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Chromosomes Exam 2 > 10/08 - Sex Determination > Flashcards

10/08 - Sex Determination Flashcards

1
Q

Origin of Germ Cells

A
  • Drosophila and C. elegans egg polarity determines origin of germ cells (posterior end of the fertilized egg)
  • Egg polarity not yet demonstrable in mammals
  • In mammals, germ cells arise from proximal epiblast (embryonic ectoderm)
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2
Q

What proteins appear essential in inducing formation of primordial germ cells

A

Bmp4 & Bmp8b

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3
Q

What is the earliest known marker in the origin of germ cells?

A

TNAP - non-specific tissue alkaline phosphatase

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4
Q

What effect does TNAP KnockOut have on germ cell formation

A

No effect

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5
Q

Folliculogenesis

A

Folliculogenesis describes the progression of a number of small primordial follicles into large preovulatory follicles that enter the menstrual cycle.

Once the oocytes are rested in meiosis I; at stage called primordial follicle. You will recruit many oocytes of which only one will be ovulated (until menopause)

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6
Q

What processes begin in folliculogenesis?

A

Embryogenesis and fertilization

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7
Q

What is the default pathway? And how do we know this?

A
  • Female pathway is the default
  • We know this because of Alfred Jost’s experiments with removing the ovaries and testes from rabbit fetuses. Both became female adult.
  • In male fetus, the wolfian duct regressed and uterus, oviduct, and upper vagina formed
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8
Q

What actually causes sex determination?

A
  • Y chromosome is a very gene poor region and the majority of genes involving sex determination are on autosomes; not the Y.
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9
Q

Human WT1 gene

A
  • Wilms tumor suppressor/activator gene - regulates transcription
  • Causes Frasier syndrome, Denys-Drash symdrome (Wilms tumor + pseudohermaphroditism
  • Denys-Drash greater renal tumors risk
  • Gonadal dysgenesis
  • Gonadoblastoma
  • Autosomal dominant
  • 46, XY sex reversal
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10
Q

What happens when you knock out the WT1 gene in mice?

A
  • Die between E13.5 and birth
  • Fail to develop kidneys and gonads
  • Heart, lung, and spleen also affected
  • Mouse replicates human phenotype
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11
Q

What happens when you knockout SF1 in mice?

A
  • Die before postnatal day 8

- male and female had internal FEMALE genitalia

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12
Q

What happens when you knockout SF1 in humans?

A
  • phenotypic female
  • karyotype XY
  • high ACTH
  • low cortisone
  • low aldosterone
  • laparoscopy showed streak gonads, normal mullerian (female) structures otherwise
  • Estrogen and progesterone induced periods
  • she lacks gonads and has adrenal hypoplasia
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13
Q

Describe the role of ACTH

A

ACTH: adrenal glands produce cortisol which provides negative feedback on pituitary gland which produces ACTH. If pituitary gland isn’t getting enough cortisol, the pituitary glad will jack up ACTH trying to get all the cortisol possible out of adrenal glands.

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14
Q

Why are streak gonads streaks?

A
  • Because there are no germ cells inside
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15
Q

Describe the phenotype and etiology of 46,XX males

A

Phenotype: male external genitalia and testes, often well virilized, sterile
Etiology: X-Y interchange during paternal meiosis

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16
Q

What happens if you have an X and a Y chromosome with faulty recombination?

A

If you have X and Y chromosome (TDF = SRY gene) If there is a faulty recombination and SRY ends up on X chromosome; If this happens; the karyotype would be XY, but phenotypically female. This accounts for 46% of 46,XX males

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17
Q

SRY is TDF

A
  • Expressed from E10.5 to E12.5 (immediately prior to seminiferous tubule appearance)
  • Expressed in pre-Sertoli Cells
  • Y linked inheritance
  • Conserved in mammals
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18
Q

What happens when you add SRY to females?

A

Will have male genitalia

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19
Q

46, XY females

A

Sry negative:
Due to Y chromosome deletion from X-Y interchange
Y-autosome translocations possible but rare

Sry mutations:
Mostly in the HMG box
Only 10-20% XY females have Sry mutations

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20
Q

Is SRY the only sex determining gene?

A

No; but it is the only one on the Y chromosome

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21
Q

Human SOX9

A
  • Mutations in SOX9 cause Campomelic Dysplasia (bone abnormalities)
  • 46, XY sex reversal with ambiguous or female genitalia
  • Death in neonatal period due to respiratory insufficiency
  • SRY-related gene
  • Autosomal dominant

BOWING OF THE BONES IS STRIKING IN THESE CASES

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22
Q

What happens when you add SOX9 to female

A
  • will lead to male phenotype
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23
Q

Amh

A
  • Also known as MIS, is a member of the TGF beta family.
  • Secreted by Sertoli Cells/Granulosa cells
  • Cryptoorchidism
  • Causes regression of Mullerian derivatives
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24
Q

Amh/Amhr human mutations

A

Persistent Mullerian duct syndrome

Typically: male with uterus and fallopian tubes

Amh and its receptor have same phenotype

Mice Amh/Amhr KOs show similar phenotype

These men can be infertile, can also have problem with descent of their testes.

