Making Eggs Flashcards
describe pre natal FEMALE GERM CELL DEVELOPMENT – OVERVIEW
generation of starting population of oocytes
all go through same prenatal
describe post natal FEMALE GERM CELL DEVELOPMENT – OVERVIEW
after birth
growth of the oocyte and its follicle
happens at different times - not all at once
meiotic maturation of fully grown oocyte - after oocytes grown
describe prenatal oocyte development - onwards
pcgs generate and migrate to genital ridge – proliferate- if become oogonia = meiosis, oocytes enter meiosis and assemble into primordial follicles - before birth - up to 6 months babygirl
starts cycle - after puberty - some before, after birth
what happens to oocyte population after birth
declines steadily after birth
~300,000 - make many oocytes but once 5 months old = steadily decrease
ends up ~1000 at 50 y/o
hard to get data from humans
what happens to oocyte population after birth - in mice
oocytes goes down before birth
what is reason to make so many then eliminate before birth = do not know theories = fetal ovary can sense unhealthy oocytes, do no know how they identify bad ones, also not all are actually individualized cells, some joined by cytoplasmic bridges * nurse cells, 1 oocyte –> 15 nurse cells that help oocyte, feed components to one winning oocyte, NO EVIDENCE THO
not super big decrease before birth in humans - could be true but not sure
describe the post natal ovarian follicles - histology components
preovulatory follicle - shortly before ovulation
much bigger - must become very large since all components
many oocytes of primordial follicles - begun meiosis (recomb) then arrest
surrounded by small molecules of follicle cells
concentric circles
oocyte = cells
zona pellucida = not cell, extracellular coat
granulosa cells = close to oocyte
antrum = space
theca = outside bm, more elongated -stretched nuclei
blood vessels run in interstitial space between follicle - not inside, always around
name stages of oocyte and follicle growth
primordial
primary
antral
pre ovulatory (graafian)
describe stages of oocyte and follicle growth- primordial
oocyte
small number granulosa cells enclose
describe stages of oocyte and follicle growth- primary
Granulosa cells activate and begins growth, enlarges
granulosa cell proliferation mitotically
Multiple layers to enclose oocyte which is grown
describe stages of oocyte and follicle growth-antral
theca cells outside
antrum = later in development, space between population of granulosa cells, filled with fluid (cavity), growth factors and steroids
antrum gets bigger - very big, before ovulation
describe stages of oocyte and follicle growth- pre ovulatory
antrum increase in size = more and more fluid
mural granulosa cells = close to theca cells
cumulus granulosa cells = around oocyte
these 2 categories = express diff genes and have diff functions
describe growth of oocyte and its follicle - length
very slow
3-4 months of oocyte and follicle to complete growth once it started
ex = begin to grow in jan, completed - ready to be ovulated in march/april
super slow growth (primordial to ready oocyte for fertilization)
describe how/when primordial follicles enter growth phase
cohorts of primordial follicles continuously enter growth phase
enter into growth phase at different times
like leaky sink
why is the continuous entry of primordial follicles into growth phase important
ensures all follicles not used up at once
regulation of entry into growth phase
so always follicles to ovulate, so do not use all at once
Follicles can continue to grow into menopause
where do all the oocytes go
1- oocytes grow and are ovulated (12x~40 =~500)
2- oocytes begin but do not complete growth, are not ovulated
3- oocytes do not grow and are eventually degraded
do not know where most of them go
describe initiation of growth - histologically
primordial = squamous granulosa cells, nuclei of granulosa elongated thin form
primary = cuboidal granulosa cells, spherical form, change shape now = more cuboidal
can recognize follicle has begun to grow by changed shape granulosa
describe initiation of growth - signals from granulosa cells - gen
maybe signal comes from granulosa cells
known to be a ligand receptor pair active in follicles
describe initiation of growth - signals from granulosa cells - ligand and receptor
granulosa = produces kit ligand
oocyte = expresses kit receptor
also play roles in other cells too
what is kit receptor - describe initiation of growth - signals from granulosa cells
receptor tyrosine kinase
growth factor binds = signalling pathway = end result is increase in protein synthesis, triggers initiation into oocyte growth
cancer when pathways deregulated
what happens if increase kit ligand
growth
what happens if inhibit kit ligand
no growth
what activates primordial follicles
local relaxation of ovarian stroma
describe experiment - for activation of primordial follicles- generally
exp 1 = made cuts in ct of ovary = stimulated to grow
other = eggs and granulosa only, cells reconstructed, ended up growing and no ct there
