chapter 1 - Bentham Science

Neurohormones and Second Messengers in Lepidoptera HPFP: Recent Advances in Insects and Other Arthropods Vol. 1 113
larvae of D. melanogaster has also been isolated using chromatographic techniques and amino acid
sequence analysis [20], and is composed of A and B fragments, each consisting of 21 amino acid residues
of about 2310 daltons each, linked to an oligosaccharide and arranged to form a glycopeptide of 66 KDa.
Bombyx PTTH and Drosophila PTTHs are not chemically related and do not appear to be mutually
antigenic [20]. Bombyxin resembles vertebrate insulin A, and can affect carbohydrate metabolism as well
as other tasks [10] including induction of ecdysteroidogenesis in ovaries of the blowfly Phormia regina
[22]. The structure of OEH, the larger brain factor that induces ovaries to synthesize ecdysteroid, was
derived from a preparation of 6 million mosquito heads. It is a peptide composed of 31 amino acid residues
(PTNVEMRCKLYSGPAVQNTGECVHGAELN), although longer sequences up to 108 residues and
polymeric forms were also identified. No sequence similarity to the PTTHs was detected, although 29% of
the OEH sequence resembled another insect neuropeptide, locust neuroparsin [14]. The sequence of LTE
was derived from a homogenate of 13,000 brains of L. dispar pupae by using protein sequence analysis and
electrospray mass spectrometry. The most prevalent fraction, active in inducing ecysteroid synthesis by
testes from H. virescens and L. dispar, proved to be a 21 amino acid residue with a molecular weight of
2473 da. Its molecular sequence was determined to be NH2-ISDFDEYEPLNDNDDDEVLDF-OH, [23-
24]. An analog of TE stimulated ecdysteroid synthesis by cricket ovarian mesenteries [25] but was not
active in eliciting ecdysteroid synthesis by prothoracic glands of either L. dispar or B. mori [cited in 24].
Lymantria TE does not share any sequence with the large dimeric form of B. mori PTTH [19], nor was it
immunologically interactive with the 66 KDa PTTH isolated from D. melanogaster [20] or Aedes aegypti
OEH [14]. A U.S.National Institutes of Health peptide database (BLAST) search of Lymantria TE indicated
homology with inhibitory peptides, such as those inhibiting cytolysis [26]. Fullbright et al [27] have shown
that the Bombyx ovarian receptor for the prothoracicotropic hormone Bombyxin is similar to the
mammalian insulin receptor, while Rewitz et al. [28] report that the prothoracotropic hormone receptor in
Drosophila is a tyrosine kinase. Thus, the various steroidogenic peptides probably stimulate different
receptors and/or physiological cascades in their respective target tissues even though the steroid hormones
they induce in the various organs appear similar. The ecdysteroid hormones that are produced in each case
may have local effects or play different roles at different times in development.
Figure 2: Schematic diagram of sagittal (A) and frontal (B) view of the regions of the pupal central nervous system
containing LTE-reactive cells and nerve tracts. AL: antennal lobe; AN: antennal nerve; CA: corpus allatum; CC: corpus
cardiacum; E: esophagus; FC: frontal connectives; FG: frontal ganglion; LNC: lateral neurosecretory cells; MNC:
medial neurosecretory cells; NCCI, II: nervi corporis cardiaci; OLC: optic lobe neurosecretory cells; P: protocerebrum;
SG: subesophageal ganglion; T: tritocerebrum [18].