chapter 1 - Bentham Science

174 HPFP: Recent Advances in Insects and Other Arthropods Vol. 1 Manabu Kamimura
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Figure 2: Comparison of three-dimensional structures of P. separata GBP and mouse EGF. Ribbon diagrams of GBP
(left) and EGF (right) were generated using the atomic coordinates obtained from the PDB (entry sets 1BQF and 1EPG,
respectively) [10].
The ENF peptide gene is expressed in many stages and tissues of moths. Transcripts of multiple sizes were
detected during the embryogenesis of B. mori and M. brassicae [15, 18]. The mRNAs were not detected
immediately following the oviposition, but were detected within the next 24 h, indicating that their origins
were not maternal but zygotic. The M. brassicae GBP mRNA is specifically expressed in the
suboesophageal body in the embryo under the control of a HOX transcriptional factor, Deformed [15, 35].
In M. sexta eggs, expression of the PP2 mRNA was enhanced by parasitization of the parasitoid wasp
Trichogramma evanescens [36].
In the larval stage, the ENF peptide mRNAs were expressed in the fat body, hemocytes, central nervous
system, epidermis, muscle, wing disc, and gonads (ovary and testis), and among these tissues their
expressions, in general, were predominant in the fat body [12, 16-18, 37]. In contrast, these mRNAs were
detected in small amounts in the silk gland, midgut or Malpighian tubules. While a 0.6-0.8 kb ENF peptide
mRNA is predominantly expressed in many tissues, longer transcripts of sizes >2 kb were strongly
expressed in the central nervous systems of P. separata and P. includens [13, 16]. In B. mori, the
expression level of PP mRNA changed during the last larval instar under the control of juvenile hormone
and molting hormone ecdysone [18]. In the P. separata larvae, expression of the GBP mRNA in the central
nervous system was enhanced by parasitization of the parasitoid wasp A. kariyai [38].
Recently, it has been shown that a 1.5 kb embryonic PP mRNA of B. mori and a 2.5 kb larval GBP mRNA
of P. separata are tricistronic mRNAs that encode not only the ENF peptide precursor but also two
cytokine precursor-like proteins [19]. Orthologous tricistronic ENF peptide mRNAs were found in M.
brassicae, S. cynthia pryeri, T. japonica, and N. himachala sangaica.
4. PROTEIN EXPRESSION, ACTIVATION, AND INACTIVATION
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The ENF peptide is translated as an inactive larger precursor, consisting of 120 to 150 amino acids, and the
bioactive ENF peptide is located at the C-terminal end of the precursor (Fig. 3A). This precursor protein
(preproprotein) has a signal peptide containing a number of hydrophobic residues at the N-terminus end and
is secreted out of the cells. The secreted protein is still an inactive precursor (proprotein) and is
subsequently cleaved to form the active peptide after receiving special stimuli, such as bleeding and
microorganism infection [17-18, 39]. Serine proteases, which are yet to be identified, are presumably
responsible for this cleavage [17, 39]. For example, following an infection of B. mori by a microorganism,
a cellular component of the microorganism, such as the peptidoglycan of bacteria or -1, 3-glucan of fungi,
stimulates hemocytes to generate reactive oxygen species (ROS) (see for detail chapter number 8), and the
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