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

Abstract

Although the expression of the POU homeodomain gene nubbin (nub) has been examined in several arthropod species, its function has been studied only in Drosophila. Here, we provide the first insight into functional roles of this gene in a hemimetabolous insect species, Oncopeltus fasciatus. The analysis of its function using RNAi resulted in the altered morphology of antennae and labial tubes in the head, legs in the thorax, and, most notably, the growth of ectopic appendages originating from abdominal segments A2-A6. This change in the morphology of the abdomen can largely be attributed to the altered expression patterns of two hox genes, Ubx and abd-A, in RNAinub embryos. First, abd-A expression is completely abolished in A3-A6. Second, weak Ubx expression expands posteriorly to encompass novel domains in A2 and A3. Concomitant with these changes, limbs on A2 and A3 are small and less developed, whereas limbs on A4-A6 are large thoracic-like legs. These results show that nub function is necessary for normal abd-A expression and thus plays a critical role in suppressing leg formation on the abdomen. The loss of this regulation leads to upregulation of Distal-less, and subsequent development of appendages. In Drosophila, however, abd-A expression is unaffected in a nub-depleted background, indicating that no such regulatory relationship exists between these two genes in the fruit fly. These differences reveal that variation exists in the genetic mechanisms that maintain an ancient insect feature, the limbless abdomen.

Extent With Modification: Leg Patterning in the BeetleTribolium castaneumand the Evolution of Serial Homologs

“…Data from other genes and taxa also suggest mixed support for the two hypotheses. For example, pdm / nubbbin has exceptionally labile expression (Li and Popadić 2004) and functional domains (Hrycaj et al 2008; Turchyn et al 2011) among insects, but there is some consistency across special homologs, as predicted by the independent model. More extensive comparative functional studies will be necessary in the future to evaluate the extent of developmental dependence among serial homologs, and to examine whether genes involved in certain developmental processes are more prone to divergence in limited or universal ways.…”

Anterior and posterior centers jointly regulate Bombyx embryo body segmentation

“…The gap gene candidates that were examined included Bm-ems (Bombyx empty spiracles) and Bm-kr. Bm-nub (Bombyx nubbin) was also examined because the orthologs of these genes appeared to show gap-like expression in the abdomen (Hrycaj et al, 2008). Of these, Bm-ems and Bm-nub was identified in this study (see Materials and methods).…”

Functional analysis of Scr during embryonic and post-embryonic development in the cockroach, Periplaneta americana

“…However, what is only now becoming evident is that there may be an extensive amount of lineage-specific variation in these networks. For example, a recent functional analysis of the paired-domain gene nubbin ( nub ) in the milkweed bug Oncopeltus fasciatus has shown that the limbless abdomen is established differently as compared to Drosophila (Hrycaj et al, 2008). In a similar fashion, functional studies of the homeotic gene Cephalothorax ( Cx ), an ortholog of Sex combs reduced ( Scr ), have shown that in the absence of this gene, an extra supernumerary segment forms between the labial and T1 segments in Tribolium (Shippy et al, 2006).…”