Social exploitation of hexamerin: RNAi reveals a major caste-regulatory factor in termites

Abstract

Lower termites express a unique form of eusocial polyphenism in that totipotent workers can differentiate into either soldier or reproductive caste phenotypes. In this initial effort using RNA interference in termites, we found that two hexamerin genes, Hex-1 and Hex-2, participate in the regulation of caste polyphenism. Our methodology involved a dual gene-silencing approach that used a single short-interfering RNA fragment to silence the two homologous hexamerin genes. We performed validation studies that evaluated effects on nontarget housekeeping genes, silencing of a nonhousekeeping control gene, and effects at the protein level. We found that the two hexamerin proteins, which are inducible by the morphogenetic juvenile hormone and which constitute a significant proportion of total termite protein, suppress juvenile-hormone-dependent worker differentiation to the soldier caste phenotype. This mechanism allows termite colonies to retain high proportions of altruistic worker caste members, thus apparently enhancing colony-inclusive fitness. These findings demonstrate a unique status quo regulatory mechanism for termite worker caste retention and provide an example of previously undescribed preadult developmental͞caste-regulatory genes from any social insect.sociogenomics ͉ RNA interference ͉ short-interfering RNA ͉ juvenile hormone ͉ phenotypic plasticity

Molecular traces of alternative social organization in a termite genome

“…Just as honey bees appear to utilize Vg to pace caste development via interactions with the endocrine system, termites may use hexamerins, P450s, and possibly Vg, as these families have gone through termite-specific gene duplication and are differentially expressed among castes. Evidence from other termites strongly indicates that hexamerins interact with JH and that a high expression of hexamerins, through interaction with JH, inhibits soldier development 53,54 . Vg may play a similar role, although this remains to be tested.…”

“…These latter two are involved in modulating soldier differentiation, probably by controlling JH availability 53 . Specifically, it has been proposed that hexamerins reduce JH availability in workers and nymphal stages, thereby inhibiting soldier development 54 . High hexamerin expression during these relatively plastic stages (Fig.…”

A diapause pathway underlies the gyne phenotype inPolisteswasps, revealing an evolutionary route to caste-containing insect societies

“…Elevated levels of a hexameric storage protein in gyne-destined individuals also can point to a causal basis for the diapause-derived characteristics of this class of offspring. Hexamerins were recently implicated in regulation of caste differentiation in termites, where binding of juvenile hormone to the hexameric molecule results in physiological silencing of hormone action (44). Diapause is characterized by low juvenile hormone levels (45), and application of a juvenile hormone analog can trigger P. metricus gynes to initiate ovarian development (46).…”

Pre-exposure ofGalleria mellonellalarvae to different doses ofAspergillus fumigatusconidia causes differential activation of cellular and humoral immune responses

“…25 The expression of the 32 kDa ferritin subunit (spot 3, gi:17901818, mass: 26.5 kDa score: 270, peptides matched: 7, coverage: 25%) was increased approximately 2.08-and 1.96-fold in the larvae that received 10 4 or 10 5 conidia (Figs. 5 and 6).…”