Genetic patterning in the adult capitate antenna of the beetle Tribolium castaneum

Abstract

Antenna structure varies widely among insects, in contrast to the well-conserved structure of legs. The adult capitate antenna of the red flour beetle, Tribolium castaneum, is composed of eleven articles, organized into four distinct morphological regions (scape, pedicel, funicle and club). Here, we report the use of RNA interference to examine the functions of 21 genes during antenna metamorphosis in T. castaneum. Genes with conserved functions relative to the developmental model species Drosophila melanogaster include Distal-less and EGF signaling (antennal growth), spineless (determination of antennal identity) and the Notch signaling pathway (antennal growth, joint formation, and sensory bristle development). However, the functions of many genes differed from those predicted from the Drosophila model. In addition to a conserved gap phenotype, depletion of dachshund transformed funicle articles toward club-like identity. Depletion of Distal-less or homothorax did not cause antenna-to-leg transformation. Lim1 was required only for development of the scape-pedicle joint. Depletion of odd-skipped-related genes led to the loss of the entire funicle, while spalt, rotund, spineless, and dachshund affected smaller regions. Growth and joint formation were linked developmentally in the funicle, but not in the club. Joint formation within the club required bric-a-brac, aristaless, apterous, and pdm. Gene functions are discussed in terms of a model of antenna development in T. castaneum. This model provides a contrast to knowledge of antenna development in D. melanogaster, insight into the likely ancestral mode of antenna development, and a framework for considering diverse antenna morphologies.

The function of appendage patterning genes in mandible development of the sexually dimorphic stag beetle

“…The developmental patterning of this proximal-distal axis in insect appendages is highly conserved and regulated by many genes (Kojima 2004, Angelini & Kaufman 2005. Based on previous studies of appendage morphogenesis in Drosophila and Tribolium (Lecuit & Cohen 1997, Kojima 2004, Angelini et al 2009, Angelini et al 2012, we focused on seven of these appendage-patterning genes, Distal-less (Dll), aristaless (al), Epidermal growth factor receptor (Egfr), Keren (Krn), dachshund (dac), homothorax (hth) and escargot (esg), as likely candidates for the regulation of mandible growth.…”

“…Mutation or experimental silencing of dac leads to the loss or reduction of medial regions in the antenna and leg in Drosophila, Tribolium, and Onthophagus (Mardon et al 1994, Angelini et al 2009, Moczek & Rose 2009. Two previous studies have also investigated dac function in adult beetle mandible development.…”

“…During embryonic and post-embryonic appendage development, hth is expressed proximally in the developing discs and if deleted the resulting phenotypes show defects in these regions of the appendage (Wu & Cohen 1999, Kojima 2004. The proximal selector role of hth is also conserved in other insects including Tribolium (Angelini et al 2009(Angelini et al , 2012. In mandibles of Onthophagus, Simmonet & Moczek (2011) revealed that hth expression is necessary for proper formation of the mandible molar.…”

“…6). Tribolium has a capitate antenna with 11 segments (Angelini et al 2009). The size of the scape (first segment) and pedicel (second segment) are similar to the flagellum segments (3rd to 11th segment) (Angelini et al 2009).…”

“…Tribolium has a capitate antenna with 11 segments (Angelini et al 2009). The size of the scape (first segment) and pedicel (second segment) are similar to the flagellum segments (3rd to 11th segment) (Angelini et al 2009). In contrast, Cyclommatus (and most other Lucanidae species as well (Ratcliffe 1991)) has a geniculate antenna with a long scape (proximal first segment) and relatively short pedicel/flagellum segments (2nd to 10th segments).…”