Lecture 18

Question 1

The thickened area on the side of a salamander that gives rise to the limb is the?

Answer 1

Limb disc

Question 2

What is the peripheral region around the disc called that can give rise to the limb if the disc is removed?

Answer 2

Morphogenetic field (if removed no limb will form)

Question 3

Remove half the limb disc?

Answer 3

Remaining half will form a complete limb

Question 4

Vertically divide disc into 2 halves?

Answer 4

each half will form a normal limb

Question 5

fuse two discs together?

Answer 5

a single normal limb will form

Question 6

this gene initiates future forelimb

Answer 6

Tbx5*

Question 7

this gene initiates future hindlimb

Answer 7

Tbx4* and Pitx-1

Question 8

the three axes that define the vertebrate limb are?

Answer 8

dorsoventral, anterior-posterior, proximodistal

Question 9

what happens if you transplant a limb disc to the opposite side?

Answer 9

AP axis is reversed but not the DV axis.

Question 10

what happens if you rotate a limb disc 180 degrees?

Answer 10

Both the AP and the Dv axis will be reversed.

Question 11

Regarding asymmetry in the vertebrate limb, this gene determines the position of ZPA via its highest concentration and is induced by RA?

Answer 11

Hoxb8

Question 12

Regarding asymmetry in the vertebrate limb, this genes signal is produced by ZPA, maintains AER, induces expression of gremlin

Answer 12

sonic hedgehog

Question 13

Regarding asymmetry in the vertebrate limb, this gene inhibits the expression of shh in ANTERIOR part of limb bud

Answer 13

Gli-3

Question 14

the AER is located at the border between dorsal and ventral ectoderm, what does the dorsal ectoderm express? ventral?

Answer 14

radical fringe, engrailed-1 (En-1)

Question 15

cells in the distal limb bud express what genes?

Answer 15

Msx-1

Question 16

this gene is involved in pattern formation in the proximodistal limb axis?

Answer 16

Hoxd

Question 17

cartilage formation is restricted to the central core of the limb bud and produces what gene

Answer 17

Wnt-7a

Question 18

mesenchymal pre-cartilage condensations express what genes

Answer 18

Bmp-2 and Bmp-4

Question 19

this gene is necessary to maintain cartilage development in the formation of joints

Answer 19

BMP

Question 20

this gene inhibits BMP in the region of the future joint cavity

Answer 20

noggin

Question 21

in limb muscle development, proximal cells of the limb bud produce what

Answer 21

scatter factor

Question 22

in limb muscle development, premuscle cells in the somite express what

Answer 22

c-met (receptor for scatter factor)

Question 23

in limb muscle development, migrating pre-muscle cells express what gene

Answer 23

Pax-3 and N-cadherin

Question 24

differentiation of premuscle cells within the limb bud depend on what gene expressed by the limb bud ectoderm

Answer 24

Wnt-6

Question 25

in limb development, this gene is expressed by the CT associated with the muscle masses

Answer 25

Tcf-4

Question 26

major axons originate from the spinal cold during what week?

Answer 26

5

Question 27

axons originating from the medial locations in the spinal cord grow into the __ muscle mass

Answer 27

ventral

Question 28

axons originating from the lateral locations in the spinal cord grow into the __ muscle mass

Answer 28

dorsal

Question 29

if the forelimb rudiment of a salamander embryo is removed and the limb fails to develop what happens?

Answer 29

the nerves of the brachial plexus remain smaller (thinner)

Question 30

if an additional limb rudiment is transplanted to the flank of a salamander embryo what happens?

Answer 30

local nerves increase in thickness

Question 31

if the normal path of nerves is blocked what happens?

Answer 31

nerves will form loops around the mica plate and still rich hindlimb rudiments