Notogenesis, neurulation, somitogenesis
The embryonic axial structures development :
1. primitive streak
2. notochord
3. neural tube
4. somites
3 weekdevelopment of primitive straek as crucial structure in
transformation of bilaminar into trilaminar embryo
Implantation beginning - 7ED
endometrium, LP
endometrium, epitel
syncytiotrofoblast
cytotrofoblast
dutina blastocysty
2 week
implantation continuesEmbryo is at bilaminar blastoderm stage.
By bilaminar blastoderm development the period of blastogenesis terminates and begins the period of embryogenesis.
3 week development of bilaminar into trilaminar
blastoderm/embryo consisting of 3 germ layers: ectoderm, mesoderm, endoderm
Primitive streak morphogenetic centre in mesoderm,
endoderm and ectoderm development • regulate epiblast cells migration
and differentiation, that invaginate in its axis
• mechanism?• production of particular growth
factor s/morphogenss• FGF8- fibroblast growth faktor• mechanism of its activity?• E-cadherin expression decrease
in epiblast cells
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
Cranio-caudal axis
1) Cell signaliling 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 straek formation)
PP, primitive streak - factor Nodal, belongs to TGF- transforming growth factor
2) Cell - signalling from primitive node and notochord, gen Brachyury – dorsal mesoderm formation in the middle and caudal part of embryo
X 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, bloodm vessels
2) mesoderm dorsalisation – Noggin, Chordin, Follistatin block the BMP , that results in notochord and somites formation, neuroectoderm diffrenetiation from ectoderm, differentiation of notochord and paraxial mesoderm
Firstly, 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 .
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 dvelopment (interaction notochordu/adjacent ectoderm)
neural folds
neural groove
neural tube
Neural tube development by activity of caudal morphogenetic systém results 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• neurulutaion (plate to tube development)
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