2. First Week to Cleavage Flashcards
fertilization:Fertilization leads to the formation of the ____.oocyte completes ___ but cell is arrested in ___male and female ___ fuse to form chromosomes of the zygote -how does the sperm get to the oocyte?
include the layers -how is polyspermy blocked? -how many cells is the zygote
-formation of the zygote initiates ______
zygote.**oocyte completes second division but cell arrested in metaphase -
sperm has to get through 2 layers:1) penetrates the corona radiata surrounding the oocyte
2) sperm penetrates the zone pellucida via release of degradative enzymes from acrosome block polyspermy: cortical granules fuse with oocyte membrane and causes hardening of zona pellucida
zygote is one cell-formation of zygote initiates embryonic development
What are the major events of week 1 of development
-conception
-cleavage&
blastocyst formation with inner cell
-initiation of implantation
describe cleavage-cells cleave asynchronously or synchronously?
- polar or non polar
- ration of cytoplasm to nucleus?
- why is it so rapid?
- what are the cellular and molecular events?-what restricts growth?
cleavage: embryo moves down oviduct and cleaves -asynchronously (like mouse) but volume stays constant-and cell compaction and cells polarized
- every 12-24 hours because has no G1 or G2 -go from 600:1 cytoplasm to nucleus to 3:1 -
cellular events: cell division, activation of embryonic genome, blastocyst formation
-zona pelluida restricts growth
describe day one of cleavage -observable charact.-location-zona pellucida
secondary oocyte undergoes meisosis II and forms zygote-unicellularity
locatioN: oviduct, outer 1/3 zona pellucida is present
describe day 1.5 to 3 -observable charact
- location
- zona pellucida
2- 16 cell stage charac: multicellular,
-by 8 to 16 cell stage we see cavity formation with outer and inner cells
no cavity*compaction of the embyo oviduct, location: mid inner 1/3
zp is there
describe day 4/5-observable charact.-location-zona pellucida-how many cells
morula develops to blastocyst
charact: cavity present, unattached location: oviduct/uterus
- zp is partially in tact
and negative8-16 cell stage- 2 cell lineages:outer: trophoblast -in between is the blastocyst cavity: capable of implantation and inner cells: but they are not morphologically distinguishable 64 cells with 2 layers
what are blastomeres
daughter cells of cleavage divisions
what genome controls cleavage, embryonic or maternal?
Prove it.
when are paternal genes expressed?
maternal genome controls 1st cell division-embryo’s genome activated at 4-8 cell stage bc those are needed to direct cleavage and
blastocyst formation
-paternal genes expressed after embryo genome activated experimental evidence:-stopping RNA synthesis stops development after the 4 cell stage
why is the trophoblast important?
- type of tissue?
- is the cell polarized?
- genetic expression?
- gives rise to?
- influenced by?
it is the first tissue of the embryo recognizable at (32-64) cell stage
- true epithelium-it will form only extraeembryonic tissue (placenta and amnion)
- cell is polarized
- expression of Oct4 and Nanog genes turned off (bc these are for maintaining pluripotency) in trophoblast but maintained in the inner cell mass-influenced by genomic imprinting (influence of 1 parentally derived allele over another)
- requires expression of unknown PATERNALLY derived alleles
describe the experimental evidence for genomic imprinting
- what does maternal chromosomes dictate?
- what do paternal chromosomes dictate?
conclusion:maternal important for embryo formation
paternal important for placenta
experiment:-only 2 male nuclei—> get normal placenta but stunted embryo
-only 2 female nuclei—> get well developed embryo but poorly developed placenta
-2 males and 1 female nuclei–> over expression of placenta
what is the molecular mechanism for genome imprinting?
-when does it happen
-methlyation of DNA in gene promoters -think CpG islands (stretches of alternating C and G )
imprinting is erased during formation of primordial germ cells. and reestablished according to sex -during gametogenesis
give clinical example of genomic imprinting
what chromosome number is this?
maternal: chromosome 15 deletion
- angelman syndrome: developmental delay, speech and balance disorder, unique happy demeanor,
paternal: chromosome 15 deletion-prader-willi syndrome: rapid weight gain leading to morbid obesity, mild mental retardation and hypergonadism
what do most of the inner cell mass cells become?
- what is the genetic expression?
- when is first axis of polarity formed?
- which side is dorsal/ventral?
- ICM remodels into bilaminar disc– now the cells are polarized. bilaminar disk is epiblast and hypoblast
- upper epiblast (primitive ectoderm) and lower hypoblast (primitive endoderm-
- most of the cells become part of embryo-expression of pluipotency genes so Oct4, Nanog, and Sox2
extra embryonic)-dorsal side is the side of the embryo which is the epiblast while the lower side is the ventral side
when and why does the embryo hatch from the ZP?
what was the function of the ZP?
hatching allows small increase in size of embryo and facilitates implantation
-hatching occurs days 4-5-
ZP kept blastomeres together, was an immunological barrier,and prevents premature implantation
define regulation and potency and how it relates to the cleavage stage of embryos
- how does this change with time?
- describe totipotent, pluripotent
regulation= ability of field to produce normal embryo structure when parts removed or addedthe cleavage stage exhibits potential for regulationpotency: full range of developmental capabilities of blastomere-ability to regulate decreases with age 1-4 cell stage:
cells totipotent meaning they can form entire conceptus, include placenta4-8 cell stage: all cells pluripotent, can form any cell type in embryo, but not extra embryonic tissues
16+ cells: only inner cell mass cells are pluripotent
alternative sources of multi potent stem cells
amniotic fluid
adult cells transfected with transcription factors : Oct4, Nanog)
normally expressed in the early embryo
those are induced pluripotent stem cells (iPS)
factors that mediate cell diversity
- cell position (outer or inner)
- number of cell divisions
- cell to cell interactions
describe what happens in twinning and the 3 types
monozygotic twins- the blastomere/inner cell mass separates
conjoined twins- incomplete separation of the embryo
dizygotic twins- double ovulation and fertilization. this makes up 2/3 of all twins
trophoblast of implanted embryo secretes___
HCG human chorionic gonadotropin hormone
function and structure of the syncytiotrophoblast
multinucleate and has microvilli
secretes proteases for controlled invasion of endometrium
what is the function and structure of the cytotrophoblast
this is the original trophoblast layer of the blastocyst
retains epithelium properties bc polarized and has distinct cell boundaries
