Endocrine factors modulating vitellogenesis and oogenesis in insects: An update

Nocturnin promotes NADH and ATP production for juvenile hormone biosynthesis in adult insects

BACKGROUND

Juvenile hormone (JH) is a key endocrine governing insect development, metamorphosis and reproduction. JH analogs have offered great potential for insect pest control. In adulthood, JH titer rapidly increases in the previtellogenic period and reaches a peak in the vitellogenic phase. However, the regulatory mechanisms of JH biosynthesis in corpora allata (CA) of adult insects remain largely unknown.

RESULTS

We observed that the mitochondrial abundance, as well as the levels of NADH (nicotinamide adenine dinucleotide, reduced form) and adenosine triphosphate (ATP), increased in the CA of previtellogenic adults, peaking during the vitellogenic stage. The transcripts of Nocturnin (Noct), which converts nicotinamide adenine dinucleotide phosphate (NADPH) to NADH for ATP production, were more abundant in the CA compared to those of other enzymes involved in conventional NADH-producing metabolic pathways. The developmental expression pattern of Noct was like that of ATP and NADH level. RNA interference-mediated knockdown of Noct caused a significant decrease of NADH and ATP contents, along with markedly reduced expression levels of 12 genes involved in JH biosynthesis pathway. Loss of Noct function resulted in remarkably reduced expression of vitellogenin, accompanied by arrested ovarian growth and oocyte maturation.

CONCLUSION

Our results demonstrated that Noct plays a crucial role in high levels of JH biosynthesis in adult insects via regulating NADH and ATP production. The findings reveal a previously unknown aspect of mitochondrial metabolism in JH biosynthesis and provide valuable information for developing pest control strategies targeting hormone pathways. © 2025 Society of Chemical Industry.

Insect Mating Behaviors: A Review of the Regulatory Role of Neuropeptides

Insect mating behaviors are complex, diverse, and primarily regulated by neuropeptides and their receptors. Neuropeptides are peptide signaling molecules mainly secreted by insects' central nervous system (CNS) to reach target organs. A substantial body of research on the role of neuropeptides in regulating mating behaviors in insects has been undertaken. This review aims to (1) synthesize existing knowledge on insect mating behaviors, (2) elucidate the neuropeptidergic mechanisms governing these behaviors, and (3) identify knowledge gaps and propose future research directions. The mating process, covering mate attraction, courtship rituals, copulation, and post-mating behaviors, was elucidated with appropriate examples. Additionally, specific neuropeptides involved at each stage of the mating process, their functions, and mechanistic aspects were discussed as demonstrated in research. The review highlights that insects display behavioral dimorphism in the mating process driven by a complex underlying neuropeptidergic mechanism. While previous publications have generally addressed the role of neuropeptides in insect behavior, none has intensively and methodically examined their role in mating behaviors. In this review, we synthesized 18 neuropeptides that we found to regulate mating behaviors in insects. We note that some of the neuropeptides are malfunctional in their regulatory roles, while others are specific. We also note that these neuropeptides execute their regulatory functions through the G protein-coupled receptor (GPCR) signaling pathway but may take different routes and messengers downstream to effect behavioral change. Neuropeptides also interact with other regulatory systems, such as the endocrine system, to discharge their functions. Given their significance in mediating mating and reproduction, targeted manipulation of the signaling system of neuropeptides could serve as viable targets in the production of ecologically friendly pest management tools. Tools that could disrupt the mating process would be applied in crop production systems to reduce the population pressure of destructive pests, consequently reducing the urge to use chemical pesticides that are ecologically unfriendly. Our findings not only advance the understanding of neuropeptide-mediated mating regulation but also highlight their potential as eco-friendly pest control targets.

