29 research outputs found
Precocious Metamorphosis in the Juvenile Hormone–Deficient Mutant of the Silkworm, Bombyx mori
Insect molting and metamorphosis are intricately governed by two hormones, ecdysteroids and juvenile hormones (JHs). JHs prevent precocious metamorphosis and allow the larva to undergo multiple rounds of molting until it attains the proper size for metamorphosis. In the silkworm, Bombyx mori, several “moltinism” mutations have been identified that exhibit variations in the number of larval molts; however, none of them have been characterized molecularly. Here we report the identification and characterization of the gene responsible for the dimolting (mod) mutant that undergoes precocious metamorphosis with fewer larval–larval molts. We show that the mod mutation results in complete loss of JHs in the larval hemolymph and that the mutant phenotype can be rescued by topical application of a JH analog. We performed positional cloning of mod and found a null mutation in the cytochrome P450 gene CYP15C1 in the mod allele. We also demonstrated that CYP15C1 is specifically expressed in the corpus allatum, an endocrine organ that synthesizes and secretes JHs. Furthermore, a biochemical experiment showed that CYP15C1 epoxidizes farnesoic acid to JH acid in a highly stereospecific manner. Precocious metamorphosis of mod larvae was rescued when the wild-type allele of CYP15C1 was expressed in transgenic mod larvae using the GAL4/UAS system. Our data therefore reveal that CYP15C1 is the gene responsible for the mod mutation and is essential for JH biosynthesis. Remarkably, precocious larval–pupal transition in mod larvae does not occur in the first or second instar, suggesting that authentic epoxidized JHs are not essential in very young larvae of B. mori. Our identification of a JH–deficient mutant in this model insect will lead to a greater understanding of the molecular basis of the hormonal control of development and metamorphosis
4,5-Substituted 3‑Isoxazolols with Insecticidal Activity Act as Competitive Antagonists of Housefly GABA Receptors
The insect GABA receptor (GABAR),
which is composed of five RDL
subunits, represents an important target for insecticides. A series
of 4,5-disubstituted 3-isoxazolols, including muscimol analogues,
were synthesized and examined for their activities against four splice
variants (ac, ad, bc, and bd) of housefly GABARs expressed in Xenopus oocytes. Muscimol was a more potent agonist
than GABA in all four splice variants, whereas synthesized analogues
did not exhibit agonism but rather antagonism in housefly GABARs.
The introduction of bicyclic aromatic groups at the 4-position of
muscimol and the simultaneous replacement of the aminomethyl group
with a carbamoyl group at the 5-position to afford six 4-aryl-5-carbamoyl-3-isoxazolols
resulted in compounds that exhibited significantly enhanced antagonism
with IC<sub>50</sub> values in the low micromolar range in the ac
variant. The inhibition of GABA-induced currents by 100 μM analogues
was approximately 1.5–4-fold greater in the ac and bc variants
than in the ad and bd variants. 4-(3-Biphenylyl)-5-carbamoyl-3-isoxazolol
displayed competitive antagonism, with IC<sub>50</sub> values of 30,
34, 107, and 96 μM in the ac, bc, ad, and bd variants, respectively,
and exhibited moderate insecticidal activity against houseflies, with
an LD<sub>50</sub> value of 5.6 nmol/fly. These findings suggest that
these 3-isoxazolol analogues are novel lead compounds for the design
and development of insecticides that target the orthosteric site of
housefly GABARs