Structure–activity studies with endogenous allatostatins from Periplaneta americana: Expressed receptor compared with functional bioassay

The A-allatostatins (F/YXFGLamides) are insect neuropeptides with inhibitory actions on juvenile hormone (JH) synthesis, muscular contraction and vitellogenesis. They exist in multiple forms within each species. In the cockroach, Periplaneta americana, only one receptor for A-allatostatin has been identified thus far. Here, we have characterised the receptor response to all 15 of the endogenous A-allatostatins encoded by the P. americana allatostatin prohormone gene, together with some analogues, using an indirect heterologous system involving co-expression of the receptor and a potassium channel subunit in Xenopus laevis oocytes and electrophysiological measurements. We have also determined the relative potency of the same peptides to inhibit JH synthesis in corpora allata. Our data reveal that the heterologously expressed receptor responds to all of the endogenous allatostatins and, although differences in potency are recorded, this cannot readily be related to particular differences in the primary structure of the peptides. Similarly, all allatostatins act on the corpora allata to inhibit the synthesis of JH, again with varying potency not readily related to peptide structure. Interestingly, some of the peptides did not perform consistently across the two assays.We show that the receptor is widely expressed in adult P. americana tissues (head, retrocerebral glands, fat body, ovary, male accessory gland, gut, leg muscle, Malpighian tubule and nerve cord) as well as in early larval instars. The spatial expression supports the known pleiotropic activity of allatostatins and role as a paracrine effector. This is the first report of such a detailed characterisation of an invertebrate receptor for allatostatin.