describe experiment 1 - for activation of primordial follicles- A B C D
A= regular, starting situation
B = partial digest small pieces with enzyme = partially degrade ct
C= that was enough to trigger growth, but if increase pressure = growth stops
D= cell in mitosis
made cuts in ct, stimulated eggs to grow, something about ct between follicles = prevents from growing unless activated = appropriate signal
what prevents growth of follicle - fully explain
dense matrix of ct between follicles - exerts pressure and flattens granulosa cells = prevent growth of follicle
local degradation of ct = oocyte can growth, so pressure released
change in ct sends signal to granulosa which then sends signal to oocyte to start growing
do not know what degrades ct, could be blood vessels - release factors that degrade matrix
TIGHTLY REGULATED SO SUPPLY LASTS THROUGHOUT REPRODUCTIVE LIFE
what happens when oocyte grows - vol/accumulate
volume increases by factor of 100 10x diameter
by end = almost 100 microns - by time finished growth = one of biggest cells in body
what does oocyte while growing store
Translated mrna, stored mrna and mitochondria
mrna, proteins, ribosome, standard cell components
accumulates factors needed for growth and for embryo (for few days after fertilization)
how many kinds of messages does oocytes store
2 kinds = translated and untranslated
very transcriptionally active when growing
describe the translated messages oocyte stores
acquire poly a tail in nucleus, 3’ end
long poly a tail = associated with high translational activity
sent to cytoplasm and then translated
makes all proteins oocyte needs to survive and grow
describe the untranslated messages oocyte stores
some undergo deadenylation = enzymes chew up poly a tail
no translation
stored in ribonuclear protein particles, stored to be translated later = final stage oocyte development or after fertilization
cpe = cytoplasmic polyadenylation element, message has this UUUUUAAU element in 3’ utr = deadenylation element, so shut down = translationally silent and stored, must have this sequence
as oocytes get bigger…
= more mitochondria
larger oocytes make more and more mito and generate more and more ribosomes
what is essential for embryonic development
large oocytes
vol increase ~100 fold
need big oocyte
why do oocytes need to be large
after fertilization = embryo undergoes cleavage division for first few days = cell division without increase in size, number of cells increase but total amount of cellular material the same
Produces a large cell that will be divided into many small cells by cleavage after fertilization
divides into 50-100 cells
NEED HUGE OOCYTE SO IT CAN GO THROUGH CLEAVAGE DIVISIONS (also accumulate nutrients and organelles embryo needs)
what is role of granulosa cells in oocyte growth?
essential role in growth process
sends signal to oocyte to grow
kit ligand activates kit receptor
do the oocytes need to be in contact with granulosa cells for growth
yes experiment = take oocyte in early stage of growth, if remove granulosa cells= strip off cells and incubate in vitro = oocyte does not grow
need granulosa cells for growth, and must be in physical contact with oocyte
cannot just have granulosa cells in same area - needs contacts
what connects oocytes and granulosa cells
gap junctions
channel between cells - permits passage of molecules between cells
describe what happens when inactivate gap junctions
no gap junctional communication between oocytes and granulosa cells
oocytes grow to only ~75% of normal sized
oocytes cannot undergo final stage of development = meiotic maturation. Cannot complete it
COMMUNICATION ESSENTIAL FOR GROWTH
what cant oocytes do themselves
oocytes can take up some amino acids by itself but does not have receptors for some so granulosa cells = pick up aas and transfer to oocyte
glucose too
explain how granulosa feeds oocyte
for some aas
glucose made inot pyruvate, transfers pyruvate to oocyte since oocyte not good at taking up glucose or pyruvate so depends on granulosa cells
provide cholesterol synthesis too
granulosa cells feed building blocks to oocyte to help it grow
where is zona pellucida
structure between granulosa and zona pellucida
very thick
around oocyte of egg of mammals (other species have something similar)
what is zona composed of
zp 1-4 (zona pellucida proteins)
mesh like network
how do granulosa and oocyte cells communicate since zona in the way
filopodia termed transzonal projections (TZPs) extend from granulosa cells to oocyte
tzps come from granulosa cells to oocyte, mediate contact and communication between oocyte and granulosa
Extension of cytoplasm
what happens if mutation in actin
tzps made of actin
no tzps then but also huge problem for many other tissues
WHAT ABOUT THE SOMATIC COMPARTMENT OF THE FOLLICLE? - 5
proliferation of granulosa cells
Recruitment of thecal cells
production of estrogen- by growing follicle, major source of estradiol in females
