Many cockroach species have adapted to urban environments, and some have been serious pests of public health in the tropics and subtropics. Here, we present the 3.38-Gb genome and a consensus gene set of the American cockroach, Periplaneta americana. We report insights from both genomic and functional investigations into the underlying basis of its adaptation to urban environments and developmental plasticity. In comparison with other insects, expansions of gene families in P. americana exist for most core gene families likely associated with environmental adaptation, such as chemoreception and detoxification. Multiple pathways regulating metamorphic development are well conserved, and RNAi experiments inform on key roles of 20-hydroxyecdysone, juvenile hormone, insulin, and decapentaplegic signals in regulating plasticity. Our analyses reveal a high level of sequence identity in genes between the American cockroach and two termite species, advancing it as a valuable model to study the evolutionary relationships between cockroaches and termites.

During Drosophila metamorphosis, the single-cell layer of fat body tissues gradually dissociates into individual cells. Via a fat body-specific RNAi screen in this study, we found that two matrix metalloproteinases (MMPs), Mmp1 and Mmp2, are both required for fat body cell dissociation. As revealed through a series of cellular, biochemical, molecular, and genetic experiments, Mmp1 preferentially cleaves DE-cadherin-mediated cell-cell junctions, while Mmp2 preferentially degrades basement membrane (BM) components and thus destroy cell-BM junctions, resulting in the complete dissociation of the entire fat body tissues into individual cells. Moreover, several genetic interaction experiments demonstrated that the roles of Mmp1 and Mmp2 in this developmental process are cooperative. In conclusion, Mmp1 and Mmp2 induce fat body cell dissociation during Drosophila metamorphosis in a cooperative yet distinct manner, a finding that sheds light on the general mechanisms by which MMPs regulate tissue remodeling in animals.

Corpus allatum (CA) ablation results in juvenile hormone (JH) deficiency and pupal lethality in Drosophila. The fly CA produces and releases three sesquiterpenoid hormones: JH III bisepoxide (JHB3), JH III, and methyl farnesoate (MF). In the whole body extracts, MF is the most abundant sesquiterpenoid, followed by JHB3 and JH III. Knockout of JH acid methyl transferase (jhamt) did not result in lethality; it decreased biosynthesis of JHB3, but MF biosynthesis was not affected. RNAi-mediated reduction of 3-hydroxy-3-methylglutaryl CoA reductase (hmgcr) expression in the CA decreased biosynthesis and titers of the three sesquiterpenoids, resulting in partial lethality. Reducing hmgcr expression in the CA of the jhamt mutant further decreased MF titer to a very low level, and caused complete lethality. JH III, JHB3, and MF function through Met and Gce, the two JH receptors, and induce expression of Kr-h1, a JH primary-response gene. As well, a portion of MF is converted to JHB3 in the hemolymph or peripheral tissues. Topical application of JHB3, JH III, or MF precluded lethality in JH-deficient animals, but not in the Met gce double mutant. Taken together, these experiments show that MF is produced by the larval CA and released into the hemolymph, from where it exerts its anti-metamorphic effects indirectly after conversion to JHB3, as well as acting as a hormone itself through the two JH receptors, Met and Gce. Methyl farnesoate (MF) is the immediate precursor of juvenile hormone (JH) III in the JH biosynthetic pathway, and lacks the epoxide moiety characteristic of JHs. The potential role of MF as a JH in arthropods has been an issue of a long-standing debate. In this report, comprehensive molecular genetics studies demonstrated that MF plays a dual role in regulating Drosophila metamorphosis. MF is produced by the larval CA and released into the hemolymph, from where it exerted its anti-metamorphic effects indirectly after conversion to JHB3, as well as acting as a hormone itself through a direct interaction with Met and Gce, the two JH receptors.

Juvenile hormone (JH) receptors, methoprene-tolerant (Met) and Germ-cell expressed (Gce), transduce JH signals to induce Kr-h1 expression in Drosophila. Dual luciferase assay identified a 120-bp JH response region (JHRR) in the Kr-h1α promoter. Both in vitro and in vivo experiments revealed that Met and Gce transduce JH signals to induce Kr-h1 expression through the JHRR. DNA affinity purification identified chaperone protein Hsp83 as one of the proteins bound to the JHRR in the presence of JH. Interestingly, Hsp83 physically interacts with PAS-B and basic helix-loop-helix domains of Met, and JH induces Met-Hsp83 interaction. As determined by immunohistochemistry, Met is mainly distributed in the cytoplasm of fat body cells of the larval when the JH titer is low and JH induces Met nuclear import. Hsp83 was accumulated in the cytoplasm area adjunct to the nucleus in the presence of JH and Met/Gce. Loss-of-function of Hsp83 attenuated JH binding and JH-induced nuclear import of Met, resulting in a decrease in the JHRR-driven reporter activity leading to reduction of Kr-h1 expression. These data show that Hsp83 facilitates the JH-induced nuclear import of Met that induces Kr-h1 expression through the JHRR.

Tissue remodeling is a crucial process in animal development and disease progression. Coordinately controlled by the two main insect hormones, juvenile hormone (JH) and 20-hydroxyecdysone (20E), tissues are remodeled context-specifically during insect metamorphosis. We previously discovered that two matrix metalloproteinases (Mmps) cooperatively induce fat body cell dissociation in Drosophila. However, the molecular events involved in this Mmp-mediated dissociation are unclear. Here we report that JH and 20E coordinately and precisely control the developmental timing of Mmp–induced fat body cell dissociation. We found that during the larval–prepupal transition, the anti-metamorphic factor Kr-h1 transduces JH signaling, which directly inhibited Mmp expression and activated expression of tissue inhibitor of metalloproteinases (timp) and thereby suppressed Mmp–induced fat body cell dissociation. We also noted that upon a decline in the JH titer, a prepupal peak of 20E suppresses Mmp–induced fat body cell dissociation through the 20E primary-response genes, E75 and Blimp-1, which inhibited expression of the nuclear receptor and competence factor βftz-F1. Moreover, upon a decline in the 20E titer, βftz-F1 expression was induced by the 20E early–late response gene DHR3, and then βftz-F1 directly activated Mmp expression and inhibited timp expression, causing Mmp–induced fat body cell dissociation during 6–12 h after puparium formation. In conclusion, coordinated signaling via JH and 20E finely tunes the developmental timing of Mmp–induced fat body cell dissociation. Our findings shed critical light on hormonal regulation of insect metamorphosis.