Nematodes offer several advantages for studying the molecular biology of anhydrobiosis. Their genome size is small (typically ~100 Mb); free-living anhydrobiotic nematodes are amenable to laboratory culture; and they have rapid generation times. In addition, complete annotated genome sequences are available for the model organisms Caenorhabditis elegans and Caenorhabditis briggsae; several other nematode genomes are becoming available. Many molecular tools and techniques for functional genomics have been developed by C. elegans researchers and several of these techniques have been adapted for other nematodes; in addition, C. elegans can also be used as a surrogate expression system for novel genes from other nematodes.
Many, but not all, species of nematode are anhydrobiotic; indeed, C. elegans is desiccation sensitive: at 75% relative humidity (RH), all worms die within 48 h (A.T. group, unpublished). Dauer juveniles (DJs) of C. elegans, typically produced in response to periods of starvation, show increased resistance to desiccation (e.g. ~75% survival after 24 h at 97% RH; Gal et al. 2004), but do not display the extreme tolerance of anhydrobiosis.
Anhydrobiotic species themselves exhibit varying requirements for survival of desiccation: in Aphelenchus avenae, a slow initial rate of dehydration is necessary (e.g. up to 72 h at 97% RH, before drying at 10% RH for 24 h; Browne et al. 2004), whereas many nematodes which inhabit exposed environments, such as the bacterivore Panagrolaimus superbus, can survive rapid drying (Shannon et al. 2005). These species are referred to as slow, and fast, dehydration strategists, respectively.
Working on the assumption that slow dehydration strategists need to upregulate genes involved in desiccation tolerance during their slow dehydration phase, our collaborators at the National University of Ireland Maynooth, Prof Ann Burnell and colleagues, have isolated a set of dehydration-induced genes from A. avenae. This anhydrobiosis gene set includes those encoding a number of hydrophilic proteins such as the Group 3 LEA protein, AavLEA1, and anhydrin (Browne et al. 2002; Browne et al. 2004), whose functions we are investigating.
Nematode Research Topics:
Browne, J., Tunnacliffe, A. and Burnell, A. (2002) Plant desiccation gene found in a nematode. Nature 416: 38.
Browne, J. A., Dolan, K. M., Tyson, T., Goyal, K., Tunnacliffe, A. and Burnell, A. M. (2004) Dehydration-specific induction of hydrophilic protein genes in the anhydrobiotic nematode Aphelenchus avenae. Eukaryot. Cell 3: 966-975.
Gal, T. Z., Glazer, I. and Koltai, H. (2004) An LEA group 3 family member is involved in survival of C. elegans during exposure to stress. FEBS Lett. 577: 21-26.
Shannon, A. K., Browne, J. A., Boyd, J., Fitzpatrick, D. A. and Burnell, A. M. (2005) The anhydrobiotic potential and molecular phylogenetics of species and strains of Panagrolaimus (Nematoda, Panagrolaimidae). J. Exp. Biol. 208: 2433-2445.