1. Drosophila homeotic mutants

2. Homeotic (Hox) gene complexes in Drosophila
lab pb
Dfd
Scr
Antp
Ubx
abdA
AbdB
labial
Deformed
Antennapedia
abdominal-A
proboscipedia
Sex combs reduced
Ultrabithorax
Abdominal-B
Antennapedia Complex (ANT-C)
Bithorax Complex (BX-C)

3. Expression patterns of homeotic genes in embryogenesis
labial
Antennapedia
Ultrabithorax
abdominal A
Abdominal B
proboscipedia
Deformed
Sex combs reduced
lab pb
Dfd
Scr
Antp
Ubx
abdA
AbdB

4. Two types of homeotic mutants in Drosophila
dominant mutations
gain-of-function
Transformations “anterior to posterior“
recessive mutations
loss-of-function
Transformations “posterior to anterior“

5. serially homologous limbs
Antennapedia - a homeotic mutant
antennenal segments
Arista
coxa
claw
tarsal segments
troch-
anter
tibia
femur
Antp / +
antenna and leg are
serially homologous limbs
antenna transformed into leg

6. proboscipedia - transformation of mouthparts into legsmx
mx* lb
lb*

7. Complex homeotic gene regulation
regulatory
mutations
Coding-region
Bithorax Complex
(BX-C)

8. Ubx is expressed in T3 and A1

10. Ultrabithorax binds DNA and regulates genes required for T3 and A1
Ultrabithorax expression
Ubx protein
OFF ON
T2 specific gene
OFF
T3 specific gene ON
A5 specific gene
A1 specific gene

11. All abdominal segments take on a T2 identity if the bithorax complex is deleted
ubx abdA abdB
triple mutant
Wild type T2 T3 A1 T2 A8 T2

12. Antennapedia expression expands in flies mutant for the Bithorax complex genes
ANT-C
BX-C
Figures\Chapter09\DevBio7e09264.jpg

13. Ultrabithorax, AbdA, and AbdB normally repress expression
of the thorax-specific “leg gene” Distalless
in the abdominal segments
wild-type
ubx abdA abdB triple mutant
abdomen
T1 T2 T3

15. Persistence of homeotic gene expression through development
Adult
Imaginal
discs
larva
embryo

16. Maintenance of homeotic gene expression
maintenance of transcriptionally inactive state
maintenance of transcriptionally active state
trithorax group (Trx-G)
Polycomb group (Pc-G)
extradenticle
realisator gene
Trx-G
Pc-G
transcriptionally
open
chromatin
Dfd
Exd pb
Scr
Antp
closed

17. Lewis hypothesized
that the duplication
and diversification
of homeotic
master regulators
underlies the evolution of
an increasingly complex
body plan

18. Distal-less gene Drosophila Precis (butterfly)
required for limb development
Drosophila
Precis (butterfly)

19. The human body
is also
built up from
reiterated units (segments)
with different
identities along
the A/P axis

21. Hox gene expression in mouse embryos

22. Mouse HOX gene expression patterns

23. Mouse hoxa3 and hoxd3 mutants
from Nature 370: (1994)

24. Wild-type mouse forelimb
hoxa-11 hoxd-11
Human hoxD13 mutation