Midterm 1 Flashcards
(115 cards)
1
Q
Stages of (frog) Development
A
- Gametogenesis
- Fertilization
- Cleavage
- Gastrulation
- Organogenesis
- Larval Stages
- Maturity
2
Q
Blastula forms during …
A
Cleavage
3
Q
Blastocoel, blastopore, germ layers and body topology form during …
A
Gastrulation
4
Q
Oocyte Content and Cleavage
A
- Oocyte size and yolk content depends on the needs of the growing embryo
- Cleavage pattern is affected by oocyte structure (yoke content)
5
Q
T or F: amphibians and amniotes show differences in gastrulation and embryo patterning
A
T
6
Q
Sperm vs. Oocytes
A
Sperm: divide into 4 haploid cells
Oocytes: uneven division of cytoplasm leading to one, large haploid cell that usually has all cytoplasm/material in it
Takeaway: Meiosis between sperm cells and oocytes is different
7
Q
Why are frog embryos a good model for studying development?
A
- Easy to understand in 3D
- Produce a lot of eggs
- Larger eggs (relatively)
8
Q
Blastula
A
- Forms during fertilization
- Where germ cells are located
9
Q
Zygote
A
A fertilized egg, containing a full set of chromosomes from each parent
10
Q
Blastomere
A
Cell that results from division of zygote
11
Q
Cell divisions are ___________ (complete) but unequal
A
holoblastic
This means the cytoplasm is cut completely
12
Q
What does the vegetal pole contain? Explain what it is and what it does.
A
The yolk: mixture of proteins, lipids, carbs, and vitamins that support embryonic growth. Inhibits cell division.
13
Q
T or F: The animal pole divides faster than the vegetal pole, so there are more cells at the animal pole.
A
T
14
Q
Where is the blastocoel and what does it look like?
A
The blastocoel forms inside the blastula (which forms from the morula), and it is like a liquid-filled center
15
Q
The 12th Division
A
Up until the 12th division: Embryo is running on maternally derived RNAs. Zygotic genes are not active yet.
After the 12th division: Zygotic genes transcribed and embryo runs on its own genes. This leads to individual variation.
Mechanism for activating zygotic gene transcription involve epigenetic changes that affect chromatin structure.
16
Q
Important Purposes of Gastrulation. Generally, what happens?
A
- Layers
- Planes of symmetry
Cells migrate into interior of developing embryo in a process called involution. From this, topological differences emerge.
17
Q
Explain topologically inside vs. topologically outside
A
Topologically inside is when you cannot come in contact with something from the outside
18
Q
Phylogenetic Classification: Protostomes vs. Deuterostomes
.. and then Amniotes
A
Protostomes: mouth first
Deuterostomes: mouth second
(Division based on what the first hole gives rise to in gastrulation)
Amniotes have an amniotic sac (i.e., chickens, mice, and humans
19
Q
Amniotes and their common extra-embryonic membranes
A
Food: Yolk
Waste management: Allantois
Blanket: Amniotic cavity
20
Q
Chicken vs. Human embryo
A
In humans, the embryo gets nutrients from the mother, replacing the function of the allantois and yolk (even though they are still present)
21
Q
Amniotes (mammals and birds): similar and different patterns
A
Different early cleavage patterns but similar gastrulation and embryo patterning and overall embryo structure
22
Q
Where is CNS derived from? Where is PNS derived from?
A
CNS: ectoderm via neurulation (forms neural tube)
PNS: neural crest cells and placodes (ectodermal structures)
23
Q
Match the animal to the cleavage pattern.
Mammal
Chick
Holoblastic
Meroblastic
A
Mammal: holoblastic (complete cleavage)
Chick: meroblastic (incomplete cleavage)
24
Q
Meroblastic Cleavage
A
Blastomeres are still partially connected (incomplete cleavage)
25
Zona Pellucida
- Tough ECM shell that covers early embryo
- Prevents embryo from implanting ectopically
- Blastula digests and "hatches" from zona pellucida, usually in uterus
26
Ectoderm, Mesoderm, Endoderm and what they give rise to
Ectoderm: nervous system, epidermis, lining of mouth and anus
Mesoderm: dermis, muscle, vasculature, skeleton, gonads, kidneys
Endoderm: stomach, intestine, bladder, lungs
27
Induction
Influencing cell fate through cell-cell interaction
28
In what direction does chick neurulation proceed and what end develops earlier?
