Remodeling of the corpora cardiaca and the corpora allata during adult metamorphosis in Bombyx mori: identification of invisible corpora cardiaca by the expression of adipokinetic hormone

It is problematic to identify the corpora cardiaca (CC) of pupal and adult stages of Bombyx mori because of the presence of tissues similar in appearance near the associated corpora allata (CA). To find the CC, we performed in situ hybridization experiments using the adipokinetic hormone II (AKH-II) gene as a probe, as AKH-II expression occurs only in the CC. Shortly after pupation, the CC and CA began to move toward the esophagus and had attached there tightly by 4 days; during this period, the distance between the CC and CA increased from 65 to 507 μm. The CC became flattened during the remodeling period, although the CA stayed globular until adult ecdysis. In situ hybridization analyses, after the CC had been correctly identified during adult development, showed that the mRNA expression of all the mevalonate enzymes and juvenile hormone acid O -methyltransferase involved in JH synthesis occurred only in CA cells, indicating that the fluctuations of enzyme mRNA amounts in CC-CA complexes (Kinjoh et al. in Insect Biochem Mol Biol 37:808–818, 2007) were derived solely from those in the CA.