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Embryogenesis

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inner cell

mass

All living things are made of cells.

Humans develop from a single cell -

the fertilized egg

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Sea urchin eggs divide in half about an hour after fertilization.Each cell divides again in half an hour later.

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Cleavage patterns differ between different organisms but

gastrulation is very similar in them all. Cell movements during

gastrulation generate the middle layer of cells - the mesoderm.

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A blastula (or blastocyst) is a hollow ball of hundreds of cells.

Cells move into the blastocoel through the blastopore.

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Gastrulation generates the 3 main cell layers:

ectoderm, mesoderm, and endoderm.

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Specific tissues and organs are derived from the cell layers.

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There are similarities and differences between embryos of different phylla.

Vertebrates all have a dorsal backbone along the anterior/posterior axis.

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8 weeks7 weeks

5 weeks4 weeks2 weeks 3 weeks 6 weeks

HUMAN EMBRYOGENESIS

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4 months -14 cm

9 months -35 cm

ready to be born

7 months -27 cm

may survive if born

prematurely

5 months -18 cm

mother may feel

movements (quickening)

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Subjects discussed:

1) Sperm and egg fuse at fertilization

2) Early stages: cleavage, blastula, gastrula

3) Cell layers: endoderm, mesoderm, ectoderm

Lecture 4

Embryos of all animals have much in common

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Gene Regulation

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exon 1 exon 2 exon 3intron intron

transcriptionstart

3end5 end transcriptionstop

5 end 3 end

exon 1 exon 2 exon 3

Primary transcript

Processed mRNA

Gene transcription and mRNA processing

in eukaryotes

DNA

transcriptional start transcriptional stop

RNA

polymerase

primary transcript

translation of open reading frame (ORF)on ribosomes

elongation

3 5

5

3

5

RNA

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In bacteria, regulatory proteins block binding of RNA polymerase

by covering the site in the promoter. Other proteins, such as CAP,

bind upstream and facilitate polymerase binding. Small molecules

regulate the binding affinity of regulatory proteins.

+ cAMP

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Proteins recognize specific sequences of 6-10 bases in DNA

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The lac operon encodes 3 proteins all made from the same transcript

induction

in growth media

containing lactose

no induction

in growth media

without lactose

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In eukaryotes the DNA is compacted by wrapping it around

nucleosomes which are then rolled into a selenoid. Further

compaction is necessary to get mitotic chromsomes. DNA

unrolls when it is being transcribed.

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Transcriptional activation is more complicated in eukaryotes.

Many proteins interact.

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Some complexes of regulatory proteins bind at a distance, but the DNA

can loop around to allow interaction with RNA polymerase.

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Transcription polymerizes RNA from 5' to 3' making a complementary copy

of only one strand of DNA ie. there is polarity to transcription.

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Genes are selected to make proteins.

Their mRNAs have to be translated on ribosomes.

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The code is read 5' to 3' in groups of 3 bases [triplet codons].

Translation always starts at AUG which encodes methionine.

So thephase is important.

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All proteins startwith the amino acid

methionine

The Universal Genetic Code

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Protein Folding

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Subjects discussed:

1) Initiation of transcription of DNA sequence into RNA sequence is regulated

2) mRNAs are translated into specific proteins on ribosomes using triplet code3) Most proteins fold up into their final forms by themselves

Lecture 5

To transcribe or not to transcribe

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Chapter 2: Human potential

Life as it is

Christopher Reeve Superman

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In vitro fertilization

At the 8 cell stagea cell can be removed

for analysis of the genes

Extra embryos can bestored frozen for later use.

day 5

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Establishing embryonic stem cell lines (ES cells)

from the inner cell mass of a blastocyst

mouse ES cells expressing

Pitx3:GFP in the midbrain

human ES cells proliferate

in vitro

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pancreatic insulin

producing ES cells

implanting ES cells

into a blastocystneurons from ES cells

When injected into mice, ES cells

form teratomas that include:

a. neuroepithelium

b. trabecular bone

c. cartillaged. skeletal muscle

e. primitive glomeruli

f. gut-like columnar epithelium

ES cells can be induced to differentiate

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Actor Michael J. Fox was struck with Parkinson's

disease. He is a strong advocate of support for

stem cell research.

Physicist Stephen Hawking has had ALS

(Lou Gehrig's disease) for 40 years.

He might have benefited from neural stem cells

that could replace his motor neurons.

Those with juvenile onset diabetes

might benefit from pancreatic stem cell

therapy.

The promise of stem cell therapy

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Sir John Gurdon

A nucleus from an intestinal

epithelial cell injected into

an enucleated egg gave rise

to a swimming tadpole.It did not work every time.

Nuclear transplantation in the South African Clawed Toad

Xenopus laevis first showed the totipotency of somatic nuclei

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Therapeutic cloning

Somatic cell nuclear transferThe dream

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Somatic stem cells

Intestinal stem cellsdividing in the crypt.

New hairs are continuously

produced from stem cells.

Sperm are continuouslyproduced from stem cells.

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Subjects discussed:

1) Embryonic stem cells can be grown from inner cell mass.

2) Support for stem cell research?3) Somatic nuclei have all the genes and can be transfered to ES cells.

Lecture 6

Stem cell questions