Anterior to posterior
The anterior end develops earlier
29
Neural tube closure in mammals
- Tube "zips up" along the middle from anterior to posterior
- Neuropores are holes on either end of the tube filled with amniotic fluid and are eventually closed and form a separate compartment
30
T or F: The brain cannot develop in the presence of amniotic fluid
T
31
Craniorachischisis
- Open brain and spinal cord
- Incompatible with life
- Soft tissue doesn't develop properly - Brain degenerates
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Anencephaly
- Failed closure of anterior neuropore
- Brain protrudes from cranium and then degenerates
- Inside skull
33
Spina Bifida
- Failed closure of posterior neuropore
- Can be covered or exposed
- Can range from mild to severe
34
Neural tube defects have been related to ___________ deficiencies.
Folate (Vitamin B9)
35
Match the neuron to the horn.
Sensory neurons
Motor neurons
Dorsal horn
Ventral horn
Sensory neurons: dorsal horn
Motor neurons: ventral horn
36
Neural tube gives rise to
CNS (brain, spinal cord) and retina
37
Neural crest gives rise to
PNS (sensory and autonomic neurons, Schwann cells)
38
Ectodermal placodes give rise to
Special sensory structures (olfactory epithelium, vestibular and auditory inner ear)
39
Placode
Specialized portions of ectoderm that thicken and differentiate into neural and non-neural structures (stay in epithelium). Forms just outside developing neural plate
40
Olfactory system/placodes
- Form along with neural plate
- Derived from cells that reside at edge of neural tube from same tissue as CNS
41
Development of olfactory placode
Curls in/invaginates and then becomes complex (epithelium filled with neurons)
42
When does neural cell fate specification happen around?
Fertilization
43
Hans Spemann (1920s) Two-Cell Blastomere Separation
- Zygote has patch of cytoplasm called gray crescent
- Separated blastomeres containing gray crescent produce normal embryos BUT separated blastomeres without gray crescent led to abnormalities: no dorsal tissues, disorganized ventral belly piece
- So, it was concluded that cells from the gray crescent form the dorsal lip of the blastopore
44
Spemann and Mangold (1920s) Dorsal Blastopore Transplantation
- Transplanted dorsal lip of one newt embryo into ventral surface of another (donor was pigmented for detection and newt embryo was albino)
- Second site of gastrulation and second body axis induced
- Dorsal lip transplant becomes mesodermal structure called notochord
- You get conjoined twins with their own nervous systems, d/v axes, and a/p axes
45
What is "The Organizer?"
Dorsal lip of blastopore
46
The Organizer: has dorsal lip cells that...
1. Initiate gastrulation
2. Dorsalize central tissues (neural induction: ventral ectoderm to neural ectoderm, ventral mesoderm to dorsal mesoderm/somites)
3. Define complete body axes (d/v, a/p)
47
Induction
Process by which embryonic cells in one part of the embryo influence the developmental fate of surrounding cells
Plays crucial role in development of neural ectoderm, eyes/lens, heart
48
What organizes The Organizer?
The oocyte
- Gray crescent is positioned opposite the point of sperm entry through rotation of oocyte cytoplasm
49
B-catenin
Transcription factor that initiates dorsal fate
Stabilized in dorsal embryo by protein complex
Acts as dorsal signal (dorsal lip -> notochord -> mesoderm)
50
Nodal
Protein secreted from vegetal cells that induces mesoderm to form in neighboring cells by interacting with cells just above them
51
B-catenin and nodal signaling overlap in ______________
The Organizer
52
What is the blastocoel doing when nodal is at work?
Preventing nodal from affecting the ectoderm
53
Cells become what before gastrulation?
Mesoderm
Dorsal mesoderm is where gastrulation begins
54
What about changes in ectodermal cell fate?
The newly formed dorsal mesoderm may interact with the ectoderm, leading it to form the nervous system
55
Spemann (1918) Ectodermal Transplant in Early vs. Late Gastrula
EARLY:
1. Remove ectoderm (that would become nervous system)
2. Transplant to region that would become ventral epidermis
Result: transplanted ectoderm became epidermis, so dorsal ectoderm takes on identity of final transplant location
LATE:
^ Same procedure as above
Result: transplanted ectoderm becomes nervous system, so dorsal ectoderm restricted to nervous system during gastrulation
56
Ectoderm and its induction
Ectoderm no induction = epidermis
Ectoderm induction = neural
Ectoderm single cells = neural
Takeaway: Neural cell fate is the default
57
BMP4
- Produced by ectodermal cells onto each other
- Acts on TGFB receptors to inhibit neural differentiation/neural fate (they become epidermis)
58
noggin, follistatin, and chordin
- BMP inhibitors released by newly formed dorsal mesoderm
- Disrupt BMP4 signaling in overlying ectoderm, which becomes neural plate
59
Prosencephalon and its vesicles
Forebrain (most anterior)
1. Telencephalon
2. Diencephalon
60
Mesencephalon and its vesicles
Midbrain
1. Mesencephalon
61
Rhombencephalon and its vesicles
Hindbrain (most posterior)
1. Metencephalon
2. Myelencephalon
62
T or F: Drosophila's body plan is defined in the embryo (early on in development)
T
63
AP patterning in flies: A? P?
