chapter 1 - Bentham Science

Insulin-Related Peptides in Insects and Other Arthropods HPFP: Recent Advances in Insects and Other Arthropods Vol. 1 163
[19]. Although bombyxin genes are expressed mainly in the brain, they are also expressed at minute levels
in other tissues, such as the silk gland, gonads, and gut [34]. In D. melanogaster, 7 insulin-like peptide
(DILP) genes, dilp1 - dilp7, were found in the genome. The dilp1, dilp2, dilp3, and dilp5 transcripts of
these genes were detected in the median neurosecretory cells [5, 35] and dilp4 and dilp6 transcripts were
detected in the larval gut and dilp7 transcript was done in the nerve cord [5, 36]. These expressions indicate
that DILPs are produced in a tissue- and stage-specific manner. The expression level of bombyxin and other
insulin-like peptide genes also changes temporally during development [34, 36] and is influenced by
nutrient conditions. For example, when the larvae of D. melanogaster were subjected to starvation, dilp3
and dilp5 expression levels were reduced but dilp2 expression levels remained unchanged [35].
Table 1: Tissue distribution and detection methods of insulin-like peptides
Lepidoptera
Diptera
Other orders
Species Distribution Method
Manduca sexta Brain median neurosecretory cells,
Frontal ganglion
Anti-bovine insulin immunostaining [12, 13]
Bombyx mori Brain median neurosecretory cells Purification as Samia-PTTH [3]
Anti-bombyxin immunostaining [14]
in situ hybridization [15]
Galleria mellonella Brain median and lateral neurosecretory
cells
Samia cynthia ricini Brain median and lateral neurosecretory
cells
Anti-bombyxin immunostaining [16]
Gene identification [17]
Anti-Samia bombyxin immuno- staining [18]
Agrius convolvuli Brain median neurosecretory cells cDNA cloning, in situ hybridization [19]
Spodoptera littoralis Brain median neurosecretory cells PCR-based cloning, anti-bombyxin immunostaining
[20]
Calliphora vomitoria Brain median neurosecretory cells Anti-bovine insulin immunostaining [21]
Eristalis aeneus Brain median neurosecretory cells Anti-bovine insulin immunostaining [22]
Drosophila
melanogaster
Brain median neurosecretory cells* Anti-bovine insulin immunostaining [23]
Genome information [5]
Anti-DILP immunostaining [24]
Aedes aegypti Brain lateral neurosecretory cells Anti-DILP immunostaining [24]
Locusta migratoria Brain median neurosecretory cells Isolation from a cDNA library of brain median
neurosecretory cells [4]
Purification [25]
Schistocerca
gregaria
Brain median neurosecretory cells Purification, anti-Locusta insulin immunostaining
[26]
Leucophaea maderae Brain median neurosecretory cells* Anti-bovine insulin immunostaining [27]
*Brain median neurosecretory cells: in addition to the median neurosecretory cells, the genes encoding DILPs are expressed in
various tissue cells including neurons, gut cells, fat body cells, and ovarian cells.
3. SUGAR METABOLISM
In mammals, insulin is widely accepted as a hypoglycemic hormone. The hypoglycemic effect was
demonstrated when an extract from D. melanogaster was injected into mice [29], suggesting that insulinlike
hormones are present in both insects and mammals. In insects, the major type of blood sugar is the
non-reducing disaccharide trehalose, not glucose [37]. Normann [38] suggested that the hypertrehalosemia
associated with decapitation of the blue blowfly, Calliphora erythrocephala, was due to the lack of a
hypotrehalosemic hormone in the brain. In fact, when the median neurosecretory cells were ablated
surgically from the brain of C. erythrocephala, the hemolymph trehalose and glucose levels were
significantly elevated. After surgery, the elevated levels of both sugars were reduced by injection of the
homogenate of the brain median neurosecretory cells [39]. In addition to the brain, hypotrehalosemic
activity was found in the extract of the corpora allata and corpora cardiaca of M. sexta and in the fraction