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rds > gametogenesis, fertilisation & preimplantation development > Flashcards

gametogenesis, fertilisation & preimplantation development Flashcards

1
Q

testis cell types and functions

A

leydig: testosterone production
sertoli: production of activin, inhibin, AMH and androgen binding proteins, regulate internal environment of seminiferous tubules

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2
Q

izumo1

A

binds to folate receptor 4 (Juno) essential for sperm egg fusion

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3
Q

path of PGC migration

A

from dorsal body wall to genital ridges

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4
Q

regulation of PGC migration

A

chemotaxis: stem cell factor binds to and activates C-kit (PGCs have C-kit receptor) failure of migration -> teratomas

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5
Q

how does the SRY cause sexual differentiation and testes cell types

A

SRY (on long arm of Y chromosome) -> SOX9 ->

  1. FGF9 -> differentiation of Sertoli from coloemic epithelium (threshold of Sertoli cells needed for male differentiation; proliferation determines size of male gonad)
  2. steroidogenic factor 1 -> Leydig
  3. PDGF -> interstitial cells (occurs later than other 2)
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6
Q

development of male ductal system

A

Wolffian ducts -> male ductal system

AMH -> degeneration of Mullerian ducts by apoptosis

testosterone/DHT important for formation of epididymis, vas deferens, seminal vesicles

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7
Q

formation of seminiferous cords

A

Sertoli cells cluster and surround germ cells

perimyoid cells surround these cords

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8
Q

differentiation of perimyoid cells

A

Dhh (desert hedgehog) produced by Sertoli cells binds to PTCH1 (patched 1)

DAX-1 receptor also important

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9
Q

difference between oogonia and oocytes

A

PGCs are oogonia once they have migrated into the genital ridge

oogonia differentiate into oocytes which can no longer proliferate

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10
Q

formation of primordial follicles

A

pregranulosa cells (origin unknown) surround oocytes

inner oocytes (medulla) form follicles first

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11
Q

role of Sertoli cells

A

production of AMH (until puberty), inhibin, oestrogen and androgen binding proteins

regulates internal environment of seminiferous tubule

FSH -> proliferation

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12
Q

mouse study demonstrating potential therapy for male infertility

A

cells from testes of other mouse that express Oct-4 (stem cell potential) injected into infertile mouse restored spermatogenesis

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13
Q

spermatogenesis (5)

2017 SAQ

A
  1. Primordial germ cells
  2. Spermatogoonia: undergo mitosis
    1. Type A: undifferentiated, sits on basement membrane
    2. Type B differentiate to…
  3. Spermatocyte: undergo meiosis (can no longer undergo mitosis)
    1. Primary (meiosis I)
    2. Secondary (meiosis II)
  4. Spermatids (round)
  5. Mature spermatozoa (elongated) develops flagellum, forms acrosome, released from Sertoli cell
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14
Q

functions of epididymis (4)

A
  1. concentration of sperm
  2. functional maturation
  3. storage
  4. removal of decapacitated sperm
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15
Q

segments of epididymis and functions (4)

A
  1. initial segment: water reabsorption via sodium channels
  2. caput: synthesis of compounds in epididymal fluid
  3. corpus
  4. cauda: synthesis of compounds in epididymal fluid
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16
Q

function of epididymal proteins

A

mask membrane proteins on sperm, released when exposed to female reproductive tract environment, allowing binding to zona pellucida of oocyte

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17
Q

loss of cytoplasmic droplet in sperm function? when does it occur?

A

during transit from caput to corpus

ejaculate w/o cytoplasic droplets leads to decreased fertility and proportion of spermatozoa

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18
Q

how do sperm overcome acidic pH (<5) of vagina

A

seminal fluid pH is ~7 and coagulates

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19
Q

effects of oestrogen on cervical mucus

A

oestrogen (during ovulation) -> increased hydration of cervical mucus -> easier for sperm to penetrate

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20
Q

role of progesterone in fertilisation

A

progesterone (released by cumulus cells of oocyte) → ↑calcium permeability of membrane → calcium influx into spermatozoa →

  1. capacitation of spermatozoa
  2. acrosome reaction: persistent Ca entry via TRPC2 channel
  3. oocyte activation: calcium oscillations caused by a sperm-specific PLCζ released into oocyte following gamete fusion
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21
Q

characteristics of capacitated sperm

A
  1. hyperactivated motility
  2. change in surface properties
  3. ability to undergo acrosome reaction
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22
Q

stages of follicular development (9)

