Dusky works upstream of Four-jointed and Forked in wing morphogenesis in Tribolium castaneum

Arpc2 integrates ecdysone and juvenile hormone metabolism to influence metamorphosis and reproduction in Tribolium castaneum

BACKGROUND

Actin-related protein 2/3 complex regulates actin polymerization and the formation of branched actin networks. However, the function and evolutionary relationship of this complex subunit 2 (Arpc2) has been poorly understood in insects.

RESULTS

To address these issues, we performed comprehensive analysis of Arpc2 in Tribolium castaneum. Phylogenetic analysis revealed that Arpc2 was originated from one ancestral gene in animals but evolved independently between vertebrates and insects after species differentiation. T. castaneum Arpc2 has a 906-bp coding sequence and consists of 4 exons. Arpc2 transcripts were abundantly detected in embryos and pupae but less so in larvae and adults, while it had high expression in the gut, fat body and head but low expression in the epidermis of late-stage larvae. Knockdown of it at the late larval stage inhibited the pupation and resulted in arrested larvae. Silencing it in 1-day pupae impaired eclosion, which caused adult wings to fail to close. Injection of Arpc2 dsRNAs into 5-day pupae made adults have smaller testis and ovary and could not lay eggs. The expression of vitellogenin 1 (Vg1), Vg2 and Vg receptor (VgR) was downregulated after knocking down Arpc2 5 days post-adult emergence. Arpc2 silencing reduced 20-hydroxyecdysone titer by affecting the enzymes of its biosynthesis and catabolism but increased juvenile biosynthesis via upregulating JHAMT3 expression.

CONCLUSION

Our results indicate that Arpc2 is associated with the metamorphosis and reproduction by integrating ecdysone and juvenile hormone metabolism in T. castaneum. This study provides theoretical basis for developing Arpc2 as a potential RNA interference target for pest control. © 2024 Society of Chemical Industry.

The zona pellucida protein piopio regulates the metamorphosis and reproduction in Tribolium castaneum

The zona pellucida domain protein piopio (Pio) was only reported to mediate the adhesion of the apical epithelial surface and the overlying apical extracellular matrix in Drosophila melanogaster, but the developmental roles of Pio were poorly understood in insects. To address this issue, we comprehensively analyzed the function of Pio in Tribolium castaneum. Phylogenetic analysis indicated that pio exhibited one-to-one orthologous relationship among insects. T. castaneum pio had a 1236-bp ORF and contained eight exons. During development pio was abundantly expressed from larva to adult and lowly expressed at the late stage of embryo and adult, while it had more transcripts in the head, epidermis, and gut but fewer in the fat body of late-stage larvae. Knockdown of pio inhibited the pupation, eclosion, and reproduction of T. castaneum. The expression of vitellogenin 1 (Vg1), Vg2, and Vg receptor (VgR) largely decreased in pio-silenced female adults. Silencing pio increased the 20-hydroxyecdysone titer by upregulating phm and spo expression but decreased the juvenile hormone (JH) titer through downregulating JHAMT3 and promoting JHE, JHEH-r4, and JHDK transcription. These results suggested that Pio might regulate the metamorphosis and reproduction via modulating the ecdysone and JH metabolism in T. castaneum. This study found the novel roles of pio in insect metamorphosis and reproduction, and provided the new insights for analyzing other zona pellucida proteins functions in insects.

Eukaryotic initiation factor 6 modulates the metamorphosis and reproduction of Tribolium castaneum

Eukaryotic initiation factor 6 (eIF6) is necessary for ribosome biogenesis and translation, but eIF6 has been poorly elucidated in insects. Phylogenetic analysis demonstrated that eIF6 originated from one ancestral gene among animals and exhibited specific duplication in Tribolium, yielding three homologues in Tribolium castaneum, eIF6, eIF6-like 1 (eIF6l1), and eIF6-like 2 (eIF6l2). It was found that eIF6 was highly expressed in the embryonic and early adult stages, eIF6l1 had peak expression at the adult stage, and eIF6l2 showed peak expression in late adults of T. castaneum. Tissue-specific analyses in late-stage larvae demonstrated that eIF6 was abundantly expressed in all tissues, while eIF6l1 and eIF6l2 had the highest expression in the gut and the lowest expression in the head of T. castaneum. Knockdown of eIF6 caused precocious pupation and eclosion, impaired ovary and testis development and completely repressed egg production. The expression levels of vitellogenin 1 (Vg1), Vg2 and Vg receptor (VgR) significantly decreased in ds-eIF6 females 5 days post-adult emergence. Silencing eIF6 activated ecdysteroid biosynthesis and juvenile hormone degradation but reduced the activity of insulin signalling in T. castaneum, which might mediate its roles in metamorphosis, reproduction and gene expression regulation. However, silence of eIF6l1 or eIF6l2 had no effects on metamorphosis and reproduction in T. castaneum. This study provides comprehensive information for eIF6 evolution and function in the insect.

