Biology Reference
In-Depth Information
Belles (2009)
studied metamorphosis in hemimetabolous insects using RNA inter-
ference (RNAi) methods and showed that microRNAs are involved in metamorpho-
sis of
Blattella germanica
, perhaps by regulating genes that are juvenile hormone
targets.
Zhang et al. (2009)
showed that 106 microRNAs are expressed in all stages
of
Bombyx mori
, but 248 miRNAs were egg- and pupa-specific, suggesting that
they are important in embryogenesis and metamorphosis.
4.15 Interactions During Development
Normal development requires the coordinated expression of thousands of struc-
tural genes in a controlled manner. Because independent control of individual
structural genes would result in chaotic development, controlling genes regulate
the activity of groups of structural genes in a coordinated manner. Such genes are
presumably arranged hierarchically or form a controlling network that ensures
the correct timing of development so that the proper pattern develops. Although
development in
Drosophila
is not fully understood, many of the genes and their
interactions are known, including those that regulate the development of meso-
derm (
Furlong et al. 2001
), appendages (
Morata 2001
), and the eye (
Thomas and
Wassarman 1999
). It is likely that understanding development in
D. melanogaster
will elucidate many of the principles by which other higher eukaryotes develop.
The molecular genetics of sex determination is discussed in Chapter 10 and pro-
vides another example of the hierarchical nature of development.
4.16 Similarities and Differences in Development in Other Insects
Although developmental studies are most advanced in
D. melanogaster
, it is
important to carry out comparable research with other insects to determine
whether our knowledge of development in
D. melanogaster
can be extrapo-
lated to other insects (
Klingler 1994, Buning 1994, Davis and Patel 2002, Lynch
et al. 2012
).
Drosophila
represents a relatively specialized type of development,
the long-germ development pattern, in which segmentation occurs essentially
simultaneously along the anterior-posterior axis with the process of segmen-
tal specification under the control of homeotic genes in the Antennapedia and
bithorax complexes.
Lynch et al. (2012)
compared the embryonic development
of
Drosophila
,
Nasonia
, and
Tribolium
.
Nasonia
has a long-germ band mode of
embryogenesis, similar to that of
Drosophila
, but
Tribolium
has an intermedi-
ate mode of embryogenesis, which is more like the ancestral mechanism. In this
system, only the most anterior segments are specified before gastrulation and
the posterior segments are patterned from a posterior region called the growth
zone. Understanding the development of
Nasonia
and
Tribolium
has been
enhanced by the availability of fully sequenced genomes, so that
orthologs
