MCB 141

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MCB 141
Lecture 6 Feb. 5, 2009
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Segment polarity Deletions/duplications
in every segment gooseberry engrailed hedgehog w
ingless patched armadillo etc.....
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Pair-rule Two segment periodicity fushi
tarazu even-skipped paired odd-skipped runt hairy
odd-paired sloppy paired
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WT
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WT
Pair-rule mutant
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Gene X mRNA
Gene X protein
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B F
C G
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7 Cervical 12 Thoracic 5 Lumbar 5
Sacral 4 Coccygeal
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William Bateson - 1894 Materials for the Study
of Variation For animals made of repeating
units (segments), Bateson noted that sometimes
the number of segments was altered, but other
times the total number of segments was unchanged,
but th identity of segments was changed. Coined
the term homeosis and homeotic (from the Greek
root for the same) Something has been changed
into the likeness of something else
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Examples
Normal 7C, 12T, 5L, 5S, 4Cg Meristic 7C, 13T, 5L,
5S, 4Cg Homeotic 7C, 11T, 6L, 5S, 4Cg
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A fundamental pattern of living organisms is the
repetition (with modification) of units
Meristic variation - variation in the number of
units Homeotic variation - constant number of
units, but one or more transformed to another
identity
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Homeotic mutants in Drosophila
Wild-type Antennapedia
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Homeotic mutants in Drosophila
Wild-type Antennapedia proboscipedia
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Mn Mx La T1 T2 T3 A1 A2 A3 A4 A5 A6 A7 A8
WT
Ubx
Mn Mx La T1 T2 T2 T2 A2 A3 A4 A5 A6 A7 A8
abd-A
Mn Mx La T1 T2 T3 A1 A1 A1 A1 A5 A6 A7 A8
Abd-B
Mn Mx La T1 T2 T3 A1 A2 A3 A4 A4 A4 A4 A4
In homeotic mutants, still the right number of
segments, but the identity of some are
transformed to the identity of others.
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Mn Mx La T1 T2 T3 A1 A2 A3 A4 A5 A6 A7 A8
WT
Ubx
Mn Mx La T1 T2 T2 T2 A2 A3 A4 A5 A6 A7 A8
abd-A
Mn Mx La T1 T2 T3 A1 A1 A1 A1 A5 A6 A7 A8
Abd-B
Mn Mx La T1 T2 T3 A1 A2 A3 A4 A4 A4 A4 A4
Ubx / abd-A
Mn Mx La T1 T2 T2 T2 T2 T2 T2 A5 A6 A7 A8
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Mn Mx La T1 T2 T3 A1 A2 A3 A4 A5 A6 A7 A8
WT
Ubx
Mn Mx La T1 T2 T2 T2 A2 A3 A4 A5 A6 A7 A8
abd-A
Mn Mx La T1 T2 T3 A1 A1 A1 A1 A5 A6 A7 A8
Abd-B
Mn Mx La T1 T2 T3 A1 A2 A3 A4 A4 A4 A4 A4
In homeotic mutants, still the right number of
segments, but the identity of some are
transformed to the identity of others.
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Normal fly
Ubx mutant
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Normal fly Ubx expressed T3 post.
Loss of Ubx expression from T3 late in
development
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Homeotic mutants in Drosophila
Wild-type Antennapedia
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Hunchback
Ubx
What happens to Ubx in a hunchback mutant?
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Hunchback
Ubx
But how can this work given that Hunchback
protein (at least In gap pattern) is gone by the
onset of gastrulation?
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Hunchback
Ubx
Polycomb group genes provide cellular memory
and an epigenetic mechanism.
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Burke et al., 1995
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Normal mouse 13T 6L 4S Hox10 expression
Lumbar to posterior Hox11 expression Sacral to
posterior
Hox 10 11 mutant 23 Thoracic vertebrae No
lumbar No sacral
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Normal fly Ubx expressed T3 post.
Loss of Ubx expression from T3 late in
development
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