Lowfat functions downstream of Myo20 to regulate wing and leg morphogenesis in Tribolium castaneum

Myosin Myo20 plays vital roles in the morphogenesis of wings and legs among insects, but the function and signalling of Myo20 remain unclear. We show that Myo20 regulates wing cell division, ecdysteroid and amino acid metabolism, and gene expression in Tribolium castaneum. By RNA-seq, we identified 582 differentially expressed genes (DEGs) between control and ds-Myo20 larvae of T. castaneum. Of these DEGs, silencing Myo20 significantly decreased the mRNA and protein levels of lowfat. During development, lowfat has the highest expression in early pupae and the lowest level in 1-day embryos. Tissue-specific analysis indicated that lowfat was abundantly expressed in the head, fat body and epidermis of late-stage larvae and in wings and legs of 1, 2 and 5-day pupae. Likewise, knockdown of lowfat affected wing and leg morphogenesis, ecdysteroid and amino acid metabolism, and gene expression in T. castaneum. Silencing Myo20 or lowfat activated CYP18A1 to degrade ecdysteroids, stimulated amino acids catabolism to increase the transcription of 4E-BP but reduce S6K and cycE expression. These results suggest that Lowfat works downstream of Myo20 to employ target of rapamycin (TOR) signalling for wing and leg morphogenesis in insects.

Functional analysis of zona pellucida domain protein Dusky in Tribolium castaneum

The zona pellucida domain protein Dusky (Dy) plays a vital role in wing morphogenesis in insects, but little information on its function has been reported. In this study, we found that dy regulated wing cell size, larval and pupal duration, and the metabolism of amino acid and 20-hydroxyecdysone in Tribolium castaneum. Using RNA-seq, 413 differentially expressed genes were identified between physiological buffer-injected and dy-double-stranded RNA-treated larvae, including 88 downregulated genes and 325 upregulated genes. Among these genes, dy knockdown increased CYP18A1 expression to elevate the 26-hydroxylation of 20-hydroxyecdysone, which ultimately led to growth defects in wing cells. Silencing of dy upregulated the transcription of genes encoding tyrosine aminotransferase, 4-hydroxyphenylpyruvate dioxygenase, homogentisate 1, 2-dioxygenase, and Pale to promote the catabolism of tyrosine and phenylalanine, which eventually reduced amino acid content. Furthermore, dy knockdown upregulated 4E-BP expression, and 4E-BP silencing partially phenocopied dy RNA interference-mediated wing morphogenesis. These results suggest that Dy controls 20-hydroxyecdysone and amino acid metabolism to regulate wing morphogenesis in the insect.

Role of Chitin Deacetylase 1 in the Molting and Metamorphosis of the Cigarette Beetle Lasioderma serricorne

Chitin deacetylases (CDAs) are chitin-modifying enzymes known to play vital roles in insect metamorphosis and development. In this study, we identified and characterized a chitin deacetylase1 gene (LsCDA1) from the cigarette beetle Lasioderma serricorne. LsCDA1 contains a 1614 bp open reading frame encoding a protein of 537 amino acids that includes domain structures typical of CDAs. LsCDA1 was mainly expressed in the late larval and late pupal stages. In larval tissues, the highest level of LsCDA1 was detected in the integument. The expression of LsCDA1 was induced by 20-hydroxyecdysone (20E) in vivo, and it was significantly suppressed by knocking down the expression of ecdysteroidogenesis genes and 20E signaling genes. RNA interference (RNAi)-aided silencing of LsCDA1 in fifth-instar larvae prevented the larval–pupal molt and caused 75% larval mortality. In the late pupal stage, depletion of LsCDA1 resulted in the inhibition of pupal growth and wing abnormalities, and the expression levels of four wing development-related genes (LsDY, LsWG, LsVG, and LsAP) were dramatically decreased. Meanwhile, the chitin contents of LsCDA1 RNAi beetles were significantly reduced, and expressions of three chitin synthesis pathway genes (LsTRE1, LsUAP1, and LsCHS1) were greatly decreased. The results suggest that LsCDA1 is indispensable for larval–pupal and pupal–adult molts, and that it is a potential target for the RNAi-based control of L. serricorne.

Crinkled employs wingless pathway for wing development in Tribolium castaneum

Crinkled is associated with embryonic denticle formation and auditory organ development in Drosophila melanogaster. However, the functions of Crinkled have not been fully investigated. Additionally, the genes that participate in the Crinkled pathway are unknown. Phylogenetic analysis indicates that crinkled exhibits a one-to-one orthologous relationship in insects. In Tribolium castaneum, the crinkled gene is 6,498 bp in length and consists of six exons. Crinkled expression peaked during two phases in Tribolium: late embryonic and pupal stages. High levels of crinkled mRNA were detected in the fat body, head, epidermis, ovary, and accessory gland of late adults. Knockdown of crinkled using RNA interference (RNAi) severely affected wing morphogenesis in T. castaneum. We further showed that crinkled silencing reduced forked expression through wingless and shaven-baby, and RNAi of forked phenocopied the effects of crinkled knockdown in T. castaneum. This study investigated the development role of crinkled in postembryonic stages and indicated that forked mediates the functions of crinkled during wing morphogenesis in T. castaneum.