Dissecting the Isoform-Specific Roles of FTZ-F1 in the Larval–Larval and Larval–Pupal Ecdyses in Henosepilachna vigintioctopunctata

MicroRNA miR-7-5p targets MARK2 to control metamorphosis in Galeruca daurica

The MARK2 gene, coding microtubule affinity-regulating kinase or serine/threonine protein kinase, is an important modulator in organism microtubule generation and cell polarity. However, its role in the metamorphosis of insects remains unknown. In this study, we found a conserved miRNA, miR-7-5p, which targets MARK2 to participate in the regulation of the larval-pupal metamorphosis in Galeruca daurica. The dual luciferase reporter assay showed that miR-7-5p interacted with the 3' UTR of MARK2 and repressed its expression. The expression profiling of miR-7-5p and MARK2 displayed an opposite trend during the larval-adult development process. In in-vivo experiments, overexpression of miR-7-5p by injecting miR-7-5p agomir in the final instar larvae down-regulated MARK2 and up-regulated main ecdysone signaling pathway genes including E74, E75, ECR, FTZ-F1 and HR3, which was similar to the results from knockdown of MARK2 by RNAi. In contrast, repression of miR-7-5p by injecting miR-7-5p antagomir obtained opposite effects. Notably, both overexpression and repression of miR-7-5p in the final instar larvae caused abnormal molting and high mortality during the larval-pupal transition, and high mortality during the pupal-adult transition. The 20-hydroxyecdysone (20E) injection experiment showed that 20E up-regulated miR-7-5p whereas down-regulated MARK2. This study reveals that the accurate regulation of miRNAs and their target genes is indispensable for insect metamorphosis.

A critical role for the nuclear protein Akirin in larval development in Henosepilachna vigintioctopunctata

Akirin is a nuclear protein that controls development in vertebrates and invertebrates. The function of Akirin has not been assessed in any Coleopteran insects. We found that high levels of akirin transcripts in Henosepilachna vigintioctopunctata, a serious Coleopteran potato defoliator (hereafter Hvakirin), were present at prepupal, pupal and adult stages, especially in larval foregut and fat body. RNA interference (RNAi) targeting Hvakirin impaired larval development. The Hvakirin RNAi larvae arrested development at the final larval instar stage. They remained as stunted larvae, gradually blackened and finally died. Moreover, the remodelling of gut and fat body was inhibited in the Hvakirin depleted larvae. Two layers of cuticles, old and newly formed, were noted in the dsegfp-injected animals. In contrast, only a layer of cuticle was found in the dsakirin-injected beetles, indicating the arrest of larval development. Furthermore, the expression of three transforming growth factor-β cascade genes (Hvsmox, Hvmyo and Hvbabo), a 20-hydroxyecdysone (20E) receptor gene (HvEcR) and six 20E response genes (HvHR3, HvHR4, HvE75, HvBrC, HvE93 and Hvftz-f1) was significantly repressed, consistent with decreased 20E signalling. Conversely, the transcription of a juvenile hormone (JH) biosynthesis gene (Hvjhamt), a JH receptor gene (HvMet) and two JH response genes (HvKr-h1 and HvHairy) was greatly enhanced. Our findings suggest a critical role of Akirin in larval development in H. vigintioctopunctata.

Molecular characterization of the cytochrome P450 enzyme CYP18A1 in Henosepilachna vigintioctopunctata

In insects, the expression of 20E response genes that initiate metamorphosis is triggered by a pulse of 20-hydroxyecdysone (20E). The 20E pulse is generated through two processes: synthesis, which increases its level, and inactivation, which decreases its titer. CYP18A1 functions as an ecdysteroid 26-hydroxylase and plays a role in 20E removal in several representative insects. However, applying 20E degradation activity of CYP18A1 to other insects remains a significant challenge. In this study, we discovered high levels of Hvcyp18a1 during the larval and late pupal stages, particularly in the larval epidermis and fat body of Henosepilachna vigintioctopunctata, a damaging Coleopteran pest of potatoes. RNA interference (RNAi) targeting Hvcyp18a1 disrupted the pupation. Approximately 75% of the Hvcyp18a1 RNAi larvae experienced developmental arrest and remained as stunted prepupae. Subsequently, they gradually turned black and eventually died. Among the Hvcyp18a1-depleted animals that successfully pupated, around half became malformed pupae with swollen elytra and hindwings. The emerged adults from these deformed pupae appeared misshapen, with shriveled elytra and hindwings, and were wrapped in the pupal exuviae. Furthermore, RNAi of Hvcyp18a1 increased the expression of a 20E receptor gene (HvEcR) and four 20E response transcripts (HvE75, HvHR3, HvBrC, and HvαFTZ-F1), while decreased the transcription of HvβFTZ-F1. Our findings confirm the vital role of CYP18A1 in the pupation, potentially involved in the degradation of 20E in H. vigintioctopunctata.

