchyme (undifferentiated tissue)

Question 9

3 early development steps: limb field to limb bud

Answer 9

induction of limb development –> establishment of AER and ZPA signaling centers –> promotion of outgrowth and patterning in established limb bud

Question 10

origination of limb buds (what/where)

Answer 10

ridges in ventrolateral body wall

Question 11

2 types of limb buds

Answer 11

forebud
hindbud

Question 12

which limb bud develops first

Answer 12

forebud

Question 13

3 axes where limbs develop simultaneously

Answer 13

proximodistal
dorsoventral
craniocaudal

Question 14

AER/apical ectodermal ridge: definition

Answer 14

thickened, specialized epithelium

Question 15

what does AER induce proliferation of

Answer 15

limb bud mesenchyme through progress zone

Question 16

progress zone: definition, function

Answer 16

area of mesenchyme just proximal to AER
encourages growth

Question 17

proximodistal axis determined by

Answer 17

fibroblast growth factor acting at the AER

Question 18

dorsoventral axis determined by

Answer 18

non AER dorsal ectoderm
folding initiated by Wnt7a

Question 19

craniocaudal axis determined by

Answer 19

sonic hedgehog genes acting at zone of polarizing activity

Question 20

feedback loop of limb development and continued AER growth

Answer 20

lateral plate mesoderm expressing fibroblast growth factors to create more growth at AER

Question 21

what happens to each limb bud once acquiring terminal length

Answer 21

terminal portion flattened to form hand and foot plates

Question 22

what divides portion of each limb bud once they’ve become hand and foot plates

Answer 22

2 constrictions

Question 23

proximal-distal development steps (3/4)

Answer 23

formation of hand and foot plates
2 constrictions
limb bud with 3 main segments = stylopod, zuegopod, autopod
mesenchyme condenses into cartilage for future long bones

Question 24

stylopod

Answer 24

arm/thigh

Question 25

zeugopod

Answer 25

forearm/leg

Question 26

autopod

Answer 26

hand/foot

Question 27

what directs pattern formation in dorsal ventral axis

Answer 27

non AER ectoderm

Question 28

what gene expression initiates limb forming interactions between ectoderm and mesoderm

Answer 28

Fgf 10

Question 29

how are final constrictions and separation of digits formed (what process)

Answer 29

apoptosis/programmed cell death

Question 30

dorsal and ventral aspects of limb follow what process

Answer 30

lateral folding of embryo

Question 31

what is dorsal-ventral axis important for

Answer 31

patterning muscles

Question 32

where does D/V (dorsal/ventral) center reside

Answer 32

dorsal ectoderm

Question 33

result of AER signaling in cranial-caudal axis

Answer 33

Shh (sonic hedgehog) expression and formation of ZPA

Question 34

what is the origin of all nerves

Answer 34

ventral primary ramus

Question 35

what nerves follow growing muscle and provide motor innervation

Answer 35

ventral and dorsal branches of ventral ramus

Question 36

what cells express retinoic acid and sonic hedgehod

Answer 36

ZPA cells

Question 37

what 2 inputs are required for ZPA and sonic hedgehog expression

Answer 37

AER dorsal ectoderm

Question 38

homology definition

Answer 38

existence of shared ancestry between a pair of structures or genes in different species

Question 39

pentadactyl limb

Answer 39

ancestral 5 digit condition

Question 40

digit reduction is the result of what

Answer 40

species specific evolutionary history

Question 41

2 types of patterning changes of cell death

Answer 41

patterning post patterning

Question 42

post patterning changes: starting condition, order to digit reduction

Answer 42

initial limb segments laid out in cartilage digits I and V eliminated digits II and IV reduced

Question 43

what 2 mammals have post patterning changes

Answer 43

horses camels

Question 44

patterning changes: starting condition, order of digit reduction

Answer 44

never start with a pattern digit loss and shift of central axis of foot between digits III and IV (loss occurs at SAME time as pattern formation)

Question 45

order to digit loss

Answer 45

I, V, II, IV

Question 46

what directions do forelimb and hindlimb rotate leading to final limb position

Answer 46

forelimb rotates dorsally hindlimb rotates ventrally

Question 47

Cingulum, stylopodium, zeugopodium and autopodium in forelimb

Answer 47

Scapula and clavicle —> humerus —> radius and ulna —> carpal bones, metacarpal bones and phalanges

Question 48

Cingulum, stylopodium, zeugopodium and autopodium in hindlimb

Answer 48

Ox coxae/hip (ileum, pubis, ischium) —> femur —> tibia and fibula —> tarsals, metatarsals and phalanges