Notogenesis, neurulation, somitogenesis

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

1 weekfrom zygote to beginning of implantation

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.

Implantation completed 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 • 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

Axial orientation establishment

Body axiscranio-caudal, dorso-ventral , right-left

established during 3rd week

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

Signalling molecules and transription factors in primitive streak

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 .

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 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)

Neuroporus anterior ED 25Neuroporus posterior ED 28

Histogenesis of neural tube wall

Neuroepithelium differentiation

Neural crest formation and its derivates

Neural tube dvelopment and intraembryonic mesoderm differentiation

4 weekneural tube , somites

Somites, 42 – 44 pairs of paraxial mesoderm, 1st pair in occipiteal region, 20EDSegmentation: Notch, WNT, segmentational genesretinoic acid, FGF8, kraniocaudal gradient

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