A
  1. activation of follicle growth (regulation unknown)
  2. primordial follicle: single layer of flattened pre-granulosa cells surrounding
  3. transitional follicle: granulosa cells at one pole become cuboidal
  4. primary follicle: one layer of cuboidal granulosa cells
  5. secondary follicle: two layers + theca cells surrounding + zona pellucida
  6. pre-antral follicle: multilayered, oocyte growth
  7. antral follicle: antrum (fluid-filled cavity prevents necrosis of centre of follicle)
  8. graafian follicle: matured and ready for ovulation
  9. corpus luteum: structure left after ovulation
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23
Q

theca and granulosa cell hormone secretion

A

LH -> theca cells -> produce androgens

FSH -> granulosa cells convert androgens to oestrogens

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24
Q

regulation of folliculogenesis (4)

A

hormones not necessary for early follicle development

FIGL-alpha: essential for formation of follicles

GDF-9: essential for granulosa cell proliferation (multilayering), theca formation

connexin-43: gap junction protein, communication between granulosa cells, KO -> arrest at primary stage

cx-37: communication between oocyte and granulosa cells, KO -> loss of antral follicle formation

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25
Q

selection of dominant follicle

A

dominant follicle most sensitive to FSH, produces most E2 which inhibits FSH production

LH receptors so that can respond to LH surge

26
Q

what effects does the LH surge have (6)

A
  1. decreased cAMP -> resumption of meiosis
  2. cumulus expansion: hyaluranon produces attracts water -> gel-like complex more easily picked up by fimbriae of Fallopian tube
  3. ovulation
  4. luteinsation: corpus luteum formation, switch from granulosa cell oestrogen production to progesterone
  5. withdrawal of granulosa cell transzonal processes from oocyte
  6. decreased gap junction communication
27
Q

luteolysis

A
  1. functional: decreased progesterone production -> development of new follicles
  2. structural: removal of corpus luteum
  3. corpus luteum -> corpus albicans: scar of collagen, eventually resorbed
28
Q

factors required for entry into meiosis (3)

prev SAQ

A

Intrinsic factor DAZL: PGC → meiosis competent germ cell

Extrinsic factor retinoic acid produced by mesonephros

Females: RA important for expression of Stra8, which is required for premeiotic DNA replication → oogonium

Males: Cyp26b1 in testis degrades retinoic acid, preventing Stra8 expression → spermatogonium

29
Q

functions of meiosis

A
  1. maintain chromosome numbers by producing haploid gamete
  2. increased genetic variation by: random assortment of parental chromosomes and recombination of genetic material
30
Q

stages of meiosis until LH surge

A

inner oocytes (medulla) enter meiosis first

DNA synthesis -> 2 chromosomes connected by cohesins

  1. leptotene: chromosomes condense
  2. zygotene: distance pairing (homologues lie side by side)
  3. pachytene: paired homologues synapse and form bivalent, recombination w formation of chiasmata
  4. diplotene: synaptonemal complexes removed -> homologues held together by chiasmata only

meiotic arrest until LH surge

31
Q

c-Kit receptor

  1. ligand, produced where?
  2. location
  3. function
  4. KO -> ?
A
  1. Kit-L produced by granulosa cells
  2. binds to c-Kit receptor on oocyte
  3. triggers oocyte growth and theca cell recruitment
  4. KO -> loss of fertility (mice)
32
Q

functions of gap junctions between granulosa cells and oocyte

A

avascular environment within basal lamina

  1. allows passage of small molecules e.g. cAMP
  2. coordination of luteinzation, atresia, etc.
  3. transport of growth factors, metabolic precursors e.g. amino acids, nucleotides
33
Q

interactions between oocytes and granulosa cells

A

oocytes -> GDF9 -> granulosa cell proliferation

granulosa cells -> Kit-L -> oocyte growth

34
Q

how is diplotene meiotic arrest maintained (cellularly)

A

cGMP from granulosa cells -> oocyte via gap junction

cGMP inhibits PDE31 (phosphodiesterase) which usually degrades cAMP -> maintenace of meiotic arrest by cAMP

35
Q

function of anaphase promoting complex (APC)

A

APC degrades securin, releasing separase, which cleaves Rec8 (cohesin between long arms of chromosomes) -> separation of homologues -> cell cycle progress

cyclin B/Cdk1 complex (MPF: maturation-promoting factor) degrades APC → meiotic arrest

cytostatic factors e.g. mos and emi2 help to inhibit APC

36
Q

stages of meiosis after LH surge

A

resumption of meiosis following LH surge

metaphase I: homologues align at metaphase plate and attach to spindle

anaphase I: separation of homologues between poles

telophase I: asymmetrical cell division -> extrusion of 1st polar body arrest at metaphase II

37
Q

uncapacitated sperm store

A

at isthmus of fallopian tube

only few sperm become capacitated and migrate towards oocyte (~100)

38
Q

zona pellucida glycoproteins in humans and mice + functions

A

ZP1, 2, 3 in mice / ZP1 - 4 in humans

ZP3: primary sperm receptor, binds to head of sperm and interacts w TRPC2 channels -> calcium influx, induces acrosome reaction, provide species specificity

ZP2: secondary sperm receptor (binds acrosome reacted sperm)

