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Reproductive System > Gametogenesis > Flashcards

Gametogenesis Flashcards

1
Q

what are epigenetic effects (3) main points

A
  • non-DNA changes
  • can affect gene expression
  • can influence lifetime outcomes
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2
Q

what are the gonads

A
  • ovaries
  • testes
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3
Q

where do the gonads develop

A

at the genital ridge

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4
Q

which migrating cell populations give rise to the gonads. which also multiply?

A
  • primordial germ cells - these also multiply
  • germinal epithelial cells
  • mesonephric cells
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5
Q

what are gonads

A

specialised organ that produces the gametes (sperm or oocyte / egg) and sex hormones of organism

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6
Q

where do the cell populations that give rise to gonads go

A

they migrate to the genital ridge

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7
Q

what determines if testes or ovaries (gonads) develop

A

what chromosome sperm is carrying
- X chromosome -> ovaries develop
- Y chromosome -> testes develop

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8
Q

why does Y-chromosome carrying sperm result in testes

A

SRY gene on Y chromosome (sex-determining region of Y chromosome) ‘makes’ a testis

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9
Q

what chromosome is the egg carrying?

A

X chromosome

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10
Q

what are the gamete precursors

A

primordial germ cells

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11
Q

what are gametes

A
  • sperm
  • oocyte (immature egg cell) or egg
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12
Q

from the cell populations that give rise to gonads which do and don’t contain SRY gene

A

germinal epithelial cells express SRY
primordial germ cells and mesonephric cells do not express SRY

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13
Q

what do the cell populations that give rise to the gonads contribute to in testis formation

A
  • primordial germ cells -> gamete precursors: give rise to sperm and egg
  • germinal epithelial cells -> give rise to primitive sex cords and Sertolli cells that enclose the primordial germ cells (prespermatogonia)
  • mesonephric cells -> give rise to the vasculature, Leydig cells, seminiferous tubules
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14
Q

what is spermatogonia

A
  • spermatogonia = germ cells responsible for producing sperm cells (spermatozoa) thru spermatogenesis
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15
Q

what do Leydig cells produce

A

androgens (male sex hormones; class of steroid hormones) - incl testosterone, DHT

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16
Q

what do the cell populations that give rise to the gonads also contribute to in ovary formation

A
  • primordial germ cells -> gamete precursors: give rise to sperm and egg
  • germinal epithelial cells -> cluster around PGCs (oogonia) to form primordial ovarian follicles
  • mesonephric cells -> give rise to the vasculature, stroma
17
Q

what occurs after gonad formation

A

internal genitalia

18
Q

how do internal genitalia form

A

two unipotential primordia (organ/tissue in earliest stage of development) located next to gonads give rise to internal genitalia

  • unipotential - ability of primordia to give rise to a specific type of organ or tissue not into multiple types; here: two early developmental structures specialised and predetermined to develop into internal genitalia only
19
Q

what 2 main hormones to foetal testis (gonads) make & their function

A
  • androgens in Leydig cells -> stimulate Wolffian ducts (male) to make epididymis, vas deferens, prostate
  • anti-mullerian inhibitor (AMH) in sertoli cells -> causes mullerian ducts to regress (preventing formation of female internal reproductive structures)
20
Q

what is the role of the mullerian ducts

A
  • arise during early embryonic development
  • paired embryonic structures
  • present in both male and female embryos
  • crucial role in development of reproductive system, esp in females
21
Q

what happens to mullerian ducts in females

A

absence of AMH, mullerian ducts become oviducts, uterus, cervix, upper vagina

22
Q

what occurs after internal genitalia formation in males

A
  • external genitalia form in presence of androgens
  • bipotential precursors become scrotum and penis in
  • bipotential precursors: structures in early embryonic development that have potential to differentiate into either of 2 distinct cell types
23
Q

gametogenesis same but different

A
  • gametogenesis is process of producing gametes
  • spermatogenesis in males & oogenesis in females
  • meisosis of spermatogonia and oogonia - into mature gametes - sperm or eggs- capable of fertilisation ie/ diploid cell (46) reduced to haploid cell (23)
    BUT timing is different
24
Q

how is gametogenesis different explanation

A
  • sperm produced continuously from puberty until death (decline in sperm quality overtime) ; spermatogenesis occurs at puberty
  • oogenesis starts before birth => number of oocytes (potential eggs) fixed at birth. Oocytes suspended at Prophase 1 in meiosis at birth until puberty
  • meiosis resumes at ovulation (continues till most oocytes been ovulated or lost to atresia)
  • meiosis completed following fertilisation (ovulated oocyte that’s fertilised)
    => 99% oocytes do not ovulate and lost through atresia (oocyte not chosen each menstruation) by time of menopause (~50yrs old)
25
Q

connect epigenetics to tissue type

A
  • each cell in body contains same genes
  • various cell types due to different expression of these same genes
26
Q

how is expression of same genes different (epigenetics)

A
  • some genes imprinted ie/ only maternal or paternal copy expressed - seen in many genes for growth and development eg/ IGF2 gene
  • no DNA changes / “marks” in gene expression come thru various processes such as methylation, histone modification, RNAs
27
Q

methylation in epigenetics

A

formation of methyl groups on DNA -> prevents those genes from being transcribed and expressed

28
Q

histone modifications in epigenetics

A

histone proteins wrap DNA up
depending on how tightly wrapped -> whether genes transcribed and expressed
- more tight => prevents
- loose wrapped => more open

29
Q

when do epigenetic changes in methylation occur?

A

during gametogenesis, embyro development and foetal development
affecting lifetime gene expression
natural rise and drops on oocyte growth to embryo gene activation

30
Q

what can also influence pattern of gene expression in epigenetics

A
  • external factors such as environment (eg/ pollutants), lifestyle (eg/ exercise), alcohol and diet and smoking
  • intergenerational effects in utero on oocytes and sperm and embryos
  • WW2 dutch famine
31
Q

explain intergenerational effects in utero on oocytes, sperm, embryos

A

at time that oocytes forming (w/ patterns of demethylation and re-established methylation) other modifications during embryo development - they not only affect the foetus being born but also their children as it is also the time that the gonads are forming

32
Q

explain dutch famine on epigenetics

A

pregnant women were severely malnutrition which we saw affects in those children and their children
due to effects of malnutrition on gametogenesis and embryo development

33
Q

what can the pattern of gene expression in epigenetics influence

A
  • increased risk of major disease including hypertension, heart disease, obesity
  • for the ‘developmental origins of adult disease’
34
Q

what are the things in IVF that we do which can affect gene expression

A

hormonal stimulation, culture embryos

35
Q

what is the result of the effects IVF can have on gene expression

A
  • increase in some imprinting defects / birth defects esp Beckwith-Wiedemann syndrome and Angelman syndrome
  • BWS characterised by overgrwoth of certain congenital features seen in children and increased risk of childhood cancer

Reproductive System (21 decks)

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