A Crucial Caste Regulation Gene Detected by Comparing Termites and Sister Group Cockroaches

Abstract

Sterile castes are a defining criterion of eusociality; investigating their evolutionary origins can critically advance theory. In termites, the soldier caste is regarded as the first acquired permanently sterile caste. Previous studies showed that juvenile hormone (JH) is the primary factor inducing soldier differentiation, and treatment of workers with artificial JH can generate presoldier differentiation. It follows that a shift from a typical hemimetabolous JH response might be required for soldier formation during the course of termite evolution within the cockroach clade. To address this possibility, analysis of the role of JH and its signaling pathway was performed in the termite and compared with the wood roach, a member of the sister group of termites. Treatment with a JH analog (JHA) induced a nymphal molt in RNA interference (RNAi) of JH receptor () was then performed, and it inhibited the presoldier molt in and the nymphal molt in Knockdown of in both species inhibited expression of 20-hydroxyecdysone (20E; the active form of ecdysone) synthesis genes. However, in, several 20E signaling genes were specifically inhibited by RNAi. Consequently, RNAi of these genes were performed in JHA-treated termite individuals. Knockdown of 20E signaling and nuclear receptor gene, (/) resulted in newly molted individuals with normal worker phenotypes. This is the first report of the JH-Met signaling feature in termites and JH-dependent molting activation is shared by both taxa and mediation between JH receptor and 20E signalings for soldier morphogenesis is specific to termites.

Evolutionary transition of doublesex regulation in termites and cockroaches: from sex-specific splicing to male-specific transcription

“…25°C in constant darkness. Three families of C. punctulatus were collected at Mountain Lake Biological Station, Giles County, VA in April 2015-2017 38 and kept at 15°C in constant darkness. Testes and ovaries were dissected from three males and three females, respectively, and stored at −80°C until RNA extraction for subcloning and expression analyses of Cpun_dsx .…”

“…AB520714), GstD1 (gene id RS001168), EIF-1 (RS005199), and RPS18 (RS015150)] were evaluated using the GeNorm 47 and NormFinder 48 software (Table S4). For C. punctulatus and N. takasagoensis , according to previous studies 38,49 , three genes [ β-actin (nos. Cp_TR19468 and AB501107), NADH-dh (Cp_TR49774 and AB50119), and EF1-α (AFK49795 and AB501108)] were evaluated (Tables S5 and S6).…”

“…The “findMotifsGenome.pl” program was executed to search for Drosophila motif collections using the “-mcheck” option against the promoter of Rspe_dsx , which was the 1.0 kbp upstream region from its transcription start site. The nucleotide sequences of Drosophila transcription factors that were detected in their binding sites were subjected to a BlastX search for orthologues against the protein database of R. speratus 38 using BLAST+ (2.10.1) 51 . The expression levels of these orthologues were extracted from their transcriptome data 27 and statistically analysed using GLMs with gamma error distribution and log link function, as mentioned above.…”

The making of the defensive caste: Physiology, development, and evolution of the soldier differentiation in termites

“…The JH signaling that activates the imaginal development in cockroaches, that is, MEKRE93 pathway (Met-Krh1-E93), could work as a regulator of caste differentiation in termites (Korb & Belles, 2017). The knockdown of Krh1, however, did not affect the soldier differentiation in Z. nevadensis, suggesting that E93 cannot be downstream of Met at least during presoldier molt of this species (Masuoka, Toga, Nalepa, & Maekawa, 2018). Indeed, expression analyses on some JH pathway genes between queens and workers in three termite species with genome information (Z. nevadensis, Cryptotermes secundus, and Macrotermes natalensis), suggested that the JH signaling would be diversified among termite lineages, especially between lower (the first two) and higher (the third) termites (Jongepier et al, 2018).…”

“…Schematic diagram of the hormonal regulations leading to soldier differentiation in termites, focusing on crosstalks among signaling pathways, that is revealed in Zootermopsis nevadensis (Masuoka, Toga, et al, 2018; Masuoka, Yaguchi, et al, 2018). High JH levels in workers are required for soldier differentiation, through two molting events with specific morphogenesis, that is, weapon formation.…”