Functional characterization of vitellogenin unveils novel roles in RHBP uptake and lifespan regulation in the insect vector Rhodnius prolixus

In insects, vitellogenesis plays a critical role in providing the energy reserves needed for embryonic development as it ensures the accumulation of yolk in the oocytes. Vitellogenin (Vg), the precursor to vitellin (Vt), is primarily synthesized in the fat body of females and transported to the oocytes via receptor-mediated endocytosis. In Rhodnius prolixus, a key vector of Chagas disease, two Vg genes, Vg1 and Vg2, were characterized. These genes share 65 % amino acid identity and present the conserved Vitellogenin_N, DUF1943, and VWD domains typical of Vg proteins across various species. We found that Vg1 is expressed at significantly higher levels than Vg2 in adult females. Still, the expression of both isoforms was also detected in organs such as the flight muscle, midgut, and ovary, as well as in males and nymphs. RNAi-mediated knockdown of Vg1 and Vg2 in adult females resulted in the production of yolk-depleted eggs with drastically reduced levels of Vg and RHBP, the second most import yolk protein in this species. Despite regular oviposition rates, most of these eggs were inviable, highlighting the essential role of Vg and RHBP in embryo development. Although Vg expression was detected in adult males, the mating of Vg-knockdown males with wild-type females did not impact oviposition or egg viability, indicating that male Vg is not crucial for oogenesis in this species. Interestingly, Vg knockdown increased lifespan for both males and females, suggesting additional physiological functions beyond reproduction. These findings reveal the importance of Vg in oogenesis and embryonic development in R. prolixus while also suggesting potential non-reproductive roles of Vg in adult insect physiology.

CRISPR/Cas9-mediated vitellogenin receptor knockout impairs vitellogenin uptake and reproduction in Bactrocera dorsalis

BACKGROUND

Reproduction is a critical process in the insect life cycle, with the ovary serving as the central organ responsible for population maintenance. Successful development of the ovary is dependent on vitellogenin (Vg) transport into oocytes via the vitellogenin receptor (VgR). Exploring the VgR function is crucial for understanding the physiological mechanisms of insect ovarian development. However, the functional role of VgR in Bactrocera dorsalis (Hendel), a notorious agricultural invasive pest with exceptional reproductive plasticity, remains unclear.

RESULTS

Here, we identified BdVgR, an ovary-specific receptor with 1903 amino acids, as a critical determinant of reproductive success. CRISPR/Cas9-mediated BdVgR knockout resulted in a 211-bp genomic deletion spanning exonic (126 bp) and intronic (85 bp) regions, leading to near-complete loss of VgR expression in female adults. Functional analyses revealed that BdVgR deficiency disrupted ovarian Vg (Vg1/Vg2/Vg3) accumulation, impaired ovary maturation, and thus caused severe reproductive defects, including a decrease in the size of the ovaries by 49%, mating rates by 45%, egg production by 38%, and hatching rate by 22%.

CONCLUSION

Collectively, these findings indicate that BdVgR plays a key role in the reproductive process in B. dorsalis, and that disrupting VgR function can inhibit egg production, leading to sterility, which highlights the potential that targeting VgR via CRISPR can create genetically sterile females. Data are discussed with regard to integration of a sterile insect technique approach in the design of novel, efficient and safe pest management tactics. © 2025 Society of Chemical Industry.

Insect Flight and Lipid Metabolism: Beyond the Classic Knowledge

Insects are the most successful animal group by various ecological and evolutionary metrics, including species count, adaptation diversity, biomass, and environmental influence. This book delves into the underlying reasons behind insects' dominance on Earth. Lipids play pivotal roles in insect biology, serving as fuel for physiological processes, signaling molecules, and structural components of biomembranes and providing waterproofing against dehydration, among other functions. The study of insect flight has been instrumental in advancing our understanding of insect metabolism, with the migratory locust (Locusta migratoria) and the tobacco hornworm (Manduca sexta) serving as prominent models. Throughout the 1980s and 1990s, numerous studies shed light on the role of adipokinetic hormone (AKH), a crucial neuropeptide in lipid mobilization, to support the extraordinary energy demands of insect flight. Remarkably, AKH was the first identified peptide hormone in insects. These pioneering works linking lipids and flight laid the groundwork for subsequent research characterizing the physiological roles of other neuroendocrine factors in energy substrate mobilization across diverse insect species. However, in the omics era, one may be surprised by the limited understanding of the complex cascade of events governing lipid supply to insect flight muscles. Thus, this chapter aims to provide a concise overview of the evolutionary significance of insect flight, emphasizing key advancements that expand our classical knowledge in this field. Ultimately, we hope this chapter serves as a modest tribute to the pioneering researchers of one of the most captivating areas in insect biology, inspiring further exploration into the myriad roles of lipids in insect biology.

