Neural Induction

Question 1

what is signal induction

Answer 1

signal originating in one tissue, causing another responsive tissue to differentiate into something else

Question 2

from neural precursor to neuron

Answer 2

1. competent neural precursor
   ability to become neon if exposed to appropriate signals
2. specified neural precursor
   has received signals to become neural precursor. still responds to signals that repress neural fate
3. committed neural precursor
   received signals to become neural precursor. becomes neuron in presence of signals that repress neural character
4. differentiation into mature neuron

Question 3

embryonic developmental stages of Xenopus embryo

Answer 3

egg –> blastula –> gastrula –> neurula

Question 4

determining embryonic polarity

Answer 4

animal pole is pigmented, vegetal hemisphere is nit

grey crescent forms, where the pigmented half slides relative to egg opposite to point of sperm entry. first cell division always divides grey crescent in half

so have dorsal and ventral, and a anterior and posterior

Question 5

what is the blastula

Answer 5

hollow ball of rapidly dividing cells

Question 6

fate map

Answer 6

defined positions of where everything is and where all cell divisions happen

you know exactly all cells from certain position are going to be for certain fate

Question 7

what happens during gastrulation

Answer 7

dorsal lip of the blastopore forms. this is the driver and first sign of invagination
cells migrate towards the inside of the mrbyo through a hole.

result: three apposed germ layers
outer: ectoderm
middle: mesoderm
inner: endoderm

Question 8

fates of the three germ layers

Answer 8

ectoderm: CNS, PNS, skin, hair
mesoderm: muscle, blood, bone, kidney, gonads
endoderm: epithelial lining GI, resp tract,

Question 9

axial mesoderm

Answer 9

lies along central axis under neural tube
gives rise to notochord

Question 10

paraxial mesoderm

Answer 10

flanks neural tube
forms at same time as neural tube
gives tissue to somites

Question 11

somites

Answer 11

blocks of tissue running along both sides of neural tube
gives rise to muscles and tissues of back

Question 12

stages of neurulation

Answer 12

1. neuroectoderm differentiates from ectoderm and thickens to become neural plate
2. neural plate folds dorsally. two edges join with neural plate borders eventually touching and fusing. border cells become roof plate & neural crest
3. closure of neural tube disconnects epidermis, neural crest, neural tube.
4. notochord degenerates, persisting in the intervertebral discs.

Question 13

what happens to neural crest cells

Answer 13

they migrate laterally to form DRG

Question 14

spemann and mangold: dorsal lip transplantation 1924

Answer 14

took dorsal lip from donor embryo and transplanted it to a ventral site of host embryo
resulted in 2 neural tubes giving rise to 2 nervous systems w/o ventral tissue

conclusion: dorsal lip is the Spemmann organiser. it produces some sort of factor that induces formation of spatially distinct tissues

Question 15

how does inducing signal move through tissues

Answer 15

1. vertical induction
2. planar induction

Question 16

evidence for vertical induction

Answer 16

put in high salt water, cells migrate to outside instead. allowed to develop, couldn’t see any nervous tissue. conclusion –> planar induction not sufficient to induce nervous system

mesoderm transplant: neurula anterior mesoderm grafter into early gastrula induces a head. posterior mesoderm induces trunk and tail.
conclusion –> vertical induction required. mesoderm contains regionalised inducers

Question 17

evidence for planar induction

Answer 17

homeobox genes
exogastrula embryos labelled with neural markers
keller sandwhiches: two bits tissue sandwiched together but are identical to only planar possible

Question 18

is planar signalling sufficient

Answer 18

no.
no floor plate in developing spinal cord, so there are dorso-ventral patterning defects
can’t induce most anterior part CNS

both vertical and planar are required

Question 19

neural default model

Answer 19

default state for ectoderm is neural tissue, not epidermis

therefore, the absence of an intracellular signal is required for neural differentiation

Question 20

neural default model: spemann organiser

Answer 20

it spews out antagonists of epidermal inducer, to stop it interacting with receptor and inducing epidermal tissue

Question 21

activin

Answer 21

induces mesoderm
when binds its receptor causes it to dimerise. Activates cytoplasmic serine-threonine kinase signalling. causing secondary mesoderm signal to convert ectoderm to neuronal fate

blocking activin signalling results in neural tissue formation without secondary mesoderm signalling. therefore, activin inhibit leads to formation of neural tissue