A: bicoid
P: nanos
These are RNAs unequally deposited into the oocyte by the mother
64
Bicoid and nanos
- Locally translated after fertilization
- Are morphogens that form opposing concentration gradients
65
Morphogen
Protein that is non-uniformly distributed and acts in a concentration-dependent manner to determine cell identity
65
Bicoid LOF vs. GOF
LOF: two tails
GOF: two heads
66
Bicoid and nanos and the subsequent cascade
Bicoid and nanos set up a cascade of TFs that further divides the embryo into increasingly smaller segments with well-defined borders
67
The types of genes in the bicoid-nanos cascade
Maternal polarity
Gap genes
Pair-rule genes
Segmented polarity genes
Homeotic/Hox genes
68
Hox genes
- Encode TFs
- Turn on/off other genes to define identity of fly segments
- Found in clustered arrays
69
Colinearity
Spatial expression matches genomic location. Anterior-posterior follows 3'-5' arrangement of genes in cluster
70
Specific Hox genes and what they do
Ubx: in 3rd thoracic segment, deletion converts T3 to T2 and duplication of T2 makes 2 sets of wings
Antp: expressed in T2 and T3
abd-A: not expressed in T2 nor T3
71
Hox Code Hypothesis
The identity of a segment can be determined by a unique combination of TFs that are expressed in that cell
72
T or F: Effects of gene mutations are typically more subtle than in flies
T
73
T or F: Hox genes are duplicated in multiple clusters in mammals
T
74
Homolog vs. Paralog vs. Ortholog
Homolog: gene that looks like another gene (related to common ancestor gene)
Paralog: Homologs in same organism
Ortholog: Homologue in another species
75
A/P patterning in mammals?
Wnt (high in posterior end)
Early gradient of Wnt parses ectoderm into different domains
76
Wnt-B catenin pathway
1. Wnt activates frizzled and LRP5/6
2. Protein complex with B-catenin is recruited to receptor complex
3. B-catenin released and translocated to nucleus
4. B-catenin binds to TCF to form activating TF
Ultimately: regulates gene expression.
77
Segmentation of the rhombencephalon (hindbrain)
8 rhombomeres each giving ice to unique set of neurons and brain regions (unique combination Hox genes). Transient segments in developing rhombencephalon
78
What happens when you delete a Hox gene in rhombomere segments?
Facial motor neurons (normal) to trigeminal-like motor neurons
79
D/V patterning
Also determined by morphogens (gradient of identity)
Recall: dorsal sensory, ventral motor
80
Notochord
- Transient structure made of axial mesoderm (chordamesoderm), so presence defines chordates
- Induces ectoderm to become neural tube
- Morphogen source of Sonic Hedgehog protein to specify ventral neural tube
- Forms central part of invertebrate discs of spinal column in adult vertebrates
81
Morphogens and their 3 characteristics
1. Emanate from a source
2. Diffuse to form non-uniform distribution
3. Induce concentration-specific changes in gene expression
Cells closer to morphogen have more of a response
82
T or F: You don't need multiple morphogens to give rise to multiple cellular identities--it can be achieved with different concentrations of the same morphogen
T
83
BMP and Shh
BMP: dorsal to ventral. Roof plate; these cells can now secrete BMP.
Shh: ventral to dorsal. Floor plate; these cells can now secrete Shh.