How Insects Balance Reproductive Output and Immune Investment

Insects face the constant challenge of balancing energy allocation between reproduction and immune responses, both of which are highly energy-demanding processes. Immune challenges frequently result in decreased fecundity, reduced egg viability, and delayed ovarian development. Conversely, heightened reproductive activity often suppresses immune functions. This trade-off has profound ecological and evolutionary consequences, shaping insects' survival, adaptation, and population dynamics. The intricate interplay between reproduction and immunity in insects is regulated by the neuroendocrine and endocrine systems, which orchestrate resource distribution alongside other biological processes. Key hormones, such as juvenile hormone and ecdysteroids, serve as central regulators, influencing both immune responses and reproductive activities. Additionally, macromolecules like vitellogenin and lipophorin, primarily known for their functions as yolk protein precursors and lipid carriers, play crucial roles in pathogen recognition and transgenerational immune priming. Advancements in molecular and omics tools have unveiled the complexity of these regulatory mechanisms, providing new insights into how insects dynamically allocate resources to optimize their fitness. This delicate balance underscores critical evolutionary strategies and the integration of physiological systems across species. This review synthesizes insights from life history theory, oogenesis, and immunity, offering new perspectives on the trade-offs between reproductive output and immune investment.

Evolution of insect metamorphosis - an update

Metamorphosis endowed the insects with properties that enabled them to conquer the Earth. It is a hormonally controlled morphogenetic process that transforms the larva into the adult. Metamorphosis appeared with the origin of wings and flight. The sesquiterpenoid juvenile hormone (JH) suppresses wing morphogenesis and ensures that metamorphosis takes place at the right ontogenetic time. This review explores the origin of insect metamorphosis and the ancestral function of JH. Fossil record shows that the first Paleozoic winged insects had (hemimetabolous) metamorphosis, and their larvae were likely aquatic. In the primitive wingless silverfish that lacks metamorphosis, JH is essential for late embryogenesis and reproduction. JH production after the embryo dorsal closure promotes hatching and terminal tissue maturation.

miR-276 and miR-182013-5p modulate insect metamorphosis and reproduction via dually regulating juvenile hormone acid methyltransferase

Juvenile hormone (JH) represses insect metamorphosis and stimulates reproduction. JH titers are generally low in juveniles, drop to a nadir during metamorphosis, increase after eclosion and peak in vitellogenic phase. We found that Jhamt, a rate-limiting enzyme in JH biosynthesis, mirrors JH titer patterns in the migratory locust. Knocking down Jhamt reduced JH titers, led to precocious nymphal ecdysis, metamorphosis and impaired vitellogenesis. Jhamt is negatively regulated by miR-276 and positively by miR-182013-5p. miR-276 is abundant in late nymphal but low in adults, while miR-182013-5p shows the opposite pattern. In nymphs, miR-276 binds more to Jhamt, while in adults, miR-182013-5p dominates. Functionally, miR-276 reduced Jhamt and JH levels, shortening nymphal development and inhibiting Vg expression. Conversely, miR-182013-5p increased Jhamt and JH levels, prolonging nymphal development and enhancing Vg expression. Our findings identify miR-276 and miR-182013-5p as dual regulators in JH biosynthesis, acting as "brake" and "accelerator," respectively. This study provides new insights into JH titer fluctuations and miRNA regulation in insect metamorphosis and reproduction.

