Hi, this is a summary of the neurodevelopment course 2023/2024. There are all the lectures inside of it and there are also the practice questions for the exam, plus some extra questions that may be helpful.
Neural Induction
Evolutionary perspectives
Neurons throughout the evolution of multicellular organisms have had many features in
common.
The Cnidarians have nerve networks with electrical synapses, but synaptic transmission
between neurons is also very ancient.
Derivation of neural tissue
The three germ layers
ECTODERM: gives rise to the central nervous system (the brain and spinal cord); the peripheral
nervous system; the sensory epithelia of the eye, ear, and nose; the epidermis and its
appendages (the nails and hair); the mammary glands; the hypophysis; the subcutaneous
glands; and the enamel of the teeth
Ectodermal development is called neurulation regarding nervous tissue neural
induction.
(The nervous system shares a common cellular lineage with the ectoderm)
The AB blastomere generates both skin (=hypodermis) as well as nervous system
, During Gastrulation
The next phase (= proliferation phase) in the
development of C. elegans also highlights the
shared lineages of hypodermis and neurons.
The neurons are primarily derived from the
ventrolateral surface, through the divisions of
the AB progeny cells and migrate into the
interior to form the nerve rings.
Gastrulation
DROSOPHILA
The nervous system of Drosophila (fruit fly) is
derived from the ventrolateral region of the
ectoderm (red).
Involution of the mesoderm at the ventral surface
brings the neurogenic region closer to the midline >
neuroblasts enlarge > migrate to interior > neurons
and glia will form nerve cords.
The neuroblasts of the Drosophila separate
from the ectoderm by delamination. The
delaminating neuroblasts then generate several
neurons through a stereotypic pattern of
asymmetric cell divisions.
,FROG EMBRYO
The development of the CNS in a frog embryo:
The involuting cells go on to form mesodermal tissues
(blue) and induce the cells of the overlying ectoderm
to develop into neural tissue, labelled as the
neurogenic region (red).
The neurogenic region forms the neural plate and is
now restricted to give rise to neural tissue.
Induction of the neural tissue
The neurulation process:
The neural plate begins to roll up, forms the
neural walls which fuse at the dorsal margins to
form the neural tube.
A group of cells known as the neural crest (bright
red) arises at the point of fusion of the neural
tube.
(Mesoderm is important for the induction of ectoderm)
Experimental studies revealing the interactions with neighbouring tissues in making neural
tissue:
1. Isolation of fragments of embryos at different developmental stages shows when tissue
becomes committed to the neural lineage (Experiments like these led to the idea that
the neural lineage arises during gastrulation).
, 2. Transplantation experiment of Spemann and Mangold showing the effects of
transplanted dorsal blastopore lip from a pigmented embryo (in red) to a non-
pigmented host embryo (the dorsal lip cells, called the Spemann organizer, “organize”
the host cells to form a new body axis).
3. Determination of ectoderm during gastrulation: Early gastrula tissue transfer yields one
neural plate as presumptive neural tissue transforms into epidermis. Late-gastrula
tissue transfer results in two neural plates on the host as presumptive neural cells form
neural tissue. Early gastrula cells are uncommitted late gastrula cells are determined.
The molecular nature of the neural inducer
1. Interactions between the animal and
vegetal cells of the amphibian embryo
are necessary for induction of the
mesoderm: In the amphibian embryo,
the animal pole gives rise to epidermal
cells and neural tissue, the vegetal pole
gives rise to endodermal derivatives, like
the gut, while the mesoderm (blue) arises from the equatorial zone.
2. Indirect neural induction versus direct neural induction: The organizer transplant
experiments show that the involuting mesoderm has the capacity to induce neural
tissue in the cells of the animal cap ectoderm.
3. The identification of noggin as a
neural inducer - The noggin
gene induces neural tissue from
isolated animal caps, without
any induction of mesodermal
genes (neural tissue is shown in red in all panels).
4. Like noggin, Chordin, and other organizer molecules (for example follistatin) are
putative neural inducers.
5. Expression of a truncated activin (TGF beta family) receptor blocks normal signalling
through the receptor and induces neural tissue (inhibiting this signalling pathway might
be how neural inducers function).
6. Dissociation of animal cap cells prior to gastrulation causes most of them to
differentiate into neurons in culture (neural fate is actively suppressed by cellular
associations in the ectoderm).
Conservation of neural induction
(The Drosophila embryo in cross section resembles an inverted Xenopus embryo.)
Effects of elimination of chordin and/or noggin: Loss of noggin and chordin in
developing mice causes severe defects in head development.
Do the neural inducers (chordin, noggin and follistatin) act
equivalent to inhibit BMP4 signalling?
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