Recent advances in sunlight-induced carcinogenesis using the Xiphophorus melanoma model

Unlike breast and prostate cancers, the nature and sequence of critical genetic and epigenetic events involved in the initiation and progression of melanoma are not well understood. A contributing factor to this dilemma, especially given our current understanding of the importance of UV light in melanoma etiology, is the lack of quality UV-inducible melanoma animal models. In this study we elaborate on the capability of UV light to induce cutaneous malignant melanomas (CMM) in Xiphophorus fishes, which were previously found to develop melanomas after acute neonatal UVB irradiation. In two separate tumorigenesis experiments, we exposed adult Xiphophorus hybrids to either acute UVB irradiations (5 consecutive daily treatments) or chronic solar irradiations (continuous UVA/UVB treatment for 9 months). Acute adult UVB irradiation resulted in the significant induction of melanomas, and moreover, this induction rate is equivalent to that of animals exposed to acute neonatal UVB irradiation. This study represents the first evidence that acute adult UVB irradiation, in the absence of any early life exposures, induces CMM. Similar to the findings conducted on other divergent melanoma models, including HGF/SF transgenic mice and Monodelphis domestica, prolonged chronic solar UV was not a factor in melanomagenesis.     

The role of tumor suppressor menin in IL-6 regulation in mouse islet tumor cells

Menin is a gene product of multiple endocrine neoplasia type1 (Men1), an inherited familial cancer syndrome characterized by tumors of endocrine tissues. To gain insight about how menin performs an endocrine cell-specific tumor suppressor function, we investigated the possibility that menin was integrated in a cancer-associated inflammatory pathway in a cell type-specific manner. Here, we showed that the expression of IL-6, a proinflammatory cytokine, was specifically elevated in mouse islet tumor cells upon depletion of menin and Men^−/− MEF cells, but not in hepatocellular carcinoma cells. Histone H3 lysine (K) 9 methylation, but not H3 K27 or K4 methylation, was involved in menin-dependent IL-6 regulation. Menin occupied the IL-6 promoter and recruited SUV39H1 to induce H3 K9 methylation. Our findings provide a molecular insight that menin-dependent induction of H3 K9 methylation in the cancer-associated interleukin gene might be linked to preventing endocrine-specific tumorigenesis.     

Steinernema feltiae: ammonia triggers the emergence of their infective juveniles

Entomopathogenic nematodes complete their life cycles inside dead insects. The emergence of new infective juveniles from the cadaver has been attributed (but never demonstrated) to food depletion or to the accumulation of metabolites from the breakdown of the host's tissues. Here we give evidence that emergence is triggered by ammonia, a product of nematode defecation. We found that the emergence of Steinernemafeltiae infective juveniles from Galleriamellonella cadavers was stimulated by a particular level of ammonia. Emergence was delayed when ammonia in the cadaver was decreased and was prompted when increased. These findings will further improve the understanding of the nematode life cycle. Here we speculate that production of infective juveniles can be mediated by ammonia and work in a manner analogous to that of the dauer recovery inhibiting factor (DRIF) in Caenorhabditiselegans.     

Fine mapping of the NRC-1 tumor suppressor locus within chromosome 3p12

Identification of tumor suppressor genes based on physical mapping exercises has proven to be a challenging endeavor, due to the difficulty of narrowing regions of loss of heterozygosity (LOH), infrequency of homozygous deletions, and the labor-intensive characterization process for screening candidates in a given genomic interval. We previously defined a chromosome 3p12 tumor suppressor locus NRC-1 (Nonpapillary Renal Carcinoma-1) by functional complementation experiments in which renal cell carcinoma microcell hybrids containing introduced normal chromosome 3p fragments were either suppressed or unsuppressed for tumorigenicity following injection into athymic nude mice. We now present the fine-scale physical mapping of NRC-1 using a QPCR-based approach for measuring copy number at sequence tagged sites (STS) which allowed a sub-exon mapping resolution. Using STS-QPCR and a novel statistical algorithm, the NRC-1 locus was narrowed to 4.615-Mb with the distal boundary mapping within a 38-Kb interval between exon 3 and exon 4 of the DUTT1/Robo1 gene, currently the only candidate tumor suppressor gene in the interval. Further mutational screening and gene expression analyses indicate that DUTT1/ROBO1 is not involved in the tumor suppressor activity of NRC-1, suggesting that there are at least two important tumor suppressor genes within the chromosome 3p12 interval.     

