Functional Identification of Px-fringe and Px-engrailed Genes under Heat Stress in Chlorpyrifos-Resistant and -Susceptible Plutela xylostella (Lepidoptera: Plutellidae)

In our previous research, the fitness cost of resistance of the diamondback moth (DBM), Plutella xylostella found in insecticide-resistant DBM (Rc-DBM) under heat stress was based on heavier damage to wing veins when compared to insecticide-susceptible DBM (Sm-DBM). To investigate the molecular mechanism of the damage to the veins between Rc- and Sm-DBM, the full-length sequences of two related genes involved in the development of wing veins, fringe (Px-fng) and engrailed (Px-en) of DBM were cloned, and the mRNA expressions of both Px-fng and Px-en were studied. The Px-fng and Px-en cDNA contained 1038 bp and 1152 bp of open reading frames (ORFs), respectively, which encoded a putative protein comprising 345 and 383 amino acids with a calculated molecular weight of 39.59 kDa and 42.69 kDa. Significantly down regulated expressions of Px-fng and Px-en under heat stress were found in pupae and adults of Rc-DBM compared to Sm-DBM, and a result of higher damage to wing veins in Rc-DBM under heat stress. Based on RNAi experiments, significant inhibitions on expressions of Px-fng and Px-en in both Sm-DBM and Rc-DBM were found when the pupae were infected by dsFng or dsEn. Corresponding to these, infections of dsFng or dsEn resulted in significant decrease of eclosion rate and increase malformation rate of DBM. Our results suggest that the higher damage of wing veins in DBM might be related to the heavier inhibitions of Px-fng and Px-en expression, and the Px-fng and Px-en are involved in the development of wings and veins.

Parasegmental organization of the spider embryo implies that the parasegment is an evolutionary conserved entity in arthropod embryogenesis

Spiders belong to the chelicerates, which is a basal arthropod group. To shed more light on the evolution of the segmentation process, orthologs of the Drosophila segment polarity genes engrailed, wingless/Wnt and cubitus interruptus have been recovered from the spider Cupiennius salei. The spider has two engrailed genes. The expression of Cs-engrailed-1 is reminiscent of engrailed expression in insects and crustaceans, suggesting that this gene is regulated in a similar way. This is different for the second spider engrailed gene, Cs-engrailed-2, which is expressed at the posterior cap of the embryo from which stripes split off, suggesting a different mode of regulation. Nevertheless, the Cs-engrailed-2 stripes eventually define the same border as the Cs-engrailed-1 stripes. The spider wingless/Wnt genes are expressed in different patterns from their orthologs in insects and crustaceans. The Cs-wingless gene is expressed in iterated stripes just anterior to the engrailed stripes, but is not expressed in the most ventral region of the germ band. However, Cs-Wnt5-1 appears to act in this ventral region. Cs-wingless and Cs-Wnt5-1 together seem to perform the role of insect wingless. Although there are differences, the wingless/Wnt-expressing cells and en-expressing cells seem to define an important boundary that is conserved among arthropods. This boundary may match the parasegmental compartment boundary and is even visible morphologically in the spider embryo. An additional piece of evidence for a parasegmental organization comes from the expression domains of the Hox genes that are confined to the boundaries, as molecularly defined by the engrailed and wingless/Wnt genes. Parasegments, therefore, are presumably important functional units and conserved entities in arthropod development and form an ancestral character of arthropods. The lack of by engrailed and wingless/Wnt-defined boundaries in other segmented phyla does not support a common origin of segmentation.