Neural Induction

Neural Induction

specification of the neural tissue in the early embryo

Neural Patterning

specification of the regions of the nervous system

Neurogenesis

birth of neurons

Gliogenesis

birth of glial cells

Neuronal migration

migration of neurons to their correct place in the brain

Neuronal morphogenesis

acquisition of a specific shape and properties (leads to formation of synapses and neuronal circuits)

Day 1

zygote

zygote

sperm, egg, zona pellucida, and nuclei

cleavage stages

cell divisions

Morula

32 cells

Compaction stage

morula develops embryoblasts and trophoblasts

embryoblast

gives rise to cells of the embryo

trophoblast

gives rise to placenta

blastulation

cells from compaction stage turn into a blastocyst

blastocyst

trophoblasts make a ring around the cell and embryoblasts form a clump in the middle above the blastocoele

blastocoele

empty cavity in the middle of the blastocyst

implantation

zona pellucida disappears

embryoblast separation

separate into epiblasts (top layer of inner cell mass) and hypoblasts (bottom layer of inner cell mass)

bilaminar disk

formed from epiblasts and hypoblasts of inner cell mass

gastrulation

epiblasts migrate to the middle of the two layers in bilaminar disk

trilaminar disk

after gastrulation there are three germ layers: ectoderm, endoderm, and mesoderm

embryonic axes

epiblasts are dorsal and hypoblasts are ventral

ectoderm

skin, hair teeth, nails, sweat glands, and nervous system

mesoderm

bones, cartilage, muscles, fat tissue, tendons, circulatory system, heart, and sex organs

endoderm

digestive system, lungs, liver, and pancreas

When is the nervous system induced?

During neurulation, after gastrulation

Neurulation step 1

neural induction

neural induction

specification of the neural tissue into neural plates and borders

neurulation step 2

formation of the neural tube and neural crests (in vertabrates)

invagination

formation of the neural tube

ectoderm forms

neural plate and neural plate borders

mesoderm forms

notochord

as invagination of neural plate occurs

forms neural tube into the mesoderm and the neural plate borders form the neural crest cells

notochord has an important role in

tissue and cell development

neural tube forms the

CNS

neural crest cells form the

PNS

after the neural tube closes

ectoderm covers it and becomes the epidermis

blastopore

small cavity used to identify placements in animals - forms anus in humans and mouth in other animals

goal of Spemann and Mangold experiments

find out how neural induction is triggered and started using frogs

animal part of frog egg

ectoderm/ top

vegetal part of frog egg

bottom

middle

mesoderm

Spemann Mangold Experiment steps

took 2 eggs, one before gastrulation and one after and added ectoderm from each into a petri dish

the isolated ectoderm before gastrulation

gave rise to skin

isolated ectoderm after gastrulation

gave rise to neural tissues, or neurons

SM Hypothesis

mesoderm cells signal ectoderm to form nervous system

testing SM hypothesis

added extra mesoderm from non pigmented frog where it shouldn’t be on a pigmented frog 

Results of SM hypothesis

extra head was created on host frog due to incorrect placement of mesoderm

conclusion of SM hypothesis

mesoderm cells act as neural inducers in embryo and organize host cell

Notochord is important because it

is involved in how mesoderm tells ectoderm to form nervous system

Neuralizing activity lost at 150 C

a protein is responsible for neuralizing activity and is secreted by the mesoderm to send a message to the ectoderm

Animal Cap assay

piece

s of animal cap