Stage-specific regulation of caspase activity in drosophila oogenesis

In Drosophila oogenesis, the programmed cell death of germline cells occurs predominantly at three distinct stages. These cell deaths are subject to distinct regulatory controls, as cell death during early and midoogenesis is stress-induced, whereas the cell death of nurse cells in late oogenesis is developmentally regulated. In this report, we show that the effector caspase Drice is activated during cell death in both mid- and late oogenesis, but that the level and localization of activity differ depending on the stage. Active Drice formed localized aggregates during nurse cell death in late oogenesis; however, active Drice was found more ubiquitously and at a higher level during germline cell death in midoogenesis. Because Drice activity was limited in late oogenesis, we examined whether another effector caspase, Dcp-1, could drive the unique morphological events that occur normally in late oogenesis. We found that premature activation of the effector caspase, Dcp-1, resulted in a disappearance of filamentous actin, rather than the formation of actin bundles, suggesting that Dcp-1 activity must also be restrained in late oogenesis. Overexpression of the caspase inhibitor DIAP1 suppressed cell death induced by Dcp-1 but had no effect on cell death during late oogenesis. This limited caspase activation in dying nurse cells may prevent destruction of the nurse cell cytoskeleton and the connected oocyte.     

Strongyloides stercoralis: Amphidial neuron pair ASJ triggers significant resumption of development by infective larvae under host-mimicking in vitro conditions

Resumption of development by infective larvae (L3i) of parasitic nematodes upon entering a host is a critical first step in establishing a parasitic relationship with a definitive host. It is also considered equivalent to exit from the dauer stage by the free-living nematode Caenorhabditis elegans. Initiation of feeding, an early event in this process, is induced in vitro in L3i of Strongyloides stercoralis, a parasite of humans, other primates and dogs, by culturing the larvae in DMEM with 10% canine serum and 5mM glutathione at 37 degrees C with 5% CO(2). Based on the developmental neurobiology of C. elegans, resumption of development by S. stercoralis L3i should be mediated, in part at least, by neurons homologous to the ASJ pair of C. elegans. To test this hypothesis, the ASJ neurons in S. stercoralis first-stage larvae (L1) were ablated with a laser microbeam. This resulted in a statistically significant (33%) reduction in the number of L3i that resumed feeding in culture. In a second expanded investigation, the thermosensitive ALD neurons, along with the ASJ neurons, were ablated, but there was no further decrease in the initiation of feeding by these worms compared to those in which only the ASJ pair was ablated.     

Spatial and temporal regulation of the homeotic selector gene Antennapedia is required for the establishment of leg identity in Drosophila

Antennapedia is one of the homeotic selector genes required for specification of segment identity in Drosophila. Dominant mutations that ectopically express Antennapedia cause transformation of antenna to leg. Loss-of-function mutations cause partial transformation of leg to antenna. Here we examine the role of Antennapedia in the establishment of leg identity in light of recent advances in our understanding of antennal development. In Antennapedia mutant clones in the leg disc, Homothorax and Distal-less are coexpressed and act via spineless to transform proximal femur to antenna. Antennapedia is negatively regulated during leg development by Distal-less, spineless, and dachshund and this reduced Antennapedia expression is needed for the proper development of distal leg elements. These findings suggest that the temporal and spatial regulation of the homeotic selector gene Antennapedia in the leg disc is necessary for normal leg development in Drosophila.     

Diversity of benzimidazole-resistance alleles in populations of small ruminant parasites

The resistance of gastro-intestinal nematodes of small ruminants (sheep and goat) to benzimidazole anthelmintic drugs seems to be linked primarily to a single mutation in the isotype 1 beta-tubulin gene. This study was carried out to investigate the origin and diversity of benzimidazole-resistance alleles in trichostrongylid nematodes. We sequenced a 550 bp fragment of the isotype 1 beta-tubulin gene from several benzimidazole-resistant Teladorsagia circumcincta populations isolated from dairy goat farms in the central and south-western France. We also sequenced the same beta-tubulin fragment from Trichostrongylus colubriformis and Haemonchus contortus populations in south-western France. We found eight benzimidazole-resistance alleles in all T. circumcincta populations studied, six in H. contortus populations, and only one in T. colubriformis populations. In most cases, only one benzimidazole-resistance allele was present in T. circumcincta and H. contortus populations, but two alleles were found in a fewer number of them. Some T. circumcincta populations shared the same benzimidazole-resistance allele whereas some others had a specific benzimidazole-resistance allele. Similar findings were obtained for H. contortus. As no parasites are introduced once the flock of dairy goat farms has been constituted, these data indicate for the three studied species that rare pre-existing benzimidazole-resistance alleles already present before the isolation of populations had been selected. On the other hand, the fact that some benzimidazole-resistance alleles were specific to one population of T. circumcincta or H. contortus, seems to be in agreement with the hypothesis of the selection of spontaneous mutations. Thus, the origin of benzimidazole-resistance alleles in trichostrongylid nematodes seems to involve primarily the selection of rare alleles and possibly of spontaneous mutations.