Nuclear Receptor FTZ-F1 Controls Locust Molt by Regulating the Molting Process of Locusta migratoria

Fushi-tarazu factor 1 (FTZ-F1) is a class of transcription factors belonging to the nuclear receptor superfamily and an important molting regulator in insects; however, its detailed function in the molting process of Locusta migratoria is still unclear. This study identified two FTZ-F1 transcripts (LmFTZ-F1-X1 and LmFTZ-F1-X2) in L. migratoria. The classical domains of FTZ-F1 were present in their protein sequences and distinguished based on their variable N-terminal domains. Reverse-transcription quantitative polymerase chain reaction analysis revealed that LmFTZ-F1-X1 and LmFTZ-F1-X2 were highly expressed in the integument. RNA interference (RNAi) was used to explore the function of LmFTZ-F1s in the molting of the third-instar nymph. Separate LmFTZ-F1-X1 or LmFTZ-F1-X2 silencing did not affect the normal development of third-instar nymphs; however, the simultaneous RNAi of LmFTZ-F1-X1 and LmFTZ-F1-X2 caused the nymphs to be trapped in the third instar stage and finally die. Furthermore, the hematoxylin-eosin and chitin staining of the cuticle showed that the new cuticles were thickened after silencing the LmFTZ-F1s compared to the controls. RNA-seq analysis showed that genes encoding four cuticle proteins, two chitin synthesis enzymes, and cytochrome P450 303a1 were differentially expressed between dsGFP- and dsLmFTZ-F1s-injected groups. Taken together, LmFTZ-F1-X1 and LmFTZ-F1-X2 are involved in the ecdysis of locusts, possibly by regulating the expression of genes involved in cuticle formation, chitin synthesis, and other key molting processes.

Dual function of the transcription factor Ftz-f1 on oviposition in the cockroach Blattella germanica

The transcription factor Ftz-f1 has multiple functions in insect development in a spatial-temporal line. One of these roles is in the insect ovaries, specifically in the regulation of steroidogenic enzymes production. We studied the function of F in Blattella germanica oogenesis, as it shows two moments of high expression in ovaries: before the imaginal moult, and just before ovulation in the adult. Injecting dsftz-f1 into adult females, either just after the imaginal moult or just prior to choriogenesis, prevented oviposition, with differences between the two approaches. In 3-day-old adult females treated with dsftz-f1 just after the emergence, the expression of ftz-f1 was not modified, but the steroidogenic genes increased their expression. ftz-f1 transcript levels in the ovaries of 5-day-old dsftz-f1-treated females were significantly depleted, and the expression levels of the same steroidogenic genes began to decrease. These results suggest that Ftz-f1 regulates the expression of steroidogenic genes in B. germanica, with phm possibly being a key target. Ftz-f1 has a different temporal function in the cytoskeleton of follicular cells of the basal ovarian follicles. Early in the gonadotrophic cycle, Ftz-f1 promotes the expression of genes related to the cytoskeleton and muscle proteins, while at the end of the cycle it maintains the expression levels of these genes, thus ensuring correct ovulation.

Dusky-like Is Critical for Morphogenesis of the Cellular Protuberances and Formation of the Cuticle in Henosepilachna vigintioctopunctata

Dusky-like (Dyl) is a transmembrane protein containing a zona pellucida domain. Its physiological roles during metamorphosis have been well explored in Drosophila melanogaster and have also been documented in Tribolium castaneum. However, Dyl has undergone a functional shift between Diptera and Coleoptera insects. Further investigation of Dyl in other insects will be helpful to further clarify its function in insect growth and development. Henosepilachna vigintioctopunctata is an important Coleoptera that causes enormous economic losses in agriculture in China. In this study, we found that the expression of Hvdyl was detectable in embryos, larvae, prepupae, pupae, and adults. We knocked down Hvdyl in third- and fourth-instar larvae and pupae with RNA interference (RNAi). RNAi of Hvdyl mainly caused two phenotypic defects. Firstly, the growth of epidermal cellular protuberances was suppressed. Injection of dsdyl (double-stranded dusky-like RNA) at the third-instar larval stage truncated the scoli throughout the thorax and abdomen and shortened the setae on the head capsules and mouthparts of the fourth-instar larvae. Introduction of dsdyl at the third- and fourth-instar stages led to misshapen pupal setae. The setae were shortened or became black nodules. Treatment with dsdyl at the larval and pupal stages resulted in deformed adults with completely suppressed wing hairs. Moreover, the knockdown of Hvdyl at the third-instar stage caused deformed larval mouthparts at the fourth-instar period. As a result, foliage consumption was inhibited, and larval growth was slowed. The results indicate that Dyl is associated with the growth of cellular protuberances throughout development and with the formation of the cuticle in H. vigintioctopunctata.

Knockdown of Ecdysone-Induced Protein 93F Causes Abnormal Pupae and Adults in the Eggplant Lady Beetle

Ecdysone-induced protein 93F (E93) plays triple roles during post-embryonic development in insects whose juvenile instars are more than four. However, it only acts as a specifier of adult structures in Drosophila flies whose larval instars are fixed at three. In this study, we determined the functions of E93 in the eggplant lady beetle (Henosepilachna vigintioctopunctata), which has four larval instars. We uncovered that E93 was abundantly expressed at the prepupal and pupal stages. A precocious inhibition of the juvenile hormone signal by RNA interference (RNAi) of HvKr-h1 or HvHairy, two vital downstream developmental effectors, at the penultimate instar larval stage increased the expression of E93, Conversely, ingestion of JH by the third-instar larvae stimulated the expression of HvKr-h1 but repressed the transcription of either HvE93X1 or HvE93X2. However, disturbance of the JH signal neither drove premature metamorphosis nor caused supernumerary instars. In contrast, depletion of E93 at the third- and fourth-instar larval and prepupal stages severely impaired pupation and caused a larval-pupal mixed phenotype: pupal spines and larval scoli were simultaneously presented on the cuticle. RNAi of E93 at the pupal stage affected adult eclosion. When the beetles had suffered from a dsE93 injection at the fourth-instar larval and pupal stages, a few resultant adults emerged, with separated elytra, abnormally folded hindwings, a small body size and short appendages. Taken together, our results suggest the larval instars are fixed in H. vigintioctopunctata; E93 serves as a repressor of larval characters and a specifier of adult structures during the larval–pupal–adult transition.