Limb development

Question 1

What are the origins of the limb development?

Answer 1

Outgrowth from embryo (Limb buds)
Mesoderm derived cells covered in epirdermis
Limb bud cells must recieve positional information resulting in positional value - THIS MAY BE PROVIDED BY MORPHOGEN GRADIENT

Question 2

what are the three regions of a limb?

Answer 2

Stylopod - upper part
Zeugopod - lower
Autopod - hand/foot

Question 3

What forms skeletal elements + connective tissue in limb formation?

Answer 3

Condensation limb mesenchyme

Question 4

What is muscle derived from?

Answer 4

Migrating cells from somites

Question 5

What determines the sites where limbs form?

Answer 5

TBX3 - the gene encoding Tbx3 is expressed at sites where limb buds form.
MUTATION - unliateral ectopic expressions of Tbx3 results in shift of limb position - resembles Sprengler anomaly

HOX GENES - vertebrates have hox gene clusters. expresserd in overlapping domains along anteroposterior axis of body. Example: in chicken embryo forelimb buds form immediately anterior to boundary of hoxc6 expression.

Question 6

What do hoxc6 and hoxc8 help to spcify development of?

Answer 6

thoracic - rib vertebrae.
example: in python expression domains of hoxc6 and hoxc8 are extended, eliminating forelimb bud - leading to rib formation on almost all vertebrae

Question 7

What are the AER and ZPA in relation to key signalling centres?

Answer 7

AER AND ZPA are key signalling centres
AER produces fibroblast growth factors (FGF’s)
ZPA produces SONIC!
AER needed for development of limb along proximodistal axis.

Question 8

Describe the progress zone model of limb development

Answer 8

Proposes that cells become specifiedas they exit progress zone
Proposes that specification varies depending on the amount of time spent in the progress zone.
proposes AER produces signals which maintain proliferation of cells in progress zone, and prevents them from differentiating

Question 9

Describe the two signal model in limb development

Answer 9

proposes retinoic acid from flank causes cells to be specified as stylopod
fgfs specify cells as autopod
cells out of range of either become zeugopod.
HOWEVER problem with theory is that transgenic mice lacking rdh10 gene make no retinoic acid in