Module 5 part 1: Gameteogenesis and ART Flashcards
1
Q
What is gametogenesis known as in males?
A
spermatogenesis –> produces spermatozoa
2
Q
What is gametogeneis?
A
process whereby a haploid cell (n) is formed
from a diploid cell (2n) through:
-meiosis
- cell differentiation
3
Q
What is gametogenesis known as in females?
A
oogenesis –> forms ova (eggs)
4
Q
When do males start producing sperm and where does this occur?
A
- when they reach puberty (10-16 years old)
- in the testes –> SEMINIFEROUS TUBULES (kept separate from systemic circulation by the blood-testes barrier)
5
Q
What is the Blood-testes barrier?
A
- formed by Sertoli cells
- prevents hormones and constituents of the systemic ciruclation from affecting the developing sperm
- prevents the immune system from recognizing the sperm as foreign
6
Q
What are the two common types of cells in spermatogenesis and what are their jobs?
A
- sertoli cell
- “nurse cell”
- form blood-teste barrier
- support developing sperms
- produce fluid and control release of sperm into lumen
- secrete inhibin –> slows sperm production - leydig cell
- mixed in walls of tubules
- produce high levels of testosterone once male reaches adolescence
7
Q
What are 4 hormones involved in spermatogenesis?
A
- Lutenizing hormone (LH)
- Follicle stimulating hormone (FSH)
- Testosterone
- inhibin
8
Q
What does LH and FSH do in spermatogenesis?
A
stimulatory effect
stimulate spermatogenesis and testosterone secretion by the testes
9
Q
What does testosterone and inhibin do in spermatogenesiS?
A
inhibitory effect
- inhibit secretion of GnRH by hypothalmus
- inhibit secretion of LH and FSH by pituitary
10
Q
What is spermatogonia?
A
the initial pool of diploid
cells that divide by mitosis to give two identical cells
11
Q
What is the difference between type A and type B spermatogonia? (NEED TO CLARIFY THIS ONE)
A
type a = primary spermatocytes that undergo MEIOSIS
type B = replicate by mitosis several times to form identical diploid cells (primary spermatocytes)
12
Q
Is there 2 stages to meiosis?
A
YES
*Meiosis I produces two haploid cells;
known as secondary spermatocytes.
*Meiosis II produces four haploid cells, known as spermatids
13
Q
What is spermiogenesis?
A
when spermatid mature and differentiate into sperm
14
Q
what is spermiation?
A
when the cytoplasmic bridges break down and the spermatids are released into the lumen of the seminiferous tubule
15
Q
How long does spermatogenesis take?
A
approximately 70 days
16
Q
What is capacitation?
A
when the sperm removes the cholesterol and glycoproteins from it’s head
- allows the sperm to bind to the zona pellucida of the egg cell in female reproductive tract
17
Q
What is seminal fluid responsible for?
A
nutritional support —> has lots of sugars for ENERGY!
suppresses possible immune response by female
18
Q
What makes up most of the fluids in semen?
A
seminal fluid
19
Q
What are 4 reasons a male may be infertile?
A
- low sperm concentration
- poor sperm motility
- abnormal morphology
- aberrant epigenetic
reprogramming of the genome
20
Q
There is significant increase of structural abnormalities with paternal age. true or false
A
true
21
Q
Not all chromosomes are susceptible to non-disjunction. true or false
A
false –> they are
22
Q
Meiotic errors are very common in humans. true or false
A
true
23
Q
majority of the errors are
chromosome breaks and acentric fragments for the structural anomalies of sperm. true or false
A
true
24
Q
What are some sperm abnormalities that can occur?
A
- double head
- giant head
- amorphous head
- pinhead
- tapered head
- constricted head
- double tail
- coiled tail
- no tail (spermatid)
25
What are the epigenetics like of sperm?
Sperm DNA is
- tightly packed
- histones are largely replaced with protamines
- large degree of DNA methylation
26
What is oocyte epigenetics like?
- less dna methylation
- more open chromatin
27
What are protamines?
basic proteins that wrap around DNA more stringently
than histones
- create compact structures to protect the DNA
- undergo post-translational modification
28
What are some epigenetic modifications that can occur with spermatogenesis?
