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Many nuclear proteins are released into the cytoplasm at prometaphase and are transported back into the daughter nuclei at the end of mitosis. To determine the role of this reentry in nuclear remodelling during early interphase, we experimentally manipulated nuclear protein uptake in dividing cells. Recently we and others have shown that signal-dependent, pore complex-mediated uptake of nuclear protein is blocked in living cells on microinjection of the lectin wheat germ agglutinin (WGA), or of antibodies such as PI1 that are directed against WGA-binding pore complex glycoproteins. In the present study, we microinjected mitotic PtKz cells with WGA or antibody PIt and followed nuclear reorganization of the daughter cells by immunofluorescence and electron microscopy. The inhibitory effect on nuclear protein uptake was monitored by co-injection of the karyophilic protein nucleoplasmin. When injected by itself early in mitosis, nucleoplasmin became sequestered into the daughter nuclei as they entered telophase. In contrast, nucleoplasmin was excluded from the daughter nuclei in the presence of WGA or antibody PI1 . Although PtKz cells with blocked nuclear protein uptake completed cytokinesis, their nuclei showed a telophaselike organization characterized by highly condensed chromatin surrounded by a nuclear envelope containing a few pore complexes. These findings suggest that pore complexes become functional as early as telophase, in close coincidence with nuclear envelope reformation. They further indicate that the extensive structural rearrangement of the nucleus during the telophase-G1 transition is dependent on the influx of karyophilic proteins from the cytoplasm through the pore complexes, and is not due solely to chromosome- associated components.
PtK2 cells in which pore complex-mediated transport is blocked by microinjection early in mitosis of a monoclonal antibody (specific for an Mr 68000 pore complex glycoprotein) or of wheat germ agglutinin (WGA) complete cytokinesis. However, their nuclei remain stably arrested in a telophase-like organization characterized by highly condensed chromatin and the absence of nucleoli, indicating a requirement for pore-mediated transport for the reassembly of interphase nuclei. We have now examined this requirement more closely by monitoring the behavior of individual nuclear macromolecules in microinjected cells using immunofluorescence microscopy and have investigated the effect of microinjecting the antibody or WGA on cellular ultrastructure. The absence of nuclear transport did not affect the sequestration into daughter nuclei of components such as DNA, DNA topoisomerase I and the nucleolar protein fibrillarin that are carried through mitosis on chromosomes. On the other hand, lamins, snRNAs and the p68 pore complex glycoprotein, all cytoplasmic during mitosis, remained largely cytoplasmic in the telophase-arrested cells. Electron microscopy showed the nuclei to be surrounded by a doublelayered membrane with some inserted pore complexes. In addition, however, a variety of membranous structures with associated pore complexes was regularly noted in the cytoplasm, suggesting that chromatin may not be essential for the postmitotic formation of pore complexes. We propose that cellular compartmentalization at telophase is a two-step process. First, a nuclear envelope tightly encloses the condensed chromosomes, excluding non-selectively all macromolecules not associated with the chromosomes. Interphase nuclear organization is then progressively restored by selective pore complex-mediated uptake of nuclear proteins from the cytoplasm.
In the humid tropics of SE Asia there are some 14 myrmecophytic species of the pioneer tree genus Macaranga (Euphorbiaceae). In Peninsular Malaysia a close association exists between the trees and the small, non-stinging myrmicine Crema togas ter borneensis. These ants feed mainly on food bodies provided by the plants and have their colonies inside the hollow intemodes. In a ten months field study we were able to demonstrate for four Macaranga species (M. triloba, M. hypoleuca, M. hosei, M. hulletti) that host plants also benefit considerably from ant-occupation. Ants do not contribute to the nutrient demands of their host plant, they do, however, protect it against herbivores and plant competition. Cleaning behaviour of the ants results in the removal of potential herbivores already in their earliest developmental stages. Strong aggressiveness and a mass recruiting system enable the ants to defend the host plant against many herbivorous insects. This results in a significant decrease in leaf damage due to herbivores on ant-occupied compared to ant-free myrmecophytes as well as compared to non-myrmecophytic Macaranga species. Most important is the ants' defense of the host plant against plant competitors, especially vines, which are abundant in the well-lit pioneer habitats where Macaranga grows. Ants bite off any foreign plant part coming into contact with their host plant. Both ant-free myrmecophytes and non-myrmecophytic Macaranga species had a significantly higher incidence of vine growth than specimens with active ant colonies. This may be a factor of considerable importance allowing Macaranga plants to grow at sites of strongest competition.
A long-range restriction map of part of the short arm of ehromosome 11 including the WAGR region has been constructed using pulsed-field gel electrophoresis and a number of infrequently cutting restriction enzymes. A total of 15.4 Mbp has been mapped in detall, extending from proximal 11p14 to the distal part of 11p12. The map localizes 35 different DNA probes and reveals at least nine areas with features eharaeteristle of BTF islands, some of which may be candidates for the different loci underlying the phenotype of the WAGR syndrome. This map will furthermore allow screening of DNA from individuals with WAGR-related phenotypes and from Wilms tumors for associated chromosomal rearrangements.
Chromosome translocations involving llpl3 have been associated with familial aniridia in two kindreds highlighting the chromosomal localization of the AN2 locus. This locus is also part of the WAGR complex (Wilros tumor, aniridia, genitourinary abnormalities, and mental retardation). In one kindred, the translocation is associated with a deletion, and probes for this region were used to identify and clone the breakpoints of the translocation in the second kindred. Comparison of phage restriction maps exclude the presence of any sizable deletion in this case. Sequences at the chromosome 11 breakpoint are conserved in multiple species, suggesting that the translocation falls within the AN2 gene.
The WAGR (Wilms tumor, aniridia, genitourinary anomalies, and mental retardation) region has been assigned to chromosome 11p13 on the basis of overlapping constitutional deletions found in affected individuals. We have utilized 31 DNA probes which map to the WAGR deletion region, together with six reference loci and 13 WAGR-related deletions, to subdivide this area into 16 intervals. Specific intervals have been correlated with phenotypic features, leading to the identification of individual subregions for the aniridia and Wilms tumor loci. Delineation, by specific probes, of multiple intervals above and below the critical region and of five intervals within the overlap area provides a framework map for molecular characterization of WAGR gene loci and of deletion boundary regions.