1. Evolution of Sex-Specific Traits
through Changes in HOX- Dependent
doublesex Expression "
Presenter: Peng, Yi-Hung"
♀
♂

2. Introduction

4. “Sexual Dimorphism”
性別二型性
4

5. The origin of sex- specific structures
from sexually monomorphic
precursors implies the evolution of
new, sexually dimorphic regulatory
pathways.
5

6. Drosophila species including the melanogaster and
obscura species groups
6

7. “Sex Comb”
on T1 leg, ta1 segment.
on T1 leg, ta1 segment.
(A sexually Dimorphic trait of
(A sexually Dimorphic trait of
Male D. melanogaster)
Male D. melanogaster)
7

8. ♂
Sex Comb

9. ♀
No Sex Comb

11. dsx
(doublesex)
11

12. dsx (doublesex gene) establishes and modifies
sexually dimorphic traits of Drosophila melanogaster
12

13. DM domain genes share the same characteristic DNA
binding domain; dsxM and dsxF both share a common
binding domain
13

14. DSX M!
Common DNA binding domain
DSX F DSX M
Bind Control Expression!
Gene’s binding site for DSX
DNA
14

16. Scr
(sex comb reduced)
16

17. Sex comb development requires both
dsx and the HOX gene Sex combs
reduced (Scr), suggesting that dsx and
Scr cooperate to induce sex- and
segment-specific downstream targets
17

18. They affect each other…
But How?
18

19. Experiments Results

20. 20

21. What is the expression
pattern of dsx
correlated with sex comb?
21

22. Sex
Comb
TBR:
transverse
bristle
rows
Male
Female
In the male, the most distal TBR is modified into the
sex comb
22

23. Green
:
Dsx
Red
:
Scr
late non-wandering L3 Stage, T1 leg:
high levels of Scr; no Dsx expression
23

24. Green
:
Dsx
Red
:
Scr
wandering L3 and white prepupal stages, T1 leg:
Dsx expression is apparent in both male and female
24

25. Green:
Dsx
Red:
Scr
wandering L3 and white prepupal stages, T1 leg:
Dsx expression was not detected in T2 or T3 leg discs
25

26. Green:
Dsx
Red:
Scr
M
M
M
F
Prepupal legs at 5 h after pupariation (5 h AP):
Dsx expression is clearly seen
26

27. Male
Green:
Dsx
Red:
Scr
Female
The overlap with high Scr expression, which extends
more proximally, is more extensive in males than in
females
27

28. Male
Green:
Dsx
Red:
Scr
Male
In males, but not in females, Dsx expression is also
seen in clusters of cells in ta2–ta5 segments
28

29. Dsx expression becomes
sexually dimorphic at the
prepupal stage
29

30. Male
presump=ve
sex
comb
Male
Female
Prepupal legs at 16 h after pupariation (16 h AP):
Males : Dsx is expressed strongly in and around the
presumptive sex comb
Female : expression is consistently lower
30

31. Male
Male
Female
Male-specific expression of Dsx in ta2–ta5 disappears
by this time
31

32. Dsx,
Sex
comb
Scr
24 h AP male : Dsx and Scr develop complementary
expression patterns
32

33. 36 h AP male T1 leg:
This pattern is maintained at later stages
33

34. Both Dsx and Scr are expressed in
restricted and sex-specific patterns in
the sex comb at the critical time in its
development.
“dsx Expression Is Regulated in a
Spatio-Temporal and
Sex-Specific Manner”
34

35. 35

36. Is dsx regulation transcriptional ?
36

37. Male
T1
leg
RNA probe, in situ hybridization (L3 and white prepupal):
dsxM transcript is the same as the Dsx protein
37

38. This transcript is undetectable either in the male T2
and T3 discs or in the female T1
38

39. Male
T1
leg
At 24 h AP:
dsxM transcript is similar to the protein distribution
39

40. Male
Female
Ectopic UAS-dsxM expression, rn-Gal4 driver:
no evidence for a post-transcriptional mechanism
40

41. Quantitative rt-PCR:
not reveal any differences
41

42. Spatially restricted expression of dsx
is caused by transcriptional regulation.
“dsx Regulation Is Transcriptional”
42

43. 43

44. What are the roles of dsx and scr in
sex comb development?

45. We examined the effects of loss and
ectopic expression of dsxM
in different cell types.
45

46. First thing first, you should know the
“Gal4-UAS system”
46

47. (接下來文中省略)
tub-Gal80ts; rn-Gal4/UAS-ScrRNAi
Prmoter
Target
47

48. ♂
Different
-Gal4 line
Collect
♀
X!
UAS-Bline
F1 (First offspring generation) Only!

