Biology Reference
In-Depth Information
injection of hundreds or thousands of embryos to obtain multiple transfor-
mant lines for analysis of expression level and fitness. Third, the size of the con-
struct that can be inserted is small (usually 10-15 kb, which is smaller than many
genes). It also is unclear whether multiple genes can be inserted that could mod-
ify an entire metabolic pathway. Fourth, TE insertions are likely to be unstable
for several reasons, which is undesirable if the transformed arthropod is to be
released into the field.
In an effort to resolve some of these issues, other transformation methods are
being developed, including RNAi (
Box 9.1
), Zinc-finger nucleases (ZFN), transcrip-
tion activator-like effectors (TALEs), homing endonucleases (HEs) or meganucle-
ases (
Box 9.2
), and nanotechnology approaches.
Box 9.1 Steps Involved in the Basic Mechanism of RNAi and Categories of RNAi
Deliver long double-stranded (ds) RNA by injection, soaking, or feeding
The cytoplasmic enzyme Dicer (an RNase) attaches to the ds RNA
ds RNA is cut into small ds interfering RNAs (siRNAs) that are ~ 21 nt in length by Dicer
The siRNAs unwind and the antisense strand attaches to the
R
NA-
I
nduced
S
ilencing
C
omplex (RISC)
which carries them to the target mRNA
The RISC and the siRNAis bind to the target mRNA, blocking and degrading it
Categories
RNAi can be
cell-autonomous
(silencing limited to cell in which the dsRNA is introduced/expressed). The
diagram above refers primarily to cell-autonomous RNAi.
Non-cell-autonomous RNAi
takes place in tissues or cells different from the location or the production of
the dsRNA. This is divided into two types: environmental RNAi and systemic RNAi.
Environmental RNAi involves the uptake of dsRNA by a cell from the environment.
Systemic RNAi
takes
place in multicellular organisms when a silencing signal is transported from one cell to another or from
one tissue type to another.
Derived, in part, from
Belles (2010) and Huvenne and Smagghe (2010)
.
