lecture 23: diseases and disorders 1: non-human sex differentation

Question 1

What is vertebrate phylogeny?

Answer 1

• hormonal influence
  
  • gold fish
  • frog
  • snakes
  • birds
• genetic influence
  
  • platypus → XY chromosome arise
  • kangaroo
  • mouse
  • human
• common ancestory drosophila

Question 2

What are different animal models of sexual differentiation?

Answer 2

• mouse model (Genetic sex determination, XY/XX)
• marsupial model (GSD, XY/XX)
• avian model (GSD, ZW/ZZ)
• reptile model (environmental sex determination)
• fish sex differentiation (GSD/ESD)
• drosophila (GSD, XY/XX)
• nematode sex differentiation (XO/XX)

Question 3

What are sexual differentiation events?

Answer 3

• days from fertilisation
• E9.5 germ cell migration to gonads
• E10.5 indifferent gonads, onset of testicular differentiation
• E10.5 to 12.5 sex determination window
• E13.5 onset of ovarian differentiation
• E13.5 entry into meiosis

Question 4

How do testes develop in the mouse?

Answer 4

• testis cord in testes
• adjacent to mesonephros
• germ cells are surrounded by sertoli cells, PM cells to form testis cords
• leydig cells reside outside testis cords

Question 5

What is gonad development in the mouse embryo?

Answer 5

• Sf1, Wt1, Lhx9, M33, Emx2 → at this stage gonad has potential to form testis or ovaries
• E10.0-11.5 - indifferent gonad
  
  • SRY → SOX9 (Fgf9 [important for proliferation of somatic cells and differentiation of sertoli cells], AMH [important for regression of the mullerian duct], Dmrt1 [related to double sex in drosophila, promotes and maintains testis development]) → E12.5 XY gonad
  • wnt 4 Fst → E12.5 XX gonad → E18.5 XX gonad

Question 6

What is the model of sex development in the tammar wallaby (marsupial)?

Answer 6

• postnatal development → short gestation, long lactation
• before birth there is no difference between testis and ovary
• male:
  
  • onset of testicular differentiation v soon after birth (before 1 day)
  • testicular cords visible from day 2
• female
  
  • onset of ovarian differentiation 6.5 days after birth
  • cortex and medulla visible ~8 days
  • slower

Question 7

What determines sex differentiation in the marsupial?

Answer 7

• GSD XX:XY (SRY)
• marsupial key sex determining and differentiation genes
  
  • SRY, Sf1, Fgf9 → Sox 9 → male specific targets
  • master regulator → Wnt4 (beta catenin → female specific targets), FoxI2 (aromatase → E2-ER, inhibits Sox9, female specific targets, self promotion)

Question 8

What is eostrogen sex reversal?

Answer 8

• testes become ovary when treated with oestrogen
• formation of cortex and medulla

Question 9

What was seen when doing RT-PCR of the cells in the E2-treated testes?

Answer 9

• SRY and AMH are greatly downregulated when treated with E2
• however SOX9 levels had no change
• where is SOX9 located

Question 10

What is the sox9 protein distribution in sex reversed testes?

Answer 10

• cytoplasmic
• usually in sertoli cell nucleus

Question 11

What is the effect of oestrogen treatment on the female pathway?

Answer 11

• genes are greatly upregulated

Question 12

So what is the effect of oestrogen on the sex differentiation pathway?

Answer 12

• inhibits SRY
• inhibits nulcear sox9
• inhibits AMH
• therefore inhibits testis
• upregulates female pathway leading to development of ovary e.g. Wnt4, FoxL2

Question 13

What is sex determination in the chicken?

Answer 13

• genetic sex determination
• ZZ (male): ZW (female)
• testis
  
  • seminiferous cords
  • reduced cortex
  • arrested germ cells
• ovary
  
  • fragmented medulla
  • thickened cortex
  • meiotic germ cells

Question 14

What is gona development in the chicken?

Answer 14

• at 4.5 days the gonads are undifferentiated
• morphological differentiation incubation day 6.5
• lots of genes are expressed in these processes
• SF1
• two genes important for the male pathway: Dmrt1, SOX9
• different chromosomes, conserved genes

Question 15

How is sex determined in most reptiles?

Answer 15

• environmental
• temperature sex determination in reptiles
• for macroclemys temminckii → betewen 24.5 and 27 degrees C, more than 50% are male, higher than that majority female
• for trachemys scripta, below 28, 100% male
• alligator has a similar curve but at different temperatures
• with climate change, if temperature increases 2 degrees, huge impact on ratio of males to females

Question 16

What is environmental sex determination (ESD)?

Answer 16

• occurs in most turtles and all crocodilians
• incubation temperature of eggs in critical time window → sex
• small change can have huge effect on sex ratios
• primarily controlled by modifying oestrogen production
• male temp → inhibits aromatase gene → testicular development
• female temp → aromatase gene → oestrogen → ovarian development

Question 17

How is sex determined in fish?

Answer 17

• over 32,000 types of species
• two type of sex determination systems - GSD and ESD

Question 18

What is fish sex reversal?

Answer 18

• many fish are serial hermaphrodites
  
  • juvenile → male → female
  • juvenile → female → male
• which pathway is better in terms of reproductive strategy?
  
  • female to male
• sex changed
  
  • colouration
  • behaviour
  • gonadal sex
  • nemo?
    
    • clown fish
    • dominant female and nondominant male and undifferentiated
    • remove dominant female and the male becomes female

Question 19

What is medaka fish sex differentiation?

Answer 19

• GSD XX XY (DMY)
• DMY → foetal testis → Dmrt1 → adult testis

Question 20

How is sex determined in drosophila?

Answer 20

• the ratio of X chromosomes : autosomes determines sex
• (A)X:A ration = 1.0 = female
• = 0.5 = male

Question 21

What is the mechanism for sex determination in drosophila?

Answer 21

• female
  
  • primary signal: 1.0
  • key gene: SXL (active)
  • subordinate control genes: TRA (active)
  • TRA-2
  • double-switch: DSX
  • female
• male
  
  • primary signal: 0.5
  • key gene: SXL (inactive splice)
  • subordinate control genes: TRA (inactive splice)
  • double-switch: DSX
• DSX is alternatively spliced

Question 22

How is sex determined in C. elegans?

Answer 22

• XX hermaphrodite: both ovary and testes
• XO male: testis only
• the primary sex determination depends on the ratio of X chromosome to autosomes same as drosophila

Question 23

What is the mechanism of sex determination in C. elegans?

Answer 23

• master sex switch gene: xol-1
  
  • on in X:A = 0.5
  • off in X:A = 1.0
• DM domain transcription factor:
  
  • mab3: on if xol-1
  • male

Question 24

In summary:

Answer 24

• conserved sox9 in vertebrates
  
  • XX/XY: most mammals SRY, medaka fish DMY
  • ZZ/ZW: chickens dmrt1
  • temperature: many species
  • all lead to production of SOX9 → sertoli cell differentiation → testis
• Dmrt1: DSX and mab-3 related transcript 1
  
  • mammals
    
    • signal: dominant Y → SRY-mediated regulation of gonad development, hormones → Dmrt1 (key male target gene)
  • drosophila
    
    • X:A ratio → cascade of regulated mRNA splicing → Dsx
  • c elegans
    
    • X:A ratio → secreted ligand-membrane receptor pathway → mab-3
• underlying genetic controls highly conserved
• Y determines gonadal sex in most mammals
• environments can stimulate sex differentiation
• X:A ratio determines sex in drosophila and C. elegans
• sex determining switch is highly variable across species