Evolution of sex specific traits through changes in hox dependent doublesex expression(論文討論)

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Published on February 17, 2014

Author: BillPeng

Source: slideshare.net

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

Introduction

“Sexual Dimorphism”
 性別二型性 4

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

Drosophila species including the melanogaster and obscura species groups 
  6

“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

♂   Sex Comb"

♀   No Sex Comb"

dsx
 (doublesex) 11

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

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

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

Scr
 (sex comb reduced) 16

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

They affect each other…
 
 But How? 18

Experiments & Results

20

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

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

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

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

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

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

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

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

Dsx expression becomes 
 sexually dimorphic at the 
 prepupal stage 29

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

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

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

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

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

Is dsx regulation transcriptional ? 36

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

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

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

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

Quantitative rt-PCR:
 not reveal any differences 41

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

43

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

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

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

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

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

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

So……

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

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

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

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

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

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


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

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

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

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

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

62

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

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

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

66

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?

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

Bigger picture! 69

70

71

72

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

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

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

dsx is expressed in temporally dynamic, 
 rapidly evolving 77


 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

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

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

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

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

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

Discussion 

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

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

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

90

Positive Feedback Loop? 91

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

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

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

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

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

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

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

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

Thank you 100

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