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Development Exam 1 Flashcards

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1
Q

What is epistasis?

A

A functional interaction occurring between two or more genes, usually required for normal developmental outcome. It reveals the existence of genetic pathways and networks, which are usually composed of simple interactions.

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2
Q

Describe a positive interaction in a linear dependent pathway.

A

A→B→C→FSE. So gene A is required for gene B, which is required for gene C to function properly. The accumulation of C defines the role/specificity of a specific developmental tissue

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3
Q

Describe a negative interaction in a linear dependent pathway.

A

A-|| B-|| C→FSE. The function of gene A is to suppress gene B, which functions to suppress gene C. This pattern results in the genes alternating ON, OFF as you go down the pathway.

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4
Q

In the negative linear dependent pathway A-|| B-|| C→FSE, what does the loss of function of A cause?

A

If A does not function, then B will be on instead of off. B will suppress C, leading to a loss of C activity. Thus, the resulting phenotype of a LOF mutation of A would be due to a lack of gene functioning of C.

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5
Q

Describe network interactions.

A

If a gene influences more than one pathway, then a network of gene pathways occurs. This results in parallel pathways leading to two different FSE’s

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6
Q

Why is mRNA more useful than DNA for studying gene functions and specific developmental roles in individual cells?

A

All cells have the same DNA, so the differences must occur at a later stage. If mRNA for a certain gene accumulates within a specific cell, it suggests that the gene function is important in that cell.

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7
Q

What are problems with looking at mRNA for studying developmental roles of genes?

A

1) mRNA does not always mean that the corresponding proteins are being expressed 2) There could be tonic levels of mRNA expression that does not mean that the gene function is required.

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8
Q

What are problems with looking at proteins for studying developmental roles of genes?

A

1) They do not act alone. The presence of protein doesn’t always lead directly to function. 2) alternative splicing can lead to some cells having dysfunctional protein

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9
Q

Describe the method of screening via mutagenesis.

A

Induce a new mutation using a mutagen (Xrays, gamma rays … etc.) and then establish lines via crossing. The lines are then tested for mutations. This is a very tedious process (i.e. 7 mutants in a million lines)

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10
Q

What is segregation analysis?

A

A method of determining whether a mutation is dominant or recessive. Cross the mutant with the wild type. Helps to see whether mutation is loss of function or gain of function.

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11
Q

What does the network look like in situations with genetic redundancy?

A

Parallel regions within the network join back together to lead to one pathway causing a specific FSE. Mutations in one, or the other, parallel pathways will not completely eliminate the FSE.

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12
Q

How does Dr. P define developmental fate?

A

The establishment/programming of an intermediate or final functional role played by a cell or it’s daughter cells in an organism. Fate is generally established in cells early in development, and often has no obvious immediate effect on cell morphology.

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13
Q

What are the two different theories addressing the question of where fates come from?

A

Epigenesis Theory and Preformation Theory

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14
Q

What is the Epigenesis theory?

A

New structures arise by progressing through a number of different stages of informational and histological complexity. This is a progressive process suggesting a slow programming of cells over time.

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15
Q

What is preformation theory?

A

All structures exist from the very beginning and just become larger over time. A subtheory, the theory of the homunculus, suggested that little human embryos existed in the head of every sperm.

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16
Q

Describe the fates available within the zygote.

A

The zygote is 1 totipotent cell which contains all possible developmental fates.

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17
Q

What is the definition of development?

A

Coordinated cell division and adoption of distinct developmental fates by daughter cells

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18
Q

What is specification?

A

Assignment of a fate to a cell by regulation

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19
Q

What is determination?

A

Loss of ability for fate reassignment

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20
Q

What is differentiation?

A

The construction of appropriate tissue, organ, limb… etc.

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21
Q

What is pluripotent?

A

A subset of fates available to a cell in relation to the set of fates available to a totipotent cell

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22
Q

After a specification event, are cells totipotent or pluripotent?

A

A specification event divides up the totipotent fates into subsets of pluripotent fates.

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23
Q

In a simple animal development model, what does the vegetal pole develop into?

A

The yolk sac

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24
Q

In a simple animal development model, what does the animal pole develop into?

A

The head, thorax and tail.

