Project description:In the current study a systematic investigation of life stage, tissue and cell dependent sensitivity to ionizing radiation in the nematode Caenorhabditis elegans was conducted. This revealed that individuals that have reached the post-mitotic L4 stage showed no significant effects with respect to mortality, morbidity or reproduction when subjected to either acute dose ≤6 Gy(1500 mGy/h) or chronic exposure ≤4 Gy( ≤ 100 mGy/h). In contrast, chronic exposure from embryo to young adult stage caused a dose and dose rate dependent reprotoxicitiy with 43% reduction in total brood size at 6.7Gy (107 mGy/h). Systematic targeted irradiation of developmental stages showed that exposure during L1 to young L4 was sufficient to induce reprotoxic effects. Exposure during these stages was associated with a dose rate dependent genotoxic effects on gonads with 1.7 to 3.2 fold increase in germ cell apoptosis in larvae subjected to 40-100 mGy/h, respectively. Importantly, exposure to gamma radiation significantly impaired spermatogenesis in a dose rate dependent manner. The observed reduction in the number of spermatids accounted for xx% of the reprotoxic effects, thus signifying spermatids as the most radiosensitive cell type in C. elegans. Molecular responses analyzed by RNAseq of nematodes irradiated from L1 to L4 stage revealed a significant enrichment of genes related to both male and hermaphrodite reproductive processes. Gene network analysis identified adverse genotoxic effects related to down-regulation of genes required for spindle formation and sperm meiosis/maturation, including smz-1, smz-2 and htas-1. The expression of a subset of 28 set-17 regulated Major Sperm Proteins (MSP) required for spermatids production was correlated to the reduction in reproduction and the number of spermatids, thus corroborating the impairment of spermatogenesis as the major cause of gamma radiation induced life-stage dependent reprotoxic effect. Furthermore, the progeny of irradiated nematodes showed significant embryonal DNA damage that was associated with persistent effect on somatic growth. Unexpectedly, these nematodes did however maintain much of their reproductive capacity in spite of the reduced growth.

Project description:Expression data from Caenorhabditis elegans let-418(RNAi), mep-1(RNAi) and gfp(RNAi) L1 larvae. The C. elegans genome encodes two homologs of the human protein Mi-2, namely LET-418 and CHD-3. LET-418 plays an essential role during development; its depletion leads to a pleiotropic and lethal phenotype that includes larval arrest, an everted vulva and sterility. Without maternal contribution, let-418 mutants stop their development at the L1 larval stage (von Zelewsky et al., 2000). We further characterized this arrest and showed that it is very similar to the L1 diapause induced by starvation; both germline and somatic cells remain in a quiescent state in let-418 L1 arrested larvae, indicating that LET-418 activity is required to bypass the L1 arrest in presence of food. The let-418 L1 larvae express ectopically the P granule component PGL-1 in somatic cells (Unhavaithaya et al., 2002). Interestingly, the phenotype of mep-1 mutants is remarkably similar to that of let-418: RNAi targeting mep-1 also induced an L1 arrest phenotype; furthermore, MEP-1 and LET-418 have been shown to physically interact (Unhavaithaya et al., 2002 and M. Passannante). The null allele mep-1(q660) is temperature sensitive and shows a more severe phenotype at higher temperatures. At 20Â°C, about 10% of mep-1 homozygotes derived from heterozygous mothers arrest as young larvae, whereas the remaining 90% develop into sterile adults (Belfiore et al., 2002). Later in development, the somatic gonad is affected in mep-1(q660) mutants. This results in an abnormal and disorganized gonad, a phenotype also observed in let-418(s1617) mutants. Both let-418 and mep-1 mutants produce a very limited number of oocytes and have pseudovulvae derived from P8.p (Belfiore et al., 2002; von Zelewsky et al., 2000 and C. Wicky, personal communication). Preliminary quantitative real-time PCR revealed that the expression of genes coding for P granule components was deregulated in both mep-1(RNAi) and let-418(RNAi) L1 larvae (data not shown). To further investigate this issue, we performed a complete gene expression analysis. Given the fact that mep-1(q660) mutants are sterile, we used RNA interference to generate mep-1 depleted worms. Bacteria expressing gfp dsRNA (pPE128.110 in HT115) were used as reference, since RNA interference may induce gene expression changes by itself. C. elegans L1 larvae treated with RNA interference were selected for RNA extraction and hybridization on Affymetrix microarrays. Synchronized wild type L4 animals were grown at 25Â° on bacteria expressing either gfp, let-418 or mep-1 dsRNA. Eggs were collected by bleaching gravid adults and allowed to hatch in the absence of food at 25Â°C. Newly hatched L1 larvae were fed on bacteria expressing the different dsRNA for three hours to recover from starvation. Three replicates per RNAi.

Project description:Expression data from Caenorhabditis elegans let-418(RNAi), mep-1(RNAi) and gfp(RNAi) L1 larvae. The C. elegans genome encodes two homologs of the human protein Mi-2, namely LET-418 and CHD-3. LET-418 plays an essential role during development; its depletion leads to a pleiotropic and lethal phenotype that includes larval arrest, an everted vulva and sterility. Without maternal contribution, let-418 mutants stop their development at the L1 larval stage (von Zelewsky et al., 2000). We further characterized this arrest and showed that it is very similar to the L1 diapause induced by starvation; both germline and somatic cells remain in a quiescent state in let-418 L1 arrested larvae, indicating that LET-418 activity is required to bypass the L1 arrest in presence of food. The let-418 L1 larvae express ectopically the P granule component PGL-1 in somatic cells (Unhavaithaya et al., 2002). Interestingly, the phenotype of mep-1 mutants is remarkably similar to that of let-418: RNAi targeting mep-1 also induced an L1 arrest phenotype; furthermore, MEP-1 and LET-418 have been shown to physically interact (Unhavaithaya et al., 2002 and M. Passannante). The null allele mep-1(q660) is temperature sensitive and shows a more severe phenotype at higher temperatures. At 20°C, about 10% of mep-1 homozygotes derived from heterozygous mothers arrest as young larvae, whereas the remaining 90% develop into sterile adults (Belfiore et al., 2002). Later in development, the somatic gonad is affected in mep-1(q660) mutants. This results in an abnormal and disorganized gonad, a phenotype also observed in let-418(s1617) mutants. Both let-418 and mep-1 mutants produce a very limited number of oocytes and have pseudovulvae derived from P8.p (Belfiore et al., 2002; von Zelewsky et al., 2000 and C. Wicky, personal communication). Preliminary quantitative real-time PCR revealed that the expression of genes coding for P granule components was deregulated in both mep-1(RNAi) and let-418(RNAi) L1 larvae (data not shown). To further investigate this issue, we performed a complete gene expression analysis. Given the fact that mep-1(q660) mutants are sterile, we used RNA interference to generate mep-1 depleted worms. Bacteria expressing gfp dsRNA (pPE128.110 in HT115) were used as reference, since RNA interference may induce gene expression changes by itself.

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Caenorhabditis elegans

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