Manipulation of Ploidy in Caenorhabditis elegans

Mechanisms that involve whole genome polyploidy play important roles in development and evolution; also, an abnormal generation of tetraploid cells has been associated with both the progression of cancer and the development of drug resistance. Until now, it has not been feasible to easily manipulate the ploidy of a multicellular animal without generating mostly sterile progeny. Presented here is a simple and rapid protocol for generating tetraploid Caenorhabditis elegans animals from any diploid strain. This method allows the user to create a bias in chromosome segregation during meiosis, ultimately increasing ploidy in C. elegans. This strategy relies on the transient reduction of expression of the rec-8 gene to generate diploid gametes. A rec-8 mutant produces diploid gametes that can potentially produce tetraploids upon fertilization. This tractable scheme has been used to generate tetraploid strains carrying mutations and chromosome rearrangements to gain insight into chromosomal dynamics and interactions during pairing and synapsis in meiosis. This method is efficient for generating stable tetraploid strains without genetic markers, can be applied to any diploid strain, and can be used to derive triploid C. elegans. This straightforward method is useful for investigating other fundamental biological questions relevant to genome instability, gene dosage, biological scaling, extracellular signaling, adaptation to stress, development of resistance to drugs, and mechanisms of speciation

THE GOLDANSKII-KARYAGIN EFFECT IN Gd2M2O7 AND Eu2M2O7 COMPOUNDS

Un effet Goldanskii-Karyagin (G. K.) important a été mis en évidence dans les spectres Mössbauer d'un monocristal de Eu2Ti2O7 obtenus à l'aide du rayonnement γ de 103 keV de 153Eu. La grandeur de l'effet est compatible avec les résultats antérieurs relatifs à des poudres. L'effet G. K. est également présent dans les spectres de Gd2Ti2O7, Gd2Sn2O7, Gd2CrSbO7, Gd2SnTiO7, Gd2Ru2O7 et Gd2Ir2O7, obtenus à l'aide du rayonnement γ de 105 keV de 155Gd. Dans ces composés, les paramètres de l'interaction quadrupolaire varient de manière considérable, linéairement avec la taille de la maille élémentaire. L'effet G. K. se manifeste aussi dans les spectres de Gd2Ti2O7, lorsque l'on observe le rayonnement γ de 123 keV de 154Gd. Nous examinons l'influence de divers paramètres sur la grandeur de l'effet G. K. observé.A large Goldanskii-Karayagin (G. K.) effect has been observed in the recoilless absorption measurements of the 103 eV γ ray of 153Eu in a single crystal of Eu2Ti2O7. The size of the effect is consistent with results obtained previously in a Eu2Ti2O7 powder sample. G. K. effects were observed in the Mössbauer effect of the 105 keV γ ray transition of 155Gd in Gd2Ti2O7, Gd2Sn2O7, Gd2CrSbO7, Gd2SnTiO7, Gd2RuzO7 and Gd2Ir2O7. The quadrupole interaction parameters in these compounds change drastically and linearly with the size of the unit cell. The G. K. effect was also observed in the Mössbauer spectrum of the 123 keV γ ray of 154Gd in Gd2Ti2O7. The dependence of the G. K. effect on various parameters is discussed