Functional characterization of a special dicistronic transcription unit encoding histone methyltransferase su(var)3-9 and translation regulator eIF2γ in Tribolium castaneum

Abstract

Operons are rare in eukaryotes, where they often allow concerted expression of functionally related genes. While a dicistronic transcription unit encoding two unrelated genes, the suppressor of position-effect variegation su(var)3-9 and the gamma subunit of eukaryotic translation initiation factor 2 (eIF2γ) has been found in insecta, and its significance is not well understood. Here, we analyzed the evolutionary history of this transcription unit in arthropods and its functions by using model Coleoptera insect Tribolium castaneum. In T. castaneum, Tcsu(var)3-9 fused into the 80 N-terminal amino acids of TceIF2γ, the transcription of these two genes are resolved by alternative splicing. Phylogenetic analysis supports the natural gene fusion of su(var)3-9 and eIF2γ occurred in the ancestral line of winged insects and silverfish, but with frequent re-fission during the evolution of insects. Functional analysis by using RNAi for these two genes revealed that gene fusion did not invoke novel functions for the gene products. As a histone methyltransferase, Tcsu(var)3-9 is primarily responsible for H3K9 di-, and tri-methylation and plays important roles in metamorphosis and embryogenesis in T. castaneum. While TceIF2γ plays essential roles in T. castaneum by positively regulating protein translation mediated ecdysteroid biosynthesis. The vulnerability of the gene fusion and totally different role of su(var)3-9 and eIF2γ in T. castaneum confirm this gene fusion is a non-selected, constructive neutral evolution event in insect. Moreover, the positive relationship between protein translation and ecdysteroid biosynthesis gives new insights into correlations between translation regulation and hormonal signaling.

Functional analysis of zona pellucida domain protein Dusky in Tribolium castaneum

“…The supernatant was dried and suspended with 0.2 mL methanol. The 20E titer was measured using a Xevo TQ‐XS benchtop tandem quadrupole mass spectrometer (Waters, Milford, MA, USA) (Song et al ., 2020) and analyzed as previously described (Hikiba et al ., 2013).…”

A novel GSTe2 involved in metamorphosis by regulating 20E signal pathway in Tribolium castaneum

“…Exogenous 20E treatment could partially rescue the metamorphosis deficiency due to inhibition of 20E pathway in Drosophila (Enya et al, 2014) and T. castaneum (Lin et al, 2018; Song, Pei, et al, 2020; Song, Zhong, et al, 2020). Similarly, our results showed that the molting rate of 20E injected group was higher than that of the control group (Figure 9a).…”