Retrotransposons | Retroviral retro transposon | Non LTR retrotransposon | LINEs and SINEs | molbio

Summary

This video delves into the world of retrotransposons, transposable elements that move within eukaryotic genomes via an RNA intermediate. It explains the abundance of these elements, particularly in maize and humans, and distinguishes between LTR and non-LTR retrotransposons, including LINE and SINE. The video outlines their structural differences, the process of integration into the genome, and their potential mutagenic effects, epigenetic influences, and roles in gene regulation, offering a comprehensive look at these genetic 'jumping genes'.

Takeaways

• 🧬 Retrotransposons are transposable elements that move within a genome with the aid of an RNA intermediate.
• 📈 They are abundant in eukaryotic genomes, making up 49% of Maize's genome and approximately 42% of the human genome.
• 🔍 Retrotransposons are divided into two main groups: LTR (Long Terminal Repeat) and non-LTR retrotransposons.
• 🦠 LTR retrotransposons are virus-like and have a promoter sequence and coding region for enzymes necessary for transposition.
• 📝 The process of LTR retrotransposon integration involves transcription, reverse transcription to form cDNA, and integration into the target DNA.
• 🌟 Non-LTR retrotransposons include LINEs (Long Interspersed Nuclear Elements) and SINEs (Short Interspersed Nuclear Elements), which lack LTRs but have poly(A) tails and UTRs.
• 🔬 LINEs are autonomous and encode proteins with endonuclease and reverse transcriptase activity, crucial for their own and SINEs' integration.
• 🔄 The integration of LINEs involves mRNA transcription, binding to target DNA, cleavage, and reverse transcription to form cDNA, which is then incorporated into the genome.
• 🔑 LINEs selectively transpose their own mRNAs by having a higher affinity for their specific mRNA sequence compared to other mRNAs.
• 🛠️ Retrotransposons can have various effects on the genome, including mutagenesis, epigenetic silencing, serving as a source of long non-coding RNA, and acting as enhancers.
• 📚 Additional resources for learning about retrotransposons can be found on the speaker's Facebook Channel and Instagram.

Q & A

What are retrotransposons and how do they function?

Retrotransposons are transposable elements that can move from one location to another within a genome with the help of an RNA intermediate. They reverse transcribe this RNA intermediate to form a cDNA, which then integrates into a new location.

Why are retrotransposons abundant in eukaryotic genomes?

Retrotransposons are abundant in eukaryotic genomes because they can amplify themselves very quickly, making up a significant portion of the genome in organisms like maize and humans.

What percentage of the maize and human genome is made up of retrotransposons?

In maize, retrotransposons comprise about 49% of the genome, while in humans, they account for approximately 42%.

How are retrotransposons classified into groups?

Retrotransposons are broadly classified into two groups: LTR retrotransposons and non-LTR retrotransposons. LTR retrotransposons are virus-like and have long terminal repeats, while non-LTR retrotransposons lack these features and have a poly-A tail.

What is the role of the LTR in LTR retrotransposons?

The LTR, or long terminal repeat, serves as a site for the promoter sequence in LTR retrotransposons, initiating transcription and housing a coding region that gives rise to integrase and other enzymes necessary for transposition.

How does the integration of LTR retrotransposons into the genome occur?

LTR retrotransposons first generate mRNA, which is then reverse transcribed into cDNA with the help of reverse transcriptase. The cDNA integrates into the target DNA with the help of integrase enzymes, and any open gaps are filled by cellular repair machinery.

What are LINEs and SINEs in the context of non-LTR retrotransposons?

LINEs (Long Interspersed Nuclear Elements) and SINEs (Short Interspersed Nuclear Elements) are types of non-LTR retrotransposons. LINEs are autonomous and can move independently, while SINEs are dependent on LINEs for transposition.

How do LINEs and SINEs differ in size and structure?

LINEs are larger and can vary in size, with mouse LINEs being around 6000 base pairs, whereas human SINEs are smaller, around 300 base pairs. Both have a poly-A tail and 5' and 3' UTRs, but LINEs have an ORF that encodes proteins for transposition.

What is the process of LINE integration into the genome?

LINE mRNA is transcribed and binds to the target DNA, forming an RNA-DNA hybrid. The ORF2 products bind to this mRNA and guide it to the target DNA. A reverse transcription reaction takes place, synthesizing cDNA strands, which are then incorporated into the genome by DNA joining and repair mechanisms.

How do LINEs selectively transpose their own mRNA and not other mRNAs from the genome?

The ORF2 products have a higher affinity for LINE mRNA in a sequence-dependent manner compared to other mRNAs, ensuring that LINE mRNA is preferentially integrated into new regions of the genome.

What are some of the potential effects of retrotransposons on the genome?

Retrotransposons can have mutagenic effects by disrupting coding frames if they insert into exons. They can also lead to epigenetic silencing, serve as a source of long non-coding RNA, and act as enhancers to regulate transcription.