Embryology and Feeder Layer
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Transcript of Embryology and Feeder Layer
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Basic Embryology
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Embryology
Definition: the study of the origin anddevelopment of an organism
Prenatal period: before birth
38 weeks from conception to birth (average)fetal age
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Traditional (artificial) division:
Embryonic period: first 8 weeks
All major organs formed
Fetal period: remaining 30 weeks
Organs grow larger and become morecomplex
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Fertilization to Implantation
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Ovulation: egg released into the
peritoneal cavity Travels down fallopian tube in which
fertilization occurs
At conception in fallopian tube, maternaland paternal genetic material join to form anew human life (zygote)
Cell division occurs with travel down thetube and into the uterus
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Week 1 post conception
Zygotedivides repeatedly moving down tube
toward uterus (cleavage) The daughter cells are called blastomeres
Morula: the solid cluster of 12-16 blastomeresat about 72 hours
Day 4: late 60 cell morula enters uterus, takingup fluid becoming blastocyst
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Blastocyst stage
Two distinct types of cells Inner cell mass: forms the embryo
Trophoblast: layer of cells surrounding the cavitywhich helps form the placenta
Floats for about 3 days
Implantationon about day 6 post conception
Trophoblast erodes uterine wall Takes 1 week to complete
If inner cell mass of a single blastocyst divides:monozygotic (identical) twins
_____inner cell mass
______trophoblast
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Week 2
Inner cell mass divides intoepiblast and hypoblast
2 fluid filled sacs Amniotic sacfrom epiblast
Yolk sac from hypoblast
Bilaminar embryonic disc:area of contact
(gives rise to the whole body)
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Bilaminar to trilaminar disc
Three primary germ layers: all body tissuesdevelop from these
Ectoderm
Endoderm
Mesoderm
Week 3
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Formation of the 3 germ layers
Primitive streak (groove) on dorsal surface ofepiblast
Grastrulation: invagination of epiblast cells
Days 14-15: they replace hypoblast becoming
endoderm Day 16: mesoderm(a new third layer) formed
in between
Epiblast cells remaining on surface: ectoderm
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The three germ tissues
Germ as in germinate, not germs
Early specialization of cells
Are precursors Ectoderm and endoderm are epithelial tissue
(form sheets of tissue)
Mesoderm is a mesenchyme tissueMesenchyme cells are star shaped and do not attach
to one another, therefore migrate freely
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Notochord
Days 16-18
Primitive nodeepiblast cells
invaginate andmigrate anteriorly withsome endoderm cells
Rod defining the bodyaxis is formed
Future site of thevertebral column
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Neurulation
Notochord signals overlying ectoderm Formation begins of spinal cord and brain (neurulation)
Neural plate to neural groove to neural tube: pinched offinto body
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Closure of neural tube: begins at end of week 3; completeby end of week 4 (folic acid important for this step)
Extends cranially (eventually brain) and caudally (spinalcord)
Neural crest, lateral ectodermal cells, pulled along andform sensory nerve cells and other structures
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Mesoderm begins to differentiate Lateral to notochord, week 3 Extends cranially and caudally (from head to tail or
crown to rump)
Division of mesoderm into three regions Somites: 40 pairs of body segments (repeating units,
like building blocks) by end week 4 Intermediate mesoderm: just lateral to somites Lateral plate: splits to form coelom (cavity)
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Divisions of the mesodermal lateral
plate Somatic mesoderm: apposed to the
ectoderm
Splanchnic mesoderm: apposed to theendoderm
Coelom in between will become the
serous cavities of the ventral body cavity:PeritonealPericardial
Pleural
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Foldingbeginsat week 4
(main difference
between the 3week embryoand the adultbody is that theembryo is stilla flat disc)
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24 dayembryro;protrudes
intoamnioticcavity
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Day 23, beginningto fold
Lateral foldswill join ventrally
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Cylindricalhuman bodyplan, day 28(about cm)
Simplified
cross sectionthroughabdomen ofan adult(essentially thesame as above)
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Major derivatives of the embryonic germ layers
29 d b
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29 day embryo(this is when the heart starts pumping, about 4weeks or 1 month, cm size)
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By 8 weeks, about 2 months, allmajor organs are in place in atleast a rudimentary form; this is
why drugs early in pregnancy areso important to avoid manycause birth defects; baby is a littleover 1 long (below right)
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What is a Feeder Layer?
A layer of cells in arrested growth Provide extracellular excretions to aid another cell in
proliferation
Provide higher cell densities for low density celltypes
Common cells used in feeder layers: fibroblasts andglial cells
This differs from a co-culture because only one celltype is still able to proliferate
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How to make a Feeder Layer
Before confluencythe feeder cellgrowth must bearrested
To halt cell growth
Irradiate with x-
rays or gammarays
Treat withMitomycin C
Because they lackthe able to
proliferate, feederlayers musteventually bereplenished
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Mitomycin C
How it works
Cross-links DNA
Inhibits transcription What it is used for
Chemotherapy
Treatment of fibrotic
(scar) tissue
O
O
H2N
H3CN
CH2OCNH2
O
NH
OCH3