differentiation of mural and cumulus granulosa cells = cavity is huge, biggest = ripest
growth of antrum
WHAT ABOUT THE SOMATIC COMPARTMENT OF THE FOLLICLE? - explain recruitment of thecal cells
before = around outside= just float around ovarian stroma- have no purpose
present once oocyte and follicle grow
= get called in
not in primordial or early primary stage
which cells produce estradiol
granulosa and thecal
explain synthesis of estradiol - from cholesterol
cholesterol to progesterone to testosterone to estradiol
women make both testosterone and estradiol, most testosterone concerted to estradiol
describe role of thecal cells - estradiol
synthesize testosterone from cholesterol (like leydig cells), 1st part of reaction
convert cholesterol to testosterone
describe role of granulosa cells - estradiol
2nd part = picks up testosterone
converts testosterone to estradiol
what do gonadotropins do
regulate follicle development
peak of lh triggers ovulation
Compare fsh and lh
fsh and lh closely related, both produced by piutary
have alpha and beta subunits
both have same alpha subunit
beta subunit = diff, gives them different unique activities
role in male and female - diff levels obviously
when is fsh required
for most of growth = fsh not required
women who have mutation in fsh or in receptor = follicles can grow to pre antral stage (or early antral) but final stage cannot happen (prior 2 weeks to ovulation)
fsh needed 2 weeks prior to ovulation (antral, preovulatory stage)
why do most pre antral follicles die
due to insufficient fsh
lots of follicles get to late pre antral/early antral phases
but only enough fsh to get one or 2 to grow, dominant follicle gets enough fsh and others die
what does estrogen produced by growing follicles do
inhibits fsh production
describe entire diabolical cycle of estrogen
FSH SYNTHESIS AND RELEASE (PITUITARY) = causes granulosa cells to proliferate, helps final stage of dev
GRANULOSA PROLIFERATE = takes up testosterone from theca cells and coverts to estrogen, high estradiol
INCREASED PRODUCTION OF ESTROGEN = negative feeback, inhibits fsh synthesis and release from pituitary
DOMINANT FOLLICLE Suppresses GROWTH OF OTHER FOLLICLES
does treatment with fsh help increase number of oocytes for assisted repro - explain
to increase chance of getting pregnant = can provide fsh directly or give drug to antagonist inhibitory effects of estradiol
raise fsh so then can make more cells grow
do not know if all the follicles are of the same quality tho
explain ivf fsh treatments
fsh treatments = rescued dev of follicles
describe lh - what it does
Triggers ovulation by acting on somatic cells of follicle and also triggers maturation of oocyte
describe meiotic maturation - length in humans and micce
place where things can get messed up = trisomies
in humans = 36 hrs, short
12hrs in mice
what happens during meiotic maturation - gen
1st meiotic division
asymmetric cytokinetic division
describe meiosis 1 and 2 - oogenesis
meiosis 1 during meiotic maturation
meiosis 2 after fert
oocyte frozen in late diplotene stage - undergone recomb, from before birth until meiotic maturation
describe meiosis 1 and 2 - spermatogenesis
Meiosis 1 and 2 during spermatogenesis = both happen at same time, time frame shorter
might affect frequencies of aneuploidies
what exactly happens during meiotic maturation
1st meiotic division and preparation for 2nd meiotic division
describe meiotic maturation - gv stage oocyte and gvbd
chroms underwent recomb
nucleus, zona, and oocyte
germinal vesicle
then germinal vesicle breakdown = nuclear envelop and chroms condense
describe meiotic maturation - spindle formation
chroms condensed and arranged on spindle then spindle migrates to periphery - one spindle pole becomes attached to cortex of oocyte
1st meiotic division
describe meiotic maturation - first polar body extrusion
first meiotic division = chrom segregate into 2 groups then cytokinesis= divides cells into big oocyte and small polar body
need spindle migration to get big oocyte and small polar body
polar body can be used for chromosome abnormality analysis
describe what we should see visually - meiotic maturation
polar body contains 1/2 chroms from 1st meiotic division
once 1st meiotic done = chroms in oocyte arrange in new spindle = metaphase 2 spindle but then arrest till after fert
what does lh bind to
mural granulosa cells located far from oocyte
have receptors on theca and mural but relevant binding for oocyte = lh on mural cells
lh acts then signal must be transmitted to oocyte
describe experiment - involving lh
take ovary and remove oocyte from big antral follicle
and put in culture dish = went to maturation w/o lh
= something repressing (inhibits follicle, blocks maturation, lh relieves blocking effect)
what is the hormonal regulation of maturation
release from repression - lh
what is cgmp
cyclic guanosine monophosphate
made by mural granulosa cells - main source
also made by cumulus cells
describe when maturation inhibited
