P-Elements Explained
Summary
TLDRThis 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
🐛 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.
🧬 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.
Mindmap
Keywords
💡P elements
💡Transposition
💡Terminal inverted repeats
💡Transposase
💡Excision
💡Drift
💡Integration
💡Autonomous elements
💡Non-autonomous elements
💡Hybrid dysgenesis
💡Enhancer trapping
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
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