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Announcements

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Exam regrade policy: if you have a question about how I graded an answer, send ... in patterns of 7 stripes (half the number of segments in a wild type larva) ... – PowerPoint PPT presentation

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Title: Announcements


1
Announcements
  • Exam this Wednesday my half is 40. Gerry
    Prodys half is 60.
  • Exam regrade policy if you have a question about
    how I graded an answer, send me an email
    outlining exactly how you felt I went wrong, and
    submit the exam for regrade.
  • You MUST (1) make this request in writing, and
    you MUST (2) submit the exam, both within 5
    business days of its return.
  • PLEASE NOTE that I will regrade the entire exam
    your grade may go up or it may go down (more
    likely).

2
Biol/Chem 473
Schulze lecture 4 Eukaryotic gene regulation
Early Drosophila development
3
Eukaryotic transcription is complex
4
Complexity of eukaryotic transcription
5
Insulators may function to organize the genome
into transcriptionally autonomous domains
6
Linking complex gene regulation to nuclear
organization
7
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8
The best model organism in the whole world!!!!
Drosophila melanogaster black bellied dew
lover fruit fly
9
The early Drosophila embryo is a syncytium (a bag
of nuclei)
10
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11
(Maternal effect genes)
12
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13
Patterning genes classified by mutant effect on
segmentation
The hierarchical nature of these interactions can
be shown by genetics mutations in earlier levels
of the hierarchy severely disrupt later
patterning.
14
Seminal publication and subsequent Nobel
15
Maternal genes
  • Required before the embryo starts transcribing
    its own genes
  • Mother expresses these genes during oogenesis
    (mum packs a lunch)
  • Localization of maternal gene products is the
    first step in the cascade

http//flymove.uni-muenster.de/Processes/Segmentat
ion/
16
Earliest stages of development run on mRNAs and
proteins deposited by mum during oogenesis
  • An efficient way to localize and concentrate
    proteins is by localization of mRNA in a
    translationally repressed state, followed by
    activation of translation when the mRNA reaches
    its destination.
  • How are mRNAs localized?
  • How are mRNAs repressed?
  • How are localized mRNAs then, when required,
    de-repressed?

17
Maternal effect Mum packs a lunch for the embryo
Anterior end
Posterior end
18
Maternal effect Mum packs a lunch for the embryo
  • The bicoid gene encodes a homeodomain
    transcription factor.
  • The oskar gene encodes something we are not quite
    sure about.
  • The gurken gene encodes TGFß homolog - EGF-R
    ligand, required for dorso / ventral patterning
    of the egg and embryo.
  • The nanos gene encodes a translational repressor
    - zinc finger that targets Hunchback- and
    Bicoid-mRNAs to achieve posterior identity.

19
Maternal effect Mum packs a lunch for the embryo
  • Polarity of the oocyte cytoskeleton is essential
    for maternal factor localization (gurken plays a
    role here).
  • Bicoid mRNA gets localized to anterior pole
    because another protein, called Staufen,
    recognizes a structure in the 3UTR of the bicoid
    message (and Staufen protein is itself localized
    by the polarity of the cytoskeleton.

20
Maternal effect Mum packs a lunch for the embryo
  • Bicoid mRNA gets localized to anterior pole
    because another protein, called Staufen,
    recognizes a structure in the 3UTR of the bicoid
    message (and Staufen protein is itself localized
    by the polarity of the cytoskeleton.

21
Maternal effect Mum packs a lunch for the embryo
These dsRNA UTR sequences are required for
anterior localization of bicoid mRNA by Staufen
protein
  • Bicoid mRNA gets localized to anterior pole
    because another protein, called Staufen,
    recognizes a structure in the 3UTR of the bicoid
    message (and Staufen protein is itself localized
    by the polarity of the cytoskeleton).

22
Gap genes
  • The gap genes are expressed by the zygote
    (activated in the syncytial blastoderm)
  • Their expression patterns are regulated by the
    maternal gene products, and they regulate each
    other
  • They divide the embryo into broad, unique domains
    containing different combinations of
    transcription factors

http//flymove.uni-muenster.de/Processes/Segmentat
ion/
23
Pair-rule genes
  • Pair-rule genes are expressed just before
    cellularization in patterns of 7 stripes (half
    the number of segments in a wild type larva)
  • Some pair-rule genes respond to patterns already
    laid down by the maternal and gap genes, while
    others are regulated by other pair-rule genes
  • Pair rule gene expression is very dynamic!
    (pretty pictures)

http//flymove.uni-muenster.de/Processes/Segmentat
ion/
24
Segment polarity genes
  • Segment polarity genes are expressed at the onset
    of gastrulation
  • They are expressed in 14 segment bands, refining
    the patterns of all the previous genes in the
    hierarchy. Maternal, gap and pair-rule gene
    expression begins to fade away

http//flymove.uni-muenster.de/Processes/Segmentat
ion/
25
Stripe boundaries are precisely defined
26
Control regions upstream of pair-rule genes are
complex
27
ASSIGNED PAPERTranscriptional regulation of a
pair-rule stripe in Drosophila
Small, S. et al., Genes Development (1991) 5
827-839
28
Main players
  • Even-skipped (eve) is a homeo-box containing
    transcription factor.
  • Hunchback (hb) has multiple Zn fingers.
  • Bicoid (bic) is a homeo-box containing
    transcription factor.
  • Kruppel (Kr) contains a Zn finger.
  • Giant (gt) contains a Leucine zipper.

29
Wild type expression patterns of putative
regulators of eve stripe 2
  • even-skipped protein is red
  • hunchback protein is green
  • overlap of expression is yellow

30
Wild type expression patterns of putative
regulators of eve stripe 2
  • even-skipped protein is red
  • Kruppel protein is green
  • overlap of expression is yellow

31
Wild type expression patterns of putative
regulators of eve stripe 2
  • even-skipped protein is green
  • giant protein is red
  • Overlap of expression is yellow

32
Wild type expression patterns of putative
regulators of eve stripe 2
High levels of gt
High levels of Kr
33
Wild type expression patterns of putative
regulators of eve stripe 2
High levels of gt
High levels of Kr
What predictions arise from this picture?
34
eve-lacZ gene fusion
This is a transgene gets injected into the
embryo (P transformed embryos), integrates into
the genome and is expressed stably along with all
the other genes. BUT this transgene will express
lacZ in an even-skipped-stripe 2 dependent manner!
35
Questions to ask about in vivo expression patterns
  • How do we know the order in which patterning
    genes act in development?
  • How were potential trans-acting regulators of
    stripe 2 identified?
  • What would happen to the domain of expression of
    eve stripe 2 in giant or Kruppel mutant embryos?
  • Do these vivo expression patterns indicate direct
    interaction between Kr and gt and the eve stripe
    2 regulatory region?
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