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Building an Organism:
Genes, Cells and
Development
Prof. Gareth I. Jenkins
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How is a complex multicellular organism
produced - how does it develop and
function?
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Aims of the Course:
Three key aims are to: provide a basic understanding of the developmental
processes that produce multicellular organisms
provide information on key cellular processes howcells divide, differentiate, perceive external stimuli
and communicate show that genes produce molecular instructions that
determine the organisation and behaviour of
multicellular organisms
An introduction to Molecular and Cellular Biology
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21 lectures + 1 lab
Assessment:
Class exam 15%
Laboratory 15%
Degree exam 70%
How to be successful
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Engage in lectures Use forum and contact staff
Attend lectures and lab
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A B C D E F CW CR
lecture abs (/8)
Correlation of final grade with attendance
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Lecture 1
Introduction to Development
1. What is development?
2. How is development controlled?
3. How can we discover the cellular and
molecular mechanisms responsiblefor development?
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1. What is development?
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male gamete
Development proceeds in the context of
the life cycle:
female gamete
fertilisationzygote
embryogenesisadult
The purpose is reproduction
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Big Question:
How does a single celled zygote become
a complex multicellular organism with
specialised cells, tissues and organs?
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Embryonic development of the zebrafish
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Some key processes:
Development of cell polarity:acquisition of assymetry
Animal pole
Vegetal pole
Amphibian oocyteAlgal zygote
Determines subsequent fate
How is polarity established?
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Becoming multicellularEarly stages in starfish development
Unfertilised egg
2-cell stage 4-cell stage
16-cell stage32-cell stage
How is celldivision
controlled?
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leaf epidermis
What causes cells to commit to particular
developmental fates?
Pattern formation, cell commitment, cell fate
Insect varvae
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Organogenesis
Fly head
How are complex organs produced withthe right number and spatial distribution
of parts?
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DifferentiationHow do genesdetermine the
specialisation
of cell function?
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2. How is development
controlled?
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Some aspects of regulation at the
cellular level:
Control of cell size and shape Control of cell division
Cell movement and adhesion
Communication between cells
Acquisition of polarity
Responses to external stimuli
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Genetic basis:
Genes specify the developmental blueprint
Some genes are expressed as aconsequenceof a developmental
change
Some genes controldevelopment:
e.g. some transcription factors
determine cell commitment andorganogenesis
Qu. What is a transcription factor?
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The expression of many genes is regulated e.g.
in specific cell types, at particular times indevelopment, or in response to external stimuli:
differential gene expression
This is a key factor in controlling development
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3. How can we discover the
cellular and molecular mechanisms
responsible fordevelopment?
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Imaging cellular processes
Based on the power of microscopy
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Identify gene that has become mutated
Based on the power of genetics
Isolate mutant in selected process
Draw conclusions on gene function
Wild-type apetala3
Determining gene function
The forward genetic approach
Antennapedia
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Gene/protein sequence provides
information on cellular function
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Model organisms:
Yeast
Mouse
Selected for their
suitability for the
molecular genetic
approach
Zebra fish
Caenorhabditis
Arabidopsis
Drosophila
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Advantages of model organisms for genetics
1. Small and easy to grow
2. Rapid generation time
3. Lots of progeny from each individual
4. Preferably self fertile and able to be crossed5. Easy to produce mutants
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Advantages for molecular biology
1. Small genome - enables full genomesequence to be obtained and helps gene
isolation
2. Easy to genetically transform
3. Methods for isolating genes corresponding
to mutants
Qu. What is a genome?
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Small genome enables full genome sequence to
be obtained and helps gene isolationGenome sizes:
mega base pairs
E.coli 4.6
Yeast 12Caenorhabditis 97
Arabidopsis 120
Drosophila 132
Zebrafish 1600Mouse 2200
Human 3300
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Small bacteriovorous nematode Simple development programme: lineages ofcells Usually self-fertilising hermaphrodites Life cycle ~3 days
Easy to produce mutants Genome fully sequenced
Caenorhabditis elegans
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Fruit fly Studies on e.g. control of segmentation
in larvae
Male and female flies Life cycle ~2 weeks Easy to produce mutants Genome fully sequenced
Drosophila melanogaster
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