- DNA methylation
- histone tail modifcations
- periods of reprogramming during the crucial time points can impact fertility
and embryonic competence
29
What DNA methylation occurs following fertilization?
-male pronuclei are actively and rapidly demethylated
in the zygote
- maternal genome is passively demethylated in a
replication-dependent manner
30
What is oogenesis?
-produces a gamete
-contains all the materials needed to initiate and maintain metabolism and development
- develops a complex cytoplasm
31
How does oogenesis differ from spermatogenesis?
begins in the fetus prior to birth
32
what are "primordial germ cells" in oogenesis and what do they do?
-move to colonize the cortex of primordial gonads
- replicate by mitosis to reach a peak of about 7 million by 20 weeks gestation
33
Does cell death occur after the peak in replication of eggs?
YES!! --> goes down to like 2 million cells to begin meiosis 1 before brith (these are primary oocytes!)
34
Is there further cell death during childhood and towards puberty?
YES! --> goes down to like 40 thousand eggs by puberty
35
What are the 3 stages that the primary oocytes undergo in Oogenesis?
1. Pre-antral
2. Antral
3. Preovulatory
36
What is the "pre-antral stage" of the primary oocytes in Oogenesis?
- grows dramatically
- follicular cells grow and proliferate
- granulosa cells secrete glycoproteins --> forms zona pellucida around primary oocyte
- development of theca folliculli (specialized layer of connective tissue cells)--> responsive to LH and secretes androgens when needed
37
What is the "antral stage" of the primary oocytes in Oogenesis?
fluid filled spaces form between the granulosa cells --> this will form the antrum
follicles are now called "secondary follicles"
38
What is the "pre-ovulatory stage" of the primary oocytes in Oogenesis?
- induced by LH surge
- meiosis 1 is complete
- formation of two haploid cells (one "daughter cell" and one "polar body" )within the follicile --> does NOT go on to form an egg
- the other haploid cells known as the secondary oocyte
39
What are the steps of Ovulation?
- follicle has grown in size and is mature
- called the Graafian follicle
- LH surge increases collagenase activity --> weakens follicular wall + muscular contractions of ovarian wall --> releases an egg from the ovary
40
What is the "corpeus luteum" in oogenesis?
- formed by granulosa cells and thecal cells after ovulation
- folded structure --> b/c wall of follicle collapses
- produces progesterone and estrogen
- support pregnancy
- prevents menstruation
41
When is it likely for errors causing aneuploidy in oogenesis?
Meiosis 1
42
are all chromosomes susceptible to error during oogenesis?
YES
43
what is the most significant factor in the cause of aneuploidy (abnormal # of chromosome)?
maternal age
44
What are some epigenetic modifications that occur in oogenesis?
DNA methylation
histone acetylation
45
epigenetic modification of oocytes may be
affected by advanced maternal age. True or false
true
46
Why is age a factor in affecting a womans eggs?
it affects the QUALITY of the eggs
47
profile of DNA methylation remains constant at the primordial stage to the stage of primary follicles, but it increases progressively until antrum formation. True or false
TRUE
48
Can Deficiencies in remodeling of the epigenomes can cause severe developmental defects, infertility, and long-term health issues in
offspring?
YES
49
What are 3 factors besides age that can disturb the epigenetic reprogramming and lead to probs with epigenome in offspring?
1. ART
2. parental diets
3. unhealthy parental habits
50
What is known as the "first date" of sperm and ovum called?
Fertilization!
51
How long can sperm survive in the vagina for?
3-5 days
52
When do oocytes acquire the ability to fuse with sperm?
- they reach 20 μm
in diameter
- they are arrested at the prophase of meiosis II
53
What happens if fertilization never occurs?
ocyte degenerates 24 hours after ovulation, remaining arrested in meiosis II
54
What happens if the egg is fertilized?
peristaltic movements of the
fallopian tube move the egg to the uterus where it can implant into the
posterior uterine wall.
55
What are the 4 stages of fertilization?
1) sperm preparation,
2) sperm-egg recognition and binding
3) sperm-egg fusion cortical reaction
4) fusion of sperm and egg pronuclei and activation of the zygote
56
What does stage 1 (sperm prep) of fertilization consist of?