ZP1, 2, 4 involved in induction of acrosome reaction

39
Q

what happens after sperm bind to zona pellucida

A

acrosome reaction: irreversible exocytosis -> hydrolytic enzymes break down zona pellucida

acrosomal process grows and penetrates further through coating and egg plasma membrane

egg and sperm membranes fuse

40
Q

cortical granule exocytosis

A

zona reaction: enzymes from granules

A protease cleaves ZP2

B hexosaminidase cleaves ZP3 -> removes sperm binding properties

cross-linking of tyrosine kinase residues on ZPs -> zona hardening

41
Q

how does calcium oocyte activation occur

A

sperm binds to oocyte and releases PLC-zeta which generates InsP3 which binds to receptors on ER -> calcium efflux (oscillations)

42
Q

resumption of meiosis II following fertilisation

A

anaphase II: chromatids separate

telophase II: one set of chromatids expelled in polar body

43
Q

protective functions of zona pellucida during preimplantation development

A
  1. prevents sticking of embryo to oviduct walls and each other
  2. protects attack against leukocytes (embryos w/o zona disintegrate in oviducts)
  3. maintains normal cleavage pattern
44
Q

processes during first cleavage

A
  1. pronucleus formation and migration together (but not fusion), duplication of DNA
  2. mitosis metaphase: pronuclear membranes break down, alignment of chromosomes on metaphase plate
  3. mitosis anaphase: separate of chromatids, formation of cleavage furrow
45
Q

important of E-cadherin in preimplantation development

A

calcium dependent compaction

at 16-cell stage in humans

46
Q

models for differentation of cell types in blastocyst (2)

A
  1. inside-outside model: outer cells -> trophoectoderm / inner cells -> inner cell mass
  2. polarisation model: conservative division -> 2 polar cells / differentiation division (when less space) -> 1 polar 1 apolar

polar cells -> trophoectoderm / apolar cells -> inner call mass

47
Q

functions of trophoectoderm (3)

A
  1. pumps fluid into cavity
  2. transport of metabolites between maternal tissues and ICM
  3. proliferative source of cells for placental TE
48
Q

when does activation of the embryonic genome occur

A

between 4 and 8 cell stage

49
Q

when does most embryo growth arrest occur

A

between 4 and 8 cell stages (activation of embryonic genome)

50
Q

leading cause of miscarriage (%)

A

aneuploidy (35%)

51
Q

differences in timing of meiosis in males vs females

A

F: entry into meiosis during fetal development, meiotic arrest during childhood, LH surge triggers resumption

M: entry into meiosis after puberty

52
Q

aneuploidy: true non-disjunction

A

no loss of cohesins -> both homologues go to one pole (monosomy/trisomy)

53
Q

‘achiasmate’ non-disjunction

A

no formation of chiasmata between homologues -> separate and connected to different microtubules -> chance to both can go to same pole (trisomy/monosomy)

small chromosomes (e.g. 21 -> Down’s syndrome) more likely to be achiasmate

54
Q

aneuploidy in meiosis I (3)

A
  1. true non-disjunction
  2. ‘achiasmate’ non-disjunction
  3. premature separation of sister chromatids
55
Q

mitotic non-disjunction

A

both chromatids go towards one pole (failure of loss of cohesins from centromere)

earlier in cleavage -> more cells affected

56
Q

aneuploidy in meiosis II

A

meiotic non-disjunction: failure of loss of cohesins from centromere -> both chromatids to one pole

57
Q

post-zygotic non-disjunction

A

aneuploidy that occurs during cleavage stages -> mosaicism (mixtures of diploid, monosomic and trisomic cells)

fate of abnormal cells unknown: ?apoptosis, ?slower cleavage so that normal cells predominate

58
Q

anaphase lag

A

chromosome falls off spindle

free-floating in cytoplasm -> formation of micronucleus

59
Q

examples of different origins (paternal/maternal, meiosis I/II etc.) of trisomys

A
  • trisomy 16 100% maternal, meiosis I
  • XXY mostly sperm, meiosis II
60
Q

causes of increased aneuploidy w age

A
  1. relaxed selection hypothesis: uterus less able to recognise abnormal pregnancy (now thought to not be the case)
  2. ‘two hit’ hypothesis: reduced recombination -> predisposition to non-disjunction, which increases w age due to oxidative stress, decreased microcirculation around dominant follicle, defective granulosa cells
  3. limited pool hypothesis: antral follicle no declines w age
    1. local factors hypothesis: degeneration of cohesins -> decreased cohesion between chromatids, increased FSH, prolonged exposure to environmental toxins
61
Q

key meiotic processes which predispose to aneuploidy when disrupted

A
  1. recombination
  2. cohesion between chromatids (cohesin)
  3. spindle
62
Q

what is CatSper? function?

A

sperm specific Ca channel in flagellum

Controls sperm chemotaxis and guides it to oocyte

rds (13 decks)

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