Biology Reference
In-Depth Information
If we simply know the DNA sequence of all of the protein-coding genes in
the insect genome, we do not know how to “make an insect.” The develop-
ment of a functioning insect involves the coordinated activity of many different
proteins, the information for which is encoded in the protein-coding DNA and
in the regulatory machinery, much of which is RNA. DNA also carries the code
for rRNAs, tRNAs, and many other small RNAs. Ribosomal, tRNA, and small RNA
molecules are used directly without being translated into proteins. Furthermore,
additional RNAs that are used after transcription are having their functions elu-
cidated (
He and Hannon 2004, Atkins et al. 2011
). Research to decipher how
genetic information in the protein-coding genes and the various RNAs is used
by the cells and organism during development is rapidly advancing (
Herbert and
Rich 1999, Lee and Young 2000, Taft et al. 2009, Belles 2010, Belles et al. 2010
).
Thus, a reductionist approach to understanding genetics (focusing primarily
on DNA sequences) is insufficient to understand the structure and function of
insects and other organisms. An insect brain cell and an ovary cell contain the
same DNA, but each clearly has different structure and function. How cells dif-
ferentiate into different tissues and organs during the life stages of an insect
(egg, larva, pupa, adult) is a complex process. Thus, geneticists and systems
biologists need to work together to resolve this complexity (
Alberts et al. 2010,
Nurse and Hayles 2011
).
Noncoding RNAs (ncRNAs) include microRNAs (miRNAs) and small interfer-
ing RNAs (siRNAs), small RNAs (small nucleolar RNAs [snoRNAs], small modu-
latory RNAs [smRNAs], and Piwi-interacting RNAs [piRNAs]), and medium and
large RNAs (
Box 2.1
). These ncRNAs are designated by their length and func-
tion and are called noncoding because they do not code for proteins. They
clearly code for important functions, however. miRNAs and siRNAs are com-
posed of 20-25 nucleotides (nt) in length and are involved in gene silencing
and RNA interference (RNAi). Small RNAs include snoRNAs, smRNAs, piRNAs,
and others, and they range in size from 20 to 300 nt. snoRNAs (60-300 nt) are
required for maturation of rRNA (
Dieci et al. 2009
). Small RNAs are involved in
modification of target RNAs, synthesis of telomeric DNA at the ends of chro-
mosomes, modification of chromatin structure, and modulation of transcrip-
tion. Tiny RNAs (18 nt in length) are associated with promoter regions of genes
that are highly expressed (
Taft et al. 2009
). Medium and large ncRNAs are 300-
1000 nt in length and are involved in imprinting DNA, X-chromosome inactiva-
tion, DNA demethylation, gene transcription, and generation of miRNAs and
small RNAs.
Eukaryotes differ from microorganisms (Eubacteria and Archaeabacteria)
in several important ways. First, eukaryotes typically have more than one
