RNAi analysis of nubbin embryonic functions in a hemimetabolous insect, Oncopeltus fasciatus

AbstractInsects comprise more than a million species and many authors have attempted to explain this success by evolutionary innovations. A much overlooked evolutionary novelty of insects is the serosa, an extraembryonic epithelium around the yolk and embryo. We have shown previously that this epithelium provides innate immune protection to eggs of the beetle Tribolium castaneum. It remained elusive, however, whether this immune competence evolved in the Tribolium lineage or is ancestral to all insects. Here, we expand our studies to two hemimetabolous insects, the bug Oncopeltus fasciatus and the swarming grasshopper Locusta migratoria. For Oncopeltus, RNA sequencing reveals an extensive response upon infection, including the massive upregulation of antimicrobial peptides (AMPs). We demonstrate antimicrobial activity of these peptides using in vitro bacterial growth assays, and describe two novel AMP families called Serosins and Ovicins. For both insects, qPCRs show immune competence of the eggs when the serosa is present, and in situ hybridizations demonstrate that immune gene expression is localized in the serosa. This first evidence from hemimetabolous insect eggs suggests that immune competence is an ancestral property of the serosa. The evolutionary origin of the serosa with its immune function might have facilitated the spectacular radiation of the insects.

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Development of the Pre-Gnathal Segments of the Insect Head Indicates They Are Not Serial Homologues of Trunk Segments

10.1101/2020.09.16.299289 ◽

2020 ◽

Author(s):

Oren Lev ◽

Ariel D. Chipman

Keyword(s):

Fossil Record ◽

Developmental Differences ◽

Oncopeltus Fasciatus ◽

Arthropod Evolution ◽

Hemimetabolous Insect ◽

Segment Polarity ◽

And Function ◽

Trunk Segments ◽

The Way

AbstractThe three anterior-most segments in arthropods contain the ganglia that make up the arthropod brain. These segments, the pre-gnathal segments, are known to exhibit many developmental differences to other segments, believed to reflect their divergent morphology. We have analyzed the expression and function of the genes involved in the segment-polarity network in the pre-gnathal segments compared with the trunk segments in the hemimetabolous insect Oncopeltus fasciatus. We show that there are fundamental differences in the way the pre-gnathal segments are generated and patterned, relative to all other segments, and that these differences are general to all arthropods. We argue that given these differences, the pre-gnathal segments should not be considered serially homologous to trunk segments. This realization has important implications for our understanding of the evolution of the arthropod head. We suggest a novel scenario for arthropod head evolution that posits duplication of an ancestral single-segmented head into three descendent segments. This scenario is consistent with what we know of head evolution from the fossil record, and helps reconcile some of the debates about early arthropod evolution.

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Dynamic BMP signaling polarized by Toll patterns the dorsoventral axis in a hemimetabolous insect

eLife ◽

10.7554/elife.05502 ◽

2015 ◽

Vol 4 ◽

Cited By ~ 22

Author(s):

Lena Sachs ◽

Yen-Ta Chen ◽

Axel Drechsler ◽

Jeremy A Lynch ◽

Kristen A Panfilio ◽

...

Keyword(s):

Regulatory Networks ◽

Bmp Signaling ◽

Oncopeltus Fasciatus ◽

Axis Formation ◽

Dorsoventral Axis ◽

Toll Signaling ◽

Hemimetabolous Insect ◽

Gene Regulatory ◽

Insect Embryos ◽

Regulatory Properties

Toll-dependent patterning of the dorsoventral axis in Drosophila represents one of the best understood gene regulatory networks. However, its evolutionary origin has remained elusive. Outside the insects Toll is not known for a patterning function, but rather for a role in pathogen defense. Here, we show that in the milkweed bug Oncopeltus fasciatus, whose lineage split from Drosophila's more than 350 million years ago, Toll is only required to polarize a dynamic BMP signaling network. A theoretical model reveals that this network has self-regulatory properties and that shallow Toll signaling gradients are sufficient to initiate axis formation. Such gradients can account for the experimentally observed twinning of insect embryos upon egg fragmentation and might have evolved from a state of uniform Toll activity associated with protecting insect eggs against pathogens.

