Cleavage Flashcards
early stages in human development
fertilized egg = zygote 2 cell stage 4 cell stage 11 cell stage morula blastocyst late blastocyst
post-fertilization events of the zygote
- becomes metabolically active
- cleavage = mitosis
- travels down oviduct – takes days
- loses zona pellucida before implantation
- implantation
zygote does mitosis to become 8 cell embryo, ______ continues and ______ occurs
cell division
compaction
note zona pellucida is still intact here
4 days post fertilization, _____ is transported into ? and results in the formation of a ?
water
ball of cells = morula 16 cells
blastocoel - the result of cavitation
blastocoel formation requires?
Na/K ATPase transporters
when is the embryo referred to as a blastocyst?
58 cell stage
features of the blastocyst
- zona pellucida
- large central blastocoel
- consists of 2 cell types
- polarized
what are the cell types in the blastocyst?
outer cells = trophoblasts
inner cells = inner cell mass
trophoblasts
form extraembryonic structures such as the placenta
outer cell layer of blastocyst
ICM
forms embryo proper plus some extraembryonic structures
inner cell mass of blastocyst
what causes polarity of the blastocyst?
because of the eccentric placement of blastocoel and inner cell mass
embryonic pole vs. abembryonic pole
pole of the blastocyst where ICM is located
pole marks opposite pole
control of cleavage
maternal genes til 2 cell stage
embryonic genome control by 4 cell stage
what is methylation?
addition of methyl groups to specific DNA regions
inactivates genes
including some enhancers/promoters
methylation cycle
- mature eggs/sperm highly methylated
- demethylation of ma/pa genomes shortly after fertilization
- remethylation of ICM
- levels fall after primordial germ cells enter genital ridges
- remethylation late in gemetogenesis
remethylation occurs later is gametogenesis and may lead to ?
maternal/paternal imprinting
what does polarization of blastomeres cause?
at 8-16 cell stages creates recognizable apical and basal surfaces
determines whether cells are destined for ICM or outer layer
what are the 2 theories of polarization?
inside-out hypothesis
cell polarity model
inside-out hypothesis
fate of blastomere is determined by its position w/in the embryo
not from intrinsic properties
cell polarity model
–depends on plane of cell division during cleavage
–cleavage plane parallel to outer surface of embryo = can become either
–cleavage plane perpendicular to outer surface of embryo = only trophoblast destiny
developmental potential =
potency
potency is greater than fate
genes involved in differentiation?
cdx-2
oct-4
nanog
sox2
Cdx-2
essential for trophoblast cell differentiation
antagonistic to oct-4
Oct-4
- expressed by oocytes and zygotes
- required for cleavage
- expressed in all morula cells
- role in maintenance of undifferentiated cells
w/o this inner cells become trophoblasts
Nanog
- produced by ICM
- maintain integrity of ICM
- w/o this inner cells become endoderm
Sox2
first expressed in 8 cell stage
along w/ oct4, helps control regulation of genes involved in differentiation
define genomic imprinting
is differential gene expression depending on whether a chromosome is inherited from ma or pa
certain genes derived from egg differs from expression of same genes derived from sperm
what causes genomic imprinting ? examples
due to DNA methylation differences in sperm and eggs
ex. prader-willi and angelman syndromes
parental imprinting
- occurs during gametogenesis
- involves methylation
- imprinted genes can be maintained for life
relate imprinting and rounds of gametogenesis
imprinting is erased and reestablished w/ each round of gametogenesis
Prader-Willi Syndrome
small hands and feet short poor sexual development retardation usually obese
mutation always inherited from father – deletion long arm chr15
Angelman Syndrome
exhibit frequent laughter
uncontrolled muscle mvt
large mouth
unusual seizures
mutation always from mom
deletion long arm chr15
X inactivation
occurs in humans in first few weeks of development
once inactivated it remains that way in all daughter cells then on
brought about by xist gene
XIST gene
X inactivation specific gene
located on x chr
produces RNA molecule that coats X chr and induces inactivation
RNA coat X chr
causes:
- removal of acetyl groups from histones
- methylation of histones
- alteration of histone composition
_____ region escapes X inactivation
pseudoautosomal
Barr body
- -found by murray barr
- -mary lyon proposed barr body = inactive x chromosome
define regulation
refers to ability of embryo to compensate for removal of structures or for addition of structures
list experimental methods
- chimeras or mosaics
- fate mapping
- totipotency
- production of tetra - hexparental embryos
- production of interspecies chimeras
- deletion/ablation exp.
- addition exp.
- transgenic embryos
- knock-out experiments
need book for further definition reviews
clinical correlation 3.2
