Lecture 21: Sexual Differentiaton Flashcards by Hannah Kim

What are the 3 different levels of sexual differentiation?

1) Gonads
2) Internal Gneitalia
3) External Genitalia

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When do the different levels of sexual differentiation become fixed?

1) Bipotential gonads at <6 weeks
2) Bipotential internal genitalia <7 weeks
3) Bipotential external genitalia <8 weeks

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What are the parts of the genital ridge?

Equivalent to formation of genital ridge ( precursor to the gonads.)
Arise as paired structures in intermediate mesoderm
The genital ridge area can be divided into three from anterior to posterior
- Pronephros (caudal end forms adrenal galnds)
- Mesonephros (central rige forms gonads and internal reproductive structures- the Wollfian and Mullerian ducts)
- Metanephros (posterior end forms the kidneys)
  - This suggests that if you have problems in your genitalia, you are likely to have renal problems etc.

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What ist he bipotenial gonad?

Undifferentiated gonads of XX or XY individuals are apparently identical and can form either ovaries or testes. This period is therefore called indifferent or bipotentialstage of gonadal development.

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Descibe the development of the bipotneial gonad

The development of the genital ridge is dependent on the activation of nuclear transcription factors
These proteins binds and form part of the protein complex and DNA altering gene transcription/expression
Because adrenal, gonadal and renal organogensis occurs from the genital ridge (precursor to the gonads), their development occurs from similar transcription factors.
Mutations in these can affect more than 1 organ system

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What is the gonadal ridge?

precursor to the gonads

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Describe the development of the bipontential ridge

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What is the default mode of the bipotential gonad?

female

Need testosterone/testis to become a male.

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Describe the development of male internal genitalia

The sertoli cells release AMH which causes mullerian duct regression

Leydig cells produce testostrone causes wolffian duct stabilisation

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The sertoli cells release _____ which causes ___________

Leydig cells produce _______ causes ___________

The sertoli cells release Anti-Millarian Hormone which causes mullerian duct regression (no female structures- fallopian tubes, uterus, 2/3 vagina)

Leydig cells produce testostrone causes wolffian duct stabilisation (form Wolffian duct develops into the rete testis, the efferent ducts, the epididymis, the ductus deferens and the seminal vesiclesetc.)

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Summarise the development of EXTERNAL GENITALIA

If you have undifferentiated external genitalia, and there is no androgen, it develops into a female external genitalia
If there is testosterone, it develops into a m_ale external genitalia_
At conception, you don’t have the ability to produce LH from the pituitary. So initially you get it from Human Chorionic Gonadotropin (same alpha subunit- so it binds effectly to the LH receptors on the leydig cells)
- Placental HCG in first trimester
- Pituitary LH from 2nd and 3rd trimester
Leydig cells produce testosterone (if there are steroid genes)
5a-reductase convert this into DehydroTestosterone
DHT binds to the androgen receptor and convert undifferentiated external genitalia to male external genitalia

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At conception, you don’t have the ability to produce LH from the pituitary. So initially you get it from ______________

At conception, you don’t have the ability to produce LH from the pituitary. So initially you get it from Human Chorionic Gonadotropin (same alpha subunit- so it binds effectly to the LH receptors on the leydig cells)

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What transcription factors are essential for the Intermediate mesoderm to become Genital ridge (bipotential gonad)?

1) WT1 (willm’s tumour 1)
2) SF1 (steroidogenic factor 1)

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Testicular determination is initiated by ______

SRY gene (sex determining region of Y)

The initiator of ovarian determination remains unknown

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What makes up the:

Gonad

External genitalia

Internal genitalia

Gonad: an organ that produces gametes; a testis or ovary.

Internal genitalia:

The internal male genitaliainclude the seminal vesicle, testes, vas deferens, epididymis, prostate, bulbourethral gland, and ejaculatory duct.
The internal genitalia are those organs that are within the true pelvis. These include the vagina, uterus, cervix, uterine tubes (oviducts or fallopian tubes), and ovaries

External genitalia:

The external male genitalia include the penis, urethra, and scrotum.
Female: mons pubis, labia majora, l_abia minora_, Bartholin glands, and clitoris. The area containing these organs is called the vulva.

