H8: MESODERM AND
NEUROECTODERM PATTERNING
A. ZWIJSEN
Inhoudsopgave
8.1 SPEMANN ORGANIZER (DORSAL BLASTOPORE LIP).............................................2
8.2 MESODERM PATTERNING IN XENOPUS...............................................................3
8.2.1 MARGINAL ZONE................................................................................................................... 4
8.2.2 THE ROLE OF THE ORGANIZER................................................................................................. 5
8.2.3 NOGGIN.............................................................................................................................. 5
8.2.4 BLASTOPORE LIP SECRETES DIFFERENT ANTAGONISTS OF VENTRALIZING FACTORS..............................7
8.2.5 MESODERM PRODUCES IT’S OWN PATTERNING FACTORS................................................................8
8.2.6 HOW TO ORIENT................................................................................................................. 10
8.3 MESODERM PATTERNING IN MOUSE................................................................11
8.3.1 MESODERM CLASSES........................................................................................................... 12
8.4 ECTODERM DEVELOPMENT..............................................................................13
8.4.1 SPEMANN ORGANIZER TRANSPLANTATION.................................................................................13
8.4.2 NEURAL TISSUE IS INDUCED IN ECTODERM OVERLYING THE ORGANIZER..........................................13
8.4.3 ANTAGONISTS SECRETED BY THE ORGANIZER............................................................................14
8.4.4 NEURAL INDUCTION FEATURES............................................................................................... 16
8.4.5 NEURAL PLATE-NEURAL GROOVE-NEURAL TUBE.........................................................................17
8.4.6 CO-LINEARITY (A-P) BETWEEN NEURAL TISSUE AND MESODERM...................................................18
8.4.7 NEURAL TUBE CLOSURE....................................................................................................... 19
8.4.8 NEURAL TUBE DEFECTS........................................................................................................ 19
8.4.9 DORSAL VENTRAL PATTERNING OF THE NEURAL TUBE.................................................................20
8.5 NEURAL CREST CELLS.....................................................................................24
8.5.1 CELL LINEAGE TRACING EXPERIMENTS.....................................................................................25
8.5.2 GENERATION OF A WIDE VARIETY OF CELLS AND TISSUES............................................................26
8.5.3 NEURAL CREST CELLS ARE MULTIPOTENT.................................................................................27
8.5.4 DIFFERENT TYPES OF NEURAL CREST CELLS..............................................................................27
8.5.5 DERIVATIVES OF THE NEURAL CREST LINEAGE...........................................................................28
8.5.6 CRANIAL NEURAL CREST CELL DERIVATIVES..............................................................................28
8.5.7 CARDIAC NEURAL CREST CELL DERIVATIVES..............................................................................29
8.5.8 NEURAL CREST CELLS ARE REPELLED BY EPHRIN PROTEINS IN SOMITES...........................................29
8.5.9 NEURAL CREST CELLS AND EVOLUTION BEAK MORPHOLOGY........................................................30
8.6 NEURAL CREST SYNDROMES...........................................................................30
8.6.1 PIEBALDISM....................................................................................................................... 30
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Understand concepts of:
o mesoderm induction and mesoderm patterning
o neuroectoderm development and A-P and D-V patterning
o neural crest cell development and plasticity
Understanding organizer concepts and experiments how to prove organizer activity
Understanding different mechanisms how cells can acquire positional identity
Recognizing and localizing different types of mesoderm
Proposal of working hypotheses on patterning and experimental design to test such
hypotheses
Interpretation of (unseen) embryonic patterning phenotypes and congenital defects
Let’s revise:
Patterning
Interpretation of positional information
o Hox-code (class 7)
o French flag (morphogens and threshold levels)
o Extracellular antagonists of morphogens
‘Sorting out of cells’
Lateral inhibition can give a spacing pattern
Patterning:
o Mesoderm
o Neuroectoderm
o Neural crest
Syndroms
EMT:
= Epithelial to mesenchymal transition
Cells will change there polarity and stars to migrate as indivual
cells and will transform in mesenchymal cells.
Cells that once went to the epithelial streak and can undergo a
second or even third wave of EMT
8.1 SPEMANN ORGANIZER (DORSAL
BLASTOPORE LIP)
2
,Cells become dorsal mesoderm: (prechordal plate mesoderm, notochord, paraxial mesoderm
situated beneath dorsal ectoderm (important for neural induction).
Nieuwkoop center is important for the signals for inducing mesoderm
its nodal related (= TGFβ member)
nieuwkoop center is within endoderm (high concentrations of nodal)
Signal in the vegetal side of the embryo that will induce the dorsal blastopore lip,
the cells that induce this are called the Spemann organizer. The mesoderm that is
formed here will become dorsal mesoderm (notochord!)
Dorsal mesoderm very important the for neural induction!
Mesoderm cells will get either identity of
dorsal or ventral ventroderm dependent on
which endoderm is put in the sandwich (die
gele streep denk ik)
What makes that a whole serie of
mesodermal cells can develop?
Marginal zone (MZ) = equatorial region (MZ = regionalized)
Animal cap will be hidden behind the screen when we look at it, the dorsal
side is on top and ventral on the bottom. We look at the equatorial region.
zo kijken we naar die cel
Experiment:
In situ hybridization (show-it experiment)
This is not a DNA in situ because if you do that, the DNA is the same over the cells. This
is RNA in situ hybridization because that tells us which and where genes are turned on
and off. This is a ‘show it’ experiment
Make a fate map of the equatorial region/marginal zone
⇒ you find all the types of mesoderm cells. All these markers are expressed in the
mesoderm but not in the same domain. Different regions express different markers
o Some genes specifically expressed in the ventral mesoderm
Xvent-1, Xvent-2, xMyoD (Xvent-2 covers the whole equatorial region)
o Some genes specifically expressed in the dorsal mesoderm
noggin, xMyf-5 (Noggin is always expressed in that one side of the cell.)
DMZ late blastula + VMZ co-explant:
→ DMZ and VMZ regulate patterning in mesoderm
? How !?? Something secreted by DMZ
When you culture a little piece of dorsal mesoderm in combo
with ventral mesoderm than you will obtain in the ventral mesoderm heart cells… Normally it
forms only blood and mesenchyme but now also forms cardiac myocytes and pronephros.
It can be induceed provided that the tissue are in contact with each other
Some signals in the left piece communicate with the cells in the right little piece onstaan
intermedial celtypes
Dorsal and ventral mesoderm talk to each other! And by that conversation the
intermediate region gets specified. But then the question becomes which signals are
being used?
DMZ (dorsal marginal zone, mesoderm) and VMZ (ventral marginal zone,
mesoderm) regulate the patterning in mesoderm!
Found out that the DMZ secretes something that is necessary to induce that
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