Download Notogenesis, neurulation, somitogenesis

Notogenesis, neurulation,
somitogenesis
Development 148
Gastrulation
Notogenesis, neurulation, somitogenesis
The embryonic axial structures development :
1. primitive streak
2. notochord
3. neural tube
4. somites
3 week
development of primitive streak as crucial structure in
transformation of bilaminar into trilaminar embryo
1 week
from zygote to beginning of implantation
Implantation beginning - 7ED
endometrium, LP
endometrium,
epithelium
syncytiotrophoblast
cytotrophoblast
Blastocyst cavity
2 week
implantation continues
Embryo is at bilaminar blastoderm stage.
The period of blastogenesis terminates by bilaminar blastoderm formation
and the period of embryogenesis begins.
Implantation is completed on ED14
.
3 week
development of bilaminar into trilaminar
blastoderm/embryo
consisting of 3 germ layers: ectoderm, mesoderm, endoderm
Epiblast and primitive streak
formation
Mechanism of embryonic mesoderm and
endoderm development
Primitive streak
morphogenetic centre in mesoderm,
endoderm and ectoderm development
• It regulates the epiblast cells
migration and differentiation,
they invaginate in its axis
• mechanism?
• production of particular growth
factor s/morphogenes
•
FGF8- fibroblast growth factor
• mechanism of its activity?
• E-cadherin expression decreases
in epiblast cells
All 3 germ layers develop from EPIBLAST
• ectoderm and endoderm are arranged as
epithelium
• CAM +
• mesoderm is not arranget as epithelium,
histologically it is connective tissue – primary
mesenchyme
• CAM -
Development of notochord / chorda dorsalis
epiblast precursors, invaginating in Hensen´s primitive node,
migrate toward the prechordal plate,
- creating the cord-like cellular axial structure, s.c. notochord
Axial orientation establishment
Body axis
cranio-caudal, dorso-ventral , right-left
established during 3rd week
Cranio-caudal axis
1) Cell signalling from the area of rostral/cranial end of embryo,
anterior visceral mesoderm, AVM
genes OTX2, LIM1, HESX1 and factor Cerebrus - determine the head end
(before the primitive streak formation)
PP, primitive streak - factor Nodal, belongs to TGFb - transforming growth
factor
2) Cell - signalling from primitive node and notochord, gen Brachyury –
dorsal mesoderm formation in the middle and caudal part of embryo
gene defect – longitudinal axis shortening – caudal dysgenesis /regression
Dorso-ventral axis
1) mesoderm ventralisation
BMP – bone morphogenetic protein
FGF8 – fibroblast growth factor – determine, what will
differentiate in ventral mesoderm – kidneys, gonads, blood
vessels
2) mesoderm dorsalisation – Noggin, Chordin, Follistatin block
the BMP , that results in notochord and somites formation,
neuroectoderm differentiation from ectoderm, differentiation
of notochord and paraxial mesoderm
Signalling molecules and transription factors in
primitive streak
First, cranial part/ head process of notochord is established.
Caudal part is established by caudal morphogenetic system (caudal end of
notochord, intensively proliferating, and ectoderm close to primitive node),
followed by gradual primitive streak shortening .
Neural plate induction
mechanism: interaction of notochord with adjacent ectoderm
Noggin, Chordin, Follistatin, neural inductors, for ectoderm to
neuroectoderm in the region of forebrain and midbrain
Hindbrain and spinal cord are induced by WNT and FGF
expressed in the region of the caudal morphogenetic system.
Neural plate induction and neural tube development
(interaction notochord/adjacent ectoderm)
neural folds
neural groove
neural tube
Neural tube development (by activity of caudal morphogenetic
systém) results in the formation of hindbrain and spinal cord
•
caudal morphogenetic centre – intensive proliferating caudal
end of notochord
•
caudal end of notochord gets beneath the primitive
streak/primitive groove, that becomes determined to
neuroepithelium at that region
•
primitive streak shortening
•
neural plate lengthening
•
neurulation (plate to tube development)
Neuroporus anterior ED 25
Neuroporus posterior ED 28
Histogenesis of neural tube wall
Neuroepithelium differentiation
Neural crest formation and its derivates
Neural tube development and intraembryonic
mesoderm differentiation
4 week
neural tube , somites
Somites, 42 – 44 pairs of paraxial mesoderm, 1st pair in occipital region,
20ED
Segmentation: Notch, WNT, segmentational genes,
retinoic acid, FGF8, craniocaudal gradient