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Vector design

This article explains the use of recombinant DNA methods to replace a desired structural gene, such as the insulin gene, with a positive selection marker for knockout function. The vector DNA enables the insertion of molecules into host DNA, with an example of a typical knockout (KO) vector known as tk, which contains thymidine kinase. The process involves transforming embryonic stem cells, selecting for transformed cells using the positive selection marker, and injecting successfully transformed cells into blastocysts for implantation. The outcome can result in chimeric mice with varying levels of ES cell contribution.

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Vector design

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  1. Vector design • Recombinant DNA methods: Simple KO • Structural gene desired (e.g. insulin gene) to be "knocked out" is replaced partly or completely by a positive selection marker. (knock out function!) • Vector DNA to enable the molecules to be inserted into host DNA molecules

  2. Typical KO vector *tk:thymidine kinase

  3. Embryonic stem cells • Harvested from the inner cell mass of mouse blastocysts • Grown in culture and retain their full potential to produce all the cells of the mature animal, including its gametes

  4. ES cells growing in culture

  5. ES cells are transformed • Cultured ES cells are exposed to the vector • Electroporation punched holes in the walls of the ES cells • Vector in solution flows into the ES cells • The cells that don't die are selected for transformation using the positive selection marker • Randomly inserted vectors will be killed by gancyclovir

  6. Successfully transformed ES cells are injected into blastocysts

  7. Implantation of blastocysts • The blastocysts are left to rest for a couple of hours • Expanded blastocysts are transferred to the uterine horn of a 2.5 dpc pseudopregnant female • Max. 1/3 of transferred blasts will develop into healthy pups

  8. Implanting blastocysts 1 2

  9. Implanting blastocysts (cont.) 3 4

  10. Littermates Black mouse - no apparent ES cell contribution Chimeric founder - strong ES cell contribution Chimeric founder - weaker ES cell contribution

  11. Chimeric mouse

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