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Describe the stages of testis development

SRY-(sex determining region of Y) stimulates the autosome SOX-9 which can make testes to form from the bipotential gonad
- If you have a duplication of SOX9 (on an autosome not Y chromosome), you can develop testes even if you are XX
FGF-9 and _WT1 i_s important in this development too
SOX-9 inhibits B-Catenin, RSPO1 and WnT4 (therefore female development)

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SRY-(sex determining region of Y) stimulates the ________ which can make testes to form from the bipotential gonad

SRY-(sex determining region of Y) stimulates the autosome SOX-9 which can make testes to form from the bipotential gonad

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Describe the stages of Ovary development (gonadal determination)

FOXL2 is essential in ovary formation
B-Catenin which is stimulated by RSPO1 and WnT4 inhibits SOX-9 (therefore testes formation)

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B-Catenin which is stimulated by____ and _______ inhibits ____(therefore testes formation)

B-Catenin which is stimulated by RSPO1 and WnT4 inhibits SOX-9 (therefore testes formation)

SRY gene is found soley in the _________ cells in the ____ and activation precedes development of the _____ cell.

SRY is found solely in the pre Sertoli cell in the testis and activation precedes development of the Sertoli cell which precedes other testicular cell lines.

What is the role of SRY?

Stimulate SOX-9

_____ is a _____ gene that once stimualted can complete testicular differentiation

SOX-9

Desscribe the SOX-9 gene

Stimulated by SRY

It is an autosomal gene that once stimualted can _complete testicular differentiatio_n

Cascade to drive “maleness”

Initial SOX-9 transcription by SR-1
Then markedly up-regulated by SRY
Finally SOX-9 up-regulates itself via a positive feedback loop and the stimulation of prostacyclin D and FGF-9
Thest compounds along with SOX-9 inhibit ovarian transcription factors

What are the 2 main functions of Ovaries

(not sex differenitation)

Production of steroid hormone
Generation of mature oocytes capable of being fertilised

Describe the ovarian determination

The ovary has 2 main functions: * Production of steroid hormone * Generation of mature oocytes capable of being fertilised In contrast to the testis, ovarian follicles only commence differentiation after birth Unlike the testis the ovary appears _not to affect internal genitalia development_

If the germ cells don't reach the ovary they become \_\_\_\_\_ If the germ cells don't reach the testis, they become \_\_\_\_\_\_

If the germ cells don't reach the _ovary_ they become _normal tissue_ If the germ cells don't reach the _testis_, they become _functional but small testis_

The ____ or the ______ ducts form the internal male genitalia (epididymis, vas dferences, seminal vesicles) The ______ or _______ ducts form as an invagination of the Wolffian ducts. These become the femal internal genitalia (fallopian tubes, uterus and upper thrid of the vagina)

* These develop from teh Wolffian and Mullerian ducts * The _Wollfian or mesophric ducts_ form the _internal male genitalia_ (epididymis, vas dferences, seminal vesicles) * The _Mullerian or paramesonephic ducts_ form as an _invagination of the Wolffian ducts_. These become the f_emal internal genitalia_ (fallopian tubes, uterus and upper thrid of the vagina)

The Development of INTERNAL genitalia is essentially determined by the presence of ____________ and \_\_\_\_\_\_\_\_\_\_\_.

* This is essentially determined by the presence of Leydig and Sertoli cells

Describe the development of Inernal Genitalia

* This is essentially determined by the presence of _Leydig_ and _Sertoli_ cells * **Testosterone** (**Leydig cell** function) _stabilises Wolffian structures_ (which will otherwise disappear)- needs high local (testes) concentration * **Sertoli cells,** primarily through the secretion of _antimullerian hormone_ actively cause _regression of Mullerian structure_s). In other words, Internal genitalia are determined by the presence of a testis. In the absence of a testis, mullerian structures will remain. = **_NOT BY HORMONES_** (so you can have male internal genitalia on one side and femal internal genitalia on another\_

Internal genitalia are determined by the presence of \_\_\_\_\_\_\_. In the absence of a \_\_\_\_\_\_\_, mullerian structures will remain.

Internal genitalia are determined by the presence of a _testis_. In the absence of a _testis_, mullerian structures will remain. (NOT BY HORMONES)- so you can have male internal genitalia on one side and femal internal genitalia on another

What are one of the first cells to form?

Sertoli cells

Describe the development of External Genitalia

* Can result in either normal _male or female genitalia_ * **Male** genitalia will result if the *genital tubercle* is exposed to _high concentration of dihydro-testosterone_ (not just testosterone) * _Lower concentrations_ of androgen or p_artial insensitivity_ to androgen will result in _partial virilisation_ of the external genitalia * _Absence_ or _complete resistance_ to androgen results in **female** external genitalia.

