Caste‐specific microRNA expression in termites: insights into soldier differentiation

Abstract

Eusocial insects have polyphenic caste systems in which each caste exhibits characteristic morphology and behaviour. In insects, caste systems arose independently in different lineages, such as Isoptera and Hymenoptera. Although partial molecular mechanisms for the development of eusociality in termites have been clarified by the functional analysis of genes and hormones, the contribution of microRNAs (miRNAs) to caste differentiation is unknown. To understand the role of miRNAs in termite caste polyphenism, we performed small RNA sequencing in a subterranean termite (Reticulitermes speratus) and identified the miRNAs that were specifically expressed in the soldier and worker castes. Of the 550 miRNAs annotated in the R. speratus genome, 74 were conserved in insects and 174 were conserved in other termite species. We found that eight miRNAs (mir-1, mir-125, mir-133, mir-2765, mir-87a and three termite-specific miRNAs) are differentially expressed (DE) in soldiers and workers of R. speratus. This differential expression was experimentally verified for five miRNAs by real-time quantitative PCR. Further, four of the eight DE miRNAs in soldier and worker termite castes were also differentially expressed in hymenopteran castes. The finding that Isoptera and Hymenoptera shared several DE miRNAs amongst castes suggests that these miRNAs evolved independently in these phylogenetically distinct lineages.

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

“…In addition, regulatory mechanisms underlying the specific gene expressions in soldiers and in the course of soldier differentiation should also be revealed in future, although genomic methylations and histone modifications may play few roles in caste-specific gene expression (Harrison et al, 2018;see Suzuki, Yaguchi, & Maekawa, 2019). Another candidate for the regulatory mechanisms could be the machinery via microRNA, as previously suggested (Matsunami et al, 2019). Also, although there is accumulated information about the hormonal function and upstream and downstream pathways, the interaction between hormonal actions and the induced morphogenetic processes has not been fully understood.…”

10-hydroxy-2E-decenoic acid (10HDA) does not promote caste differentiation in Melipona scutellaris stingless bees

“…Extensive research demonstrates that many biological factors—such as pheromones, hormones and differentially expressed genes—are necessary to reach the regulatory complexity of caste differentiation 63 . Accordingly, we have shown that the expression of hdac1 presents an opposite profile from kat2a , and these patterns are temporally related to JH titers in larvae 53 .…”

10-hydroxy-2E-decenoic Acid (10HDA) is not a Caste-differentiation Factor in Melipona Scutellaris Stingless Bees

“…Extensive research demonstrates that many biological factorssuch as pheromones, hormones and differentially expressed genesare necessary to reach the regulatory complexity of caste differentiation [62] . Accordingly, we have shown that the expression of hdac1 presents an opposite profile from kat2a, and these patterns are temporally related to JH titers in larvae [53] .…”