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25
What role does gene expression play in fate specification?
Gene expression determines fate specification. In the head, head genes must be on. In the tail, head genes must be off.
26
What is the mosaic model of specification?
Says that fates are waiting to be partitioned by cellular divisions. Specific determinants in the one-celled zygote that are not divided equally between the daughter cells
27
What was Roux's experiment? Why was it flawed?
He destroyed one cell of the two-cell embryo and then 1/2 of a from embryo was formed. It was flawed because he killed 1/2 the embryo, but did not remove it. The surface receptors of the dead cell were still there, so the healthy cell was able to develop normally. This lead to the incorrect conclusion that vertebrate embryos are highly mosaic.
28
What is the concept of mosaic regulators?
The original cell has discrete compartmentalized information called "Weismann's nuclear determinants." These nuclear regulators are separated via cleavages to form terminally functional cells.
29
What is regulative specification?
Interactions between parts of the developing embryo that can result in different tissues forming. Development is about cellular negotion, not partitioning of pre-existing determinants.
30
What was Driesch's experiment?
He demonstrated regulative specification by separating the two cell embryo and allowing only one cell to develop. This led to a small, but otherwise normal, larva.
31
How can you determine whether an individual cell contains cytoplasmic determinants?
If ablation of the cell leads to a change in the cell fate, then the structure may contain cytoplasmic determinants. This shows that certain cells in certain developmental stages display mosaic properties.
32
What are the key characteristics of embryogenesis?
(1) Cleavage division (2) Pattern Formation (3) Morphogenesis (4) Cell Differentiation (5)Growth
33
What is a Xenopus?
A claw toed frog that is often used to study vertebrate development.
34
Why is Xenopus a convenient model organism for studying development?
The development is relatively short, only taking about 4 hours. You can test early changes in pattern formation in the first hours of development. It is easy to stimulate ovulation and to get sperm easily.
35
How does fertilization help determine the developmental axes?
Sperm always enter at the animal pole, which appears dark. The opposite point on the egg is called the Nieuwkoop center. This center becomes the dorsal pole. This axis is the first developmental axis of the frog.
36
How are cells from the animal pole and vegetal pole structurally different?
Animal pole daughter cells are smaller than vegetal pole daughter cells.
37
Describe the cortical rotation following fertilization.
mRNA originally localized in the vegetal pole rotates towards the dorsal pole to align with the D/V axes determined by the fertilization location. This mRNA asymmetry occurs right from oogenesis. By concentrating it at the vegetal pole, the distance it will need to move to get to the dorsal pole is minimized.
38
What is the Nieuwkoop center?
A unique regional cytoplasmic area in early development that is found at the dorsal pole. It acts as a region capable of autonomously signalling the organization of dorsal identity
39
What is a fate map?
a map that tells us what cells at a given embryonic stage should become in the future
40
How can fate maps be produced?
Individual cells within the blastula can be marked with inert dyes. Then you can look later in development and see where the labeled cells end up.
41
What is inductive interaction?
The process by which one group of cells changes the fate of another group of cells.
42
What forms can inductive interactions occur by?
(1) Secreted diffusible molecules (2) Surface molecule receptors (3) Gap junctions (4) Cell-cell adhesion factors with signaling
43
What is competence?
The state of being able to respond to inductive signals due to the presence of receptor or transcription factor.
44
What happens if the ventral half of a four cell Xenopus embryo is removed from the ventral half, and then both halves are allowed to develop?
The ventral half, which lacks the Nieuwkoop center, develops into a ventralized embryo composed of belly and skin. The dorsal half develops into a dorsalized embryo that has a proper head axis developed, but has very poor ventral development. This shows the importance of the Nieuwkoop center.
45
How can a "twinned" (two headed) embryo be produced experimentally?
Removing the Nieuwkoop center from a donor embryo and transplanting it into an ectopic region in a recipient embryo leads to two dorsal axes being formed. The embryo will then develop with two heads.
46
What role does Wnt/Wingless play at the Nieuwkoop center and Spemann Organizer?
It gives positional information by regulating transcription. When Wnt is present, receptors are able to lock up the complex that degrades beta-catenin. Without beta-cat degradation, it begins to accumulate and can enter the nucleus, which leads to gene activation and transcription.
