Lamitina ST et al. (2004) Am J Physiol Cell Physiol "Adaptation of the nematode Caenorhabditis elegans to extreme osmotic stress."

Moeckel GW, Lamitina ST, Morrison R, Strange K

[Am J Physiol Cell Physiol, 2004]

The ability to control osmotic balance is essential for cellular life. Cellular osmotic homeostasis is maintained by the accumulation and loss of inorganic ions and organic osmolytes. While osmoregulation has been studied extensively in many cells types, major gaps exist in our molecular understanding of this essential process. Because of its numerous experimental advantages, the nematode C. elegans provides a powerful model system in which to characterize the genetic basis of animal cell osmoregulation. We therefore characterized the ability of worms to adapt to extreme osmotic stress. Exposure of worms to high salt growth agar causes rapid shrinkage. Survival is normal on agar containing up to 200 mM NaCl. When grown on 200 mM NaCl for 2 weeks, worms are able to survive well on agar containing up to 500 mM NaCl. HPLC analysis demonstrated that levels of the organic osmolyte glycerol increase 15-20 fold in nematodes grown on 200 mM NaCl agar. Accumulation of glycerol begins 3 h after exposure to hypertonic stress and peaks by 24 h. Glycerol accumulation is mediated primarily by synthesis from metabolic precursors. Consistent with this finding, hypertonicity increases transcriptional expression of glycerol 3-phosphate dehydrogenase, an enzyme that is rate limiting for hypertonicity-induced glycerol synthesis in yeast. Worms adapted to high salt swell and then return to their initial body volume when exposed to low salt agar. During recovery from hypertonic stress, glycerol levels fall rapidly and glycerol excretion increases ~5-fold. Our studies provide the first description of osmotic adaptation in C. elegans and provide the foundation for genetic and functional genomic analysis of animal cell osmoregulation.

Kuzuoglu-Ozturk D et al. (2012) Nucleic Acids Res "The Caenorhabditis elegans GW182 protein AIN-1 interacts with PAB-1 and subunits of the PAN2-PAN3 and CCR4-NOT deadenylase complexes."

Izaurralde E, Kuzuoglu-Ozturk D, Schmidt S, Huntzinger E

[Nucleic Acids Res, 2012]

GW182 family proteins are essential for miRNA-mediated gene silencing in animal cells. They are recruited to miRNA targets via interactions with Argonaute proteins and then promote translational repression and degradation of the miRNA targets. The human and Drosophila melanogaster GW182 proteins share a similar domain organization and interact with PABPC1 as well as with subunits of the PAN2-PAN3 and CCR4-NOT deadenylase complexes. The homologous proteins in Caenorhabditis elegans, AIN-1 and AIN-2, lack most of the domains present in the vertebrate and insect proteins, raising the question as to how AIN-1 and AIN-2 contribute to silencing. Here, we show that both AIN-1 and AIN-2 interact with Argonaute proteins through GW repeats in the middle region of the AIN proteins. However, only AIN-1 interacts with C. elegans and D. melanogaster PABPC1, PAN3, NOT1 and NOT2, suggesting that AIN-1 and AIN-2 are functionally distinct. Our findings reveal a surprising evolutionary plasticity of the GW182 protein interaction network and demonstrate that binding to PABPC1 and deadenylase complexes has been maintained throughout evolution, highlighting the significance of these interactions for silencing.