P-Elements Explained

Summary

This video delves into P elements, mobile genetic elements in Drosophila's genome that transpose via a cut-and-paste mechanism. It explains the process of P element movement involving excision, drift, and integration, facilitated by the transposase enzyme. Autonomous P elements can encode transposase, while non-autonomous ones require it from elsewhere. Hybrid dysgenesis in Drosophila strains highlights the conditions under which P elements can transpose, primarily in germline cells. The video also touches on P elements' utility in enhancer trapping for gene activity studies.

Takeaways

• 🐛 P elements are transposable elements found in the genome of Drosophila, commonly known as the fruit fly.
• 🔄 They move using a cut-and-paste mechanism, involving DNA intermediates without RNA involvement.
• 🔬 P elements have 31 base pair terminal inverted repeats and a single open reading frame across four exons.
• ✂️ The transposition process includes excision, drift, and integration steps facilitated by the transposase enzyme.
• 🧬 Autonomous P elements have intact terminal inverted repeats and can encode transposase, enabling self-transposition.
• 🚫 Non-autonomous P elements lack functional transposase and require it from other elements to transpose.
• 🔄 Transposition in Drosophila occurs only in germline cells, not in somatic cells due to the absence of necessary splicing.
• 🌟 Hybrid dysgenesis is the phenomenon where P elements can move in the germline cells of offspring from a cross between P and M strains.
• 🚸 P element movement is restricted in offspring that inherit the P chromosome from the mother, due to the presence of repressor molecules.
• 🔬 P elements are used in scientific research, such as enhancer trapping, to study gene activity and regulation.

Q & A

What is a P element?

A P element is a class of transposable DNA-based mobile genetic elements found in the genome of Drosophila, commonly known as the fruit fly. It moves with a cut-and-paste mechanism using only DNA intermediates.

How does a P element differ from other transposons?

A P element is characterized by having 31 base pair terminal inverted repeats at both ends and a single open reading frame across four exons that encode the enzyme transposase.

What are the steps involved in the movement of a P element?

The movement of a P element involves discrete steps called excision, drift, and integration. This includes transcription into RNA, splicing of exons, translation into the transposase polypeptide, and the subsequent binding and excision of the transposon from the DNA.

What is the role of transposase in the movement of P elements?

Transposase recognizes and binds to the terminal inverted repeats of the P element, facilitating the excision of the entire transposon from the DNA and its subsequent movement to a recipient site.

Why are the integrated P elements always flanked by eight base pair direct repeats?

The integrated P elements are flanked by eight base pair direct repeats because of the way transposase cuts the recipient site, resulting in sticky ends on either end of the transposon insertion.

What is the difference between autonomous and non-autonomous P elements?

Autonomous P elements have intact terminal inverted repeats and a full coding gene for transposase, allowing them to encode transposase and move independently. Non-autonomous P elements have deletions or mutations preventing the expression of functional transposase protein and require transposase from other autonomous P elements to transpose.

In which Drosophila strains can P elements be found?

P elements can be found in the P strain of Drosophila, while the M strain does not contain P elements.

Why can't P elements transpose in somatic cells of Drosophila?

P elements cannot transpose in somatic cells because the necessary splicing event to create active transposase does not occur in these cells.

What is hybrid dysgenesis and when does it occur?

Hybrid dysgenesis is the movement of P elements in germline cells, which can only occur when offspring receive the P strain chromosome from their father and the M strain chromosome from their mother.

How do P elements contribute to mutagenesis?

P elements can become mutagenic if they land in a gene during their movement within the genome, potentially disrupting the gene's function.

What is enhancer trapping and how can P elements be used for this purpose?

Enhancer trapping is a technique where a modified P element inserts near an enhancer in a fly's genome. This can be used to identify and study the activity of the enhancer and the genes associated with it.

Outlines

00:00

🐛 Understanding P Elements in Drosophila

This paragraph introduces P elements, a class of transposable genetic elements found in the genome of Drosophila, commonly known as the fruit fly. P elements are DNA-based mobile genetic elements that move within the genome using a cut-and-paste mechanism. They are characterized by 31 base pair terminal inverted repeats and a single open reading frame across four exons that encode the enzyme transposase. The movement of P elements is described through the steps of excision, drift, and integration. Transposase recognizes and binds to the terminal inverted repeats, facilitating the excision and subsequent relocation of the P element to a new genomic location. Autonomous P elements have intact coding genes for transposase, enabling them to encode and excise the transposon, while non-autonomous P elements require transposase from other elements. The paragraph also discusses the role of P elements in hybrid dysgenesis, a process that occurs in the germline cells of flies but not in somatic cells due to the lack of necessary splicing events. The M and P strains of Drosophila are mentioned, with the P strain containing P elements and the M strain lacking them. The movement of P elements is restricted to germline cells, and the paragraph concludes with a discussion of potential mutagenic effects if a P element lands within a gene.

