12 – Sex Determination Flashcards
1
Q
Sex of the individual is determined by
A
- Sperm (+/- Y) and subsequent genetic control of sex differentiation
2
Q
What cells are put aside for formation of the germ line?
A
- A population of epiblast cells=PGCs
3
Q
Primordial germ cells (PGCs)
A
- Displaced from embryonic disk to the definitive yolk sac and part of the allantois
4
Q
PGC migration
A
- Into hindgut and towards GONADAL ridge
- E-cadherin (membrane adhesion protein) help keep them grouped together
- Integrins (membrane receptors) promote interaction of extracellular environment for migration to proceed
- *remain PGCs outside GONADAL ridge area=die
5
Q
Somatic cells around the PGCs
A
- Secrete CHEMOATTRACTANTS
o PGCs have receptors for them to induce their migration - Produce SURVIVAL FACTORS to maintain PGC viability during migration
6
Q
Gonadal ridge
A
- *bipotential gonad in most individuals (can become ovary or testes)
- Forms medial to embryonic kidneys (mesonephros)
7
Q
What are the origins of gonadal ridge cells (somatic)?
A
- Local mesenchymal cells
- Coelomic epithelium
- Cells from mesonephric tubules
8
Q
Degenerating mesonephric tubule cells form
A
- Compact strands of tissue=PRIMITIVE SEX CORDS to incorporate PGCs
9
Q
PGCs that enter gonadal ridge
A
- Undergo major MORPHOLOGICAL and BIOLOGICAL changes (regardless of XX or XY)
- *signals from somatic cells inducing switch from PGC to more germ-like cells to proceed to sperm or oocyte development
10
Q
Phenotypic sex is largely governed by
A
- Type of gonad that develops in the embryo
- *determined by chromosome complement or genetic sex (+/- Y chromosome)
11
Q
Gonads will produce sex-specific hormones leading to
A
- Development of internal genitalia, secondary sex characteristics and external genitalia
12
Q
Need for regulation of determination, differentiation and development of gonads
A
- TIGHTLY regulated network of transcription factors and cell signalling molecules
- *otherwise disorders of sex development (DSDs) occurs
13
Q
Y chromosome contains a gene called
A
- Sex Determining Region on Y chromosome (SRY)
- *encodes SRY protein (testis determining factor(TDF))
- **GENETIC SEX DIFFERENTIATION
14
Q
What are the critical testis-determining genes?
A
- SRY: when transcription reaches threshold = induces expression of Sox9
- Sox9: Only high in males (sexually dimorphic)
- *SRY->Sox9->Sertoli cell differentiation
15
Q
Development of seminiferous cords
A
- Solid tubes containing germ cells
- Contain 15-10 coelomic derived cells(Sox9 positive cells)=Sertoli cells
o Surround a central core of PRO-SPERMATOGONIA (gonocytes) - Mesenchymal cells and mesonephric cells between cords=Leydig or Interstitial cells
16
Q
Sertoli cells orchestrate male-specific processes
A
- Secretion of morphogens=Leydig Cells (will produce testosterone=drive toward phenotypic sex of individual)
17
Q
At puberty, seminiferous cords become
A
- Seminiferous tubules=continuation between rete testis and efferent ducts
18
Q
Mesonephric duct develops into
A
- Epididymis
- Ductus deferens
19
Q
Efferent ducts, epididymis and ductus defers are part of
A
- Excurrent extragonadal duct system
- *carry sperm through to urethra
20
Q
Cells without SRY express
A
- Female promoting genes and INHIBIT male promoting genes (ex. inhibit Sox9)
- **ovarian development LACKS A SINGLE GENETIC SWITCH
o Key genes do exist for correct development
21
Q
Forkhead box L2 (Foxl2)
A
- Gene transcription factor
- One of earliest to be induced in developing female-specific ovary
- *mutation in goats leads to female to male sex reversal
22
Q
Foxl2 in postnatal life
A
- Maintenance of ovary by suppressing genes involved in testis determination from embryonic to adult life
23
Q
Without SRY protein, some cells of degenerating sex cords and coelomic cells surround the PGCs (oogonia) and differentiate into
A
- Primitive follicular or pre-granulosa cells
24
Q
Mesonephric duct is still intact early and will begin (ovary development)
A
- Regressing while rete tubules degenerate
- *NO DIRECT DUCT OUTLETS for gametes like in male
- *paramesonephric duct develops further and ENLARGES
25
Primitive follicular cells surround PGCs (ovary development)
- Do NOT penetrate deeply into interior of developing ovary
- *STAY ORGANIZED as primordial follicles in periphery (will become the cortex)
- Sex cords disappear completely
26
What does the paramesonephric duct become once it has enlarged greatly with an opening
- Future INFUNDIBULUM
- Fuse together near attachment with urogenital sinus
o Degree of fusion leads to UTERINE TYPES (ex. duplex, bicornuate, simplex)
27
XX oocyte in developing follicle produces
- Growth Differentiation Factor 9 (GDF9)
o Induces granulosa cells to secrete morphogens to stimulate gene specific thecal cell programming
28
Thecal cells
- Will produce androgens under LH control, to be converted into estradiol within granulosa cells
29
Granulosa cells orchestrate female-specific processes
- Signals germ cells to enter meiosis
- *Secretes morphogens that induce Thecal cells (steroidogenic)
30
Interplay of testis and ovary pathways
- Male and female sex differentiation pathways ACTIVELY SUPPRESS one another
o During gonad differentiation and after testes or ovaries have developed
- Studies have show that testes and ovaries are EASILY CONVERTED
o CONSTANT EXPRESSION of specific genes is needed to prevent trans differentiation
31
DSDs: sex reversal species
- Seen in dogs, horses, pigs and goats
- Pigs and goats have high frequency compared to other species
- Ex. polled intersex syndrome in goats
32
Polled intersex syndrome in goats
- Due to DELETION within chromosome 1 that DIRECTLY effects transcription of 2 genes
o Hornlessness (Polled): dominant
o Ovarian development (Foxl2)
33
Polled intersex syndrome in goats: heterozygous polled genetic male (XY)
- No horns
- Sex determination=male (SRY is present)
- **Phenotypic male
34
Polled intersex syndrome in goats: homozygous polled genetic female (XX)
- No horns
- Infertile (no SRY) phenotypic male
- *female to male reversal
35
Polled intersex syndrome in goats: heterozygous polled genetic female (XX)
- No horns
- Still have one good copy of Foxl2
- *phenotypic female
