The effect of manipulating ecdysteroid signaling on embryonic eye development in the locust Schistocerca americana

Matrix metalloproteinase 2 degrades collagen I to regulate ovarian development by association with an insulin-like peptide

The ovary generally undergoes tissue remodeling during larval to pupal transition, which includes membrane degeneration and ovariole growth. At the same time, the hormones produced by insects significantly change during metamorphosis. However, the regulatory mechanism for ovarian development and hormones is not fully understood in insects. Herein, we found that matrix metalloproteinase 2 (MMP2) was highly expressed in the ovarian capsules and ovarioles, and the development was abnormal after knocking out MMP2 in Bombyx mori. The process of abnormal degradation of collagen I due to MMP2 deletion, which resulted in abnormal development of ovarioles and eggs, was analyzed in detail. The proteomics of ovaries in the MMP2-knock out and wild type strains showed a critically significant difference in the expression of a protein, insulin-like peptide (ILP). Additional analysis revealed significant alteration of ILP during ovarian development, and abnormal expression of ILP significantly affected ovarian development in vivo and MMP2 expression in vitro and in vivo. These results showed that MMP2 regulation of ovarian tissue remodeling is closely related to ILP expression. Our study provides new insights into the regulatory mechanism of MMP2 and ovarian development in B. mori.

The cecropin-prophenoloxidase regulatory mechanism is a cross-species physiological function in mosquitoes

This study's aim was to investigate whether the cecropin-prophenoloxidase regulatory mechanism is a cross-species physiological function among mosquitoes. BLAST and phylogenetic analysis revealed that three mosquito cecropin Bs, namely Aedes albopictus cecropin B (Aalcec B), Armigeres subalbatus cecropin B2 (Ascec B2), and Culex quinquefasciatus cecropin B1 (Cqcec B1), play crucial roles in cuticle formation during pupal development via the regulation of prophenoloxidase 3 (PPO 3). The effects of cecropin B knockdown were rescued in a cross-species manner by injecting synthetic cecropin B peptide into pupae. Further investigations showed that these three cecropin B peptides bind to TTGG(A/C)A motifs within each of the PPO 3 DNA fragments obtained from these three mosquitoes. These results suggest that Aalcec B, Ascec B2, and Cqcec B1 each play an important role as a transcription factor in cuticle formation and that similar cecropin-prophenoloxidase regulatory mechanisms exist in multiple mosquito species.

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Cecropin B is able to regulate PPO 3 expression in the pupae

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Cecropin B binds to TTGG(A/C)A motifs within the PPO 3 DNA

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The knockdown of cecropin B was rescued by sequence-similar cecropin B peptides

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The cecropin B-prophenoloxidase 3 regulatory mechanism is conserved in mosquitoes

BmFoxO Gene Regulation of the Cell Cycle Induced by 20-Hydroxyecdysone in BmN-SWU1 Cells

Simple Summary

Ecdysteroid titer determines the state of the cell cycle in silkworm (Bombyx mori) metamorphosis. However, the mechanism of this process is unclear. In this study, we reported that 20-Hydroxyecdysone (20E) can promote BmFoxO (Bombyx mori Forkhead box protein O) gene expression and induce BmFoxO nuclear translocation in BmN-SWU1 cells. Overexpression of the BmFoxO gene affects cell cycle progression, which results in cell cycle arrest in the G0/G1 phase as well as inhibition of DNA replication. Further investigations showed that the effect of 20E was attenuated after BmFoxO gene knockdown. The findings of this study confirmed that BmFoxO is a key mediator in the cell cycle regulation pathway induced by 20E. This suggests a novel pathway for ecdysteroid-induced cell cycle regulation in the process of silkworm metamorphosis, and it is likely to be conserved between Lepidoptera insects.

