Transposable Elements and types of TEs

1. Department of Zoology
Dr. Hari Singh Gour Vishwavidyalaya, Sagar
(A central university)
Presented By
Lekhan Lodhi
PhD
Department of Zoology
Transposable Elements

2. Contents
• Introduction
• TEs & their role
• Definition
• Classification
• Examples of TEs
• Regulation of Transposable Elements
• Role in Disease
• Applications
• Conclusion
• References
PPt made by Lekhan

3. Introduction
• Transposable elements (TEs), often referred to as
"jumping genes," are genetic sequences found
within the DNA of living organisms that have the
remarkable ability to move or transpose themselves
to different locations within the genome.
• These elements are crucial in shaping the structure
and evolution of genomes and can have both
positive and negative effects on an organism's
biology.
• They play a significant role in genetic diversity,
evolution, and genome stability, making them a
fundamental subject of study in genetics and
molecular biology.
Barbara McClintock discovered the first TEs
in maize (Zea mays) at the Cold Spring
Harbor Laboratory in New York.
McClintock was experimenting with maize
plants that had broken chromosomes.
PPt made by Lekhan

4. TE & their role
• Genetic Diversity: Their ability to move and
insert into new genomic locations generates
novel genetic variations, which can serve as the
raw material for natural selection.
• Evolution: TEs are considered one of the driving
forces of genome evolution. They can reshape
genomes by creating mutations, promoting
genetic recombination, and influencing gene
expression patterns.
• Gene Regulation: TEs can serve as regulatory
elements.
• Genome Stability: While TEs contribute to
genetic diversity, their uncontrolled and
excessive activity can also pose a threat to
genome stability.
PPt made by Lekhan

5. Definition
Transposable elements (TEs), also known as transposons or jumping
genes, are segments of DNA found within the genomes of organisms
that have the ability to move or transpose themselves to different
locations within the genome. They are essential genetic components that
can have significant effects on an organism's genetics, evolution, and
genome structure.
PPt made by Lekhan

6. • Campbell et al in 1977 described the nomenclature in prokaryotes
• Initially named as insertion sequence- IS, IS1, IS2, IS3 etc
• In bacteria transposons containing genes for antibiotic resistance are
named as Tn like Tn1, Tn2, etc.
Nomenclature
PPt made by Lekhan

7. Classification
PPt made by Lekhan

8. Class I Transposable Elements (Retrotransposons):
• Retrotransposons transpose
via a "copy and paste"
mechanism.
• The key steps in their
transposition process
include:
• a. Transcription:
Retrotransposons are first
transcribed into RNA by the
host cell's machinery.
• b. Reverse Transcription: The
RNA is then reverse-
transcribed into
complementary DNA (cDNA)
by a reverse transcriptase
enzyme.
Figure: Class I Transposable Elements
c. Integration: The cDNA is inserted into a new location in the genome by
an integrase enzyme.
Retrotransposons can create multiple copies of themselves in the genome,
contributing to their abundance.
PPt made by Lekhan

9. Retrotransposons are further classified into two major groups:
a. Long Terminal Repeat (LTR)
Retrotransposons: These retrotransposons
have long terminal repeats at their ends,
similar to retroviruses. Examples include
endogenous retroviruses (ERVs).
b. Non-LTR Retrotransposons: These
retrotransposons lack long terminal repeats.
Examples include LINEs (Long INterspersed
Elements) and SINEs (Short INterspersed
Elements), such as Alu elements in humans
PPt made by Lekhan
Examples of Retrotransposons
• Alu elements
• LINE-1 (L1) elements
• LTR retrotransposons

10. • DNA transposons transpose via a "cut
and paste" mechanism.
• The key steps in their transposition
process include:
• a. Activation: The transposon is
activated, leading to the synthesis of a
transposase enzyme.
• b. Excision: The transposase enzyme
physically cuts the transposon out of its
current genomic location.
• c. Transposition: The excised transposon
is inserted into a new location in the
genome.
Class II Transposable Elements (DNA Transposons):
• DNA transposons typically leave short target site duplications (TSDs)
at their insertion sites, which are direct repeats of a few base pairs.
• DNA transposons are often found as discrete, distinct elements in the
genome.
PPt made by Lekhan