- in genital tract
- prepares for acrosome reaction
- increased intracellular calcium levels
- high energy phase / "hyperactivation" --> lots of flagellar movement and swimming capacity
57
What 2 substances/hormones help with capacation and allow for energy, flagellar bending, etc.. of sperm in sperm prep?
1. glucose
2. progesterone
58
What does stage 2 (sperm egg recognition and binding) of fertilization consist of?
- sperm must penetrate the two protective layers to reach the egg.
-sperm first burrow through the cells of the corona radiata
- comes into contact with the zona pellucida and binds to receptors (SED1 protein to ZP3 in transparent zone) --> initates and acrosomal reaction
59
What is the Acrosomal reaction in stage 2 of fertilization?
- where sperm secretes digestive enzymes that break down the glycoprotein membrane of the zona pellucida
- helps expose the oocyte's plasma membrane so sperm membrane can fuse with it
60
What does stage 3 (sperm- egg fusion cortical reaction) of fertilization consist of (3 stages) ?
1. attachment: The initial membrane contact is achieved through
protein-protein-mediated or protein-carbohydrate-mediated binding of the
two membranes.
2. membrane apposition:
two membranes even closer together. Shape change in proteins results
in a hinge-like motion that draws the two membrane-inserted ends of the
protein very close together,
3. lipid mixing: leading to cytoplasmic continuity between the two cells
61
What is the first event of stage 3 in fertilization?
"attachment"
-The initial membrane contact is achieved through
protein-protein-mediated or protein-carbohydrate-mediated binding of the
two membranes
62
What is the second event of stage 3 in fertilization?
"membrane apposition"
- the activity of fusion proteins (hinge-like motion) brings the
two membranes even closer together
63
What is the third event of stage 3 in fertilization?
"lipid mixing"
- occur between the proximal membrane leaflets and then the distal
leaflets, leading to cytoplasmic continuity between the two cells
64
How is entry of other sperm prevented two ways after stage 3 of fertilization?
1. fast block --> instantaneous change in sodium ion permeability upon binding of the first sperm
2. slow block --> influx of calcium ions following sperm penetration
65
What is the cortical reaction in stage 3 of fertilization?
-cortical granules sitting immediately below the oocyte plasma membrane fuse with the membrane
-release zonal inhibiting proteins and mucopolysaccharides into the space between the plasma membrane
and the zona pellucida
66
What do zonal inhibiting proteins do?
- releases any other attached sperm
- destroy the oocyte’s sperm receptors and mucopolysaccharides
- coat the fresh zygote in an impenetrable barrier and hardened zona pellucida --> "fertilization membrane"
67
What does stage 4 (fusion of sperm and egg pronuclei and activation of the zygote) of fertilization consist of?
- Once inside the egg, the sperm nucleus decondenses to form the male
pronucleus
- sperm nucleus undergoes a dramatic transformation --> nuclear envelope vesiculates into small packets, thereby exposing the compact
sperm chromatin to the egg
- centrosome (new centriole) accompanying the male pronucleus produces its asters and contacts the female pronucleus.
- each pronucleus migrates toward the other, replicating its DNA as it travels.
68
true diploid nucleus in mammals is first
seen not in the zygote, but at the 2-cell stage. true or false
true
69
What is the difference between infertility and subfertility?
infertility = inability of a sexually active, non-contracepting couple to achieve pregnancy in one year (cannot carry a pregnancy to term)
subfertility = reduced fertility or chance of getting pregnant
70
What are Assisted Reproductive Technologies (ART)?
medical procedures primarily used to address infertility
71
What are the causes of subfertility/infertility in females?
1. problems producing eggs
- ovulation disorder
- reduced ovarian reserve
- irregular or no menstrual cycle
2. Tubal factor infertility
- egg or sperm cannot travel
3. Implantation failure
72
What are the causes of subfertility/infertility in males?
1. Low sperm quality or quantity
- sperm cant form in the testicles
- enlargement of scrotal veins
2. poor sperm transport
- blockage
- slow sperm
73
What are some other causes of subfertility/infertility in general?
