Juvenile hormone acts at embryonic molts and induces the nymphal cuticle in the direct-developing cricket

Abstract

During embryogenesis of hemimetabolous insects, the sesquiterpenoid hormone, juvenile hormone (JH), appears late in embryogenesis coincident with formation of the first nymphal cuticle. We tested the role of embryonic JH by treating cricket embryos with JH III, or the JH-mimic (JHM) pyriproxifen, during early embryogenesis. We found two discrete windows of JH sensitivity. The first occurs during the formation of the first (E1) embryonic cuticle. Treatment with JHM prior to this molt produced small embryos that failed to complete the movements of katatrepsis. Embryos treated after the E1 molt but before the second embryonic (pronymphal) molt completed katatrepsis but then failed to complete dorsal closure and precociously formed nymphal, rather than pronymphal characters. This second sensitivity window was further assessed by treating embryos with low doses of JH III prior to the pronymphal molt. With low doses, mosaic cuticles were formed, bearing features of both the pronymphal and nymphal stages. The nymphal characters varied in their sensitivity to JH III, due at least in part to differences in the timing of their sensitivity windows. Unexpectedly, many of the JH III-treated embryos with mosaic and precocious nymphal cuticles made a second nymphal cuticle and successfully hatched. JH treatment also affected the growth of the embryos. By focusing on the developing limb, we found that the effect of JH upon growth was asymmetric, with distal segments more affected than proximal ones, but this was not reflected in misexpression of Distal-less or Bric-a-brac, which are involved in proximal-distal patterning of the limb.

Knockout silkworms reveal a dispensable role for juvenile hormones in holometabolous life cycle

“…It has been shown that there are extensive differences in the roles of JHs during embryogenesis in holometabolous and hemimetabolous insects (27,29,46). Exogenous applications of JHs to the embryos of holometabolous insects elicit minor effects (27), whereas the application of JHs to the embryos of hemimetabolous (46) and ametabolous insects (47) has dramatic effects and disrupts normal embryogenesis.…”

“…Exogenous applications of JHs to the embryos of holometabolous insects elicit minor effects (27), whereas the application of JHs to the embryos of hemimetabolous (46) and ametabolous insects (47) has dramatic effects and disrupts normal embryogenesis. The knockout Bombyx lines generated in this study allowed us to test the effects of JH deprivation or JH signaling deprivation during the embryonic stages in lepidopteran insects.…”

The pupal specifier broad directs progressive morphogenesis in a direct-developing insect

“…In both crickets and milkweed bugs, br mRNA is present during the latter half of embryonic development (28). In these hemimetabolous embryos, this period is characterized by differential growth as the embryo progresses from the phylotypic germ band stage to a miniature version of the adult (27,29). In contrast, br mRNA is not present in the epidermis of holometabolous embryos (30), and the growth during the corresponding phase of embryogenesis is more isometric (31).…”

The hormonal and circadian basis for insect photoperiodic timing

“…In fact, the CC continues to release the adipokinetic hormone (AKH), which binds a G-coupled receptor and stimulates lipolysis, glycogenolysis and trehalose synthesis in the fat bodies, analogous to mammalian glucagon [16][17][18][19]. The CA maintains the secretion of Juvenile hormone (JH), a lipid-like hormone that modulates many developmental processes in insects, such as ovarian growth, imaginal disc proliferation, polyphenism (the process whereby different traits arise from environmental changes), diapause and metamorphosis [20][21][22][23][24][25][26][27][28][29][30].…”