Fig. 2.

gpdh transcriptional GFP reporters are activated by hypertonic stress. (a Upper) P_gpdh-2::GFP is constitutively expressed in the hypodermis, intestine, and excretory cell under control conditions. (a Lower) P_gpdh-1::GFP expression is undetectable under isotonic conditions and is dramatically elevated after exposure to 200 mM NaCl. P_gpdh-1::GFP is expressed in the intestine (Lower Right, arrowhead) and hypodermis (Lower Right, arrows). (b) Effect of NaCl concentration on P_gpdh-1::GFP expression in young adult worms. Animals were placed on agar plates containing the indicated amounts of NaCl for 24 h. Values are means ± SE (n > 1,000). P_gpdh-1::GFP expression was also induced by hypertonic KCl, sucrose, or sorbitol (data not shown), indicating that gpdh-1 expression is regulated specifically by hypertonicity-induced water loss rather than elevated Na⁺ or Cl⁻ levels. (c) Changes in P_gpdh-1::GFP expression in young adult worms during hypertonic stress or heat shock (30°C). Values are means ± SE (n > 150). GFP expression in b and c was quantified by using a COPAS BioSort and normalized to time-of-flight (i.e., GFP fluorescence divided by time-of-flight).