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Shifting roles of Drosophila pair-rule gene orthologs: segmental expression and function in the milkweed bug Oncopeltus fasciatus

10.1101/721217 ◽

2019 ◽

Author(s):

Katie Reding ◽

Mengyao Chen ◽

Yong Lu ◽

Alys M. Cheatle Jarvela ◽

Leslie Pick

Keyword(s):

Oncopeltus Fasciatus ◽

Regulatory Pathways ◽

Milkweed Bug ◽

Regulatory Circuits ◽

Hemimetabolous Insect ◽

Pair Rule Gene ◽

Summary Statement ◽

And Function ◽

Gene Orthologs ◽

Pair Rule

AbstractThe discovery of pair-rule genes (PRGs) in Drosophila revealed the existence of an underlying two-segment-wide prepattern directing embryogenesis. The milkweed bug Oncopeltus, a hemimetabolous insect, is a more representative arthropod: most of its segments form sequentially after gastrulation. Here we report the expression and function of orthologs of the complete set of nine Drosophila PRGs in Oncopeltus. Seven Of-PRG-orthologs are expressed in stripes in the primordia of every segment, rather than every-other segment, Of-runt is PR-like, and several are also expressed in the segment addition zone. RNAi-mediated knockdown of Of-odd-skipped, paired and sloppy-paired impacted all segments, with no indication of PR-like register. We confirm that Of-E75A is expressed in PR-like stripes, although it is not PR in Drosophila, demonstrating the existence of an underlying PR-like prepattern in Oncopeltus. These findings reveal that a switch occurred in regulatory circuits leading to segment formation: while several holometabolous insects are “Drosophila-like,” utilizing PRG-orthologs for PR-patterning, most Of-PRGs are expressed segmentally in Oncopeltus, a more basally-branching insect. Thus, an evolutionarily stable phenotype – segment formation – is directed by alternate regulatory pathways in diverse species.Summary StatementDespite the broad of conservation of segmentation in insects, the regulatory genes underlying this process in Drosophila have different roles in the hemipteran, Oncopeltus fasciatus.

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Development of the Pre-gnathal Segments in the Milkweed Bug Oncopeltus fasciatus Suggests They Are Not Serial Homologs of Trunk Segments

Frontiers in Cell and Developmental Biology ◽

10.3389/fcell.2021.695135 ◽

2021 ◽

Vol 9 ◽

Author(s):

Oren Lev ◽

Ariel D. Chipman

Keyword(s):

Rna Interference ◽

Gene Function ◽

Expression Patterns ◽

Developmental Differences ◽

Oncopeltus Fasciatus ◽

Segment Polarity Genes ◽

Hemimetabolous Insect ◽

Segment Polarity ◽

And Function ◽

Trunk Segments

The three anterior-most segments in arthropods contain the ganglia that make up the arthropod brain. These segments, the pre-gnathal segments (PGS), are known to exhibit many developmental differences to other segments, believed to reflect their divergent morphology. We have analyzed the expression and function of the genes involved in the conserved segment-polarity network, including genes from the Wnt and Hedgehog pathways, in the PGS, compared with the trunk segments, in the hemimetabolous insect Oncopeltus fasciatus. Gene function was tested by manipulating expression through RNA interference against components of the two pathways. We show that there are fundamental differences in the expression patterns of the segment polarity genes, in the timing of their expression and in the interactions among them in the process of pre-gnathal segment generation, relative to all other segments. We argue that given these differences, the PGS should not be considered serially homologous to trunk segments. This realization raises important questions about the differing evolutionary ancestry of different regions of the arthropod head.

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