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Reproductive Biology > Mammalian sex determination, development 2 > Flashcards

Mammalian sex determination, development 2 Flashcards

1
Q

migration of primordial germ cells

A
  • sometimes migrate to extragonadal sites (adrenals or kidneys)
  • all of them differentiate as oocytes and enter meiosis at the same stage as oocytes
  • later degenerate
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2
Q

what are all germ cells potentially

A

female (irrespective of genetic sex) unless they migrate to a developing testis and are enclosed in the seminiferous cords

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3
Q

what happens when germ cells enter seminiferous cords

A

both XX and XY germ cells will enter mitotic arrest and develop as t-spermatogonia

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4
Q

what is the fate of germ cells to continue mitosis (testis) or meiosis (ovary) determined by

A

exposure to either Fgf9 (prevents entry into meiosis) or retinoic acid (promotes it)

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5
Q

what does differentiation into oocytes or spermatogonia depend on

A

the gonadal environment in which they find themselves, not their genetic makeup

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6
Q

what does the presence of only one X chromosome do in oogonia

A

causes a reduction in ocoyte survival during meiosis

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7
Q

what does the presence of XX in germ cells of the testicle result in

A

infertility

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8
Q

what does differentiation of the bipotential gonad determine

A

its major hormonal products –> determines further sexual differentiation

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9
Q

what do functional testes secrete

A
  • testosterone
  • anti-mullerian hormone (AMH)/mullerian-inhibiting substance (MIS)
  • insulin-like factor 3 (INSL3)
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10
Q

what is estrogen vital for

A
  • changes seen during and after puberty

- no role in development of the ovary or female phenotype during fetal life

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11
Q

once a testicle has been formed, the remainder of mammalian sexual differentiation is due to what

A

hormonal products (testosterone, MIS, INSL3) –> drive genetic cascades to give male phenotype (castration before testis determination results in phenotypically female animal)

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12
Q

where are androgens produced

A

from cholesterol in the leydig cells of the testicle

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13
Q

2 androgens

A
  • testosterone (major androgen produced)

- dihydrotestosterone (formed from testosterone by 5alpha-reductase enzyme)

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14
Q

3 stages of testosterone secretion

A
  1. during gestation (masculinize fetal genetalia)
  2. perinatal (sets brain sex)
  3. puberty (secondary sex characteristics, spermatogenesis)
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15
Q

mullerian inhibiting substance

A
  • glycoprotein produced by sertoli cells
  • causes regression of mullerian ducts in males
  • male specific until after birth (high levels)
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16
Q

when do rudimentary female ducts develop

A

after the early indifferent gonad is visible

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17
Q

names of male and female ducts

A
  • male: mesonephric or wolffian

- female: paramesonephric or mullerian

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18
Q

what do efferent ducts do and where do they arise from

A
  • connect the rete testes to the epididymus

- arise from residual mesonephric tubules

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19
Q

what happens to urogenital folds in males

A

elongate and fuse to form penile shaft

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20
Q

what happens to genital swellings in males

A

fuse to form the scrotum

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21
Q

what happens to the genital tublercle in males

A

develops into glans penis

22
Q

what are positive effects of reproductive tract male sex differentiation controlled by

A

androgens

23
Q

what are negative aspects of male differentiation controlled by

A

MIS (AMH)

24
Q

testosterone and androgen receptor

A
  • signals differentiation of the wolffian duct in male embryo
  • regulates hypothalamo-pituitary axis for LH secretion
  • vital role in spermatogenesis
25
Q

dihydrotestosterone and androgen receptor

A
  • signals development of external genitalia and prostate
  • elongation and ventral closure of the penile anlagen
  • pubertal changes, baldness, external genitalia maturation, male behavior
26
Q

what causes different effects of T and DHT when they have the same receptor

A
  • differences in binding affinity (DHT has higher affinity for AR (androgen receptor) than T)
  • effect on receptor function (DHT-AR activates some genes more easily than T-AR)
27
Q

what does MIS/AMH do

A

causes regression of the mullerian ducts in male fetuses –> acts locally by diffusion

28
Q

what occurs first - regression of mullerian duct in males or regression of wolffian duct in females

A

regression of mullerian duct in males

29
Q

when are mullerian ducts of developing embryos sensitive to MIS

A

for a limited period of time shortly after gonadal sex differentiation

30
Q

what happens to the ducts in the absence of testosterone

A

wolffian ducts in female fetuses regresses while mullerian ducts develop in the absence of MIS

31
Q

where do the oviducts develop from

A

the cranial portion of the mullerian duct adjacent to the ovary

32
Q

when do the fimbria develop

A

after the rest of the oviduct (may be after birth)

33
Q

uterine and cervical development

A

fusion of the left and right mullerian ducts to varying degrees

34
Q

do females have angrogen receptors and/or 5alpha-reductase enzyme present

A

yes –> could be masculinized if exposed to androgens

35
Q

steps in X inactivation

A
  1. x chromosomes counted
  2. choose which to inactivate
  3. developmental cue triggers inactivation at the x-inactivation center (xic)
  4. inactivation spreads
  5. inactivation is stabilized and clonally transmitted
36
Q

what cells does x-inactivation involve

A

all somatic cells of the female embryo

37
Q

model for x-inactivation

A
  • Xp inactivated in all cells before differentiation
  • early blastocyst: Xp re-activated in cells of inner cell mass (ICM)
  • cells of ICM undergo random x-inactivation
38
Q

do all parts of affected chromosome undergo inactivation

A

no –> some parts escape it (especially in homologous genes - PAR)

39
Q

2 stages of testicular descent (biphasic model)

A
  • transabdominal descent

- inguino-scrotal descent

40
Q

overview of transabdominal testicular descent

A
  • testicles go from abdomen to internal inguinal ring

- gubernaculum thickens, testicle anchored to internal inguinal region

41
Q

what happens to gubernaculum in females

A
  • regresses to a long, thin band of tissue

- female gonad relatively tightly bound to the dorsal body wall

42
Q

what hormone is responsible for gubernacular growth

A

insulin-like factor 3 from leydig cells –> GREAT receptor

43
Q

what is another name for the gubernaculum

A

caudal suspensory ligament

44
Q

overview of inguinoscrotal desent

A
  • testicles go through inguinal canal to scrotum

- gubernaculum regresses, pulls epididymis and testicle into scrotum

45
Q

what forms from the outer ring of the gubernaculum

A

cremaster muscle

46
Q

what is inguinoscrotal movement of the gubernaculum controlled by

A

angrogens, acts via genitofemoral nerve

47
Q

what does the genitofemoral nerve do under the influence of androgens

A

releases the neurotransmitter calcitonin gene-related peptide (CGRP)

48
Q

what does CGRP do

A

causes growth of the tip of the gubernaculum and directs its migration through the inguinal canal and into the scrotum

49
Q

causes of cryptorchidism

A
  • defect in the androgen pathway for inguinoscrotal descent
  • defect in prenatal androgen secretion
  • mechanical, neurological problems
50
Q

problems with cryptorchidism (3)

A
  • infertility
  • tumor formation (sertoli cell tumor, seminoma)
  • heritability (autosomal recessive)

Reproductive Biology (7 decks)

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