Biology Reference
In-Depth Information
methyltransferases. The hymenopterans
Apis mellifera
and
Nasonia vitripennis
have different numbers of subfamily 1 in their genomes (two and three, respec-
tively). When additional arthropod genomes are completely sequenced and
their methyltransferase genes discovered, we understand more about the role
of methylation as an epigenetic mechanism in arthropods.
The ability to modify gene expression through epigenetics adds another
method by which an insect can respond to environmental conditions. For exam-
ple, in honeybees, DNA methylation is important in differential gene expression
in castes (
Elango et al. 2009
), in its social interactions, and in complex brain func-
tions (
Wang et al. 2006, Kronforst et al. 2008, Kucharski et al. 2008, Lyko et al.
2010
). Queen and worker honeybees are behaviorally and reproductively differ-
ent despite their identical genome sequences. However, the intake of royal jelly
and the methylation of DNA make queens very different. Methylation patterns
of 550 genes in the brains of queens and workers were found to be different
(
Lyko et al. 2010
). Thus, despite workers and queens having identical genomes,
their phenotype, biology, and behavior are dramatically different. The methy-
lome of the silkworm has been analyzed and, as seems common in insects, a rel-
atively low level of DNA methylation is found (
Xiang et al. 2010
). The silkworm
has only two DNA methyltransferase genes.
2.18 Eukaryotic Genomes and Evolution
The discovery of split genes and RNA splicing was a critically important discov-
ery and has elicited considerable thought regarding the origin and evolution of
eukaryotic genomes (
Deamer and Szostak 2010, Atkins et al. 2011, Darnell 2011
).
Gene regulation, and especially RNA splicing and DNA methylation, is probably
central to understanding the development of complex multicellular eukaryotic
organisms. Alternative RNA splicing produces multiple mRNAs that encode dif-
ferent proteins (
Sharp 1994
). The spliceosome process for excising introns is prob-
ably as old as the ribosomal process for translation. Thus, the eukaryotic cell has
two compartments: the nucleus, where the spliceosome processes pre-mRNAs by
RNA catalysis; and the cytoplasm, where the ribosome translates mRNAs by RNA
catalysis.
Evolution in eukaryotes by changes in RNA processing is aided by the avail-
ability of intron-rich, repeat-rich genomes, allowing new gene products to
evolve based on changes in RNA processing (
Herbert and Rich 1999
). The eukary-
otic genome can be thought of as a “junkyard” in which solutions to any num-
ber of problems can occur with the assembly of old components into new
combinations by changes in RNA processing.