84
Shh and other developmental mechanisms
1. AP axis of limbs
2. Split prosencephalon into left and right hemispheres (affects facial development)
85
Holoprosencephaly
Failure of prosencephalon to form 2 distinct hemispheres (genesis of corpus callous to cyclopia)
86
BMP: MAP Kinase and SMAD pathways
BMP receptor gets phosphorylated and activates pathways to affect gene expression
87
TF Cross-Repression
Expression of one TF inhibits the transcription of another (Olig2 represses Nkx22 and vice versa)
- Happens in single cells (conversion occurs in "winner takes all" process)
- Initial gradient of expression give sharp boundary
88
Pia
Innermost meningeal layer
89
Neuroepithelial cells
- Rapidly dividing multipoint stem cells
- Give rise to more neuroepithelial cells
- Give rise to radial glia
90
Totipotent, pluripotent, and multipotent stem cells
Totipotent: cells in extra embryonic membranes, early cell type, can become anything
Pluripotent: cells in embryo proper, give rise to any cell in embryo proper
Multipotent: give rise to several cells types (neurons and glia arise from radial glia)
91
Neural progenitor cells
Limited capacity to divide and restricted to becoming on of a few cells types. Not self-renewing.
92
Neuroblast
No longer dividing cell and differentiates into neuron
93
Nuclear migration in neural tube directionality
Apical to basal
94
Stem cell mitosis in neuroepithelium
Go to apical surface to divide and then come back up to basal surface
95
Symmetric vs asymmetric division of cells in neuroepithelium
Self-renew stem cells vs. give rise to other cell types (neuroblasts)
Asymmetric inheritance of par protein complex
96
Radial glia can give rise to
Neuroblasts, intermediate progenitors, glia through symmetric and asymmetric divisions
Radial glia are transient cell type
97
Processes of a glial cell
Highway for daughter cells to migrate
98
Intermediate Progenitors
Migrate up to subventricular zone (SVZ), resulting daughter cells become neurons and intermediate progenitors
Intermediate progenitors greatly amplify the number of neurons that can be produced by radial glia
99
Cortical plate
Developing cortex
100
T or F: The cortex is built for inside out
T
101
Building cortex with early and late born neurons
Early born neurons migrate to cortical plate and start differentiating. Late born neurons migrate past them into superficial layers. Think: inside first, outside last
102
Type 1/Classical Lissencephalies (smooth brain, less cortex)
Mutations in several genes that impact neuronal migration/microtubule function
Symptoms: hypotonia, seizures, mental disability, often fatal. Relatively rare.
103
Proneural genes vs Hes genes
Proneural: trigger neuronal and inhibit stem cell identity
Hes genes: promote stem cell and inhibit neuronal identity
104
Notch Pathway in radial glial cells
Ligand: delta
Receptor: notch
1. Binding of delta to notch activates He's genes (stem cell fate promotion)
2. Hes turns off pro neural genes
3. Proneural genes turn on delta expression
105
What happens to cortex size if you inhibit Notch in radial glia?
Cortex gets smaller because you make all neurons early and don't invest in the future by creating stem cells that can alter give rise to more neurons). Without notch, you can't reinforce radial glial cells, so you just get neuroblasts.
106
NOTCH2NL Deletion
Deletion: microcephaly
Duplication: macrocephaly
Overtime, NOTCH2NL was repaired to correct a disrupted gene, and we now have an extra copy that changed cortical development in modern humans
107
Neural Crest and the cells there
Cells at neural plate border undergo an epithelial-to-mesenchymal transition--this process is called delamination (neural tube folds over)
108
Head vs. Trunk neural crest
Head: Sensory neurons, Schwann Cells, Melanocytes, Bone & Cartilage
Trunk: Autonomic neurons (sympathetic and parasympathetic), Sensory neurons Schwann cells, Melanocytes, Adrenal Medullary cells
109
Post vs Pre ganglionic cells
Post: cell bodies in ganglion (neural crest)
Pre: projections to periphery from spinal cord (neural tube)
110
Parasympathetic vs Sympathetic neurons and their derivations
Para: vagal and sacral neural crest
Sympathetic: trunk neural crest
111
LeDouarin's Quail-Chick Chimeras
Trunk neural crest placed in head became cholinergic and head neural crest placed in trunk became adrenergic
Takeaway: transplanted neural crest took on identity of new position (potential to become other things)
112
Fate of neural crest cells is strongly influenced by
Environment (e.g., chemical cues)
113
Dorsolateral pathway vs ventral pathway
Dorsal: melanoctyes
Ventral: Schwann cells, sensory, autonomic neurons, adrenal medullary cells
114
Adrenal medulla
A modified postganglionic sympathetic ganglion
Ventrally migrating sympathy-adrenal neural crest cells become sympathetic and adrenal chromatin cells (driven by local glucocorticoids from develop adrenal cortex)
