We investigated the mode of migration of presumptive primordial germ cells (pPGC) in the endoderm cell mass of Xenopus embryos at stages 7-40. The molecules underlying the migration were also studied cytochemically and immunocytologically. By examining the relative positions of pPGC and somatic cells derived from the single, fluorescein-dextran lysine (FDL)-injected, germ plasm-bearing cells of stage 6 embryos, pPGC in embryos at stages 7-23 and those at stages later than 24 were assumed to passively and actively migrate in the endoderm cell mass, respectively. This assumption was supported by the observation that F-actin, essential for active cell migration, was recognized on pPGC of the latter stages, but never on those of the former ones. In addition, the molecule like CXC chemokine receptor 4 (CXCR4) found on directionally migrating PGC in mouse and zebrafish, probably Xenopus CXCR4 (xCXCR4), was detected on pPGC only at latter stages. Accordingly, F-actin and xCXCR4, and probably ␤ 1-integrin and collagen type IV, which are indispensable for the formation of F-actin, are thought to be involved in the active migration of pPGC in the endoderm cell mass.

Nucleocytoplasmic transport factors mediate various cellular processes, including nuclear transport, spindle assembly, and nuclear envelope/pore formation. In this paper, we identify the chromokinesin human kinesin-like DNA binding protein (hKid) as an import cargo of the importin-α/β transport pathway and determine its nuclear localization signals (NLSs). Upon the loss of its functional NLSs, hKid exhibited reduced interactions with the mitotic chromosomes of living cells. In digitonin-permeabilized mitotic cells, hKid was bound only to the spindle and not to the chromosomes themselves. Surprisingly, hKid bound to importin-α/β was efficiently targeted to mitotic chromosomes. The addition of Ran–guanosine diphosphate and an energy source, which generates Ran–guanosine triphosphate (GTP) locally at mitotic chromosomes, enhanced the importin-β–mediated chromosome loading of hKid. Our results indicate that the association of importin-β and -α with hKid triggers the initial targeting of hKid to mitotic chromosomes and that local Ran-GTP–mediated cargo release promotes the accumulation of hKid on chromosomes. Thus, this study demonstrates a novel nucleocytoplasmic transport factor–mediated mechanism for targeting proteins to mitotic chromosomes.

Genital mycoplasmas, including Ureaplasma spp., are among the smallest human pathogenic bacteria and are associated with preterm birth. Electron microscopic observation of U. parvum showed that these prokaryotes have a regular, spherical shape with a mean diameter of 146 nm. U. parvum was internalized into HeLa cells by clathrin‐mediated endocytosis and survived for at least 14 days around the perinuclear region. Intracellular U. parvum reached endosomes in HeLa cells labeled with EEA1, Rab7, and LAMP‐1 within 1 to 3 hr. After 3 hr of infection, U. parvum induced the cytosolic accumulation of galectin‐3 and was subsequently entrapped by the autophagy marker LC3. However, when using atg7 −/− MEF cells, autophagy was inadequate for the complete elimination of U. parvum in HeLa cells. U. parvum also colocalized with the recycling endosome marker Rab11. Furthermore, the exosomes purified from infected HeLa cell culture medium included U. parvum. In these purified exosomes ureaplasma lipoprotein multiple banded antigen, host cellular annexin A2, CD9, and CD63 were detected. This research has successfully shown that Ureaplasma spp. utilize the host cellular membrane compartments possibly to evade the host immune system.

The present results indicate that S1-1 contains multiple NLSs that act cooperatively. Among them, the OCRE is a hitherto unreported NLS. The nuclear localisation of S1-1 appears to be regulated under certain circumstances. We discuss these NLSs in relation to the biochemical processes they are involved in.

HighlightsExposing cells to nanosilver particles (AgNPs) immediately induces ROS.Smaller AgNPs induce mitochondrial ROS production.AgNP-induced mitochondrial ROS are independent of particle internalisation.