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25
Q

What do we know about female development

A
  • Very little
  • Only two genes have been identified
  • DAX1 not really involved
  • Wnt4 = weak association
26
Q

AHC (DAX-1, Nr0b1, Chr. Xp21.3)

A

Nuclear hormone receptor with DNA binding domain
Deletions cause congenital adrenal hypoplasia, and hypogonadism
Expressed in Sertoli cells
Duplication of Xp21 (XY individuals) develop as females, external genitalia, impaired testes by histology (DSS- dosage sensitive)
Female fertility is unaffected
Maybe duplication of gene drives female development? But when you knock out Ahch gene; you find that female development is not affected.

27
Q

Does knocking out Ahch affect female development in mice?

A

No

28
Q

Wnt4 mouse KO

A

Lacks mullerian structures (uterus, upper vagina, fallopian tubes)

Germ cells are lacking

Testosterone biosynthesis activated in females

29
Q

WNT4 mutant humans are masculinized

A 
Mayer-Rokitansky-Kuster-Hauser syndrome
Primary  amenorrhea
Short vagina
No uterus, no fallopian tubes
Ovaries of normal size 
Aplastic right kidney
Elevated levels of androstenedione, testosterone, DHEAS
30
Q

GENITAL AMBIGUITY

A

True hermaphroditism (46, XX ovotesticular disorder of sex development)

Female pseudohermaphroditism (46, XX disorders of sex development)

Male pseudohermaphroditism (46, XY disorders of sex develpoment)

31
Q

Pseudohermaphroditism

A

The discrepancy between gonadal tissue (histologic diagnosis) and external genitalia appearance is called pseudohermaphroditism.
If gonadal tissue is a testis, term male pseudohermaphrodite.
If ovary is present the term is female pseudohermaphrodite.
Archaic term. Coined prior to X and Y knowledge.
Disorders of sexual development/differentiations is a better term

32
Q

46,XX ovotesticular disorder of sex development (true hermaphroditism)

A

Both testicular and ovarian tissue

Oocytes, not just fibrous stroma

Testicular tubules or spermatozoa
Male external genitalia (70%)
Pubertal feminization (Most)
Uterus (90%) (Tubal occlusion associated)
Pregnancies (46,XX)
Some gonadal neoplasia
33
Q

46, XX DISORDERS OF SEX DEVELOPMENT AND ADRENAL HYPERPLASIA (female pseudohermaphroditism )

A

21-Hydroxylase deficiency

11alpha-hydroxylase deficiency

34
Q

17 alpha-OH PROGESTERONE

A

Elevation in serum indicates block at 21-hydroxylase site in adrenal biosynthetic pathways

Reliable rapid assay

35
Q

21-HYDROXYLASE DEFICIENCY (FEMALES)

A 
Phenotype:	Ambiguous genitalia 
		Uterus and ovaries normal
		Fertility with treatment normal
		Salt wasting
Diagnosis:	Elevated 17-OH Progesterone

Treatment: Cortisol
Mineralocorticoids

36
Q

11beta-HYDROXYLASE DEFICIENCY

A

Phenotype:Ambiguous genitalia (XX)
Hypertension due to salt retention (XX and XY)
Hypertension in 11 differentiates it from 21 hydroxylase deficiency
Lab: Deoxycortisol and deoxycorticosterone levels are elevated.
Treatment:Cortisol

37
Q

AROMATASE DEFICIENCY (CYP19)

A 
Clitoral hypertrophy
Affected XX and (tall) XY sibs, delayed epiphyseal closure
Virilization of the pregnant mother
Primary amenorrhea
Autosomal recessive
Therapy: Estrogen!
38
Q

TERATOGENIC 46, XX disorders of sex development

A

Virilization of female fetuses possible if androgens or androgenic progestens given pregnant mother in first trimester
Once (1950’s, 1960’s) relatively frequent but now rare: - Doses of inadvertent oral contraceptives low
- Hormonal support now rare
Can occur with danazol

39
Q

46, XY disorders of sex development (male pseudohermaphroditism )

A 
45,X/46,XY mosaicism
Testicular biosynthetic errors
5-reductase deficiency
Complete and partial androgen insensitivity
Agonadia
Leydig cell agenesis
40
Q

45,X/46,XY

A

Variable phenotype: female or ambiguous external genitalia
Variable frequency of somatic anomalies (Turner stigmata)
Uterus usually present
Increased gonadal neoplasia

41
Q

SELECTION BIAS IN 45,X/46,XY

A

Most cases detected in neonates show female or ambiguous external genitalia
Approximately 85% of cases detected in utero (amniocentesis, CVS) show male external genitalia

42
Q

5 alpha-REDUCTASE DEFICIENCY

A

Enzyme Block: T DHT

Normal male levels of T but DHT low

T/DHT ratio elevated

Males only, autosomal recessive condition

Normal male external genitalia, ambiguous genitalia, or Normal female genitalia. 