Abstract

Ecdysteroid titer determines the state of the cell cycle in silkworm (Bombyxmori) metamorphosis. However, the mechanism of this process is unclear. In this study, we demonstrated that the BmFoxO gene participates in the regulation of the cell cycle induced by 20-Hydroxyecdysone (20E) in BmN-SWU1 cells. The 20E blocks the cell cycle in the G2/M phase through the ecdysone receptor (EcR) and inhibits DNA replication. The 20E can promote BmFoxO gene expression. Immunofluorescence and Western blot results indicated that 20E can induce BmFoxO nuclear translocation in BmN-SWU1 cells. Overexpression of the BmFoxO gene affects cell cycle progression, which results in cell cycle arrest in the G0/G1 phase as well as inhibition of DNA replication. Knockdown of the BmFoxO gene led to cell accumulation at the G2/M phase. The effect of 20E was attenuated after BmFoxO gene knockdown. These findings increase our understanding of the function of 20E in the regulation of the cell cycle in B. mori.

Ecdysone Receptor (EcR) and Ultraspiracle Protein (USP) Genes From Conopomorpha sinensis Bradley Eggs: Identification and Expression in Response to Insecticides

Conopomorpha sinensis Bradley (Lepidoptera: Gracilariidae) is the dominant insect pest of litchi (chinensis Sonn.) and longan (Euphoria longan Lour.) fruit trees. Management of this pest species is a challenging task due to its cryptic borer behavior. Controlling C. sinensis at the egg stage is the best alternative strategy to chemical control of C. sinensis adults. However, thorough studies regarding the indirect and sublethal effects of chemicals on the different developmental stages of C. sinensis are insufficient. In this study, the effect of some insecticides was evaluated on C. sinensis eggs. The ovicidal activity of chlorbenzuron, abamectin, chlorantraniliprole, and λ-cyhalothrin was confirmed by morphological observation of the defects in C. sinensis eggs. Moreover, we characterized four essential ecdysone receptor proteins in insects [i.e., two isoform ecdysone receptors (EcR: CsEcRA. CsEcRB) and two isoform ultraspiracle proteins (USP: CsUSP1, CsUSP2)] from C. sinensis eggs. The CsEcRA, CsEcRB, CsUSP1, and CsUSP2 genes consisted of 1521-, 1614-, 1410-, and 1236-bp open reading frames which encoded proteins of 506, 527, 469, and 413 amino acid residues, respectively. Furthermore, the embryonic differential responses of CsEcRs, CsUSPs, and vitellogenin receptor (VgR: CsVgR) to insecticides were evaluated by qRT-PCR. Among the five tested genes, CsVgR and CsUSP1 were the most sensitive to all the tested insecticides, with fold change of the expression diminished by 4.27–8.70 times compared with untreated control insects. The data suggests that these insecticidal compounds regulate the expression of these specific proteins, which might eventually lead to reduced viability of C. sinensis eggs. We present here the first data providing molecular elucidation of ecdysone receptor genes and their differential responses to insecticides in C. sinensis eggs. Together with our previous report of insecticide sublethal effects on two reproduction-related genes in C. sinensis adults, CsVgR and CsUSP1 seem to be appropriate molecular parameters for the evaluation of insecticide impact on C. sinensis. This study exemplifies the potential utility of transcriptional measurement of nuclear receptors as the molecular biomarkers for ecotoxicological evaluations of ovicidal impact of insecticides.

Drosophila as a developmental paradigm of regressive brain evolution: proof of principle in the visual system

Evolutionary developmental biology focuses heavily on the constructive evolution of body plan components, but there are many instances such as parasitism, cave adaptation, or postembryonic growth rate optimization where evolutionary regression is of adaptive value. This is particularly true in the nervous system because of its massive energy costs. However, comparatively little effort has thus far been made to understand the evolutionary developmental trajectories of adaptive nervous system reduction. This review focuses on the organization and evolution of the Drosophila larval brain, which represents an exceptional example of miniaturization, most dramatically in the visual system. It is specifically discussed how the dependency of outer optic lobe development on retinal innervation can be assumed to have facilitated a first evolutionary phase of larval visual system reduction. Afferent input-contingent development of neu- ral compartments very likely plays a widespread role in adaptive brain evolution. Understanding the complete deconstruction of the larval optic neuropiles in Drosophila awaits expanded comparative analysis but has the promise to inform about further developmental trajectories and mechanisms underlying regressive evolution of the brain.