recall = all cells (oocyte, mural, cumulus) connected by gap junctions (allows small molecules through)
HIGH LEVELS OF CGMP IN OOCYTE = BLOCKS MATURATION
describe when maturation initiated
lh can directly inhibit cgmp (also by egfr acted on by egfr ligands)
lh binds receptor and activates signalling pathways on mural cells activate egfr signalling pathway, and egfr recptor on mural and cumulus cells
levels of cgmp in granulosa fall so cgmp levels in oocyte also fall bc of gap junctions = initiate maturation = when CGMP LOW
describe whole pathway of cgmp
cgmp = if high blocks pde3A (phosphodiesterase pde3a) –> inhibits camp, if high camp (so pde3a low) –> much activate protein kinase a –> inhibits = blocks cdc25b, so cdk1 in active = highly phosphorylated
but if cdc25b (phosphatase) active = cdk1 active with one phosphorus and cyclin b1 active = drive into metaphase of cell cycle for all cells
describe age dependent decline of fertility in women
Probability of success decreases as age
older = harder to get pregnant
must turn to art
what happens if give young donor oocytes to older woman
probability does not change much so can still get pregnant with young oocytes
Conclusion = egg quality declines, nothing else wrong (not blood supply, uterus, hormones etc)
describe meiotic errors - what do they depend on
mainly maternal - oocyte and age
probability of aneuploidy increases with maternal age
Origin = during 1st and second meiotic divisions
not much difference from men
describe meiotic errors - what do they depend on - TRISOMY 21
Down syndrome = mild case of triploidy, they usually survive and we can se where extra chrom comes from
usually associated with high maternal age
incorrect function of meiotic spindle
mostly 1st division, then 2nd, not usually paternal or mitotic error
DESCRIBE TIming of meiotic progression
all oocytes get to diplotene/diakinesis before birth then meiotic division resume after like maybe 40 years,
1 month, no arrest = meiotic process for sperms
could difference in timing of meiosis underly the difference in how frequently errors of meiosis originate on oocyte side
describe roles of cohesion in chrom segregation
rec8 - cohesin holds chroms together
degradation of some of cohesin molecules located in certain regions of chromosomes away from centromeres = permits 1st meiotic division
2nd meiotic= more degradation around centromeres of sister chromatids
regulated disassembly important for meiosis to occur properly
describe roles of cohesion in chrom segregation - connection with mistakes in meiosis
no turnover of cohesin in molecule = put on before birth so maybe not acting well so increased mistakes
cohesin that is so important in regulating chromosome separation is getting messed up
EXOGENOUS COHESINS TO RESCUE AGE-RELATED ANEUPLOIDY?- describe experiment
remove cumulus oocyte complex from preovulatory follicle = ones that are ready to mature, and put in petri dish and will mature in vitro spontaneously
inject cohesin into oocyte = before maturation, will replenish supply - will stick together as they should
permit meiotic maturation
fertilize egg = see if fewer meiotic errors in oocyte of old mic, compared to ones that did not get new cohesin
DO NOT ACTUALLY KNOW IF WORKS
what is cytoplasmic maturation
changes that happen in cytoplasm as same time as oocyte goes through meiotic divisions
describe key events of cytoplasmic maturation - 5
changes in protein synthesis
Beginning of degradation of oocyte (maternal) mRNA
Redistribution of mitochondria
Redistribution of endoplasmic reticulum Accumulation of cortical granules at the cortex
why translation regulation
when oocytes grow = v transcriptionally active, make many mrnas
once reach full size = transcriptional activity drops
some mrnas that have accumulated are now degraded
after fertilization = remain silent during most until 4 cell stage (until stage specific activation of transcription)
after fertilization = do not need these genes that were for making oocyte = so maybe messages for embryo development will only be left - not mixture of embryo dev and oocyte dev
what is a key event of cytoplasmic maturation
TRANSLATIONAL ACTIVATION OF CPE-BEARING MRNAS
messages made during growth have to sustain development throughout maturation and during first couple of cleavages after fertilization = translational activation of previously silent message= proteins at right time of dev
describe TRANSLATIONAL ACTIVATION OF CPE-BEARING MRNAS
during maturation = many repressed rnas become translationally activated
poly a tail becomes long bc cytoplasmic conditions of maturing oocyte change = increase translation of messages
very important part of maturation = helps oocyte complete maturation and undergo embryonic development after fert
if translation activation does not occur properly = oocytes do not develop into embryo
what can pass through gap junctions
sugars, nucleotides, atp, amino acids
NO proteins or mrna, bigger proteins, too large
xxy - klinefelter - is it from mom or dad
equally frequently from male or female
