Four isoforms of the Na؉ /H ؉ exchanger (NHE6 -NHE9) are distributed to intracellular compartments in human cells. They are localized to Golgi and post-Golgi endocytic compartments as follows: mid-to trans-Golgi, NHE8; trans-Golgi network, NHE7; early recycling endosomes, NHE6; and late recycling endosomes, NHE9. No significant localization of these NHEs was observed in lysosomes. The distribution of these NHEs is not discrete in the cells, and there is partial overlap with other isoforms, suggesting that the intracellular localization of the NHEs is established by the balance of transport in and out of the post-Golgi compartments as the dynamic membrane trafficking. The overexpression of NHE isoforms increased the luminal pH of the compartments in which the protein resided from the mildly acidic pH to the cytosolic pH, suggesting that their in vivo function is to regulate the pH and monovalent cation concentration in these organelles. We propose that the specific NHE isoforms contribute to the maintenance of the unique acidic pH values of the Golgi and post-Golgi compartments in the cell.The luminal ionic composition of intracellular compartments differs from the cytoplasm, and each compartment is characterized by a unique, organelle-specific ion concentration. This specific ionic composition is thought to be an important determinant for organelle function and is maintained by the concerted action of ion transport carriers on the membrane (1, 2). Organelles of the secretory and endocytic pathways exhibit differential weak acidity in their lumen with a gradient of pH values decreasing toward the trafficking destination, from ER 1 (pH ϳ7.1) to Golgi (pH ϳ6.2-7.0), trans-Golgi network (TGN) (pH ϳ6.0), and secretory granules (pH ϳ5.0) and from early and late endosomes (pH ϳ6.5) to lysosomes (pH ϳ4.5) (1, 3, 4). This progressive acidification is essential for compartmentalizing cellular events, such as post-translational modifications, sorting of newly synthesized proteins into the secretory pathway, and the degradation or recycling of internalized ligandreceptor complexes and fluid-phase solutes in the endocytic pathway (3, 5). Even pH differences of less than 0.5 between organelles can be essential for the compartmentalizing cellular events (6).The differential ionic milieu of the organelles is maintained by a suite of ion carriers on the membrane, including pumps, channels, and transporters. Luminal acidity is primarily generated by the vacuolar-type H ϩ -translocating ATPase (VATPase) (4, 5).

The kinesin superfamily protein, KIF1Bb, a splice variant of KIF1B, is involved in the transport of synaptic vesicles in neuronal cells, and is also expressed in various nonneuronal tissues. To elucidate the functions of KIF1Bb in non-neuronal cells, we analyzed the intracellular localization of KIF1Bb and characterized its isoform expression profile. In COS-7 cells, KIF1B colocalized with lysosomal markers and expression of a mutant form of KIF1Bb, lacking the motor domain, impaired the intracellular distribution of lysosomes. A novel isoform of the kinesin-like protein, KIF1Bb3, was identified in rat and simian kidney. It lacks the 5th exon of the KIF1Bb-specific tail region. Overexpression of KIF1Bb3 induced the translocation of lysosomes to the cell periphery. However, overexpression of KIF1Bb3-Q98L, which harbors a pathogenic mutation associated with a familial neuropathy, Charcot-Marie-Tooth disease type 2 A, resulted in the abnormal perinuclear clustering of lysosomes. These results indicate that KIF1Bb3 is involved in the translocation of lysosomes from perinuclear regions to the cell periphery.

Kinesin family proteins are microtubule-dependent molecular motors involved in the intracellular motile process. Using a Ca2+ -binding protein, CHP (calcineurin B homologous protein), as a bait for yeast two hybrid screening, we identified a novel kinesin-related protein, KIF1Bbeta2. KIF1Bbeta2 is a member of the KIF1 subfamily of kinesin-related proteins, and consists of an amino terminal KIF1B-type motor domain followed by a tail region highly similar to that of KIF1A. CHP binds to regions adjacent to the motor domains of KIF1Bbeta2 and KIF1B, but not to those of the other KIF1 family members, KIF1A and KIF1C. Immunostaining of neuronal cells showed that a significant portion of KIF1Bbeta2 is co-localized with synaptophysin, a marker protein for synaptic vesicles, but not with a mitochondria-staining dye. Subcellular fractionation analysis indicated the co-localization of KIF1Bbeta2 with synaptophysin. These results suggest that KIF1Bbeta2, a novel CHP-interacting molecular motor, mediates the transport of synaptic vesicles in neuronal cells.

