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We analysed spatial patterns of expression of a lacZ reporter gene in the gut of Drosophila larvae that had been transformed with a P-element-lacZ vector to identify regional differences in gene expression. lacZ-positive epithelial cells formed distinct domains with discrete transverse and longitudinal boundaries along the gut tube. Boundaries were often found at sites at which morphological boundaries were not obvious. The gut epithelium was subdivided into 36 compartments by the boundaries. We refer to these novel compartments as "tissue compartments". The lacZ-positive domain of each strain appeared as a single tissue compartment or as a combination of several tissue compartments. The tissue compartment is considered to be a unit of regional differentiation. The spatial organization of the tissue compartments may represent the "floor plan", determined by genes that control the regional differentiation of this nonsegmental organ.

A phylogenetic analysis of the sequences of 60 clones of archaeal small-subunit rRNA genes amplified from the termiteReticulitermes speratus revealed that most of them (56 clones) clustered in the genus Methanobrevibacter. Three clones were classified in the order Thermoplasmales. TheMethanobrevibacter-related symbionts were detected by in situ hybridization analysis.

SSU rRNA genes of symbiotic methanogens in the hindgut of four lower Japanese termites and one Australian lower termite Mastotermes darwiniensis as well as a soil sample collected near a nest of Reticulitermes speratus were amplified, cloned and phylogenetically analyzed. Most of the clones found in the lower termites were of the genus Methanobrevibacter. The symbiotic methanogens in the Japanese termites and in the soil sample were related to each other. The clones obtained from M. darwiniensis grouped separately from the clones of Japanese termites. These results suggest that the methanogen community of lower termites reflects host locality rather than phylogeny.Key words: symbiosis, termite, methanogen, phylogeny, ThermoplasmaTermites harbor methanogenic archaea in the hindgut 9) , where methane is formed by the reduction of carbon-dioxide with hydrogen. Methanogens and acetogens in the termite hindgut play a role as a hydrogen-sink. The hydrogenconsuming process facilitates the anaerobic degradation of lignocellulose 14) . The microecology of the termite gut was recently reviewed 1) .A phylogenetic analysis of methanogens in the hindgut of the lower termite Reticulitermes speratus by Ohkuma et al. 11) found only one type of sequence in PCR clones. We have also analyzed symbiotic methanogens in the hindgut of R. speratus 15) . PCR clones of SSU rDNA sequences were grouped into three types. Type 1 clones were further classified into subtypes 1A, 1B, 1C and 1D. Most of the PCR clones of methanogen in R. speratus collected around the Japan Archipelago belonged to subtypes 1A and 1B in the genus Methanobrevibacter. Fluorescence in situ hybridization analysis showed that at least some of the type 1 species live on the hindgut epithelial surface. Ohkuma et al. 10,12) have reported two other types of sequences, Cd30 and MHj4, from Cryptotermes domesticus and Hodotermopsis sjostedti, respectively. Leadbetter et al. 5,6) have isolated three species of Methanobrevibacter, M. curvatus, M. cuticularis, and M. filiformis from R. flavipes. In the present study, we examined the molecular phylogeny of symbiotic methanogens of five species that belong to four families of lower termites. Phylogenetic relationships between methanogens and host termites were also discussed.Four lower termite species of three families, Neotermes koshunensis, Hodotermopsis sjostedti, Reticulitermes kanmonensis, and Coptotermes formosanus, were collected in the Japan Archipelago. Sampling points of the Japanese termites are listed in Table 1. Another lower termite Mastotermes darwiniensis was collected in Australia and kindly donated by Dr. O. Kitade. Ten individuals of pseudergate (worker) from each colony of termite were employed for DNA extraction. Total genomic DNA of the digestive tracts of the termites was prepared as described previously 15) . PCR primers and reaction conditions were also described in a previous report 15) . The primers used were ME855F and ME1354R, which were designed to se-