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BIOL 309 > Early Vert Development (1) > Flashcards

Early Vert Development (1) Flashcards

1
Q

How can asymmetry be established with the egg? with the sperm?

A
  • egg may have asymmetrical distribution of factors (like tunicates)
  • sperm makes a point of contact with the egg which is an asymmetrical interaction
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2
Q

What is “Nature’s gift to science”?

A
  • C. elegans
  • Sydney Brenner
  • won Nobel prize in 2002 for his role in establishing C.elegans as a novel experimental model organism
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3
Q

What is an important asymmetric characteristic of the nematode?

A
  • 1st cleavage is asymmetric (one cell bigger than the other)
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4
Q

What experiment can be done to examine why the 1st cleavage in the nematode is asymmetric?

A
  • genetic screen
  • generate a bunch of genetic mutations
  • assay: look for loss of asymmetry at 2-cell stage
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5
Q

What exactly was done to examine the asymmetric 1st cleavage of nematodes?

A
  • mutagenize: fed chemical N-ethyl-N-nitrosourea in diet
  • breed the mutated worm with a normal worm
  • screen eggs and see how they divide after fertilization
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6
Q

What was found in the genetic screen to examine asymmetry of the 1st cleavae of nematodes?

A
  • several genes were identified and named Par
  • Par-1, Par-2, Par-3, all had loss of asymmetry
  • Par-4 had a reversal of asymmetry
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7
Q

What happens at fertilization in nematodes?

A
  • sperm entry demarkates the posterior region
  • Par3 is distributed evenly around the surface
  • Mex5 is evenly distributed in the cytoplasm
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8
Q

What happens after fertilization in nematodes?

A
  • cytoskeleton rearrangements occur (asters initiated by sperm centrioles)
  • pushes Mex5 away from sperm protonucleus
  • par2 begins to be distributed around surface by sperm entry however still more par3 than par2, creating asymmetry in cell size
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9
Q

What is one role of PAR proteins?

A
  • cellular localization of p-granules (ribonucleoprotein complexes) which are essential for germ cell specification
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10
Q

What has been identified for C. elegans?

A
  • cell lineage map

- know that there is a fixed number of somatic cells (1031)

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11
Q

Are par proteins conserved throughout evolution?

A
  • yes, seen in humans as well

- they are associated with establishing asymmetry with cytoskeleton but differ from c elegans

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12
Q

What is known about Par6?

A
  • adaptor protein

- interacts with other Par proteins and other proteins implicated in cytoskeletal rearrangement

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13
Q

What is known about Par6d?

A
  • in mouse

- knockout studies indicate it is not involved in germ cell formation

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14
Q

Why is the chick a good model organism?

A
  • easily manipulated in ovo because of large embryos that grow well outside of egg
  • similarly with frog
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15
Q

Why is the frog a good model organism?

A
  • eggs are synchronous and large
  • acquire 1000’s at a time
  • can dissect and graft
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16
Q

What kind of holoblastic cleavage do frogs undergo?

A
  • mesolecithal
  • displaced radial cleavage
  • the yolky material is divided into larger cells
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17
Q

How long does it take Xenopus laevis to cleavage to blastula stage?

A
  • about 7 hours at room temp

- quick

18
Q

What does the blastula of Xenopus laevis look like?

A
  • animal pole and vegetal pole
  • blastocoel (cavity) primarily in animal pole
  • looks similar to sea urchin at this stage
19
Q

What happens during gastrulation in Xenopus laevis?

A
  • bottle cells begin to crawl inwards forming the dorsal blastopore lip at a spot between the animal and vegetal poles
  • the blastocoel is diplaced and the archenteron (primitive gut) forms
  • 3 germ layers form
20
Q

What does the blastocoel become?

A
  • space that internal organs are surrounded by
21
Q

What is formed after neurulation?

A
  • notochord
  • neural tube
  • somite
22
Q

What is a neurula?

