1. The document discusses the initiation and effectors phases of the somatic piRNA pathway in Drosophila. It describes the roles of key proteins involved like Squash, Zucchini, and Armitage. 2. Experiments showed that Squash impacts the effectors phase but not piRNA levels, while loss of Zucchini reduces both piRNAs and Piwi protein. Armitage was found to be involved in both somatic and germline compartments. 3. The results provide insight into the roles of these proteins and the mechanisms of piRNA biogenesis and transposon silencing in the initiation and effectors phases of the somatic piRNA pathway.

1. Write a half a page discussion and criticism to the following
essay:
1
Probing the initiation and
effectors’
phases of the somatic piRNA pathway in
Drosophila
Introduction
To understand the combining RNAi in cultured cells and
analysis, it is important to know the roles of known Piwi-
interacting RNA(piRNA) pathway elements particularly in the
initiation and the
effecter
phases of transposon silencing. Squash is one component that is
physically with Piwi
(
Brennecke
et al.,
2007)
.
The main components involved in the process are Squash,
Zucchini or Armitage. These elements pose different effects on
the transposon, and piRNAs. When squash expression is
reduced, its effect is directly seen on the transposon. This is
because when its expression is reduced, it leads to modest

2. transposon depression but no results are seen on the piRNAs,
consistent with an
effecter
role (
Browe
r, 2007)
Zucchini, on the other hand, can reduce both piRNAs and Piwi
protein when altered or is tampered with. Alteration in Zucchini
leads to the formation of a stable Piwi RISC known as RNA-
induced silencing complex (
Brennecke
, 2008)
Continuance mutation or loss of Zucchini within its catalyst
domain led to amassing of vulnerable herald transcripts from
flamenco, steady with a role for this alleged nuclease in piRNA
biogenesis.
There are a number of mechanisms that help regulate gene
expression. The regulation is done Eukaryotic which are small
RNAs, these RNAs perform the regulatory role at both the
transcriptional and post-transcriptional levels. These small
RNAs are divided into classes in accordance to their particular
Argonaute protein partner and according to their mechanism of
biogenesis. Piwi-interacting RNAs play a role of binding Piwi –
clade Argonaute proteins and
they do this in the gonadal tissues. Here, the piRNAs silence
mobile genetic elements thereby guarding the integrity of the
genome.
The piRNA pathway is divided into a number of phases namely:
initiation phase, effectors phase and adaptation phase. There are
different things happening in the three phases and this is why
the activities were divided into the phases.
Initiati
on
Phase
There are a number of things that happen in the initiation phase:
•

3. Production of small RNAs called piRNAs. The piRNAs are
produced from their generative loci known as piRNA clusters.
•
The piRNA give rise to long, presumably single-stranded
precursor transcripts which are produced as a result of unknown
biogenesis mechanism into small RNAs that are larger than
canonical microRNAs.
•
The piRNAs are stabilized when they are associated with Piwi
proteins from Piwi RISCs.
•
The Piwi RISCs have additional proteins that help in the
facilitation of target recognition and silencing
(
Lau
et al., 2009).
Effectors
Phase
There are many things that happen in the effectors phase:
•
Identification of target which is made by the Piwi RISCs via the
complementary base-pairing
(
Lau
et al, 2006)
•
Conservation of the Argonaute catalytic triad which is also
made by the Piwi.
(
Klenov
et al, 2007).
Adaptation Phase
This phase is restricted to
germ cells and it constitutes the ping-pong cycle. In

4. this period transposon microrna
cleavage is directed by primary piRNAs to trigger the
production of secondary piRNAs
(
Klattenhoff
et al., 2009)
Later on, the produced secondary RNA triggers the production
of piRNA from the target, closing the loop that that makes it
possible for the overall small RNA population to adjust to
challenging by a particular transposon. It is also in this phase
where the piRNA in germ cells can be transmitted to the next
generation to prime piRNA responses in progeny.
However, when it comes to Drosophila follicle cells, initiation
and effectors phase are the only relevant phases. In Drosophila
follicle cells, the piRNA pathway relies on the coupling
between a single Piwi protein and a principal piRNA cluster to
silence gypsy family
retrotrasnposons
.
Results
From researches made, it was found that there are various ways
by which Piwi proteins silence targets by interfering with their
transcription. It was found out that piRNA are mostly absent
from somatic tissues, results underlying these changes are
presumed to have occurred during the development and to have
been epigenetically maintained in the adult. Drosophila Piwi
protein was found in the nucleus and it interacts with HP1. HP1
is a core part of heterochromatin. The results of the research
showed that the
effecter
mechanism is what takes
place in the Drosophila whereby Piwi-associated small RNAs
direct heterochromatin formation and silencing of targets.
It was also found that the loss of Piwi poses some results on the
transposon expression in the somatic cells

5. (
Ghildiyal
, 2009).
It was found out that the absence of Piwi proteins in the
somatic cells during development is the major cause of genetic
mutation. In simple terms, it was found that the piRNA
pathway is always required for transposon silencing.
It was also found out that Armitage is a part of the somatic
piRNA pathway. Researchers found that there are as many as
twelve proteins that have been linked to the fully elaborated
piRNA pathway that operates in germ cells (
Girard
2006)
.
Many of them were found to show germ-cell specific expression
patterns consistent with their selective biological effects (
Brennecke
2007).
In Armitage, mutilation occurs as a result of loss of both the
functional nuclear accumulation of Piwi protein and decrease in
Piwi-associated piRNAs. It was concluded that Armitage play a
role in the somatic and germline compartments
(
Cook HA
, 2004)
.
Another result showed that both Armitage and Zucchini work at
the initial stage, or phase. Different experiments which were
used to determine which phases do the two functions showed
that both function at the initiation phase
(
Cox DN
, 2000)
A proteomic analysis of Piwi RNPs was performed and it was

6. found out that Armitage is a part of Piwi RISC. It was found
that Piwi immunoprecipitates contained several peptides from
Armitage. This was a clear indication that there is the presence
of this protein in Piwi. A detection of an association of Squash
with Piwi and Armitage was also made.
It was also discovered that Squash impacts the piRNA effectors
phase. It was found out that a mutation in the squash showed
little impact on the piRNA populations in mutant ovaries.
The discovery made was of high value in the field
(
Gunawardane
2007)
This is because specialists in this field now know the different
causes of genetic mutation and when the cause is known it is
easy to apply appropriate solutions if a problem occurs (
Grivna
2006).
The results provide a road map to the specialists to know how to
tackle genetic mutation.
Conclusion
From this article, it is clear that the three; Armitage, Piwi
protein, and Squash in some point they associate with each
other.
This discovery is of great value in the field. People can now
understand the whole thing of genetic mutilation.
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