The role of the SRY gene in determing sex.

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Transcript The role of the SRY gene in determing sex.

Ahmed Mahmoud
What makes a male or female?
 In mammals, gonadal development is determined by
the sex chromosomes.
 XX usually constitutes female
 XY constitutes male
 How ever, some males have XX
 Some females have XY
 Why is this?
Key players in the sex determining
SRY gene
Stands for Sex determining region of Y chromosome.
WNT signaling pathway
a network of proteins used to control the production of
wnt signaling molecules.
 WNT4- the gene that codes for a signaling protein that is
involved in female gonadal development.
 β-catenin- protein complex that is used in the WNT
signaling pathway.
 RSPO1 gene- encodes for a small secreted protein that is
able to encourage the Wnt/β-Catenin signaling pathway.
History of the SRY
Cladogram showing evolution of
SRY Gene.
 The Y chromosome’s role in sex determination was
known since the early twentieth century.
 The Exact region was found out in 1990.
 SRY region extends 897 base pairs long
Exact location of the SRY gene on
the Y chromosome
The SRY gene: The
Male determining factor.
 SRY gene is located on the short arm of the Y
 This Gene causes male gonadal development.
SRY and The SOX family
 SRY is part of the SOX family of proteins that is
characterized by a DNA binding domain.
 There are 20 SOX genes present in humans.
 SRY however does not have a transcription domain and
closely works with another member of the SOX family;
SOX9(SRY box-9).
 In XY individuals, SOX9 was found to increase in
expression shortly after the beginning of SRY being
Sox9 Gene location & Info
SOX9 is located on Chromosome 17
It is 5,401 pairs long
Location of
SOX9 Gene
The female determining factors.
 R-Spondin 1 (Rspo 1) and The Wnt/β-Catenin pathway.
 Rspo 1 was found to increase in expression in XX
females at the time of ovarian differentiation(1).
 Rspo 1 is needed to express the Wnt4 gene and it works
through the stabilization of β-Catenin to develop
ovaries and block testis.
 Rspo 1, Wnt4 and β-Catenin are all parts of one
pathway to a ovarian result and block the development
of testis.
RSPO1 Loci.
23,645 bases long
WNT4 Loci.
25,722 bases
Pathways of determination.
Int J Biochem Cell Biol. 2008; 40(12): 2889–2900
SRY blocks Wnt Pathway
Lab experiment performed by
Pascal Bernard
Int J Biochem Cell Biol. 2008; 40(12): 2889–2900
HEK293T cells –Human embryonic
kidney cells
NT2/D1 cells-Human embryonic
carcinoma cells
TCF- T-Cell specific HMG box factor.
Protein found in the above mentioned
cells that plays a key role in Wnt
TOP-Short for TOPFLASH which is an
assay which has a binding site for
β-catenin to bind to the cell’s TCF
FOP- short for FOPFLASH which is a
a control for TOP. It contains a mutant
binding site that is unable to bind to
TCF protein.
BIO6-bromoindirubin-3’-oxime. Used to
When SRY was added, it reduced
the activation of TCF/β-Catenin
by two fold
As SRY is introduced,
the cells with the
binding site for TCF
begin to slowly
When BIO is added and no
SRY is present, TCF/βCatenin binding is strongly
Rspo1 activates β-Catenin signaling
Experiment performed by AnneAmandine Chassot
Experiment sought out to show
that Rspo1 controls the activation
of the β-catenin signaling pathway.
Urogenital ridges were stained for
finding the Lef1 which is a gene
involved in β-catenin signaling.
An XX gonad positive
for Rspo1 shows
staining that
represents the Lef1
gene for β-catenin
An XY gonad also positive
for Rspo1 does not show
staining for the Lef1 gene
which may be due to the
SRY genes inhibition of the
signaling pathway.
Human Molecular Genetics 2008 17(9):1264-1277; doi:10.1093/hmg/ddn016
An XX gonad negative for
Rspo1 showing no staining
for the Lef1 gene. Proving
that Rsp01 mediates the
β-Catenin Signaling
SRY and Sex Reversal
 Sex Reversal syndrome (SRS) is a kind of genetic
disorder which creates a conflict between gonad
development and chromosomal phenotype.
 The incidence rate of Sex reversal syndrome occurs in
about one in every 100,000 individuals
 SRS proves once more that the SRY gene is the most
important male determining factor
A study male SRS
 46 XX male sex reversal
 Study conducted on a 20 year male.
 Patient had undescended testicles.
 Physically, the patient had the sexual characteristics of a normal
 Slender skeleton and light beard.
Translocation of SRY.
The patients DNA and control samples were tested by PCR(Polymerase chain reaction)amplification in figure A.
Figure B shows fluorescent microscopy on the patients DNA.
Fluorescence in situ hybridsation of
patients DNA showed a green
fluorescence on the short arm of the X
chromosome. This gen was
translocated to Chromosome X from
Chromosome Y.
PCR amplification
showed that both
the Patient (P)
and the Normal
male (NM) were
consistent in
showing a SRY
fragment while
the Normal
female (NM) had
no such
fragments of SRY.
SRS in the Olympic games
 In the 1992 Barcelona Olympic games, female athletes
were tested through PCR
 Over 2000 test were performed and of those, 15 were
reported positive.
 In the 1996 Atlanta games, 8 reported positive.
 Gender Verification tests were abandoned in 1999 and
still are to this day.
 SRY gene is the most important male determining
 The pathway leading to ovarian development goes
through the β-catenin/Wnt signaling pathway.
 The SRY gene can inhibit the usual pathway leading to
ovarian differentiation.
 SRS is due to the translocation to an X chromosome.
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