Exam 1: Chapter 1 Flashcards
Rearrangement of cells to germ layers (neural induction)
Gastrulation
Meso/endoderm moves inward
C elegant divisions
P0 —> AB
AB makes most hypodermics, NS and glia and neurons. Spreads over outside. Neurons from ventrolateral side.
Proliferation indent on VENTRAL side
P1 —> gonands/muscles, blastomeres migrate inward
Invertebrate NS
Ventral
Vertebrate NS
Dorsal
For drosophila, initial rounds of nuclear division
NOT accompanied by cell division, nuclei in syncytum up until right before gastrulation
What marks beginning of gastrulation?
Ventral furrow, where cells of future mesoderm fold in
Neurogenic region
Provides ventral nerve cord (CNS)
Procephalic NR gives rise to cerebral ganglia/brain in embryo anterior
Neurogenesis and delamination in drosophila
Cells enlarge and more inward
Delaminates: neuroblasts separaré from ectoderm
Divides make GMC, which generate pairs of neurons/glia
Animal half for frog compared to vegetal
Faster fusions, smaller cells
Frog stage 2: gastrulation
Blastula develops 3 layer organization
Cells on surface move to blastula center (inward)
Involuting cells - mesoderm tissue
Overlying ectoderm-neural tissue.
What is the point of initiation of gastrulation for frog?
Blastopore
Amphibian: first cells invaginate on DORSAL side
Involuting Marginal zone
Part of blastula embryo interior
Gives rise to mesoderm: muscle/bone
First to involute-head, last is tail
Neural crest
Arises at point of neural tube fusion
Gives neurons/glia for PNS
Neural tube closes
Rolls up, fuses at dorsal margins to make neural crest
Human gastrulation
Developing ____ cells migrate through ____ to reach interior
_______: above mesoderm, becomes neural palate/tube.
Initially symmetrical- identical blastomeres
Blastocyst after many divisions
Outside-placenta, inner-embryo
Developing mesodermal cells migrate through PRIMITIVE STREAK to reach interior
_ECTODERM: above mesoderm, becomes neural palate/tube.
Frog experiment:
Isolate pregastrula animal cap
Isolate gastrulating animal cap
Experiment 1
Pregastrula —> epidermis
Gastrula —-> neural tissue
Spemann/Mangold frog
(What is organizer?) experiment 2
Dorsal lip from 1 embryo to another
Pigment frog -donor
Result: 2nd body from host
Implies:
Grafted bastopore cells induce neural tissue
Mesodermal structures also contribute to twin embryo
DORSAL LIP = neural induced, organizer of body axis
Nieuwkoop and inducer nature experiment #3
Isolate animal cap —> no mesoderm, no neural tissue
Isolate animal and vegetal caps —> mesoderm.
Hypothesis: signal from v induces mesoderm at animal junction
Experiment #4- how do neural lineages arise?
Organizer at dorsal lip of mesoderm but what question remains?
Unclear if neural tissue from A cap induced by exogenous factor, OR factor first induced organizer and then neural tissue.
Results:
Indirect: A cap + meso inducer= neural and mesoderm
Direct: A cap + neural inducer —> neural only (no mesoderm)
Harland’s neural inducing (experiment 5)
Uv frog: no dorsal axis, only ventral
Transplant dorsal Blastopore lip + UV = normal
Lithium: hyperdorsalized embryo
UV + extracted polyA mRNA from lithium embryo —> normal
cDNA (from organizer) + UV = normal
Noggin cDNA —> noggin protein and A cap —> neural genes
Noggin
Chordin
Follistatin
Expressed in organizer during neural induction
All 3 inhibit BMP
N/C bind to BMP4
F binds to BMP7/activin
Pro-neural
Follistatin- from pituitary inhibits activin
Melton and Follistatin: mRNA for truncated activin receptor reveals
If truncated receptor, neural tissue
If signal go through, A cap —> epidermis,
Activin: pro-epidermis, inhibits neural tissue.
Animal cap: 3 conditions
1) intact
2) dissociated
3) dissociate + BMP4
1) epidermis
2) neurons
3) epidermis
Why? Removal of lateral inhibition (dissociate by removing ca2+ ions) = neural induction
However, BMP inhibits neural induction.
What does antisense BMP result in?
Neural differentiation
AB blastomere spreads over
External surface
M, E, C, and D blastomeres migrate into
interior of embryo
Blastomere
cells from early mitotic divisions that form blastula
Blastula
Sphere of cells formed from early mitotic division
Bastocoel
Fluid filled cavity
Gastrulation
blastomeres change positions in relation to each other
Involuting Mesoderm
Overlying Ectoderm
Blastopore
indent. Lip is leading edge where cells begin to migrate, cells above IMZ
Neurogenic region is
neural plate
BMP inhibited by
peptides in organizer region on mesoderm, which initiates induction
Drosophila sog and dpp
sog- ventral, chordin
mutation= small neurogenic region
dpp- TGF-beta/BMP 4
mutation= large neurogenic region
Why do we want more than 1 thing blocking BMP?
Because look at mic.
1x KO, still ok, but multiple is bad news
What, in vertebrates, is the source of C/F to stop BMP4?
Mesoderm
Why is lateral inhibition a invertebrate thing?
They don’t have the cells to spare, need only certain amount, but if neuroblast killed, neighbor will take it’s place
Achaete-Scute
Pro neural genes
code for bHLH transcription factor which binds to E-boxes
Proneural Ac-S mutant
no neuroblasts/neurons
Neurogenic Mutant Ac-S
more neurons
Notch receptors repress
Ac-S
Notch is anti-neural
If you laser AFTER delamination of neuroblast
Doesn’t matter who has more delta or As-c, the battle doesn’t restart
