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Neuro M101B > Module 1 Lecture 2: Axis Formation and Patterning > Flashcards

Module 1 Lecture 2: Axis Formation and Patterning Flashcards

(67 cards)

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1
Q

what are the two important axes of an embryo

A

anterior-posterior and dorsal-ventral

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2
Q

what is the neural fold

A

the boundary between neural plate and outside ectoderm

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3
Q

what does the gastrula develop into

A

neurula

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4
Q

what do the neural folds do during neural tube closure

A

rise up, meet in the middle, and fuse

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5
Q

what does the notochord develop from

A

organizer

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6
Q

characteristics of notochord

A
  • mesodermal
  • critical role in D-V patterning
  • transient in vertebrates; contributes to vertebral column (usually reabsorbed)
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7
Q

somites function

A

give rise to vertebrae and other musculo-skeletal elements
- either side of neural tube, mesodermal, segmental

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8
Q

neural crest function

A

makes PNS, melanocytes, face cartilage
- migrate away
- vertebrate specific, pluripotent
- born at epidermal-neural boundary

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9
Q

types of neural tube defects

A
  1. anencephaly
  2. spina bifida
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10
Q

what causes anencephaly

A

anterior neuropore fails to close
- brain absent or does not complete development
- fatal

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11
Q

what causes spina bifida

A

posterior closure fails
- survivable but leads to leg paralysis, loss of bowel and bladder control, hydrocephaly, and learning disabilities

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12
Q

role of folic acid in neurodevelopment

A

reduces risk of neural tube defects by 50-70%

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13
Q

three primary vesicles

A

forebrain, midbrain, and hindbrain

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14
Q

primary vesicles subdivided

A
  • forebrain –> telencephalon, diencephalon
  • midbrain –> mesncephalon
  • hindbrain –> metencephalon, myelencephalon
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15
Q

what does the telencephalon subdivide into

A

olfactory lobes, hippocampus, cerebrum

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16
Q

what does the diencephalon subdivide into

A

optic residue, epithalamus, thalamus, hypothalamus

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17
Q

what does the mesencephalon subdivide into

A

midbrain

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18
Q

what does the metencephalon subdivide into

A

cerebellum, pons

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19
Q

what does the myelencephalon subdivide into

A

medulla

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20
Q

what triggers the development of the prospective forebrain from the ectoderm in the activation-transformation model

A

signal 1, “activation”
- neuralizes and specifies forebrain
- aka neural induction

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21
Q

what triggers the development of the midbrain in the activation-transformation model

A

signal 2, “transformation” (caudalizes)
- works in tension with activation & forebrain specification signals to induce more posterior structures
- signal coming from tail end

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22
Q

characteristics of signals coming from posterior end in activation-transformation model

A

soluble signaling molecules similar to BMP

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23
Q

what is the ultimate goal of the activation-transformation model

A

to change gene expression to specify neural fate

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24
Q

what does the shape of the activation-transformation effect depend on

A

interaction between caudalizing signal and dorsal mesoderm cells

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25
what does Wnt overexpression cause
induction of head structures
26
what does Wnt inhibition cause
severe reduction of the head
27
how do vitamin A derivatives affect neurodevelopment
inhibits forebrain & midbrain development in a concentration-dependent manner - consistent with a role in posterior neural tube specification
28
what does exposure to retinoic acid (RA) cause
craniofacial & brain malfunctions
29
first step of RA metabolism
make RA via retinaldehyde dehydrogenase (RALDH)
30
second step of RA metabolism
paracrine signaling - broken by Cyp26
31
types of cell signaling
- autocrine: cell targets self - gap junction signaling: cell targets a cell connected by gap junctions - paracrine: cell targets a nearby cell - endocrine: cell targets distant cell through bloodstream
32
third step of RA metabolism
response to RA: RA and retinoid X receptors heterodimerize & bind RA-response elements - activate gene transcription
33
fourth step of RA metabolism
Cyp26 generates the "sink" and breaks RA
34
what is the next step after A-P patterning
regionalization - organisms are not built step by step, but asynchronously in overlapping fashion
35
why is establishing segment identity (aka regionalization) important
critical to specification of cranial nerves, development of brain stem, inner ear, branchial arches, and the heart and large vessels
36
homeobox
a sequence of 180bp nucleotides which encodes a highly conserved 60aa DNA binding domain: homeodomain
37
what can a single homeotic protein do
-regulate (activate or repress) hundreds of different genes
38
what determines the target set of genes in a given cell
homeotic proteins mixing and matching with other transcription factors
39
co-linearity principle
Hox genes are organized in sequential clusters on chromosomes (eg 2 clusters on Chr3.)
40
how does the physical order of Hox genes on a chromosome map to their order of expression
physical order on the chromosome matches their order of expression in the AP axis of a developing animal
41
posterior dominance
activity of posterior Hox genes dominates over more anterior ones (if they are co-expressed)
42
homeosis - or homeotic transformation
a variation in body plans in which "something has been changed to the likeness of something else"
43
master regulators
homeotic genes; they turn on and off expression of so many genes, enough to reprogram entire body parts - every animal we know has Hox genes
44
what are Hox genes?
clustered, master regulators of gene expression that follow the co-linearity principle across phyla
45
what are rhombomeres
transient segments of the developing hindbrain
46
what drives regionalization of rhombomeres
retinoic acid-dependent Hox gene expression - also follow colinearity principle
47
what makes RA
somites (RALDH)
48
what shapes the RA gradient
rhombomeres (Cyp26) - shaped by where it is made and broken down
49
what interprets the RA gradient
Hox genes
50
result of vitamin A deficiency
no RA, Hox1b not expressed, hindbrain "anteriorized"
51
result of Cyp26 dysfunction
too much RA, expanded Hox1b, hindbrain "posteriorized"
52
what is a morphogen
a signaling molecule that 1. acts in a concentration dependent manner 2. on cells other than the source 3. to produce specific responses
53
characteristics of Wnt, FGF, and BMP as morphogens
their signaling gradient is shaped by where they are secreted from and where they are inhibited by antagonists
54
when does D-V closure occur
soon after neural tube closure
55
what are the 11 classes of neural progenitors set up by
expression domains of transcription factors
56
what do expression domains of transcription factors control
gene regulation and gene expression patterns - set up the 11 classes of neural progenitors
57
when is Pax7 (dorsal determinants) most present
prior to neural tube closure
58
what genes are involved after neural tube closure
- Pax7 becomes more restricted - Olig2 expands - Nkx2.2 is established
59
what does removal of notochord cause
loss of floorplate and motor neurons in the spinal cord
60
what does transplanting the notochord to the side of the spinal cord do
gives you a second floor plate and a second set of motor neurons at the dorsal side of the spinal cord
61
what induces ventral fates in spinal cord
notochord, with a diffusable signal
62
what is hedgehog
a secreted protein
63
what causes development of Sonic hedgehog (Shh)
the notochord induces the floorplate to produce it
64
what happens when cells from intermediate spinal cord are cultured with Shh
expression of ventral fate markers
65
what does higher Shh concentration cause
more ventral fates
66
is Shh a morphogen?
yes
67
what is the DV patterning of the spinal cord established by
two opposing morphogen gradients: 1. shift from the ventral side (notochord and floorplate) 2. BMP and Wnt from the dorsal side (epidermis and roof plate)

Neuro M101B (16 decks)

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