Male EXTERNAL genitalia will result if the ______ is exposed to high concentration of \_\_\_\_\_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_or __________ to _____ will result in partial virilisation of the external genitalia

Male genitalia will result if the _genital tubercle_ is exposed to high concentration of _dihydro-testosterone (not just testosterone)_ _Lower concentrations_ of androgen or _partial insensitivity_ to androgen will result in partial virilisation of the external genitalia

Female internal genitalia are retained in the absence of __________ from _________ cells

Female internal genitalia are retained in the absence of AMH from sertoli cells

Female external genitalia occurs in the absence of \_\_\_\_\_\_\_\_

Androgen effect

If a _____ does not form, the resulting internal and external sex will be female

Testis

If someone had XY chromosomes, but are androgen-insensitive, what would be present? _Internal_ and _external genitalia_ and _gonads_ _Puberty_ _Sexual hair_ _Height_

* Gonad: * Develop a _testis_ * Internal genitalia * Testis is present, so they will have _Sertoli cells_, and therefore will produce _AMH_. Consequently they willl not have _female internal genitalia_ * However because they are insensitive to androgen, they _won't have male genital structures_ either * NO internal genitalia * External genitalia * Insensitive to androgen, so they will have _female external genitalia_ They will be well _fenimised_ and will go through puberty (testosterone will be produced to estrogen) Will also have _no sexual hair_ or _body odour_ or _pimples_. Growth spurt will be like a girl (_shorter than guys)_, but will occur at the time of boys (_later_)

In assessing sexual ambiguity at birth, what tests are required?

1) Karyotype (XX or XY) 2) Pelvic Ultrasound - USS can accurately determine internal female genitalia (UTERUS + cervix) as this is large at birth

Why are Ultrasounds useful when assessing sexual ambiguity at birth?

USS can accurately determine internal female genitalia (_UTERUS_ + cervix) as this is large at birth (maternal oestrogens)

Describe Virilised females What would be observed (karyotype and USS) What does this imply about hormonal exposure?

* Karyotype: * XX * Ultrasound: * Ovaries, * Normal female internal genitalia (uterus) * Virullisation: the abnormal development of male sexual characteristics in a female * Implies _prenantal androgen exposure_ * Either from... * Fetus: * Congenital adrenal hyperplasia \* (most common) * Mother * Severe PCOS * Ingestion (OC, stilboestrol) * Adnrogen secreting tumour (rare)

What does virulisation mean?

Virullisation: the abnormal development of male sexual characteristics in a female

Describe the features of an Undervirilised Male * What would be observed (karyotype and USS) * What does this imply about hormonal exposure?

* USS * Testis * No femal internal genitalia * Karyotype * XY * Implies l_ack of prenantal androgen exposure_ or i_nability to respond to testosterone_. Often associated **hypospadias** * Fetal * LH receptor mutation * Steroid biosynthetic defect (5-enzyme) * Androgen receptor mutation * Small normally found phallus (small penis) * All above

Undervirilisation Implies ______________ or\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. Often associated \_\_\_\_\_\_\_\_

Implies _lack of prenantal androgen exposure_ or i_nability to respond to testosterone._ Often associated _hypospadias_

Diagnose: 15 year old _girl_ with pubertal delay Tanner 2-3 pubic hair and Tanner 1 (prepubertal) breast development _Genitalia are normal female_; no inguinal masses are palpable An USS confrims a s_mall prepubertal uterus_, no gonads are seen _Karyotype is XY_

* She has a uterus so she cannot have a testis * Abnormality must be at the level of the testis * Abnormality will be in... * _SRY_ * _SOX-9_ * _Genito-urinary ridge_

If someone has a uterus it means \_\_\_\_\_

They don't have a testis

Diagnose Presence of Mullerian structures, Female external genitalia, XY Karyotype indicate sex reversal and failure of testicular development.

Mullarian structures = indicate NO TETIS Possible mutation in: 1) SRY 2) SOX-9 3) SF-1 4) WT-1 (Frasier Syndrome)

When you're looking at a clinical case, what questions should you be asking in order?

1. Do they have a uterus? 2. No? Do they have a testis? 3. Does testosterone work? 4. Is there an androgen deficiency or insensitivity?