1. hormones
2. obesity
3. being underweight (BMI less than 18.5)
4. other chronic illnesses and their treatments (ex: diabetes)
5. STIs
6. Drugs
7. advanced age
74
What is average age of childbearing years?
30 years old for women
75
Why is there age related decline in female fertility?
- monthly odds of conception (until age 40)
- odds that pregnancy will
terminate after conception or
implantation
76
Does the age of the father matter too? if so, how?
YES!
- sperm quality decreases with age
- age-related declines in semen volume and sperm performance
- increases in malformed and DNA-damaged sperm
77
What is the ART of "Ovulation induction"?
use of fertility drug to stimulate the ovaries
78
What is the ART of "Intrauterine insemination"?
- inject sperm directly into the uterus --> avoids cervical mucus
- 2 inseminations on 2 consecutive days (1 before and 1 after ovulation)
- good for low sperm count, unexplained fertility, anti-sperm antibodies
79
What is the ART of "IVF"?
Eggs are fertilized with sperm outside the uterus (in a petri dish) look at slide 19 for IVF cycle
80
What is the ART of "ICSI"? What is it good for?
"Intra-cytoplasmic sperm injection"
- used in conjunction with IVF
- good for: unsuccessful IVF, poor sperm morph/motility/count
- see slide 22 for cycle
81
What are 4 ways you can improve fertility and increase success of healthy pregnancies?
1. Three parent babies
2. mtDNA screening + IVF
3. Egg rejuvenation by mt transfer?
4. spermbots
82
What are "three-parent babies"?
parent 1 = maternal chromosomes
parent 2 = paternal chromosomes
parent 3 = donor mitochondria
1.egg nucleus containing mt defectivie chromosomes that are from mother is removed and inserted into donor egg
2.donor egg with mother's nucleus is fertilised with sperm from father
3.fertilised egg is inserted into mother's womb like normal IVF
83
What is mtDNA Screening?
- Screen blastocysts for mtDNA levels -->
select and implant only those blastocysts
with appropriate mtDNA levels
- To increase IVF efficiency and success
rates
84
What is egg rejuvenation?
1. egg precursor cells taken from small biopsy of ovary
2. precursor cells cultured and frozen for storage
3. Mitochondria from precursor cells injected with sperm into IVF egg
- hope to improve embryo quality and viability
NOT IN CLINICAL PRACTICE YET
85
What are spermbots?
motorized apparatus to assist with sperm delivery and fertilization
for male infertility
NO CLINICAL APPLICATION YET
86
What are 3 things of the female reproductive tract that are important to embryo development?
1. oviduct
2. uterine fluids
3. nutrient supply
87
When Bovine embryos were culutured in the presence of oviductal fluid, what did that show?
changes in blastocyst DNA Me and mRNA expression in genomic regions of developmentally important genes
88
What a 3 other fluids that increase pregnancy rates in ART
1. intercourse during IVF cycle
2. exposure to semen --> around time of embryo transfer
3. exposure to seminal plasma --> around time of egg retrieval
89
Why is seminal plasma so special?
- rich in hormones (E2, PGs, testosterone), signalling
molecules (TGF-), cytokines, bacterial polysaccharide
- TGF- primes female immune system for implantation ( key to the post-intercourse inflammatory response &
likely initiates the process of immune tolerance to seminal antigens)
- traditionally thought of only as transport vehicle & source of
nutrients for sperm
90
Seminal bacterial community composition is associated with semen health and male fertility. true or false
true
91
Lower embryo quality, altered fertilization, implantation,
pregnancy and live birth rates, and decreases in pregnancy loss
have been associated with ART. true or false
false --> INCREASES
92
What question do we keep asking ourselves about ART?
How good is the artificial environment?
93
In many countries, embryo transfer is now restricted to 1-2 embryos only due to previously high rates of multifetal pregnancies. True or false
TRUE
94
rates of PTB and LBW may be
improved with frozen embryo transfer. TRUE or FALSE
true
95
What is 2 noticeable differences between fresh and frozen embryo transfer?
1. increased weight at birth in frozen vs fresh
2. increased chance of preterm birth in fresh vs frozen
96
Look at slides 45-64 to learn more about consequences
97
