Submitted on October 3, 2006
Accepted on January 9, 2007
Functional Analysis of the aquaporin gene family in C. elegans
Chunyi George Huang1, Todd Lamitina2*, Peter Agre3, and Kevin Strange4
1 Department of Biological Chemistry, Johns Hopkins University, Baltimore, Maryland, United States
2 Department of Physiology, University of Pennsylvania, Philadelphia, Pennsylvania, United States
3 Duke University, Durham, North Carolina, United States
4 Departments of Anesthesiology and Pharmacology, Vanderbilt University, Nashville, Tennessee, United States
* To whom correspondence should be addressed. E-mail: lamitina{at}mail.med.upenn.edu.
Aquaporin channels facilitate the transport of water, glycerol and other small solutes across cell membranes. The physiological roles of many aquaporins remain unclear. To better understand aquaporin function, we characterized the aquaporin gene family in the nematode C. elegans. Eight canonical aquaporin-encoding genes (aqp) are present in the worm genome. Expression of aqp-2, aqp-3, aqp-4, aqp-6 or aqp-7 in Xenopus oocytes increased water permeability 5-7-fold. Glycerol permeability was increased 3-7-fold by expression of aqp-1, aqp-3 or aqp-7. Green fluorescent protein transcriptional and translational reporters demonstrated that aqp genes are expressed in numerous C. elegans cell types including the intestine, excretory cell, and hypodermis, which play important roles in whole animal osmoregulation. To define the role of C. elegans aquaporins in osmotic homeostasis, we isolated deletion alleles for four aqp genes, aqp-2, aqp-3, aqp-4, and aqp-8 that are expressed in osmoregulatory tissues and that mediate water transport. Single, double, triple, and quadruple aqp mutant animals exhibited normal survival, development, growth, fertility, and movement under normal and hypertonic culture conditions. aqp-2;aqp-3;aqp-4;aqp-8 quadruple mutants exhibited a slight defect in recovery from hypotonic stress, but survived hypotonic stress as well as wild type animals. These results suggest that C. elegans aquaporins are not essential for whole animal osmoregulation and/or that deletion of aquaporin genes activates mechanisms that compensate for loss of water channel function.