47
What happens if beta-catenin is injected into an ectopic region of the blastula?
Twinned embryos develop because the beta-catenin triggers transcription of the genes that lead to head formation.
48
What is the Spemann Organizer?
The organizer for gastrulation that is found at the dorsal lip of the blastopore. It is induced by the vegetal Nieuwkoop center
49
What factor establishes early fate signals in the blastula?
TGF Beta signal gradients and antagonism between BMP4 and Chordin
50
What role do threshold concentrations play in early fate specification?
The range of concentrations of morphogens from high at the source to low at the sink cause different fates.
51
Describe the BMP and TGF beta gradients and their effect.
BMP leads to activation of Smad1,5 and 8 which has a ventralizing effect. TGF beta activates Smad2 and 3 which has a dorsalizing effect
52
Does each regulator molecule play the same role in different regions of the blastula?
No. Differential patterns of accumulation allow the same regulator to play different roles in different regions.
53
Describe the general process of amphibian gastrulation.
Mesoderm and endoderm move inside, ectoderm stays outside. This process establishes an outside and an inside.
54
What are the three germ layers?
Ectoderm, Mesoderm, and Endoderm
55
What could be considered the fourth germ layer?
The neural crest cells, which are migrating ectoderm.
56
From what germ layer does the notochord form?
The mesoderm
57
What structures form from the ectoderm?
Epidermis, brain and nervous system
58
What structures form from the mesoderm?
Notochord, Somites (Muscles, Gonads...)
59
What structures form from the endoderm?
Inner lining of GI and respiratory tracts, Glands
60
What process begins when gastrulation ends?
Neurulation, the initiation of the formation of the central nervous system.
61
What happens in neurulation?
The dorsal midline mesoderm underlying the ectoderm produces protein signals that stimulate the formation of neural plate ectoderm. The ectoderm above the notochord folds to form the neural tube, which later develops into the spinal cord and brain.
62
What is the notochord?
A rod-like structure that runs from the head to the tail and lies beneath the nervous system
63
What are the general similarities and differences between vertebrate eggs and embryos?
The egg size varies by several orders of magnitude, but the embryos all have very similar structures.
64
What are the common structures found in all vertebrate fate maps?
blastopore, dorsal organizer, lateral mesoderm, endoderm, ectoderm
65
Why is the yolk of the chicken egg so big?
The yolk cell provides all nutrition to the developing embryo because the chick development occurs completely disconnected from the mother
66
What are the major regions of the chick embryo after cleavage occurs?
area opaca, area pellucida, and the posterior marginal zone
67
What is significant about the chick posterior marginal zone?
It is the first axis pole in the developing chick. The appearance of the PMZ indicates the beginning of gastrulation.
68
What is the primitive streak?
The structure that forms along the first axis of the chick. Hensen's node migrates anteriorly as the primitive streak forms. It reaches the most anterior part, and then initiates development as it migrates back towards the tale.
69
Which region of the embryo is the oldest?
The head is the oldest fate, it forms first when Hensan's node begins to migrate posteriorly.
70
What does the chick embryo form from?
The chick embryo forms from the cleavage divisions that occur on top of the yolk cell
71
What is the blastoderm?
The packed disk of cells that forms on top of the yolk cell. Analogous to the blastula.
72
What region produces the dorsal center in a chick embryo?
The posterior marginal zone.
73
What does "Going mesenchymal" mean?
Endoblast cells are patterned to become mesoderm and endoderm from the primitive streak in the developing chick embryo
74
Describe the gastrulation process of chicks
It involves migration of the mesenchyme, NOT folding of cell layers like in other vertebrates. The endoderm and mesoderm are formed by cells migrating internally through the primitive streak.
75
What is Hensen's node?
The inductive center that organizes the A/P axis. It travels down the primitive streak differentiating tissues behind it.
76
What signaling molecules are associated with the formation of the posterior marginal zone in chick embryos?
VG1, Wnt, and beta catenin
77
Describe the autofeedback loop that occurs during the formation of the primitive streak in chick embryo development.
VG1/Wnt signal the beginning of the formation of the primitive streak in the posterior marginal zone. Nodal function begins to develop in the region adjacent (in future anterior direction) of the PMZ. Once FGF begins to interact with the nodal segment, the nodal segment begins an autofeedback loop that stimulates the next cell anterior to the PMZ. This interaction causes the node to begin to move in the anterior direction.
