Piwi/piRNAs control food intake by promoting neuropeptide F expression in locusts

Abstract

Animal feeding, which directly affects growth and metabolism, is an important physiological process. However, the contribution of PIWI proteins and PIWI-interacting RNAs (piRNAs) to the regulatory mechanism of animal feeding is unknown. Here, we report a novel function of Piwi and piRNAs in regulating food intake in locusts. Our study shows that the locust can serve as a representative species for determining PIWI function in insects. Knockdown of Piwi1 expression suppresses anabolic processes and reduces food consumption and body weight. The reduction in food intake by knockdown of Piwi1 expression results from decreased expression of neuropeptide NPF1 in a piRNA-dependent manner. Mechanistically, intronic piRNAs might enhance RNA splicing of NPF1 by preventing hairpin formation at the branch point sites. These results suggest a novel nuclear PIWI/piRNA-mediated mechanism that controls food intake in the locust nervous system.

What Are the Functional Roles of Piwi Proteins and piRNAs in Insects?

“…Piwi genes have expanded slightly in L. migratoria [ 16 ] to one gene encoding Ago3 and two genes (Piwi1 and Piwi2) that correspond to Aub/Piwi of Drosophila [ 217 ]. Piwi genes in the locust are most highly expressed in the gonads and expression of Piwi2 is pronounced in the testis [ 217 ]. However, significant expression of Ago3 and Piwi1 is observed in all somatic tissues, notably the brain.…”

“…However, significant expression of Ago3 and Piwi1 is observed in all somatic tissues, notably the brain. In the brain, significant levels of small RNAs, derived from transposons, are also detected, that have the hallmarks of piRNAs (25–27 nt size, 1U bias, ping-pong signature) [ 217 ].…”

“…The migratory locust has a very large genome size in which also the sizes of the introns have expanded considerably. The presence of large genes in the genome may have stimulated a new nuclear function of piRNAs, i.e., in the processing of large introns (>200 kb) by recursive splicing [ 217 ]. A prominent phenotype of knockdown of Piwi1 (but not Ago3) is the loss of weight caused by a decrease in food intake that was correlated with a decrease in expression of the npf1 , which encodes neuropeptide F, a peptide hormone that is expressed in neuronal tissue and is involved in the regulation of food uptake [ 219 ].…”

“…A prominent phenotype of knockdown of Piwi1 (but not Ago3) is the loss of weight caused by a decrease in food intake that was correlated with a decrease in expression of the npf1 , which encodes neuropeptide F, a peptide hormone that is expressed in neuronal tissue and is involved in the regulation of food uptake [ 219 ]. Small RNA sequencing identified two piRNAs (piRs-3-I2 and piRs-3-I3; of sense orientation) that located in the second intron of npf1 , were associated with Piwi1 and could rescue the phenotype of Piwi1 knockdown after exogenous application [ 217 ]. Functional assays indicated that piRs-3-I3 stimulated splicing efficiency by interfering with the formation of a hairpin structure at the branchpoint site in the intron that presumably affected assembly of the splicing machinery [ 217 ].…”

“…Small RNA sequencing identified two piRNAs (piRs-3-I2 and piRs-3-I3; of sense orientation) that located in the second intron of npf1 , were associated with Piwi1 and could rescue the phenotype of Piwi1 knockdown after exogenous application [ 217 ]. Functional assays indicated that piRs-3-I3 stimulated splicing efficiency by interfering with the formation of a hairpin structure at the branchpoint site in the intron that presumably affected assembly of the splicing machinery [ 217 ]. A nuclear function of Piwi proteins has been well documented in Drosophila in which piRNA complexes deposit H3K9me3 modifications to establish repressive chromatin [ 9 ].…”