Many parasitoids control the behavior of their hosts to achieve more preferable conditions. Decreasing predation pressure is a main aim of host manipulation. Some parasitoids control host behavior to escape from their enemies, whereas others manipulate hosts into constructing defensive structures as barriers against hyperparasitism. Larvae of the parasitoid wasp Cotesia glomerata form cocoon clusters after egression from the parasitized host caterpillar of the butterfly Pieris brassicae. After the egression of parasitoids, the perforated host caterpillar lives for a short period and constructs a silk web that covers the cocoon cluster. We examined whether these silk webs protect C. glomerata cocoons against the hyperparasitoid wasp Trichomalopsis apanteroctena. In cocoon clusters that were not covered by silk webs (''bare'' clusters), only cocoons hidden beneath others avoided hyperparasitism. In covered cocoon clusters, both cocoons hidden beneath others and those with a space between them and the silk web avoided hyperparasitism, whereas cocoons that contacted the silk webs were parasitized. The frequency of cocoons that were hidden beneath others increased with the increasing number of cocoons in a cluster, but the defensive effect of cluster size was thought to be lower than that of silk webs. However, the rate of hyperparasitism did not differ between covered and bare clusters when we allowed the hyperparasitoids to attack the cocoon clusters in an experimental arena. This result was thought to have been caused by low oviposition frequency by these hyperparasitoids. As a result, silk webs did not guard the cocoons from hyperparasitoids in our experiments, but would protect cocoons under high hyperparasitism pressure by forming a space through which the ovipositors could not reach the cocoons.

The introduction of a new species can change the characteristics of other species within a community. These changes may affect discontiguous trophic levels via adjacent trophic levels. The invasion of an exotic host species may provide the opportunity to observe the dynamics of changing interspecific interactions among parasitoids belonging to different trophic levels. The exotic large white butterfly Pieris brassicae invaded Hokkaido Island, Japan, and quickly spread throughout the island. Prior to the invasion, the small white butterfly P. rapae was the host of the primary parasitoid Cotesia glomerata, on which both the larval hyperparasitoid Baryscapus galactopus and the pupal hyperparasitoid Trichomalopsis apanteroctena depended. At the time of the invasion, C. glomerata generally laid eggs exclusively in P. rapae. During the five years following the invasion, however, the clutch size of C. glomerata in P. rapae gradually decreased, whereas the clutch size in P. brassicae increased. The field results corresponded well with laboratory experiments showing an increase in the rate of parasitism in P. brassicae. The host expansion of C. glomerata provided the two hyperparasitoids with an opportunity to choose between alternative hosts, that is, C. glomerata within P. brassicae and C. glomerata within P. rapae. Indeed, the pupal hyperparasitoid T. apanteroctena shifted its preference gradually to C. glomerata in P. brassicae, whereas the larval hyperparasitoid B. galactopus maintained a preference for C. glomerata in P. rapae. These changes in host preference may result from differential suitability of the two host types. The larval hyperparasitoid preferred C. glomerata within P. rapae to C. glomerata within P. brassicae, presumably because P. brassicae larvae attacked aggressively, thereby hindering the parasitization, whereas the pupal hyperparasitoid could take advantage of the competition-free resource by shifting its host preference. Consequently, the invasion of P. brassicae has changed the host use of the primary parasitoid C. glomerata and the pupal hyperparasitoid T. apanteroctena within a very short time.KEY WORDS: Cotesia glomerata (L.), host range evolution, hyperparasitoids, interspecific interactions, Pieris rapae crucivora (Boisduval), tri-trophic levels.