78
What is the function of chordin?
Chordin is a dorsalizing molecule that binds with BMP4 (a ventralizing molecule) and prevents it from binding to its receptor
79
What embryological feature follows the node as it migrates from anterior to posterior?
The neural tube
80
What is the process of turning in mouse development?
The shift in position of the embryo from a filleted structure to sealing the ventral surface and closing off the innards. It turns itself so that it is surrounded entirely by amnion, leaving the yolk behind. This process takes place after gastrulation and before organogenesis (~9.5 days after fertilization)
81
What is the Zona Pellucida?
The 'jelly coat' in which early divisions occur before the blastocyst is formed.
82
What is compaction?
After the 8-cell stage, water is lost, and you can no longer easily distinguish the tightly packed cells within the tissue. The blastocyst develops from the compacted morula.
83
What are the four main components of the mature blastocyst?
Zona Pelucida, Inner cell mass, Trophectoderm, and blastocele
84
What is the inner cell mass?
The area from which the embryo will form.
85
What is the trophectoderm?
The blastocyst region that will become the placenta
86
What is the blastocele?
The fluid filled void under the inner cell mass of the blastocyst
87
What does the epiblast produce?
primitive ectoderm
88
What does the hypoblast produce?
primitive endoderm
89
What structure forms all real ectoderm, endoderm and mesoderm?
The epiblast forms all of the germ layers during gastrulation
90
Describe the gastrulation of zebrafish.
Once the blastoderm has spread over the 'animal pole' half, involution begins to bring ventral and dorsal cells inward.
91
What was the original theory of the role that mesoderm played in CNS formation?
Most thought that the mesoderm directly induced the CNS
92
What is the modern theory for the role that mesoderm plays in CNS formation?
Mesoderm suppresses formation of the epidermis , and is thus permissive to neurogenesis
93
What is the default ectodermal fate? How was this discovered?
Neurons form by default. This was discovered through an experiment that took away all signals acting on the ectoderm. Without any signaling or regulation, the cells formed into neurons. This means that neurons are formed by suppressing the skin program.
94
What are the three major structures produced from the ectoderm?
(1) Outer ectoderm: skin and associated structures (2)Neural crest: nervous tissue, facial bones, cranial vault, jaw (3) Neural tube: CNS
95
Where is the brain formation induced and patterned?
It is induced and patterned outside and then it is "sucked" inside
96
In the early gastrula, if presumptive neural ectoderm is transplanted to the ventral ectoderm, what happens?
The ectoderm will form properly because the gastrulation has not yet occurred. The cells at this stage are naive to their future roles.
97
After gastrulation, if presumptive neural ectoderm is transplanted to the ventral ectoderm, what happens?
Because the underlying notochord has educated the ectoderm of its future roles, the transplantation will cause for neural ectoderm to form in two places: the correct place and in the ventral side.
98
BMP4 + Xwnt8 induces what?
Ectoderm to change to Epidermis
99
Noggin + Chordin + Follistatin + cerb induces what?
it blocks BMP and Xwnt8 causing ectoderm to develop into brain
100
Wnt + FGF + RA induces what?
Neural ectoderm develops into spinal cord
101
What chemical is expressed as forebrain and midbrain are specified from neurectoderm?
OTX 2 is found in forebrain and midbrain specification in the zebra fish
102
What chemical is expressed as hindbrain and cord are specified from neurectoderm?
Retinoic acid is required for patterning the hindbrain
103
Describe the expression domains of OTX2 and RaldH2 in zebrafish
The OTX2 and RaldH2 domains are complementary and provide regional identities to cells whose daughters will have specific roles in the embryo
104
What molecule determines the presomitic mesoderm positional values?
Retinoic acid gradient determines the positional values of somites
105
What happens if a section of pre-somitic mesoderm is inverted?
The somites will form in reverse order within that section
106
What happens if a presomitic region is transplanted to a different region on a younger embryo?
The embryo will differentiate according to the donation site, not the graft site. For example, rib formation can be induced within the cervical vertebrae. This shows that the presomitic mesoderm is specified and determined.
107
What are HOX genes?
Homeodomain transcription factors that regulate the A/P specification of dorsal ectoderm and mesoderm. Hox proteins determine the type of segment structures (e.g. legs, antennae, and wings in fruit flies or the different vertebrate ribs in humans) that will form on a given segment.

Development (2 decks)

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