Devo Lect 18 - Vertebrate Limb Flashcards Preview

Developmental bio > Devo Lect 18 - Vertebrate Limb > Flashcards

Flashcards in Devo Lect 18 - Vertebrate Limb Deck (17):
2

Asymmetry

Ant, post, proximal, distal parts of limbs very different

3

Comparing limbs across species

Same bones and organization, just different proportions based on function

4

Disorders in limb development

Polydactyly: extra digits; Syndactyly: fused digits; Polymelia: extra limbs; phocomelia: shortened limbs

5

Formation of limb bud

Mesenchyme cells migrate to limb field, proliferate, form AER on limb buds (essential); limbs formed by stage 23 (day 56)

6

AER

Apical ectodermal ridge; forms on top of the the limb bud mesenchyme cells. Needed for development of distal limb structures. Removal results in truncated limb, length depends on when removed

7

FGF-10 and FGF-8

Mesenchyme cells secrete FGF-10 which cause epithelium to form AER; AER secretes FGF-8 to maintain mesenchyme cells just underneath; Mesoderm-ectoderm interactoin

8

Saunders’ experiment (Fig 16.8)

Formation of limb axis - proximal-distal; mesoderm proliferation under AER; removal and addition of AER and mesoderm; AER allows proliferation, induced mesoderm tells the limb what to be, FGF responsible for signaling

9

Figure 16.8

Summarize this

10

Anterior/Posterior formation of limb bud

Defined before limb bud present; smal block of mesoderm tissue = ZPA; transplanting it caused posterior development of digits on both sides of limb

11

ZPA

Zone of polarizing activity; determines ant/post axis; releases Shh, forms a gradient (high = post., low = ant.)

12

Shh

Development of vertebrae; Somite to bone; from Hensen’s node to determine R/L symmetry; controls polarity of limbs

13

Role of Hox genes in limb

TFs, genes arranged in series on chromosome; expressed in order along limb axis; knockouts result in lack of only one structure (ie Hox 11 -/- lack forearm, but the rest is normal)

14

HoxA/D KO experiments

Stops shortly after bud; if they then add HoxD, hand developed on there

15

Hox genes and snakes

Expression is different; Hox genes expressed in certain regions in chick embryo, but the boundaries of those genes in snakes is different; some snakes form vestigial limbs, but lack Shh

16

Hox genes in fins vs mammals

Early Hox expression similar, later it is much higher in AER in mammal; important step in evolution

17

Cell death zones

apoptosis, esp. in the digits; triggered by BMPs, although these are expressed in ducks and chickens; BMPs are blocked by gremlin in the duck

18

Gremlin experiment

Put Gremlin beads in the webbing of developing chick embryo, apoptosis did not occur, proves gremlin is an antagonist of BMP