| African trypanosomiasis, a disease caused by protozoan parasites of the genus Trypanosoma, has made an epidemic comeback in sub-Saharan Africa. Untreated the disease is fatal, and without cheap, efficient drugs or a vaccine, disease intervention relies heavily on vector control. Development of new strategies requires an understanding of the molecular interaction that occurs between trypanosomes and the obligate insect vector, the tsetse fly (Diptera: Glossinidae). To facilitate these investigations, a gene discovery project was undertaken for the fat body, an organ involved in many facets of the fly's biology, including intermediary metabolism, systemic immunity, viviparous reproduction, and homeostasis. Sequencing of a normalized cDNA library constructed from the fat body of immune-stimulated Glossina morsitans morsitans generated an EST database. In parallel, a subset of this library was printed onto nylon filters, which were used in a macroarray hybridization assay to identify transcripts differentially expressed during trypanosome infection. Macroarray analysis identified several genes of interest, including two iron-binding protein homologues, transferrin and ferritin, and the major milk gland protein. Patterns of expression for these three genes were determined in males and females, in pre-adult stages, in various tissues, and in trypanosome-infected adult tsetse. Transferrin transcripts were detected in female fat body only, although both male and female reproductive tissues exhibited abundant transcript levels. Transferrin expression was adult specific and increased in trypanosome-infected adults. Its association with reproductive tissues and up-regulation during trypanosome infection suggests a more specific role for transferrin in the protection of a developing larva from pathogens. In contrast, ferritin expression was ubiquitous in male and female tissues and in all developmental stages. This expression pattern suggests a more pervasive role for this protein in iron transport and storage. The major milk gland protein, a putative lipid transport molecule involved in the delivery of nutrients to the intrauterine larva, exhibited decreased transcript levels during trypanosome infection. Reduced transcript abundance may allow for diversion of resources towards other biological processes, specifically the insect's immune system. This work contributes to the continuing effort to uncover the molecular basis of the complex biological interactions that occur between tsetse and the invasive trypanosome. |
