Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Chiba, Japan.
J Comp Neurol. 2011 Feb 1;519(2):238-46. doi: 10.1002/cne.22517.
Biosynthesis of ecdysteroids, the insect steroid hormones controlling gene expression during molting and metamorphosis, takes place primarily in the prothoracic gland (PG). The activity of the PG is regulated by various neuropeptides. In the silkworm Bombyx mori, these neuropeptides utilize both hormonal and neuronal pathways to regulate the activity of the PG, making the insect an excellent model system to investigate the complex signaling network controlling ecdysteroid biosynthesis. Here we report another group of neuropeptides, orcokinins, as neuronal prothoracicotropic factors. Using direct mass spectrometric profiling of the axons associated with the PG, we detected several peptide peaks which correspond to orcokinin gene products in addition to the previously described Bommo-FMRFamides (BRFas). In situ hybridization and immunohistochemistry revealed that orcokinins are produced in the prominent neurosecretory cells in the ventral ganglia, as well as in numerous small neurons throughout the central nervous system and in midgut endocrine cells. One of the two pairs of BRFa-expressing neurosecretory cells in the prothoracic ganglion coexpresses orcokinin, and these neurons project axons through the transverse nerve and terminate on the surface of the PG. Using an in vitro PG bioassay, we show that orcokinins have a clear prothoracicotropic activity and are able to cancel the static effect of BRFas on ecdysteroid biosynthesis, whereas the suppressive effect of BRFas on cAMP production remained unchanged in the presence of orcokinins. The discovery of a second regulator of PG activity in these neurons further illustrates the potential importance of the PG innervation in the regulation of insect development.
蜕皮甾类的生物合成，即控制蜕皮和变态过程中基因表达的昆虫类固醇激素，主要发生在前胸腺（PG）中。PG 的活性受各种神经肽调节。在桑蚕 Bombyx mori 中，这些神经肽通过激素和神经元途径来调节 PG 的活性，使昆虫成为研究控制蜕皮甾类生物合成的复杂信号网络的理想模型系统。在这里，我们报道了另一组神经肽，即 orcokinins，作为神经元促前胸腺激素。通过与 PG 相关轴突的直接质谱分析，我们除了检测到先前描述的 Bommo-FMRFamides（BRFas）外，还检测到几个对应于 orcokinin 基因产物的肽峰。原位杂交和免疫组织化学显示，orcokinins 在前胸神经节中明显的神经分泌细胞中产生，以及在中枢神经系统和中肠内分泌细胞中的许多小神经元中产生。前胸神经节中两对表达 BRFa 的神经分泌细胞之一共同表达 orcokinin，这些神经元通过横神经投射轴突，并终止于 PG 的表面。通过体外 PG 生物测定，我们表明 orcokinins 具有明显的前胸腺促活性，能够取消 BRFas 对蜕皮甾类生物合成的静态作用，而 BRFas 对 cAMP 产生的抑制作用在存在 orcokinins 时保持不变。这些神经元中 PG 活性的第二个调节剂的发现进一步说明了 PG 神经支配在昆虫发育调节中的潜在重要性。
