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Notes for U781 seminars: Vincent Harley – Australia
Disorders of sexual development – ambiguous genitalia or lesser degree eg hypospadias, or recognized at adolescence such as no development of 2e characteristics such as girl with testes or y chromosome – SRY or SF1 mutation.
Difficult decisions for management – gender assignment and identity? brain sex later on – manifest by 2-3 years of age ? Surgery controversial b/c babies can't decide for themselves early enough for societal expectations of gender assignment. How preserve maximal fertility?
Genes known: SRY, DAX1, SOX9, DMRT1, SF1, WT1, DHH, ATRX, RSPO1, WNT4. most of these when mutated or deleted lead to XY female, though RSPO1 is XX male, and Wnt4 is XX virilised.
DAX1 mutated – sex reversal but also when duplicated (XY female in mouse)
Wk 7 (human, or E10.5 mouse) gonad is bipotential. Gonad just glued above the mesonephros. SRY comes on to virilise embryos; in males this would repress RSPO upstream of WNT4, b-cat leads to ovary development. Testosterone synthesized around week 8.
Will discuss: SRY transport and interaction with Calmodulin, bringing it into nucleus.
Genotype-phenotype correlations in SRY: nuclear-localization signal; all SOX factors have the CaM binding domain.
The presenter has a cool widget which keeps a clock in the corner above the presentation so you can see how far along. Sry and CaM co-expressed at E11.5 in gonad, Co-IP and immunohistochemistry after interfering with CaM-Ca++ interaction with a product called CDZ (calmidazolium). Treatment with CDZ leads to sex reversal on sexually indifferent XY mouse gonads – lack of texticular cord development and ectopic Rspondin – ovary gene expn.
SF1-SRY transcriptional activity. Sekido and Lovell-Badge testis-specific SOX9 enhancer in 2008. "TES" – question if SRY and SF1 act on TES in humans. Transfected ovarian cell lines and the 3.2kb element was inducible by SRY. Mutations in patient maybe act on TES activation – indeed was the case. Most abolished activity in the CHO cell assay.
SF1 orphan receptor, also assoc with adrenal failure. Expn in intermediate mesoderm. KO no gonads at all. Upstream of WT1. Later in ovarian follicles.
SF1 alone initiates SOX9-TES interaction, then synergistically they upregulate TES-SOX9, then SOX9 replaces SRY to maintain high SOX9 expn. All human SF1 mutations (16 analyzed) do not synergize with SRY. A few have milder DSD forms, when partial synergy is maintained.
DAX1 – dosage-sensitive sex reversal when duplication on Xp leads to XY female phenotype. In females usually DAX1 is inactivated. in the XY people with DSS, both copies remain active, and block testis development.
SF1 expression in overdosed Dax1 mice, unchanged. But Sox9 and Amh reduced, not quite to XX gonad level. Used TES-powered LacZ; in Dax double-dose, expression reduced or absent in the early gonad.
Does Dax1 in excess lower Sox9 levels below level needed for a testis to differentiate? Sox9 +/- gonads look ok in mice (not in human) – cross with the DaxTg mice, cause "ovotesticular" DSD on that background.
Dax1 prevents SF1 binding to TES upstream of Sox9.
ATRX syndrome, testis growth. Alpha thalassemia, MR, X-linked spectrum. Also have undescended testes, or small – low testosterone? Also small penis, hypospadias, sometimes female or ambiguous genitalia (11%) carry mutations in ATRX. 2600 aa protein (!). No known target genes. Chromatin-remodeling?
Inactivated in Sertoli cells, recapitulate in mouse the human phenotype.
Is hypospadias consequence of low testosterone or loss of ATRX in external genitalia? Cre- mice to address, otherwise it's pretty ubiquitously expressed.
Elongation and branching of testicular cords between E15.5 and E17.5 usually; in mutants, some cords no longer linked to rest of network (tubes). By E17.5 the Sertoli cells, where had been inactivated, were undergoing apoptosis (8% vs <1%)
Fewer germ cells by P12, cords sometimes with no sperm, or little luminae. Looks phenocopy of androgen-receptor KO in Sertoli cells. Amh expression at P12 and P20 or AR were normal; however, AR targets needed for spermatogenesis were way downregulated. Rhox is a target.
Final discussion: gender ID
Transsexualism – brain structures in non-hormone-treated male-to-female trans-sexuals, bed nucleus of stria terminalis might resemble more female (cf Nature paper 1995).
Brain sexual dimorphism. Cyp19 aromatase convert testosterone to estradiol. Mutation of CYP10 (Lin 2007) assoc with transsexuality female to male, or in congenital adrenal hyperplasia.
Hypothesis testing if longer CAG polyglutamine repeats in AR reduce signaling efficacy – transsexuals had longer AR repeat than controls. But association weak and only add two CAG repeats.
Published last year.
family cases of transsexualism cf Charing Cross cohorts (12 cases)