Genetics, development and composition of the insect head--a beetle's view.

Many questions regarding evolution and ontogeny of the insect head remain open. Likewise, the genetic basis of insect head development is poorly understood. Recently, the investigation of gene expression data and the analysis of patterning gene function have revived interest in insect head development. Here, we argue that the red flour beetle Tribolium castaneum is a well suited model organism to spearhead research with respect to the genetic control of insect head development. We review recent molecular data and discuss its bearing on early development and morphogenesis of the head. We present a novel hypothesis on the ontogenetic origin of insect head sutures and review recent insights into the question on the origin of the labrum. Further, we argue that the study of developmental genes may identify the elusive anterior non-segmental region and present some evidence in favor of its existence. With respect to the question of evolution of patterning we show that the head Anlagen of the fruit fly Drosophila melanogaster and Tribolium differ considerably and we review profound differences of their genetic regulation. Finally, we discuss which insect model species might help us to answer the open questions concerning the genetic regulation of head development and its evolution.