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Summary H5: positional information P. Callaerts
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Summary of 22 pages for the course Developmental Biology at KU Leuven (summary)
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H5 : POSITIONAL INFORMATIONP. CALLAERTS
Inhoudsopgave
5.1 INSPIRATIONAL EXPERIMENTS..........................................................................2
5.1.1 EARLY SEA URCIN DEVELOPMENT.............................................................................................. 2
5.1.2 HYDRA HEAD FORMATION....................................................................................................... 3
5.1.3 CHICKEN LIMB DEVELOPMENT.................................................................................................. 3
5.1.4 COMPETENCE OF CELLS.......................................................................................................... 4
5.2 LEWIS WOLPERT – DEFINITION OF POSITIONAL INFORMATION............................4
5.3 THE FRENCH FLAG MODEL – A CONCEPTIONAL FRAMEWORK TO GENERATE
HYPOTHESES......................................................................................................... 5
5.3.1 MORPHOGEN: DEFINITION...................................................................................................... 5
5.4 POSITIONAL INFORMATION AND DROSOPHILA...................................................6
5.4.1 EARLY EMBRYONIC DEVELOPMENT............................................................................................ 6
5.4.2 SEGMENTATION OF A LARVA.................................................................................................... 7
5.4.3 MATERNAL/COORDINATE GENES.............................................................................................. 8
5.4.4 PATTERNING THE EMBRYO...................................................................................................... 9
5.4.5 GRADIENTS....................................................................................................................... 11
5.4.5.1 bicoid: anterior determinant....................................................................................11
5.4.5.2 bicoid: localization of mRNA....................................................................................12
5.4.5.3 maternal genes: more than one gradient................................................................13
5.4.6 SEGMENTATION GENES - CONVERTING GRADIENTS INTO STRIPES..................................................13
5.4.6.1from maternal to segmentation genes.....................................................................14
5.4.6.2 bicoid encodes a homeodomain protein..................................................................15
5.4.6.3 hunchback: gap gene regulation.............................................................................16
5.4.6.4 bicoid and gap genes.............................................................................................. 17
5.4.6.5 gap and pair-rule genes.......................................................................................... 17
5.4.6.6 even-skipped regulation.......................................................................................... 18
5.4.6.7 pair-rule and segment polarity genes......................................................................20
5.4.7 PUTTING IT ALL TOGETHER.................................................................................................... 21
5.5 IMPLICATIONS IN BIOMEDICINE.......................................................................21
5.5.1 DISCOVERY OF SIGNALING PATHWAYS.....................................................................................21
5.5.2 UNDERSTANDING TERATOGENS............................................................................................. 21
Goals:
1
, To define positional information and give some historical examples
To explain the French flag model
To define a morphogen
To know key phases in Drosophila embryonic development
To define maternal genes in Drosophila
To integrate anterior and posterior determinants and link this to segmentation genes
To know the 3 categories of segmentation genes and explain their regulatory
relationship
To discriminate syncytial and cellular blastoderm and explain the impact for key
developmental pathways
To illustrate the implications in biomedicine of Drosophila developmental pathways
exam questions you can expect.
5.1 INSPIRATIONAL EXPERIMENTS
5.1.1 EARLY SEA URCIN DEVELOPMENT
Experiment by Hans Driesch:
He allows the embryos to develop to the 8 stage.
Depending on how you separate the blastomeres, you get something else:
He removed the animal pole (4 cells on top) from the vegetal pole and allow them to
develop:
a. The cells from animal pole (4 top cells (blue/grey cells) they develop a little bit
and than get stuck in the Dauerblastula stage and not develop further.
b. Vegetal pole develop to the pluteus larva.
If he did the experiment a little different so sagitally (sagitale doorsnede).
a. They both develop to pluteus larva.
So he conclude that the information in the vegetal pole and animal pole is different. Animal
pole does not have all the info to develop normally.
è Embryo’s have polarity.
2
, 5.1.2 HYDRA HEAD FORMATION
A transplantation experiment by Lewis Wolpert:
The hypostome is an organizer:
- it induces a secondary axis upon
transplantation
- it produces the head activation signal
- it self-differentiates
- it produces a head inhibition signal
that suppresses the formation of new
organizing centers
Hydra is an animal.
a) He took a fraction close to arms and transplanted it into the accepter animal (hydra):
nothing happens.
Fully developed crown inhibits the development of a head region with arms. (first
experiment).
b) When he first remove the crown of arms by cutting them off, and than did
transplantation
than the arms grow back but there is an secondary axis, a head region grows with
additional arms.
c) If you put the graft far enough,
you get a secondary axis anyway.
The further you are removed from the head region, the more the inhibited signal is diluted. If
you removed the crown region you get a secondary axes.
He defined the organizing experiment
5.1.3 CHICKEN LIMB DEVELOPMENT
Left:
3
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