Enforcing biphasic eye development in a directly developing insect by transient knockdown of single eye selector genes

The visual system of indirectly developing insects such as Drosophila passes through two phases of development. Larval eyes form in the embryo, whereas the adult compound eyes form during metamorphosis. Comparative evidence implies that this biphasic mode of visual system development evolved from the continuously developing eye of directly developing insects. We investigated the developmental basis of this evolutionary transformation in a directly developing insect taking advantage of the time-limited nature of systemic RNAi in the grasshopper Schistocerca americana. Transient knockdown of the homologs of the early retinal genes eyes absent (eya) or sine oculis (so) both induced long-term arrest of eye development in grasshopper nymphs. Eye development, however, resumed after knockdown expiry. This finding sheds first light on the molecular regulation of postembryonic eye development in directly developing insects and unravels an inherent capacity of the underlying gene regulatory network to accommodate for partitioning visual system development into discrete phases, as in indirectly developing insects.

Tracking down the "head blob": comparative analysis of wingless expression in the developing insect procephalon reveals progressive reduction of embryonic visual system patterning in higher insects

The evolution of larval head morphology in holometabolous insects is characterized by reduction of antennal appendages and the visual system components. Little insight has been gained into molecular developmental changes underlying this morphological diversification. Here we compare the expression of the segment polarity gene wingless (wg) in the pregnathal head of fruit fly, flour beetle and grasshopper embryos. We provide evidence that wg activity contributes to segment border formation, and, subsequently, the separation of the visual system and protocerebrum anlagen in the anterior procephalon. In directly developing insects like grasshopper, seven expression domains are formed during this process. The activation of four of these, which correspond to polar expression pairs in the optic lobe anlagen and the protocerebral ectoderm, has shifted to postembryonic stages in flour beetle and Drosophila. The remaining three domains map to the protocerebral neuroectoderm, and form by disintegration of a large precursor domain in flour beetle and grasshopper. In Drosophila, the precursor domain remains intact, constituting the previously described "head blob". These data document major changes in the expression of an early patterning gene correlated with the dramatic evolution of embryonic visual system development in the Holometabola.

Continuity versus split and reconstitution: exploring the molecular developmental corollaries of insect eye primordium evolution

Holometabolous insects like Drosophila proceed through two phases of visual system development. The embryonic phase generates simple eyes of the larva. The postembryonic phase produces the adult specific compound eyes during late larval development and pupation. In primitive insects, by contrast, eye development persists seemingly continuously from embryogenesis through the end of postembryogenesis. Comparative literature suggests that the evolutionary transition from continuous to biphasic eye development occurred via transient developmental arrest. This review investigates how the developmental arrest model relates to the gene networks regulating larval and adult eye development in Drosophila, and embryonic compound eye development in primitive insects. Consistent with the developmental arrest model, the available data suggest that the determination of the anlage of the rudimentary Drosophila larval eye is homologous to the embryonic specification of the juvenile compound eye in directly developing insects while the Drosophila compound eye primordium is evolutionarily related to the yet little studied stem cell based postembryonic eye primordium of primitive insects.

Comparative analysis of Wingless patterning in the embryonic grasshopper eye

The signaling factor Wingless regulates multiple steps during the postembryonic development of the Drosophila eye. To obtain insight into the molecular regulation of embryonic eye development in primitive insects, we studied the expression of wg and genes projected to interact with wg in the grasshopper Schistocerca americana. We find that the dynamic and complex expression of wg in the early grasshopper procephalon results in three paired expression domains with relevance to eye primordium development. By comparison with Drosophila, these domains are compatible with a conserved function of wg during anteroposterior and dorsoventral axis formation by repression of retinal differentiation and stimulation of tissue proliferation. This is further supported by the expression of grasshopper orthologs of the retina determination genes sine oculis and eyes absent, and by inhibition of retina differentiation in grasshopper eye primordia cultured with LiCl. Surprisingly, the expression of wg and the grasshopper orthologs of pannier, fringe, Delta, and Iroquois complex is inconsistent with induction of midline centered Notch signaling activity, which is essential for Drosophila retina development. Similarly substantial evolutionary divergence is found concerning the control of retina versus head epidermis specification. The transcription factor Extradenticle (Exd), which cooperates with wg in specifying the Drosophila head epidermis, is not detected outside the labral and antennal primordia in the embryonic grasshopper head. Our results, which provide the first insight into the molecular control of eye primordium formation in primitive insects, suggest substantial modification of this process during the evolution of the Drosophila mode of postembryonic eye development.