A pair-rule function of odd-skipped in germband stages of Tribolium development

Same rule, different genes: Blimp1 is a pair-rule gene in the milkweed bug Oncopeltus fasciatus

Morphological features of organismal body plans are often highly conserved within large taxa. For example, segmentation is a shared and defining feature of all insects. Screens in Drosophila identified genes responsible for the development of body segments, including the "pair-rule" genes (PRGs), which subdivide embryos into double-segment units in a previously unexpected pre-patterning step. Here we show that the milkweed bug Oncopeltus fasciatus also uses a pair rule for embryo subdivision but Oncopeltus employs different genes for this process. We identified the gene Blimp1 as an Oncopeltus PRG based on its expression pattern, tested its function with RNA interference and CRISPR-Cas9, and generated the first PR mutant in this species. Although it does not have PR function in Drosophila, like Drosophila PRGs, Blimp1 encodes a transcription factor required for embryonic viability. Thus, pair-rule subdivision of the insect body plan is more highly conserved than the factors mediating this process, suggesting a developmental constraint on this pre-patterning step.

The odd-skipped related gene drumstick is required for leg development in the beetle Tribolium castaneum

BACKGROUND

The evolutionarily conserved odd-skipped related genes odd-skipped (odd), drumstick (drm), sister of odd and bowel (sob), and brother-of-odd-with-entrails-limited (bwl) act downstream of the Notch pathway in various insect tissues including the appendages and the gut. While the function of some of these genes have been analyzed in the adult Tribolium beetle, the expression during and their requirement for embryonic development is not known.

RESULTS

We describe here the embryonic expression patterns of drm, sob, and bwl and analyze the RNAi knockdown phenotypes with emphasize on the appendages and the hindgut. We show that in Tribolium, drm acts independently of other odd-family members in the formation of legs, hindgut, and the dorsal epidermis. Moreover, we establish drm and sob as further markers for segment borders in the appendages that include the gnathobasic mandibles.

CONCLUSIONS

We conclude that the regulatory interrelationship among the odd genes differs between Tribolium and Drosophila, where odd and drm seem to act redundantly. In Tribolium, the genes drm and sob uncover the relict of a precoxal joint incorporated in the lateral body wall.