Transgenic animals - A brief review

Transgenic Animals

By – Miss. Asmita Prabhudatta SagarB.Sc. Biotechnology III

CONTENTS Introduction

Methodology to produce transgenic animals :

1.Retrovial Vector Method.

2.DNA microinjection method .

3.Engineered Embryonic Stem Cell Method.

Examples

Applications

Disadvantages

Summary

References

Introduction In 1974 Rudolf Jaenisch created a transgenic mouse by introducing foreign DNA into its embryo, making it the world’s first transgenic animal.

What is a transgenic animal ? An animal whose genetic composition has been altered by the addition of foreign (exogenous) DNA is said to be transgenic . The DNA that is introduced is called a transgene and the overall process is called transgenic technology or transgenesis

He injected retrovirus DNA into early mouse embryos and showed that leukemia DNA sequences had integrated into the mouse genome and also to its offspring.

Strategy used for this :

A cloned gene is injected into the nucleus of a fertilized egg.

The inoculated fertilized eggs are implanted into a receptive female.

Some of the offspring derived from the implanted eggs carry the cloned gene in all their cells.

Animals with the cloned gene integrated in their germ line cells

are bred to establish new genetic lines.

Methodology

For transgenesis,DNA can be introduced into mice by

(1) retroviral vectors that infect the cells of an early stage embryo prior to implantation into a receptive female

(2) microinjection into the enlarged sperm nucleus (male pronucleus) of a fertilized egg, or

(3) introduction of genetically engineered embryonic stem cells into an early-stage developing embryo before implantation into a receptive female.

The Retroviral Vector Method:

i. Vectors derived from these viruses can transfer only small pieces (~8 kilobases [kb]).

ii. The genome of the retroviral strain can be integrated into the same nucleus as the transgene.

•Drawbacks:

•Advantage:

i. An effective means of integrating the transgene into the genome of a recipient cell.

DNA microinjection method:

•Advantages:

i. Most common technique for transferring the transgene.

ii. Most reliable technique for transgenesis.

iii. Process is inexpensive.

•Drawbacks: i. Requires the coordination of a number of experimental steps and

highly trained practitioner.

ii. Often multiple copies of the injected DNA are incorporated at one site which disrupts the normal physiology of the animal.

Iii. Only 5% of the inoculated eggs to develop into live transgenic animals.

The Engineered Embryonic Stem Cell Method

•Advantages:

•Drawbacks:

i. Reduction in the cost of producing a transgenic animal.

ii. Randomness of integration is avoided.

iii. ES cells enable the researcher to place new genes in advantageous places in the genome or to remove deleterious genes.

i. Requires longer time .ii.

Requires germline-competent ES cell lines.

iii. Difficulties associated with the production, characterization and maintenance of pluripotent ES cell lines.

ExamplesGlo fish : GloFish is a type of transgenic zebrafish (Danio rerio) that have been obtained via insertion of a green fluorescent protein (GFP) gene.

Super fishGrowth hormone gene inserted into fertilized egg. The transgenic salmon were larger and grew faster than the nontransgenic controls.

Alzheimer’s mouse

“ ANDI” was the first transgenic monkey, born in 2000.ANDI proves that transgenic primates can be created and can express a foreign gene delivered into their genome.

ANDI Monkey

In the brain of Alzheimer’s patients, dead nerve cells are entangled in a protein called amyloid.Mouse made by introducing amyloid precursor gene into fertilized egg of mice.

Applications Industrial importance – Toxicity sensitive transgenic animals to test chemicals. Spider silk in milk of goat.

Medical importance – Disease model. Xenotransplantation.

Agriculture importance – Disease resistant animals. For improving quality & quantity of milk, meat, eggs & wool production.

Disadvantages× Ethical issues.

× They has the potential to harm certain native species of animals or plants.

× It can also potentially affect the environment, thus altering the living conditions of many species.

× Introduction of transgenic may also affect the direction of evolution and eventually decrease the gene pool.

× Transgenic animals are costly to produce and they have high value.

× The production of transgenic animal may lead to food-safety problems like allergies or toxicities.

An animal whose genetic composition has been altered by the addition of foreign (exogenous) DNA is said to be transgenic .

There are 3 main methods of transgenesis : 1.Retrovial Vector Method. 2.DNA microinjection method . 3.Engineered Embryonic Stem Cell Method

Many transgenic animals have been successfully created for a variety of purposes, and the prospects are enormous.

It holds great potential in many fields including agriculture, medicine and industry.

There are certain disadvantages regarding this technique.

Summary

References I. Molecular biotechnology : principles and applications of

recombinant DNA / Bernard R. Glick, Jack J. Pasternak, and Cheryl L. Patten. — 4th ed.

II. Satyanarayana U, Biotechnology (2010), 1st edition, Books and allied (P) Ltd, Kolkata

III. https://en.wikipedia.org/wiki/Genetically_modified_organism#Transgenic_animals

IV. http://dsc.discovery.com/technology/tech-10/genetic-engineering/10-transgenic-animals-03.html

V. www.biomedcentral.com/1471-2407/12/209

Thank You ..