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Developmental Biology > Chapter 14 > Flashcards

Chapter 14 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

what are the three sections of a limb? describe them

A

stylopod = humerus / femur
zeugopod = radius & ulna / tibia & fibula
autopod = carpals / tarsals

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2
Q

in relation to the limb, describe the three axes (A/P, P/D, D/V)

A

anterior = thumb
posterior = pinky
proximal = inside (shoulder)
distal = outside (fingers)
dorsal = back of hand (knuckles)
ventral = palm of hand (pads)

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3
Q

what is a limb field?

A

area on the body before it becomes a limb

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4
Q

what are the three areas of the limb field? describe them

A

peribrachial = posterior side, under the arm
free limb = what sticks out
shoulder girdle = anterior side, above the arm

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5
Q

describe Harrisons experiment (1918)

A

did find it, move it, lose it experiments with mesodermal and ectodermal cells of the LIMB FIELD
- mesodermal = (L) stops limb growth
-ectodermal = (L) delayed limb growth bc it needs new skin to form before growing outwards

removed half of the limb field
- by removing any half of the limb field, it can still generate a fully functioning limb
- this occurs naturally thru parasites

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6
Q

describe how parasites alter the limb field in frogs

A

Parasites enter an animal and can break tissue into groups
- The body forms scar tissue around the parasite, preventing the cells in the limb field from talking to eachother
- Causes multiple limbs to form

*Indicator species -> if something is wrong with a frog, it can indicate something is wrong with everything in the environment

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7
Q

what hox gene is responsible for forming the forelimb bud?

A

HoxC6
- removing hox causes anteriorization
- adding RA causes posteriorization

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8
Q

describe Fgf8 in limb development

A

in the apical ectodermal ridge (AER)
- ECTODERMAL CELLS
- helps cells of the limb grow outwards (distally)

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9
Q

describe Fgf10 in limb development

A

in the mesodermal cells
- helps cells of the limb grow outwards (distally)

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10
Q

what do Tbx5 and Tbx4 transcription factors do in limb development?

A

Tbx5 = anteriorly, forelimb
Tbx4 = posteriorly, hindlimb

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11
Q

what is the progress zone (PZ)?

A

cells right under AER, mesenchymal cells

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12
Q

what are the two models for the progress zone? describe them

A

progress cell model
- the PZ is induced by Fgfs & as these PZ cells grow & divide, they induce specific structures to form
- not all cells remain w/in inducing range

early specification model
- cells decide what they will be prior to dividing

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13
Q

describes Sauder’s grafting experiment (1968)

A

AER removed = no limb
AER moved = additional limb
AER forelimb & hindlimb swapped = wing in place of leg
AER replaced w/ Fgf bead = normal limb
limb mesenchymal cells replaced = no limb
AER removed in middle of developing limb = shortened limb

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14
Q

what area is Shh located in the limb? what does it specify in limbs?

A

zone of polarizing activity (ZPA)
- specifies posterior fates

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15
Q

describe the Riddle & Tabin experiment

A

implanted cells containing Shh-producing virus into anterior portion of limb bud
- produces mirror-image duplication (two pinkies)

determined that Shh & digit identity is dependent on time of exposure (digit 3) and amount of Shh expression (digit 2) –> POLARIZING ACTIVITY
- no Shh = thumb
- lots of Shh = pinky

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16
Q

what did Chiang do?

A

made mice w/o Shh
- led to dead mice with one eye (cyclopia)
- mice also had improper motor neurons, no A/P limb structure, no spinal column, missing ribs

17
Q

what did Ohuchi do? (1997)

A

replaced anterior part of AER w/ Fgf8 = full limb
replaced anterior part of AER w/ Fgf10 = missing some ant. structures of limb
- takes time for Fgf10 to induce Fgf8
- Fgf10 can maintain ZPA, but Fgf8 does it better

*same thing happened when replacing posterior portion!

18
Q

what molecule does Fgf10 and Fgf8 use to signal and induce eachother?

A

Wnt

19
Q

what other Fgf helps keep Fgf8 expressed?

A

Fgf4
- in the ectoderm

20
Q

what does Shh do to Fgf’s?

A

induces them!!
- keeps Fgf10 and Fgf8 active!

21
Q

what drives the proximal / distal axis in the limb?

A

Fgf8 (AER) drives distal growth

22
Q

what drives anterior / posterior axis in the limb?

A

Shh (ZPA) drives posterior fates

23
Q

what drives dorsal / ventral axis in the limb?

A

Wnt7a drives dorsal fates
- engrailed drives ventral fates (blocks Wnt7a)

24
Q

where is Wnt7a made?

A

dorsal ectoderm

25
Q

describe how webbing is formed

A
  1. Shh activates Gremlin
  2. Gremlin blocks BMPs from killing webbing cells
  3. webbing stays
26
Q

what induces the apoptosis of webbing cells? (interdigital zones)

A

BMPs

27
Q

what do BMPs do to Fgfs?

A

blocks Fgfs
- this occurs once the limb as done enough distal growth and Fgf’s have accumulated (makes the AER inactive)

28
Q

importance of dinosaur digits in limb development

A

hox genes show a dino-bird relationship
- both have 3 fingers / toes

29
Q

importance of dwarfism in limb development

A

no FgfR3 (receptor)
- chondrocytes differentiate instead of dividing

30
Q

importance of giants in limb development

A

no estrogen at the end of puberty to ‘cap off’ cartilage growth at the end of bones

31
Q

importance of bats in limb development

A

extra BMP-inhibitors in webbing

32
Q

what is the Lateral Plate mesoderm?

A

causes the limb bud in the amphibian embryo to bulge outward
- generate skeletal elements of the limb

33
Q

what do the different types of mesoderm make?
- intermediate
- chorda
- lateral plate
- paraxial

A

intermediate mesoderm = kidneys, gonads (PRONEPHRON)

chorda mesoderm = notochord

lateral plate mesoderm = splanchnic/circulatory system, somatic/body cavity, extra embryonic

paraxial mesoderm = head, somites (myotome/muscle, dermatome/dermis, sclerotome/cartilage, syndrome/tendons, endothelial cells/blood vessels)

Developmental Biology (17 decks)

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