Patterning The Vertebrate Body Plan Ii: The Somites And Early Nervous System Chp4 B

Front 1

Neurulation occurs via
Induction by the _______

Back 1

organizer

Front 2

Formation of
the neural tube from
________ _______

Back 2

Formation of
the neural tube from
ectodermal tissue

Front 3

Neural crest specified from
cells at ________-
epidermis boundary

Back 3

neural plate

Front 4

Describe in detail the technique of "insertional mutagenesis" (gene knock-out)

Back 4

A targeting vector is constructed that has the central (functional) region of a gene replaced with a drug resistance gene.
This is transfected into ES cells and selected by drug exposure.
By homologous recombination, a fraction of the transformants will have one copy of the original gene replaced with the altered (non-functional) form.
These cells are injected into the inner cell mass of a blastocyst.
Resultant chimeric mice give rise to heterozygous mutants which can be bred to generate mutant homozygotes.

Front 5

Altering ____ _____ expression alters axial patterning

Back 5

Hox gene

Front 6

Why can a missing gene be partially compensated for?

Back 6

In mice, gene knock-out experiments produce mutants.
There is redundancy, where a missing gene can be at least partially compensated for the expression of related genes.

Front 7

Describe posterior dominance/prevalence

Back 7

Posterior prevalence: mutation affects the anterior extent of gene expression.
Homeotic transformations (conversion of one body part to another) result from Hox gene loss.
Loss leads to cells assuming a "more anterior value" i.e. Hoxc8 mutant mice have extra ribs.
Abnormal expression of Hox genes in anterior regions lead to tissues becoming more like posterior positioned tissues.

Front 8

Does neural tissue have to be specified?

Back 8

YES

Front 9

after gastrulation, organizer cells form the
________ and ______
and Underlie the neural tissue

Back 9

notochord + head mesoderm

Front 10

Describe an experiment which suggests that the spemann organizer is temporally dependent

Back 10

Spemann Organizer (dorsal blastopore lip) grafted to the ventral side of the marginal zone results in a twinned embryo.
The second embryo can have head, trunk and, sometimes, a tail) but will be joined to primary embryo along the axis.
Blastopore transplants vary with time.
Early gastrula induces a full 2nd embryo.
Mid-gastrula induces trunk & tail (no head).
Late gastrula induces only tail.

Front 11

As gastrulation proceeds, the A/P axis become specified and as it progresses the blastopore lip can only induce more ______ ______.

Back 11

posterior structures

Front 12

position of ______ determines induction
fate. Describe an experiment which supports this.

Back 12

mesoderm; Nervous system can be patterned by signals from the mesoderm
In newt neurula, mesoderm transplantation into younger newt embryos, anterior explants induce head and brain.
Posterior explants induce trunk & spinal cord.
Neural plate explants induce specific neural structures (depending upon position) when transplanted beneath the ectoderm of a gastrula.

Front 13

Describe the 2 signal model of neural patterning

Back 13

Signal 1 from the mesoderm induces ectoderm to become anterior neural tissue. (chordin and noggin are good candidates)
Signal 2 turns part of this into posterior neural tissue in a graded manner (FGF, Wnts & retinoic acid are candidates).
Mouse and chick grafts of the primitive streak (ie node or Hensen's node) can also induce neural tissue.
This model differs from another model which suggests that there may exist a number of region specific inducer molecules.

Front 14

Neural induction occurs via the organizer. Describe 2 experiments which suggest this.

Back 14

Isolated animal caps form neural
tissue
• Dominant negative activin
receptor (also binds BMP4)
results in all ectodermal tissue
becoming neural

Front 15

BMP4 action is required for _______ whereas BMP4 antagonism required for ______ induction

Back 15

epidermis; neural induction

Front 16

Is FGF required for neural induction?

Back 16

YES

Front 17

What are the Two signal candidates thought to be involved in neural induction?

Back 17

Inducing - BMP inhibitors (noggin and
chordin, follistatin
• Head inducing - Wnt inhibitors
(Frizbee, Dickkopf, Cerberus – binds to
and inhibits Wnt, nodal and BMP)