11. Examples of DNA Transposons
• Tn elements
• P elements
• Ac-Ds elements
PPt made by Lekhan

12. Regulation of Transposable Elements
• Organisms have evolved various mechanisms to regulate transposable elements (TEs) and
prevent excessive transposition, which could lead to genomic instability and genetic diseases.
These regulatory mechanisms involve epigenetic modifications and RNA-based processes. Here
are some key regulatory mechanisms:
DNA Methylation:
• DNA methylation involves the addition of a methyl group (CH3) to cytosine bases in DNA.
Methylation of TEs can lead to transcriptional repression, silencing their activity.
• Organisms use DNA methylation to distinguish between TEs and host genes. While host genes
are often protected from methylation, TEs are more susceptible to this modification.
• Example: In mammals, DNA methylation plays a crucial role in silencing retrotransposons like
LINE-1 and preventing their transposition.
Histone Modifications:
• Histone modifications, such as methylation and acetylation, can also regulate TEs. These
modifications can alter chromatin structure, making TEs less accessible for transcription.
• Histone methyltransferases can deposit methyl groups on histones associated with TEs, leading
to a more compact, repressive chromatin state.
• Example: In Arabidopsis thaliana, histone methylation helps regulate the activity of
transposons, ensuring proper genome stability.
PPt made by Lekhan

13. Role in Disease
• Insertional Mutagenesis:
• TEs can insert themselves into or near genes, disrupting coding sequences or regulatory regions. This
can result in gene inactivation, altered gene expression, or the creation of fusion genes.
• Example: Hemophilia A, a bleeding disorder, can result from an Alu element insertion in the factor VIII
gene, leading to reduced or absent factor VIII activity.
• Chromosomal Rearrangements:
• TEs can cause chromosomal rearrangements, such as deletions, duplications, inversions, and
translocations, when they mediate recombination between non-homologous sequences.
• Example: Williams-Beuren syndrome is characterized by a deletion of about 26 genes on chromosome
7 due to recombination between LTR retrotransposons.
• Autoimmune Diseases:
• TE-derived sequences can serve as autoantigens in autoimmune diseases, leading to immune system
attacks on the host's own tissues.
• Example: Systemic lupus erythematosus (SLE) may involve the presence of autoantibodies targeting
retrotransposon-derived RNAs and proteins.
PPt made by Lekhan

14. Applications
• Gene Knockout:
• TEs can be harnessed to disrupt specific genes in a process known as gene knockout. Researchers use TEs as molecular
tools to study gene function by observing the effects of gene inactivation.
• Gene Delivery:
• TEs can be used as vectors for delivering genes or genetic constructs into the genomes of target cells or organisms. This is
known as transgenesis.
• Transgenesis:
• TEs can be employed to create transgenic organisms, which are organisms that have been genetically modified to
carry and express foreign genes.
• For example, the piggyBac transposon system has been used to generate transgenic animals and modify their
genomes for various purposes.
• Gene Therapy:
• TEs have potential applications in gene therapy, a field focused on treating genetic diseases by introducing
functional genes into patients' cells.
PPt made by Lekhan

15. • In conclusion, the study of transposable elements (TEs) has
significantly advanced our understanding of genome dynamics,
evolution, and genetic diversity across various organisms. TEs,
encompassing retrotransposons and DNA transposons, play a complex
role in shaping genomes. While they can be agents of genetic
instability by causing mutations and genomic rearrangements, they are
also pivotal drivers of genetic diversity and adaptation.
Conclusion
PPt made by Lekhan

16. References
• Russell, P. J., & Gordey, K. (2002). IGenetics (No. QH430 R87). San
Francisco: Benjamin Cummings.
• Verma PS and Agarwal VK (2005). Cell Biology, Genetics, Molecular
Biology, Evolution, and Ecology. Multicolored Edition.
• McGee, David & Coker, Christopher & Harro, Janette & Mobley,
Harry. (2001). Bacterial Genetic Exchange. Doi:
10.1038/npg.els.0001416.
• Bailey, J. A., et al. Molecular evidence for a relationship between
LINE-1 elements and X chromosome inactivation: The Lyon repeat
hypothesis. Proceedings of the National Academy of Sciences 97,
6634–6639 (2000)
PPt made by Lekhan

17. Thank
You
PPt made by Lekhan