05:02

🧬 P Element Repression and Scientific Applications

The second paragraph delves into the repression of P elements in Drosophila, particularly in the eggs of P strain females, where a high concentration of P element repressor molecules prevents the transcription of transposase, thus inhibiting the movement of P elements. This means that hybrid dysgenesis, the movement of P elements in the germline, only occurs when the P chromosome is inherited from the father and the M strain chromosome from the mother. The paragraph then explores the scientific utility of P elements, specifically in a technique called enhancer trapping. A modified P element can be used to identify and study the activity of enhancers in the genome, which can provide insights into the activity of associated genes. The video concludes by suggesting further resources for viewers interested in learning more about transposons and enhancer trapping.

Keywords

💡P elements

P elements, also known as P transposons, are DNA-based mobile genetic elements found in the genome of Drosophila melanogaster, commonly known as the fruit fly. They are capable of moving or 'jumping' from one location in the DNA to another through a cut-and-paste mechanism. In the video, P elements are central to understanding the concept of genetic transposition, and their ability to move within the genome can lead to genetic mutations, making them a significant topic in genetic research.

💡Transposition

Transposition refers to the movement of genetic elements, such as P elements, within the genome. This process is crucial for genetic diversity and can lead to mutations. In the video, the concept of transposition is explained through the life cycle of P elements, detailing the steps of excision, drift, and integration that allow these elements to move from one genomic location to another.

💡Terminal inverted repeats

Terminal inverted repeats are sequences found at both ends of a transposon, including P elements. They are essential for the transposition process as they provide recognition sites for the transposase enzyme. The video explains that P elements have 31 base pair terminal inverted repeats, which are critical for the enzyme to bind and facilitate the excision and reinsertion of the transposon.

💡Transposase

Transposase is an enzyme encoded by the transposon itself and is responsible for the movement of the transposon within the genome. In the context of P elements, the transposase recognizes and binds to the terminal inverted repeats, facilitating the excision and integration of the P element. The video describes how the transposase is crucial for the autonomous movement of P elements.

💡Excision

Excision is the first step in the transposition process where the transposon is removed from its original location in the DNA. The video explains that the transposase enzyme facilitates this step by recognizing the terminal inverted repeats and cutting the DNA at these sites, allowing the P element to be removed.

💡Drift

Drift, in the context of P elements, refers to the movement of the transposon to a new location in the genome after excision. The video describes this as a 'drift step' where the transposon, along with the transposase, moves to a recipient site within the DNA.

💡Integration

Integration is the final step in the transposition process where the excised transposon is inserted into a new location in the DNA. The video explains that the transposase enzyme cuts the DNA at the recipient site and facilitates the insertion of the P element, resulting in the transposon becoming part of the genome at the new site.

💡Autonomous elements

Autonomous elements are P elements that have intact terminal inverted repeats and a full coding gene for transposase, allowing them to encode and excise the transposase enzyme and move independently within the genome. The video highlights that these elements can self-encode the necessary enzyme for transposition, making them capable of autonomous movement.

💡Non-autonomous elements

Non-autonomous elements are P elements that have deletions or mutations in their coding sequence, preventing them from encoding a functional transposase enzyme. As a result, they rely on transposase provided by other autonomous P elements to facilitate their movement. The video explains that these elements are dependent on 'in trans' complementation for their transposition.

💡Hybrid dysgenesis

Hybrid dysgenesis is a phenomenon where the offspring of crosses between certain strains of Drosophila, such as those containing P elements and those that do not, exhibit high levels of genetic instability due to the movement of P elements. The video describes how this process can lead to mutations and is significant for understanding the dynamics of P element movement in different genetic backgrounds.

💡Enhancer trapping

Enhancer trapping is a genetic technique mentioned in the video where a modified P element is used to identify and study the activity of enhancers in the genome. The P element's ability to insert near enhancers allows researchers to study gene regulation and expression, highlighting the utility of P elements in genetic research beyond just understanding their movement.

Highlights

P elements are a class of transposable elements found in the genome of Drosophila, the fruit fly.

They move using a cut-and-paste mechanism with only DNA intermediates.

P elements have 31 base pair terminal inverted repeats and a single open reading frame.

The enzyme transposase, encoded by P elements, facilitates their movement in the genome.

The process of P element movement involves excision, drift, and integration.

Transposase recognizes and binds to terminal inverted repeats for excision.

The transposon moves with transposase to a recipient site where it integrates.

Integration of P elements results in flanking direct repeats due to the way transposase cuts DNA.

Autonomous P elements have intact terminal inverted repeats and can encode transposase.

Non-autonomous P elements lack functional transposase and require it from other elements.

