Development of limbs

Question 1

What is the origin of muscle in the extremities

Answer 1

paraxial mesoderm –> somite

dermamyotome –> myotome –> hypomere –> dorsal lateral hypomere cells migrate to limbs

Question 2

What is the fate of migrating hypomere cells

Answer 2

become dorsal and ventral muscle masses

Question 3

what is the fate of the dorsal muscle mass?

Answer 3

becomes extensors/supinators/abductor muscles of the limbs

Question 4

what is the fate of the ventral muscle mass?

Answer 4

becomes flexors/pronators/ abductors

Question 5

What are the tendons and bones of the extremities derived from?

Answer 5

the lateral plate mesoderm

know this cause it was highlighted heavily on slides

Question 6

how is bone in the extremities formed? when does it begin

Answer 6

lateral plate mesoderm begins the process of endochondral ossification during week 5

Question 7

What happens during week 5 6 and 7-9 during bone formation

Answer 7

week 5-begins
week 6-limb cartilage forms
week 7-9-osteogensis creating long bones

Question 8

When do limb buds appear?

Answer 8

week 4

Question 9

When does the hand/foot plate appear as well as the beginning of chondrification?

Answer 9

week 5

Question 10

When do the digital rays of the hand form? also limb skeleton is cartilaginous

Answer 10

week 6

Question 11

when do the digital rays of the feet form?

Answer 11

week 7

Question 12

when does osteogenesis take place?

Answer 12

week 7

Question 13

when does limb rotation occur

Answer 13

week 7

Question 14

when are separate digits formed?

Answer 14

week 8

Question 15

what occurs during week 12?

Answer 15

primary ossification

Question 16

What direction are the limbs facing before rotation?

Answer 16

ventral surface facing medially

dorsal surface facing laterally

Question 17

What occurs during rotation of the upper limb?

Answer 17

rotates laterally so flexor compartment faces anteriorly and extensor faces posteriorly

Question 18

what occurs during rotation of the lower limb?

Answer 18

rotates medially so flexor compartment faces anteriorly and extensor faces posteriorly

Question 19

What week do axons from ventral rami innervate muscle? what is this followed by?

Answer 19

week 5
sensory axons follow it
NCC turned schwann cells myelinate it

Question 20

What muscles do axons cranial to the limb innervate?

Answer 20

dorsal muscles

Question 21

What muscles do axons caudal to the limb innervate?

Answer 21

ventral muscles

Question 22

blood supply

Answer 22

idk look it up cause i dont get it

Question 23

What are the 3 parts of the growing arm? which is proximal which is distal?

Answer 23

stylopod –> zeugopod –> autopod (proximal to distal)

Question 24

What is secreted by lateral plate mesoderm that begins the process of budding?

Answer 24

Fgf10

Question 25

What does Fgf10 do?

Answer 25

activates WNT signaling, promotes distal extension of AER and causes it to secrete Fgf8

Question 26

What occurs when WNT signaling is turned on?

Answer 26

AER secretes FgF8 --> positive feedvack loop for more Fgf10

Question 27

what is the AER?

Answer 27

apical ectodermal ridge (part that moves distally during budding)

Question 28

What occurs if you remove the AER?

Answer 28

no limb growth

Question 29

what happens if you have extra AER?

Answer 29

extra limb growth, winging

Question 30

what happens if you replace arm mesenchyme with leg mesenchyme but keep the AER intact?

Answer 30

you get a normal leg where the arm is supposed to be

Question 31

what happens if you replace arm mesenchyme with non limb mesenchyme?

Answer 31

AER regresses and nothing grows

Question 32

what happens if you replace AER with an FGF bead?

Answer 32

normal limb growth

Question 33

What causes differentiation into the 3 sections? what happens if one of these is knocked out?

Answer 33

HOX genes, if the HOX gene is knocked out that part doesnt form

Question 34

What is the HOX gene for the sytlopod?

Answer 34

HOX 9-10

Question 35

What is the HOX gene for the zeugopod?

Answer 35

HOX11

Question 36

What is the HOX gene for the autopod?

Answer 36

HOX12-13

Question 37

What causes a limb to differentiate cranial from caudal?

Answer 37

a ZPA region that is present before budding occurs

Question 38

What does the ZPA region secrete? what does this do?

Answer 38

SHH, causes pinky formation, as you move down the gradient it causes other fingers to form

Question 39

What happens if you have too much SHH or an extra ZPA region?

Answer 39

polydactyly (multiple fingers) usually an extra pinky

Question 40

You have an extra pinky. What was there too much of during your development?

Answer 40

SHH secreted from the ZPA region

Question 41

You knocked out HOX9-10, what doesnt form,?

Answer 41

stylopod

Question 42

you knocked out HOX11, what doesnt form?

Answer 42

zeugopod

Question 43

You knocked out HOX12-13 what doesnt form

Answer 43

autopod

Question 44

What causes dorsal vs ventral differentiation?

Answer 44

Lmx1B activates Wnt7a that causes dorsal differentiation

Question 45

How do you form individual digits?

Answer 45

BMP signaling causes apoptosis in cells between digits

Question 46

You have decreased BMP expression and are now a good swimmer, why is this?

Answer 46

you have webbed fingers you freak (syndactyly)

Question 47

What is meromelia and what causes this?

Answer 47

absence of PART of a limb | late or partial loss of FGF signaling

Question 48

what is amelia? cause?

Answer 48

total loss of a limb | early or complete loss of FGF signaling

Question 49

What is polydactyly? cause?

Answer 49

``` extra digits (usually pinky) over-expression of SHH, lacks muscle tho ```

Question 50

What is syndactyly? types? cause of each?

Answer 50

fusion of digits cutaneous (lack of BMP) osseous (bones, fuse) BMP or HOXD13 mutation

Question 51

what is phacomalacia?

Answer 51

absence of long bones

Question 52

what causes phacomalacia that is no longer given to females of child bearing age?

Answer 52

thalodimide

Question 53

What does thalodimide do?

Answer 53

decreases FGF or HOX signaling

Question 54

what causes split hand/lobster claw/ectrodactyly?

Answer 54

decreased FGF8 expression in part of the AER but the rest remains so its split

Question 55

what can cause physical deformities?

Answer 55

adhesion between amnion and fetal structures, club foot and stuff