Most genes encoding cytoplasmic intermediate filament (IF) proteins of the nematode Caenorhabditis elegans are required in late embryogenesis

Intestinal cells of C. elegans show an unexpectedly high complexity of cytoplasmic intermediate filament (IF) proteins. Of the 11 known IF genes six are coexpressed in the intestine, i.e. genes B2, C1, C2, D1, D2, and E1. Specific antibodies and GFP-promoter constructs show that genes B2, D1, D2, and E1 are exclusively expressed in intestinal cells. Using RNA interference (RNAi) by microinjection at 25 degrees C rather than at 20 degrees C we observe for the first time lethal phenotypes for C1 and D2. RNAi at 25 degrees C also shows that the known A1 phenotype occurs already in the late embryo after microinjection and is also observed by feeding which was not the case at 20 degrees C. Thus, RNAi at 25 degrees C may also be useful for the future analysis of other nematode genes. Finally, we show that triple RNAi at 20 degrees C is necessary for the combinations B2, D1, E1 and B2, D1, D2 to obtain a phenotype. Together with earlier results on genes A1, A2, A3, B1, and C2 RNAi phenotypes are now established for all 11IF genes except for the A4 gene. RNAi phenotypes except for A2 (early larval lethality) and C2 (adult phenotype) relate to the late embryo. We conclude that in C. elegans cytoplasmic IFs are required for tissue integrity including late embryonic stages. This is in strong contrast to the mouse, where ablation of IF genes apparently does not affect the embryo proper.     

Identification of mouse chromosomes required for murine leukemia virus replication.

The replication patterns of five ecotropic and two amphotropic strains of murine leukemia virus (MuLV) were studied by infecting 41 Chinese hamster x mounse hybrid primary clones segregating mouse (Mus musculus) chromosomes. Ecotropic and amphotropic strains replicated in mouse and some hybrid cells, but not in hamster cells, indicating that replication of exogenous virus requires dominantly expressed mouse cellular genes. The patterns of replication of the five ecotropic strains in hybrid clones were similar; the patterns of replication of the two amphotropic strains were also similar. When compared to each other, however, the replication patterns of ecotropic and amphotropic viruses were dissimilar, indicating that these two classes of MuLV require different mouse chromosomes for replication. Chromosome and isozyme analyses assigned a gene, Rec-1 (replication of ecotropic virus), to mouse chromosome 5 that is necessary and may be sufficient for ecotropic virus replication. Because of preferential retention of mouse chromosomes 15 and 17 in the hybrid clones, however, the possibility that these chromosomes carry genes that are necessary but not sufficient for ecotropic virus replication cannot be excluded. Similarly, the data indicate that mouse chromosome 8 (or possibly 19) carried a gene we have designated Ram-1 (replication of amphotropic virus) which is necessary and may be sufficient for amphotropic virus replication. Because chromosomes 8 and 19 tended to segregate together and two of the three clones excluding 19 have chromosome reaggrangements, we cannot exclude 19 as being independent of amphotropic virus replication. In addition, because of preferential retention, chromosomes 7, 12, 15, 16 and 17 cannot be excluded as being necessary but not sufficient. Hybrid cell genetic studies confirm the assignment of the Fv-1 locus to chromosome 4 previously made by sexual genetics. In addition, our results demonstrate that hybrid cells which have segregated mouse chromosome 4 but have retained 5 become permissive for replication of both N and B tropic strains of MuLV.     

The Last Month of Szent-Györgyi in Groningen

Albert (von) Szent-Györgyi started his studies on biological oxidation processes – which also resulted in the discovery of vitamin C, for which he received the Nobel Price in 1937 – in the Laboratory of Physiology of the University in Groningen in 1922–1926. These studies were later continued in Cambridge (UK) and Szeged (Hungary). When he had already received the invitation as well as the financial means to come and work in Cambridge, he still did experiments in Groningen to find out whether the adrenal extract, isolated by him and later found to be a major source of vitamin C, contained the hormone essential for the survival of cats whose adrenals were removed. He was rather upset by the negative results of this experiment, judging by the recollections of a former student of his. This history constitutes an interesting example of the difference between serendipitous discovery and planned invention.     

Discriminating causes from consequences of persistent parrotfish corallivory

A detailed understanding of the dual role of parrotfish as both key herbivores and potentially important corallivores is essential to the study of coral health and reef trophodynamics. Some Caribbean parrotfish regularly consume live coral, and discriminate both among coral species and among colonies within a particular species. While they prefer Montastraea spp. corals, which are dominant Caribbean reef builders, causes of selective and persistent grazing of certain colonies remain unknown. We manipulated coral exposure to parrotfish grazing through a long-term cage exclusion experiment in Belize, comparing initially grazed vs. intact (non-grazed) Montastraea spp. colonies. We measured nutrition-related characteristics (C:N ratio, %C, and %N) as well as defensive characteristics (nematocyst density and skeletal hardness) to determine if any of these variables accurately predicted parrotfish grazing. There were substantial reductions in coral nutritional quality (C:N) associated with parrotfish grazing, although these changes appear to be a consequence rather than a cause of parrotfish selectivity. Likewise, nematocyst densities were suppressed in grazed corals, also likely a result of chronic grazing stress. We found no intraspecific differences in skeletal hardness related to grazing. These results provide further demonstration of the physiological consequences of grazing, but the cause of preferential grazing by parrotfishes on certain Montastraea spp. colonies still requires further investigation.