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Development

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Big Questions:1. How does a multicellular organism

develop from a zygote?

2. How is the position of the parts of an organism determined?

3. How does differentiation of cell type occur in organisms?

4. How are genetics and development connected? Genetics and the environment?

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Development is Regulated The development of

an organism is coordinated by sequential changes in gene expression.

Multicellular organisms must regulate: Cell division Differentiation Morphogenesis

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Early Developmental Pathways

Cytoplasmic Determinants unequal distribution of

mRNA and proteins from mother

Embryonic Induction: Local signaling by

nearby cells send cells down a specific developmental path.

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Pattern Formation Cells need to establish their position in

the developing organism. (head/tail, right /left etc.)

Cytoplasmic determinants and induction lead to gradient morphogens.

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Cellular Differentiation Germ lines established Cell type already

determined Differentiation

accomplished by the expression of cell type-specific proteins.

There is normally no turning back.

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Differentiation Control Genes must be both

turned on and turned off at appropriate times and locations.

Regulated by internal and external cues

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Internal Cues DNA packing, micro RNA’s and

epigenetics can switch genes ON or OFF. Transcription factors must be present and

can be either stimulatory or inhibitory.

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Internal Cues A simple example of transcription factors

and gene regulation: the lac operon http

://www.sumanasinc.com/webcontent/animations/content/lacoperon.html

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External Cues (outside the cell) External cues signal to cells, causing

cells to alter their gene expression.

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Environmental Cues The presence of particular molecules

and conditions in the local environment is required for development to proceed properly. Ex. The role of temperature and

moisture in seed development.

Why do you water a seed after you plant it? Hmm…

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Environmental Cues Changing the environment around the

cells can alter gene expression.

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Apoptosis “Programmed cell death”:

Important role in defining borders and openings in the developing organism.

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Apoptosis This has been studied thoroughly in

C. elegans development – Robert Horvitz and his team won a Nobel Prize for this research! http://web.mit.edu/horvitz/www/researchlinks/programmed.html

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Apoptosis Of the 947 cells generated during C. elegans

development, 131 undergo apoptosis

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Apoptosis The genes involved in the process of cell death

(ced-3/ced-4) are closely related to the same genes in humans (Apaf-1)

Genes that PREVENT cell death (ced-9) are closely related to the same in humans (bcl-2)

This research has had many implications for cancer research!

(Thanks, little worm!)

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Homeobox (HOX) Genes A family of

related genes that serve as master regulators of animal development in all animals on the planet.

http://study.com/academy/lesson/role-of-homeotic-genes-in-drosophila-development.html

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Experimental Evidence Mutations in normal developmental pathways lead to

malformations in embryonic development

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Experimental Evidence Transplantation Experiments: Moving

regions of a developing embryo affects normal pattern formation.

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Transplantation Experiments: Moving regions of a developing embryo affects normal pattern formation.

Experimental Evidence