Agonist-dependent action of the juvenile hormone receptor

Juvenile hormone (JH) signaling is realized at the gene regulatory level by receptors of the bHLH-PAS transcription factor family. The sesquiterpenoid hormones and their synthetic mimics are agonist ligands of a unique JH receptor (JHR) protein, methoprene-tolerant (MET). Upon binding an agonist to its PAS-B cavity, MET dissociates from a cytoplasmic chaperone complex including HSP83 and concomitantly switches to a bHLH-PAS partner taiman, forming a nuclear, transcriptionally active JHR heterodimer. This course of events resembles the vertebrate aryl hydrocarbon receptor (AHR), activated by a plethora of endogenous and synthetic compounds. Like in AHR, the pliable PAS-B cavity of MET adjusts to diverse ligands and binds them through similar mechanisms. Despite recent progress, we only begin to discern agonist-induced conformational shifts within the PAS-B domain, with the ultimate goal of understanding how these localized changes stimulate the assembly of the active JHR complex and, thus, fully grasp the mechanism of JHR signaling.

Autophagy and Female Fertility: Mechanisms, Clinical Implications, and Emerging Therapies

Autophagy, an evolutionarily conserved cellular mechanism essential for maintaining internal stability, plays a crucial function in female reproductive ability. In this review, we discuss the complex interplay between autophagy and several facets of female reproductive health, encompassing pregnancy, ovarian functions, gynecologic malignancies, endometriosis, and infertility. Existing research emphasizes the crucial significance of autophagy in embryo implantation, specifically in the endometrium, highlighting its necessity in ensuring proper fetal development. Although some knowledge has been gained, there is still a lack of research on the specific molecular impacts of autophagy on the quality of oocytes, the growth of follicles, and general reproductive health. Autophagy plays a role in the maturation, quality, and development of oocytes. It is also involved in reproductive aging, contributing to reductions in reproductive function that occur with age. This review explores the physiological functions of autophagy in the female reproductive system, its participation in reproductive toxicity, and its important connections with the endometrium and embryo. In addition, this study investigates the possibility of emerging treatment approaches that aim to modify autophagy, using both natural substances and synthetic molecules, to improve female fertility and reproductive outcomes. Additionally, this review intends to inspire future exploration into the intricate role of autophagy in female reproductive health by reviewing recent studies and pinpointing areas where current knowledge is lacking. Subsequent investigations should prioritize the conversion of these discoveries into practical uses in the medical field, which could potentially result in groundbreaking therapies for infertility and other difficulties related to reproduction. Therefore, gaining a comprehensive understanding of the many effects of autophagy on female fertility would not only further the field of reproductive biology but also open new possibilities for diagnostic and treatment methods.

Octopamine is required for successful reproduction in the classical insect model, Rhodnius prolixus

In insects, biogenic amines function as neurotransmitters, neuromodulators, and neurohormones, influencing various behaviors, including those related to reproduction such as response to sex pheromones, oogenesis, oviposition, courtship, and mating. Octopamine (OA), an analog of the vertebrate norepinephrine, is synthesized from the biogenic amine tyramine by the enzyme tyramine β-hydroxylase (TβH). Here, we investigate the mechanisms and target genes underlying the role of OA in successful reproduction in females of Rhodnius prolixus, a vector of Chagas disease, by downregulating TβH mRNA expression (thereby reducing OA content) using RNA interference (RNAi), and in vivo and ex vivo application of OA. Injection of females with dsTβH impairs successful reproduction at least in part, by decreasing the transcript expression of enzymes involved in juvenile hormone biosynthesis, the primary hormone for oogenesis in R. prolixus, thereby interfering with oogenesis, ovulation and oviposition. This study offers valuable insights into the involvement of OA for successful reproduction in R. prolixus females. Understanding the reproductive biology of R. prolixus is crucial in a medical context for controlling the spread of the disease.