The document discusses gene targeting, a method to modify specific genes using a targeting vector and homologous recombination, enabling gene knockout or introduction for research and therapeutic purposes. It also details expressed sequence tags (ESTs), which are short sequences used in gene discovery and mapping, with implications for understanding gene expression and function. The significance of the work in gene targeting is highlighted by the 2007 Nobel Prize awarded to key researchers in this field.

1. GENE TARGETING AND
SEQUENCE TAGS
ALEN SHAJI
P1914015

2. GENE TARGETING
 To modifying the structure of a specific gene.
 Gene targeting vector introduced into the cell.
 Vector modifies the normal chromosomal gene through homologous
recombination.

3. HOMOLOGOUS RECOMBINATION
 Occurs within the chromosome.
 One piece of DNA to be exchanged for another piece.
 Cellular mechanism.
 DNA undergoing recombination be almost identical/homologous in sequence.
 Sequence on either side of the target should be identical, to promote more
efficient targeting and recombination.
 Modification of more or less any gene of interest, in more or less any way
desired.

4.  Mutating specific genes
 Knock out specific genes.
 Knock in specific genes – Introduction of novel pieces of DNA into a specific
chromosomal location – To examine the function of a gene in a variety of
ways.
 By changing single genes, it is possible to remove or alter large pieces of
chromosomes.
 Genes can be removed from a particular tissue.

7. THERAPEUTIC POTENTIAL OF GENE
TARGETING
 Useful in treating some human genetic disorders – Hemophilia, Duchenne
Muscular Dystrophy.
 Treating human diseases by genetic approaches – Gene Therapy.
 Gene Therapy – Replacing the defective gene by normal copy of the gene.

8. AWARDS
 Mario R. Capecchi, Martin. J. Evans and Oliver Smithies were awarded the
2007 Nobel Prize in Physiology and Medicine.
 Work – “Principles for introducing specific gene modifications in mice by the
use of embryonic stem cells”, or gene targeting.

9. SEQUENCE TAG
 Expressed sequence tag/EST is a short partial sequence, typically 200-400 bp
long, of a complimentary DNA/cDNA.
 EST is a short sub-sequence of a cDNA sequence.
 Used to identify gene transcripts, and are instrumental in gene discovery and
in gene-sequence determination.
 Approximately 74.2 million ESTs are available in public databases.
 EST results from one-short sequencing of a cloned cDNA.
 Low-quality fragments.
 Length is approximately 500 to 800 nucleotides.

10.  Complementary to mRNA.
 ESTs represents portions of expressed genes.
 Represented in databases as either cDNA/mRNA sequence or as the reverse
complement of the mRNA, the template strand.
 One can map ESTs to specific chromosome locations using physical mapping
techniques – Radiation hybrid mapping, Happy mapping, or FISH.
 Alternatively, if the genome of the organism that originated the EST has been
sequenced, one can align the EST sequence to that genome using a computer.

11.  The current understanding of the human set of genes includes the existence
of thousands of genes based solely on EST evidence.
 ESTs have become a tool to refine the predicted transcripts for those genes,
which leads to the prediction of their protein products and ultimately of their
function.
 The situation in which those ESTs are obtained gives information on the
conditions in which the corresponding gene is acting.
 ESTSs contain enough information to permit the design of precise probes for
DNA microarrays that then can be used to determine gene expression profiles.

12. REFERENCE
 Joyner, A., ed. Gene Targeting; A Practical Approach, 2nd ed. New York; Oxford
University; Press, 1999.
 Torres, R.M., and R. Kuhn. Laboratory Protocols for Conditional Gene
Targeting; New York; Oxford University; Press, 1997.
 Campagne f, Skrabanek L; Bioinformatics; 2006.
 Christoffels A, van Gelder A, Greyling G, Miller R, Hide W; “stack; Sequence
Tag Alignment and Consensus Knowledgebase”; 2001.

13. THANK YOU