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BIOL 309 > Early Vert Development (2) > Flashcards

Early Vert Development (2) Flashcards

1
Q

Why might test results say that a mother’s kids are not biologically hers even if they are?

A
  • mother could be a chimera (organism with two distinct cell types)
  • father had halotype 1 and 2
  • mother had halotype 3 and 4
  • the mother was derived from two eggs (3 and 4) and two sperm (1 and 2)
  • would typically give rise to fraternal twins but the eggs fused together
  • blood shows (1 and 3) but germline show (2 and 4) making all offspring (2 and 4)
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2
Q

What is an interesting case of twinning?

A
  • twins: a phenotypic male and a hermaphrodite
  • both shared 100% maternal alleles and 50% paternal alleles
  • this means they came from 1 egg and 2 sperm
  • pathenogenetic activation and cleavage of ovum then fertilization by two sperm or 3n egg that later split to 2 2n eggs
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3
Q

What study was conducted by Wilhelm Roux in the late 1800’s?

A
  • at the 2-cell stage, a hot needle was put into one cell to kill it
  • the cell died and no longer divided or developed, however the other cell continued to develop normally according to fate map
  • he believed this to be evidence towards mosaic development
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4
Q

What is a problem with Wilhelm Roux’s experiment?

A
  • he left the dead cell there and it could be having an effect on the living cell
  • if the dead cell is removed, you get a proper left and right axis forming
  • this provides evidence towards regulative development
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5
Q

What occurs if you split cells of mice at the 2-cell stage? At the 4-cell stage?

A
  • 2-cell: both cells can form a new embryo

- 4-cell: do not develop

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6
Q

What are the 3 cleavages of an amphibian embryo like?

A
  • mesolecithal: displace radial cleavage
  • first two cleavages are longitudinal
  • the third cleavage is equatorial (splitting the embryo so that the vegetal pole is larger)
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7
Q

How were frog late blastula fate maps formed?

A
  • generated using different dyes and markers
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8
Q

What are different layers where the blastopore will form?

A
  • chorda-mesoderm: notochord
  • head mesoderm: prechordal plate
  • pharyngeal endoderm: pharynx, tongue
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9
Q

What occurs during xenopus gastrulation?

A
  • bottle cells form and involution starts which forms the blastopore
  • cells crawl to the animal pole
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10
Q

Where do the axis lie in the gastrula of the xenopus?

A
  • blastopore is posterior (anus) opposite to pharyngeal endoderm that is now anterior
  • animal pole is dorsal and vegetal pole is ventral
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11
Q

How is ectoderm regionalized after gastrulation?

A
  • ventral: epidermis

- dorsal: neural plate

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12
Q

What occurs during neurulation?

A
  • neural plate stage to neural tube formation
  • neural groove forms and neural fold brings two sides together
  • brings us to the neurula stage
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13
Q

Does a fate map tell us what cells are at an earlier stage?

A
  • no, it tells us what they will become at the end point

- fate map is more of a guideline since cells can be influenced

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14
Q

What type of experiment can we do to see if a cell is specified and determined?

A
  • transplant to see if it changes

- separate cells from embryo and simply observe

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15
Q

What was the golden age of embryology?

A
  • early 1900’s
  • addressed fundamental questions underlying vertebrate body plan formation
  • “simple” questions and “simple” experiments
  • used large embryos and simple tools
  • amphibian embryos great for physical manipulation (big and heal fast)
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16
Q

What experiment did Hans Spemann do?

A
  • transplant neural tissue to epidermis during early gastrula stage: became epidermis (also happens if grown in isolation)
  • transplanted neural tissue to epidermis during late gastrula stage: became neural tissue
  • sometime between these two times the neural tissue fate became determined
17
Q

Following Hans Spemann experiment, what hypothesis might one come up with?

A
  • the underlying mesoderm has an instructive role in the formation of neural tissue
18
Q

What is Spemann/Mangold’s dorsal lip transplantation experiment?

A
  • remove the dorsal lip (fated to become dorsal mesoderm) from one embryo and transplant it to where epidermis is likely to form (opposite to dorsal lip)
  • results in embryo with a twinned axis
  • some cells of host changed their fate to become neural tissue
19
Q

What was the dorsal lip named?

A
  • Spemann’s organizer

- dorsal lip-axis inducing property

20
Q

What might the molecular mechanism underlying the Spemann Organizer be?

A
  • neural inducing factor

- without the neural inducing factor, the default state of the ectoderm is epidermis

21
Q

What conclusions can be made about the neural induction/ectoderm regionalization?

A
  • neural tissue is not determined until late gastrulation
  • default state of the ectoderm is skin (epidermis)
  • the dorsal lip of the blastopore is sufficient to induce secondary axis formation and neural tissue from ectoderm that had been fated to become epidermis
22
Q

What study did Nieuwkoop conduct in 1963?

A
  • he removed the animal cap and cultured it in isolation: this resulted in epidermis
  • he also removed the animal cap and dissociated it, then reaggregated it which resulted in neural tissue
23
Q

What molecular mechanism combines Nieuwkoop’s results and Spemann’s organizer experiments? **

A
  • if you add LiCl to an blastula, you get dorsalized embryos (only neural ectoderm, no epidermis)
  • used subtractive hybridization to identify mRNAs enriched in dorsal tissue
  • noggin
24
Q

Where is noggin mRNA localized?

A
  • dorsolateral region
  • prechordal mesoderm
  • notochord
25
Q

What does noggin do?

A
  • inhibits bone morphogenetic protein BMP signalling

- antagonist: prevents BMP from binding to receptors

26
Q

What is BMP?

A
  • member of the TGF-beta super family of signalling molecules
27
Q

What is the TGF-B pathway?

A
  • Activin or a TGF-B ligand attaches to receptors II and I
  • activates Smad
  • dimerization of Smad (Smad can now enter nucleus)
  • transcription occurs

BIOL 309 (14 decks)

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