embryology and feeder layer

8/2/2019 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

embryology and feeder layer

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