Mammals and insects employ similar Rel/NF-κB signaling cascades in their humoral immune responses.The mammalian interleukin-1 type I receptor (IL-1R) is one way of activating this cascade. The Drosophila Toll protein, whose cytoplasmic domain shows striking similarity to that of the IL-1R, acts in the humoral antimicrobial response. Here we demonstrate that a second IL-1R-related Drosophila protein, 18-Wheeler (18W), is a critical component of the humoral immune response. 18-wheeler is expressed in the larval fat body, the primary organ of antimicrobial peptide synthesis. In the absence of the 18W receptor, larvae are more susceptible to bacterial infection. Nuclear translocation of the Rel protein Dorsal-like immunity factor (Dif) is inhibited, though nuclear translocation of another Rel protein, Dorsal, is unaffected. Induction of several antibacterial genes is reduced following infection, relative to wild-type: attacin is reduced by 95%, cecropin by 65% and diptericin by 12%. Finally, 18-wheeler (18w) expression is induced in response to infection and, in addition to the receptor form, four immunespecific transcripts and proteins are produced.

The segmentation gene, giant, is located in 3A1 within a cloned chromosome region surrounding the zeste locus. Rearrangement breakpoints associated with giant mutations were localized on the genomic clone map, and nearby transcription units were identified. One transcription unit is active during early embryogenesis and its transcripts are spatially localized from blastoderm into extended germband stages, consistent with expected expression patterns predicted by the 'gap' phenotype of giant mutants. Germ line transformation experinents using a 10-kb DNA fragment containing this transcription unit gave complete rescue of the abdominal giant defect but only partial correction of the head defect. The effect of mutations in three other gap loci, Kr, kni and hb, were also analyzed. Key words: gap gene/head segmentation/in situ hybridization/ germ line transformation IntroductionThe segmental pattern of the larva of Drosophila melanogaster is under the control of several zygotically active genes. These genes can be divided into three classes, depending on the nature of the defects associated with mutations in a given gene (Niisslein-Volhard and Wieschaus, 1980 Baumgartner et al., 1987; wg, Baker, 1987) is expressed in 14 or more stripes during early gastrulation at intervals corresponding to every segment. In addition, analysis of larvae mosaic for one of various X-linked mutations (gt, runt, arm) revealed that these gene loci functioned primarily autonomously (although some local non-autonomy was observed; Gergen and Wieschaus, 1985), indicating that the gene function is required in those tissues fated to be affected by mutations in that locus. It was, therefore, expected that the giant gene would also be expressed only in those tissues that are affected by mutations of the giant locus.The giant locus is located in polytene band 3A1,2 and is included in a set of overlapping genomic clones isolated by Mariani et al. (1985) ventral portion of the cephalopharyngeal skeleton is extruded out of the anterior end of the larva. Larvae mutant for strong alleles (e.g. gtYA82, Figure lb and c) lack the labrum, epistomal sclerite, H-piece, hypostomal sclerite and dorsal bridge and retain in the pseudocephalon: cirri, ventral organ, antennal sense organ, maxillary sense organ (including the dorso-lateral and dorso-medial papillae), mouthhooks, the dorsal and ventral arms of the cephalopharyngeal skeleton, the ventral T-ribs and the hypopharyngeal organ. The lateralgraten are present but reduced and disorganized. Small, additional ectopic patches of naked cuticle, or cuticle covered with structures similar to dorsal hairs, can be found both dorsally and ventrally between the prothorax and the maxillary structures. Strong hypomorphic giant larvae also possess salivary glands, but these are attached to the exoskeleton at the anterior edge of the prothorax. Placement of the affected structures on the blastoderm fate map of Jurgens et al. (1986) reveals two regions of the anterior blastoderm fated to give rise to defective structu...

The Drosophila ovary is a model system for examining the genetic control of epithelial morphogenesis. The somatic follicle cells form a polarized epithelium surrounding the 16-cell germ line cyst. The integrity of this epithelium is essential for the successful completion of oogenesis. Reciprocal signaling between germ line and somatic cells establishes embryonic and eggshell polarity. The follicle cells are responsible for shaping the egg and secreting the eggshell. Follicle cells at the boundary between the nurse cells and the oocyte migrate centripetally to cover the anterior end of the oocyte and secrete the operculum. Dorsal anterior main body follicle cells undergo elaborate patterning to produce the dorsal appendages. We have examined the expression of the Toll-like receptor, 18-wheeler (18w), in the ovary and find it to be restricted to subpopulations of follicle cells. Females carrying loss-of-function 18w mutant clones in their ovaries show delayed follicle cell migrations. The eggs laid by such females also show morphological defects in egg shape and dorsal appendage morphology. We propose that the 18W protein plays an adhesive or signaling role in regions of the epithelium engaged in cell migration.

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Why do insects need immune defenses? They are so small and multiply so rapidly that it is understandable to think that, although infected individuals might die, the species could survive by sheer reproductive capacity. The fallacy of this reasoning is in the numbers. Under optimal conditions, bacteria double every 20 min or so, whereas even the rapidly maturing (and favorite model) insect, the fruit fly Drosophila melanogaster, requires close to 2 wk to reproduce. If insects were unable to fight off bacterial infections, they would never survive to reproductive maturity. Study of insect immunity has revealed striking similarities with human immunity, making insects-and Drosophila, in particular-useful model systems.