Abstract

Patterning of the anterior non-segmented part of the insect head

Nico Posnien, Sebastian Kittelmann, Johannes Schinko, Nikolaus Koniszewski, Georg Oberhofer, Gregor Bucher

The insect head is composed of several segments and anterior non-segmental tissue. While pattern formation of the segmented part of the body is well understood in Drosophila, patterning of the anterior non-segmental region remains enigmatic. We use the red flour beetle Tribolium castaneum as model for head development because of its insect typical non-involuted larval head.

In order to identify genes involved in anterior patterning, we systematically investigated expression and function of orthologs of vertebrate neural plate patterning genes in Tribolium. We find that most of them are expressed in the preocular part of the head in patterns similar to the neural plate. Further, most of them are required for head epidermis development. This approach has identified Tc-six3 as novel upstream regulator required for the development of the anterior most parts of the insect head. Specifically, Tc-six3 regulates Tc-otd1, Tc-ey/Pax6 and Tc-wg and upon RNAi, anterior median embryonic tissue including the labrum anlagen is lost. Further, neuroendocrine markers like Tc-chx and Tc-fas are missing in Tc-six3 RNAi embryos suggesting a role in neuroendocrine development like in vertebrates.

In addition, we find a second region in the non-segmental head, which is patterned by a different set of genes. It comprises an anterior median wedge shaped domain separating the head lobes and containing the anlagen of the labrum, and the mouth opening. This region is – in contrast to the preocular region mentioned above – largely non-neural. We find that Tc-six3, Tc-crocodile and Tc-cap´n´collar are the most upstream components of its patterning network.

While our candidate gene approach has been highly fruitful it will not identify a comprehensive set of insect head patterning genes. In order to gain such a comprehensive list, we screen for head defects in the genome wide RNAi screen “iBeetle” which is currently being carried out in Göttingen and Erlangen.