2. Why is gastrulation so important?
Generation of the three germ layers:
Ectoderm, mesoderm, and endoderm
Generation of the basic body plan.
Specification of the axes:
Anterior and posterior
Dorsal and ventral
Left and right

3. Primitive streak (ingression)-
gastrulation is initiated ---EPIBLAST cells move towards the midline and then anteriorly. This creates the primitive streak.
Anterior
Posterior 3

4. Primitive groove - formed by wake of the primitive streak as it moves anterior
Hensen’s node- thickening at most anterior point of the groove
-point at which cells from groove move inside blastocoel

7. hyaluronic acid and fibronectin for cell migration
epiblast
Epithelial cell
E-cadherin
„slug”
FGF8
E-cadherin
mesoderm
endoderm
hyaluronic acid and fibronectin for cell migration

9. Brachyury mRNA (T-box) expression containing transcription
The brachyury mutation was first described in mice
-affects tail length and sacral vertebrae in heterozygous animals and is lethal in homozygous animals around embryonic day 10 due to defects in mesoderm formation, notochord differentiation and the absence of structures posterior to the forelimb bud).
Brachyury mRNA (T-box)
expression containing transcription
factor

10. Gastrulation Anomalies
Caudal Dysgenesis (Sirenomelia)
-Caudal defect: Insufficient mesoderm formation
-Fused lower limbs, renal agenesis
-Genetic and teratogenic mutation of Brachyury (T) gene (the brachyury mutation was first described in mice affects tail length and sacral vertebrae in heterozygous animals and is lethal in homozygous animals around embryonic day 10 due to defects in mesoderm formation)

11. Defined MAIN axes in human anatomy
How is handed asymmetry initiated in the embryo?
Gastrulation :
Specification of the axes:
Anterior and posterior
Dorsal and ventral
Left and right
Generation of the three germ layers
Ectoderm, mesoderm, and endoderm
Defined MAIN axes in human anatomy
Defined Axis
Synonyms
Axis runs...
Anterior
Antero-posterior
Rostrocaudal, Craniocaudal, Cephalocaudal
...from head end to opposite end of body or tail.
Posterior
Dorsal
Dorso-ventral —
...from spinal column (back) to belly (front).
Ventral
Left (lateral)
Left-right
Dextro-sinister, Sinistro-dexter
...from left to right sides of body.
Right (lateral) 11

14. 1: cranial-caudal (or head-tail) axis,
Formation of the primitive streak also defines for the first time all major body axes.
1: cranial-caudal (or head-tail) axis,
2: dorsal-ventral (or back-belly) axis,
3: medial-lateral axis
4: left-right axis. 14

15. Anterior-posterior patterning in the embryo
Lim-1
mutant embryos
(headless mice)
devbio8e-fig jpg 15

16. head induction requires the inhibition of
both BMP and Wnt signals (Glinka et al. 1997). 16

17. Molecular pathway for left-right asymmetry in the embryo
Node Signals:
LEFT
Shh (Sonic Hedgehog) ––induces Nodal (symmetry breaking molecule)
(Nodal is a signaling protein which is responsible for gastrulation, left-right patterning and induction of the primitive node.)
RIGHT :
Activin – (inhibits SHH)
devbio8e-fig jpg 17

18. The cells on the surface of the primitive node have cilia that beat
Situs formation
devbio8e-fig jpg
The cells on the surface of the primitive node have cilia that beat  18

19. How does fluid flow influence molecular asymmetry?
anterior
posterior R L
Morphogen sweeping
-beating of cilia arround
the primitive node
-directional current

20. Situs formation : nodal flow model of left-right development
devbio8e-fig jpg
Mobile cilia 20

21. situs inversus viscerum totalis (-rare human disorder, (1:10.000)
-the handedness of all of the viscera is reversed. No functional impairments.

22. Kartagener’s syndrome (1:30.000): 1. Chronic bronchiectasis
Medical considerations of LR asymmetry :
-situs inversus (1:10.000, a complete mirrorimage
of asymmetrically positioned
organs)
-heterotaxia (situs ambigus)
(where each organ makes an independent decision as to its
situs),-severe complications
right or left isomerism completely symmetrical organs; polysplenia.
Kartagener’s syndrome (immotile ciliary syndrome)
-hereditary disease
-dextrocardia,
Kartagener’s syndrome (1:30.000):
1. Chronic bronchiectasis
2. Chronic sinusitis
3. Situs inversus
Kartagener syndrome patients have
mutations in DYNEIN genes:--immotile cilia

23. 23

24. As gastrulation converts the bilaminar embryonic disc into a trilaminar embryonic disc, it brings subpopulations of cells into proximity so that they can undergo inductive interactions to pattern layers and specify new cell types. The first cells to move through the primitive streak and contribute to the intraembryonic mesoderm migrate bilaterally and cranially to form the cardiogenic mesoderm. Somewhat later in development, a longitudinal thick-walled tube of mesoderm extends cranially in the midline from the primitive node; this structure, the notochordal process, is the rudiment of the notochord. Migrating bilaterally from the primitive streak and then cranially, just lateral to the notochordal process, are cells that contribute to the paraxial mesoderm. In the future head region, paraxial mesoderm forms the head mesoderm. In the future trunk region, paraxial mesoderm forms the somites, a series of segmental blocklike mesodermal condensations. Two other areas of intraembryonic mesoderm form from the primitive streak during gastrulation: the intermediate mesoderm and lateral plate mesoderm. The intermediate mesoderm contributes to the urogenital system, and the lateral plate mesoderm contributes to the body wall and the wall of the gut (gastrointestinal system).