Download PG1007 Lecture 4 Derivatives of the Ectodermal Germ Layer

TR056/PG1007 Lecture 4 Deriva7ve of the Ectodermal Germ Layer (Neurula7on) Dr. Neil Docherty My Teaching Objec/ves • To describe the formation of the neural tube from the
emergent ectoderm
• To state the origin and fate of neural crest cells
• To discuss how failure to close the neuropores leads to
anencephaly or spina bifida
The Germ Layers Derived From Gastrulation
ECTODERM
WEEK 3
MESODERM
ENDODERM
RE: Lecture 3 ECTODERM
gives rise to;
• CNS
• PNS
• Special senses epithelia
• Integumentary system
Organs and structures that
maintain contact with the
outside world
CONSTANT INTERNAL
ENVIRONMENT
FLUCTUATING EXTERNAL
ENVIRONMENT
Ectodermal Broadening During Week 3
Broadening of cephalic end
during week 3 precedes the
the specification of cells
in the ectoderm to become neural
(neuroectoderm)
1.25mm
0.68mm
Bone Morphogenic Protein (BMP) Inhibition
Regulates Neural Induction in Cranial Region
• BMPs (BMP-4) induce production of epidermis from the ectoderm
• When this is opposed the ectoderm is neuralised
Fibroblast
growth factor
Neuroectoderm
formation
+
BMP inhibitor
gene expression
(chordin, noggin, follistatin)
BLOCKADE OF
BMP SIGNALLING
Neurulation-1
Induction of the ectoderm results in the sequential development of the
-neural plate
-neural folds
-neural groove
Neural Tube Formation
Folding proceeds until the lateral edges of the neural folds meet
at the midline and fuse
This intially occurs in the cervical region and proceeds
cranially and caudally
Note that communication with the amniotic sac persists at the
anterior and posterior extremities via the neuropores
Closes day 25
Brain vesicles
Spinal cord
Closes day 28
The Neural Crest Cells
• Cells at the lateral border of the elevated neural folds undergo
a phenotypic alteration termed
EPITHELIAL-MESENCHYMAL TRANSITION
Acquire motility and invasiveness like observed previously in
The epiblast during gastrulation
The cells migrate to the mesoderm to give rise to a variety of cell
popoulations contributing to structure and connectivity in the
developed embryo;
-Melanocytes
-Neurons
-Glia
-Skeletal tissues
Formation and Migration of
Neural Crest Cells
Intermediate levels of
BMPs important
The Placodes and Pharyngeal Arches
Arise from cranial derived neural crest cells.
STRUCTURE AND SENSES
Neural Tube Defects
cranial
Failure to close neuropores
caudal
ANENCEPHALY
(lethal defect)
SPINA BIFIDA
(split spine)
Incidence varies 1:200-1:1000
Ireland has a high rate internationally
70% of cases preventable by folate supplementation
MUST START BEFORE CONCEPTION
Look up what folate is used for in foetal development
Today’s Learning Objec/ves Your learning from today should focus on being able to;
1) Describe the formation of the neural tube from the
emergent ectoderm
2) List the origin and fate of neural crest cells
3) Highlight how failure to close the neuropores leads to
anencephaly or spina bifida