Lower termites of the genus Reticulitermes are social insects that show a dramatic polyphenism (the occurrence of multiple forms in a species on the basis of differential gene expression). This polyphenism is marked both in association with caste differentiation and between castes following differentiation, but the molecular mechanisms that underlie termite differentiation and development have been poorly understood. In the September 26 Genome Biology—published by BioMed Central, a sister company of The Scientist—Michael E. Scharf and colleagues at Purdue University show differential expression of 25 genes involved in regulatory, structural, and enzymatic processes involved in determining termite castes and their developmental precursor stages (Genome Biology, 4:R62, September 26, 2003).

Scharf et al. used cDNA macroarrays to compare gene expression between polyphenic castes and intermediary developmental stages in the termite R. flavipes. The authors observed worker and nymph-biased expression of transcripts encoding termite and endosymbiont cellulases; presoldier-biased expression of transcripts encoding the storage/hormone-binding protein vitellogenin; and soldier-biased expression of gene transcripts encoding two signal transduction factors, four cytoskeletal/muscle proteins, and two transcription/translation factors that are homologs of the Drosophila developmental genes bicaudal and bric-a-brac.

"Since our experiments examined a non-differentiated caste (worker) and a developmental end point (soldier), many key developmental genes were certainly not identified. If there is a master gene that regulates caste out there in termites, it likely awaits discovery," conclude the authors.