RNAi analysis of Deformed, proboscipedia and Sex combs reduced in the milkweed bug Oncopeltus fasciatus: novel roles for Hox genes in the Hemipteran head
Cl. Hughes et Tc. Kaufman, RNAi analysis of Deformed, proboscipedia and Sex combs reduced in the milkweed bug Oncopeltus fasciatus: novel roles for Hox genes in the Hemipteran head, DEVELOPMENT, 127(17), 2000, pp. 3683-3694
Insects have evolved a large variety of specialized feeding strategies, wit
h a corresponding variability in mouthpart morphology, We have, however, li
ttle understanding of the developmental mechanisms that underlie this diver
sity. Until recently it was difficult to perform any analysis of gene funct
ion outside of the genetic model insects Drosophila melanogaster and Tribol
ium castaneum. In this paper, we report the use of dsRNA-mediated interfere
nce (RNAi) to dissect gene function in the development of the milkweed bug
Oncopeltus fasciatus, which has specialized suctorial mouthparts, The Hox g
enes Deformed (Dfd), proboscipedia (pb) and Sex combs reduced (Scr) have pr
eviously been shown to be expressed in the gnathal appendages of this speci
es. Strikingly, the milkweed bug was found to have an unusual expression pa
ttern of pb, Here, by analyzing single and combination RNAi depletions, we
find that Dfd, pb and Scr are used in the milkweed bug to specify the ident
ity of the mouthparts, The exact roles of the genes, however, are different
from what is known in the two genetic model insects. The maxillary appenda
ges in the bug are determined by the activities of the genes Dfd and Scr, r
ather than Dfd and pb as in the fly and beetle. The mandibular appendages a
re specified by Dfd, but their unique morphology in Oncopeltus suggests tha
t Dfd's target genes are different. As in flies and beetles, the labium is
specified by the combined activities of pb and Scr, but again, the function
of pb appears to be different. Additionally, the regulatory control of pb
by the other two genes seems to be different in the bug than in either of t
he other species. These novelties in Hox function, expression pattern and r
egulatory relationships may have been important for the evolution of the un
ique Hemipteran head.