Gametogenesis

Question 1

what are epigenetic effects (3) main points

Answer 1

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

Question 2

what are the gonads

Answer 2

• ovaries
• testes

Question 3

where do the gonads develop

Answer 3

at the genital ridge

Question 4

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

Answer 4

• primordial germ cells - these also multiply
• germinal epithelial cells
• mesonephric cells

Question 5

what are gonads

Answer 5

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

Question 6

where do the cell populations that give rise to gonads go

Answer 6

they migrate to the genital ridge

Question 7

what determines if testes or ovaries (gonads) develop

Answer 7

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

Question 8

why does Y-chromosome carrying sperm result in testes

Answer 8

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

Question 9

what chromosome is the egg carrying?

Answer 9

X chromosome

Question 10

what are the gamete precursors

Answer 10

primordial germ cells

Question 11

what are gametes

Answer 11

• sperm
• oocyte (immature egg cell) or egg

Question 12

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

Answer 12

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

Question 13

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

Answer 13

• 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

Question 14

what is spermatogonia

Answer 14

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

Question 15

what do Leydig cells produce

Answer 15

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

Question 16

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

Answer 16

• 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

Question 17

what occurs after gonad formation

Answer 17

internal genitalia

Question 18

how do internal genitalia form

Answer 18

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

Question 19

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

Answer 19

• 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)

Question 20

what is the role of the mullerian ducts

Answer 20

• 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

Question 21

what happens to mullerian ducts in females

Answer 21

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

Question 22

what occurs after internal genitalia formation in males

Answer 22

• 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

Question 23

gametogenesis same but different

Answer 23

• 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

Question 24

how is gametogenesis different explanation

Answer 24

• 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)

Question 25

connect epigenetics to tissue type

Answer 25

- each cell in body contains same genes - various cell types due to different expression of these same genes

Question 26

how is expression of same genes different (epigenetics)

Answer 26

- 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

Question 27

methylation in epigenetics

Answer 27

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

Question 28

histone modifications in epigenetics

Answer 28

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

Question 29

when do epigenetic changes in methylation occur?

Answer 29

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

Question 30

what can also influence pattern of gene expression in epigenetics

Answer 30

- 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

Question 31

explain intergenerational effects in utero on oocytes, sperm, embryos

Answer 31

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

Question 32

explain dutch famine on epigenetics

Answer 32

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

Question 33

what can the pattern of gene expression in epigenetics influence

Answer 33

- increased risk of major disease including hypertension, heart disease, obesity - for the 'developmental origins of adult disease'

Question 34

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

Answer 34

hormonal stimulation, culture embryos

Question 35

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

Answer 35

- 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