49. F1 (First offspring generation) Genotype
Activate!
+
5’!
5’!
A
Bind and
activate UAS!
3’!
Gal4
Produce
Gal4!
Gal4
3’!
UAS
B!
Activate!
+

50. So……

51. Reference
Knocking down dsx in rn-Gal4/UAS-dsxRNAi (MF):
Intersex phenotype, similar to the dsx null phenotype
51

52. Reference
à dsxM promotes sex comb development
in males while dsxF actively blocks it in females
52

53. Overexpression dsx - neur-Gal4/ UAS-dsxM flies,
restrictive temperature (MF):
Resulted in the transformation of all or most TBR
bristles into sex comb teeth
53

54. None of the bristles outside of the TBRs showed any
signs of transformation.
àDsxM need to express with Scr together to induce
sex comb
54

55. These results confirm that sex comb
rotation is driven by the surrounding
epidermal cells and that these cells
require high levels of both Dsx and Scr
55

56. Overexpression dsx - rn-Gal4/UAS-dsxM flies (FM):
Transformed two to four distal TBRs into small sex
combs that underwent rotation.
56

57.
Knock down Scr: 100% loss of the sex comb
However, If KD specifically in bristle precursor cells:
50% loss of the sex comb
57

58. It is possible that Scr levels determine the number of
bristle precursors during larval or prepupal stages
58

59. Thus, many functions of Scr in sex
comb development may be mediated
by the activation of dsx expression
59

60. Knock down
Overexpress
Scr: No Dsx
Scr: Dsx express
60

61. Major role of Scr in sex comb
development is to initiate a sexspecific developmental program by
turning on dsx expression.
61

62. 62

63. Scr expression in the T1 leg
is sexually dimorphic
Does Dsx modulate Scr expression in
the sex comb region?

64. Knock down
Overexpress
dsxM: medium level Scr
dsxM: high level Scr
64

65. DsxM up-regulates
DsxF down-regulates Scr
àboth isoforms are involved in
sexually dimorphic development.

66. 66

67. The spatial correlation of Dsx and Scr
expression is maintained in all species
and reflects sex comb morphology
rather than phylogenetic history
How to say it?

68. Distantly related species have evolved similar sex
combs independently (in melanogaster species group )

69. Bigger picture!
69

70. 70

71. 71

72. 72

73. Cross-regulatory relationship between
Dsx and Scr is conserved throughout
the melanogaster species group and
may contribute to the rapid evolution
of sex comb morphology.

74. 74

75. The sex comb is a recent evolutionary innovation that
is absent in most Drosophila species.
75

76. Dsx expression domain was already present in the last
common ancestor of both species groups.
76

77. dsx is expressed in temporally dynamic,
rapidly evolving
77

78.
However, dsx expression in the
presumptive sex comb region appears
to be an evolutionary innovation that
coincides with the
origin of the sex comb
78

79. 79

80. Sex combs are only one example of
sex-specific structures
80

81. Male
Female
Example 1: D. immigrans with smaller but much more
numerous and densely packed bristles
81

82. Male
Female
Example 2: genus Zaprionus TBRs on the ta1 of the T1
leg are replaced with thinner and numerous bristles
82

83. Phylogenetic analysis suggests that
male-specific morphological structures
originated independently in the
immigrans species group, Zaprionus,
and the melanogaster+obscura clade
83

84. Evolutionary gain of new dsx
expression domains through a
regulatory link between Scr and dsx
has been a key step in the origin of
novel sexually dimorphic structures.
84

85. 85

86. Discussion

87. Traditional models:
sex determination pathway functions
ubiquitously
Recent work:
has shown that dsx is expressed in
tightly restricted spatial patterns
87

88. Sexually dimorphic development may
also be regulated through localized
deployment of dsx.
88

89. Recent Discovery:
Upstream regulator of dsx
transcription, the HOX gene Scr
89

90. 90

91. Positive Feedback Loop?
91

92. the HOX and sex determination genes establish a
positive autoregulatory loop
92

93. No ‘‘master regulators,’’ both dsx and Scr are
intimately integrated into the middle of this network
93

94. The positive feedback loop between
dsx and Scr may play a major role in
generating sex comb
and its diversity across species.
94

95. Why is this idea important?
To our knowledge, the sex comb is the
first example of an evolutionary
change of this kind
95

96. Sex- specific traits:
Established by a dsx-Scr positive autoregulatory loop
96

97. Moreover, there is a constant turnover
of sex- specific traits.
Is it possible that the proximate cause
of this turnover of sex-
specific traits lies in the acquisition
and loss of new spatial expression
domains of dsx?
97

98. DSX M!
New Sex- specific traits
Other!
Scr!
Sex- specific traits lies in the acquisition and loss of
new spatial expression domains of dsx
98

99. So we believe that it is
a general role for dsx in evolutionary
innovations.
99

100. Thank you
100