A
  • stage where embryo has brain, gill area, somites, tailbud, and stomodeum
23
Q

What is known about the thyroid hormone?

A
  • tri-iodothyrodine (T3)
  • all changes are triggered by thyroid hormone
  • can induce metamorphosis prematurely with T3
  • or if removed will remain tadpole forever
24
Q

What is different about Eleutherodactylus coqui?

A
  • “direct developers”
  • they have a tail that quickly regresses but they bypass the larval stage (tadpole)
  • they still undergo metamorphosis events and are dependent on thyroid hormone
  • novel cell type not normally found in frogs: “nutritional endoderm” that does not integrate into the embryo
25
Q

What are some general characteristics of Eleutherodactylus coqui?

A
  • large eggs ~3.5 mm

- small frogs

26
Q

What is different about cell division in Eleutherodactylus coqui?

A
  • cell division does not progress through yolky division
  • leaves whole yolk to exist as its own cell type
  • “nutritional endoderm”
27
Q

What is the selective pressures/driving force that might have led to direct development in coqui?

A
  • in amniotes: was move from water to terrestrial

- here: eggs laid in leaves

28
Q

What are some important parts of amniotes?

A
  • chorion: outer most membrane, gas exchange, gives rise to placenta in mammals
  • yolk sac: nutrition (birds/reptiles)
  • allantois: stores waste, gas exchange
  • amnion: secretes fluid
29
Q

In humans, what is the yolk sac used for?

A
  • not for nutrients

- immune cells are derived from yolk sac

30
Q

What does “mero” vs “holo” mean?

A
  • mero: partial cleavage

- holo: complete cleavage

31
Q

What kind of cleavage do fish, reptiles and birds undergo?

A
  • meroblastic cleavage, more specifically discoidal cleavage

- disc of cells on top of a yolk sac

32
Q

What is mammalian early cleavage like?

A
  • asynchronous cleavage at the 8 cell stage: cells divide ‘randomly’
  • “compaction”: lose rounded appearance (may play role in blastocoel formation)
  • mediated by changes in cell adhesion properties
33
Q

What is needed for cell adhesion?

A
  • diacyl glycerol and Ca++ –> PKC –> E-cadherin (cell junctions form)
34
Q

What controls compaction?

A
  • cadherin-dependent filopodia control preimplantation embryo compaction
35
Q

What do you see if you label mCherry or e-cadherin with GFP?

A
  • mCherry is membrane localized

- e-cadherin-GFP fusion protein is localized to cell junctions

36
Q

What is ICM?

A
  • inner cell mass
  • within blastocyst (but not previous stage morula)
  • gives rise to all three layers and yolk sac?
37
Q

When does the early stage of implantation occur?

A
  • mouse: 4 days after insemination
  • humans: 6-10 fays after ovulation
  • this means that early cleavage happens in the oviduct
38
Q

What are the two types of twinning?

A
  • dizygous (fraternal): 2 eggs are released and fertilized

- monozygous (maternal): one egg

39
Q

What characterizes early monozygous twinning?

A
  • ~25%: early separation leading to two separate embryos with their own inner cell mass
  • 2 chorions and 2 amnions
40
Q

What characterizes mid monozygous twinning?

A
    • ~60-70%: mid stage separation leading to one embryo with two inner cell masses that separate after the chorion is made
  • 1 chorion, 2 amnions
41
Q

What characterizes late monozygous twinning?

A
  • ~1-2%
  • embryo with one inner cell mass
  • embryos separate after chorion and amnion are made
  • 1 chorion and 1 amnion
42
Q

What is interesting about Dasypus novemcintus?

A
  • exhibit polyembryony: more than one embryo from one egg
  • always 4 embryos
  • share a single chorion and amnion
  • could be because each embryo takes up a lot of room with its shell and sharing a chorion and amnion allow for more offspring

BIOL 309 (14 decks)

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