P elements with degraded terminal repeats are locked in their genomic position.

In Drosophila, there are M strain (without P elements) and P strain (with P elements).

P elements cannot transpose in somatic cells of M strain flies.

Transposition can occur in germline cells where splicing events necessary for transposase production happen.

Hybrid dysgenesis occurs when P strain chromosomes are inherited from the father and M strain from the mother.

P element repressor molecules in P strain females prevent transposition in their offspring.

P elements are used in enhancer trapping to identify and study gene activity.

Transcripts

in this video I will introduce the

concept of P elements a P element is a

class to transpose ax belen tin the

genome of Drosophila which is commonly

called the fruit fly a class to

transpose xi is a DNA based mobile

genetic elements that moves with a

cut-and-paste mechanism using only DNA

intermediates this piece of DNA has the

capability of jumping from one location

in the DNA to another a p element looks

like a typical class to transposon it

has 31 base pair terminal inverted

repeats at both ends and a single open

reading frame across four exons that

encodes the enzyme transposes so how

does this p element jump from one part

of the DNA to another this process

involves discrete steps called excision

drift and integration the gene is

transcribed into RNA and then a

spliceosome removes the introns and

splices the exons together this mRNA is

then translated into the polypeptide

that folds into transposes the

transposes will recognize and bind to

the terminal inverted repeats of the

transposon and multi mirai's it

facilitates the excision of the entire

transposon from the DNA the transposon

will then move with the transposes which

is the drift step to the recipient site

where the transposes will cut the DNA

and facilitate the insertion of the

transposon into the recipient site as

you can see because of the way

transposes cuts the recipient site the

integrated transposon will always be

flanked by eight base pair direct

repeats originating from the genomic

sequence of the insertion site this is

the result of the way the transposes

cuts the recipient site resulting in

sticky ends on either end of the

transposon insertion p elements when

fully functional are autonomous that

means they have intact

terminal inverted repeats that carry a

full coding gene for transposes these

autonomous elements can encode transpose

ace and that transpose ace can recognize

the terminal inverted repeats excise the

transposon and reinsert it elsewhere in

the DNA in the wild all kinds of

variants of p elements can be found some

contain deletions in the exons and

coding transposes preventing the

expression of functional transposes

protein these p elements are called non

autonomous as they require transposes

produced from other autonomous P

elements elsewhere in the genome to be

able to transpose transpose a is

produced from another element is said to

be provided for the non autonomous P

element in trans other variants include

P elements with degraded inverted

terminal repeats these P elements have

become locked in their current genomic

position as they cannot be excised by

transposes when dealing with P elements

there are two strains of Drosophila the

M strain which does not contain P

elements and the P strain which does

contain P elements P elements and P

strain flies are not just hopping around

at any point in the fly's life in peace

train flies the P element cannot

transpose in somatic cells these are the

cells making up the fly's body except

the germline cells transposition can't

happen in the somatic cells because the

splicing event necessary to create

active transposes does not occur in

somatic cells transposition of the P

element can only occur in germline cells

of flies where the splicing event can

take place this movement of P elements

in germline cells is called hybrid disc

Genesis let's take a look at possible

fertilization events between parent

generations to see when P elements have

the ability to move around the genome

and journey line cells of resulting

offspring we remember that M strain

flies do not carry P elements so in a

cross between two M strain flies we see

that

offspring carry P elements and therefore

know P element movement can occur in a

cross between a male P strain fly in a

female M strain fly the male slide

donates DNA carrying P elements in his

sperm while the female fly donates DNA

without P elements in her egg in this

situation hybrid dis Genesis does occur

in the germline of the resulting

offspring and the P element can jump to

different locations in the genome

potentially becoming mutagenic if it

lands in a gene given a piece trained

female mated with an M strain male you

would expect the resulting offspring to

have hybrid disc Genesis occurring in

their germline cells but it turns out

that in peace trained females eggs

there's a high concentration of P

element repressor molecules which

prevent the transcription of transposes

without transposes the P element cannot

be excised from the DNA and therefore it

must stay put hybrid disc Genesis does

not occur any time the mother donates a

p chromosome to her offspring so now you

can see that hybrid disc Genesis can

only occur in offspring that received

the P string chromosome from their

father and the M strain chromosome from

their mother this is the only case in

which the p element transposes is active

and able to mobilise the element in the

germline cells you may be wondering what

use p elements can be for a scientist in

a lab one use of p elements would be in

enhancer trapping a modified p element

that inserts near an enhancer in a fly's

genome can then be used to identify and

study the activity of that enhancer and

therefore the activity of the genes

generally associated with that enhancer

so those are the basics of p elements if

you want to review the basics of

transposons you can check out my video

on transposons you may also be

interested in my video on enhancer

trapping