Male gonads with testicles and Wolffian structures

Often raised as girls, male gender identity, and virilization with puberty (deepening voice, clitoral enlargement, testes descent)
Jeffrey Eugenides won a Pulitzer Prize for his 2002 novel Middlesex
43
Q

HORMONE RECEPTOR DEFECTS

A

Estrogen
Androgen
Anti-mullerian hormone

44
Q

PARTIAL ANDROGEN INSENSITIVITY

A

Variable extent of genital virilization (Labial fusion and clitoral hypertrophy)

Hypospadias

Feminization (breast development at puberty) despite testosterone being higher than in unaffected XY individuals

45
Q

Complete Androgen Insensitivity

A 
46XY individuals have bilateral testes
Female external genitalia
Blind ending vagina
No mullerian derivatives
Cells unable to respond to testosterone
Gonadal neoplasia in 5%
Well developed breasts
46
Q

Evaluation of infant with ambiguous genitalia

A

Three generation family history

Prenatal history, prenatal ultrasound, testing done

Physical examination:

Chromosomes (microarray)

Ultrasound to assess internal anatomy.

Adrenal and gonadal steroid secretion

47
Q

GONADAL FAILURE IN MONOSOMY X

A

Germ cells present in 45,X abortuses and neonates.
Pathogenesis must therefore involve increased rate of atresia.
Such a pathogenesis consistent with occasional 45,X pregnancy.

48
Q

OVARIAN MAINTENANCE DETERMINANTS

A

Located in several regions of Xp and Xq

Loci in regions Xp11 and Xq13 most important

Elucidating function of these genes would be relevant for normal ovarian development

49
Q

X-chromosome genes

A

BMP15- bone morphogenetic protein 15

FMR1- fragile X mental retardation

POF1B- premature ovarian failure region 1

PGMRC1-progesterone membrane receptor

50
Q

Inverdale and Hanna sheep

A

Missense and Nonsense mutations in Bmp15 gene, X chromosome

Heterozygous sheep have increased fertility

Homozygous sheep are infertile

Humans with Bmp15 mutations described and found to be infertile

51
Q

FRAGILE X SYNDROME

A

X-linked recessive gene localized to
Xq27.3 protein FMR1
Initially detected through chromosomal
fragility (thus “Fragile X”)

1:4000 Males: Mental retardation (most
common genetic cause in males)
1: 4000-8000 Females (Borderline IQ)

52
Q

CGG REPEATS IN FRAGILE X SYNDROME

A

Affected: >200
Premutation: 54-200
Normal: 5-54

53
Q

FMR1 AND POF

A

10-15% of premutation carriers manifest POF.
Premutation in 1-5% sporadic POF and 10-15% familial POF.
Prevalence in premutation carriers increases as (CGG)n increases up to 80-99, but plateaus thereafter or decreases.
Not increased in full mutation.

54
Q

XX GONADAL DYSGENESIS

IN FINLAND

A

Frequency: 1/8300 liveborn females
Of 75 cases, 57 sporadic
Aggregated in north central Finland where consanguinity rate 12%
Segregation ratio 0.23 for female sibs

55
Q

FSHR MOUSE MODEL

A

Knockout shows primordial, primary and secondary follicles
Females are sterile
Males are fertile (reduced sperm count)
Closely mimics human phenotype

56
Q

FSHB MUTATIONS

A

Three subjects reported to date
Clinical: Primary amenorrhea, Infertility, Normal adrenarche and absent thelarche
Small ovaries and uteri
Mutations necessary in both copies of FSH to have a phenotype
Autosomal recessive inheritance

57
Q

FSH BETA KNOCKOUT IN MICE

A

Phenotype closely mimicks what is observed in humans

Females are sterile

Males are fertile

58
Q

BLEPHAROPHIMOSIS-PTOSIS EPICANTHUS (FOXL2)

A
  • Autosomal dominant: 3q2224
  • Type II: Premature ovarian failure
  • Gene: Winged-helix/forkhead transcription factor (FOXL2)
  • Expressed in mesenchyme of mouse ovaries and eyelids
59
Q

FOXL2 BLOCKS ADULT OVARY TO TESTES TRANSDIFFERENTIATION

A
  • Conditional excision of Foxl2 caused follicular structures of the ovary to look like seminiferous tubules of the testes
  • Up-regulation testes determining genes: Sox9 and Dmrt1.
  • Adult lineage reprogramming
  • Active repression of the Sertoli cell-promoting gene Sox9, maintains mammalian ovarian phenotype through adulthood.
60
Q

Future of Sex disorders

A

Molecular studies to delineate anti-male and pro-female molecules.

Further genetic classification of DSDs

Effects of environment on germline quality and transgenerational effects

Chromosomes Exam 2 (11 decks)

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