Characterizing the Protein Isoforms of foraging (for), the PKGI Ortholog in Drosophila melanogaster

The foraging (for) gene of Drosophila melanogaster encodes a cGMP-dependent protein kinase (PKG), which is a major effector of the cGMP signaling pathway involved in the regulation of behaviour and metabolic traits. Despite being well studied at the transcript level, little is known about the for gene at the protein level. Here, we provide a detailed characterization of the for gene protein (FOR) products and present new tools for their study, including five isoform-specific antibodies and a transgenic strain that carries an HA-labelled for allele (for(BAC)::HA). Our results showed that multiple FOR isoforms were expressed in the larval and adult stages of D. melanogaster and that the majority of whole-body FOR expression arises from three (P1, P1α, and P3) of eight putative protein isoforms. We found that FOR expression differed between the larval and adult stages and between the dissected larval organs we analyzed, which included the central nervous system (CNS), fat body, carcass, and intestine. Moreover, we showed that the FOR expression differed between two allelic variants of the for gene, namely, for(s) (sitter) and for(R) (rover), that are known to differ in many food-related traits. Together, our in vivo identification of FOR isoforms and the existence of temporal, spatial, and genetic differences in their expression lay the groundwork for determining their functional significance.