Meeting Abstract
Ammonia is the major product of cellular amino acid metabolism in animals. Due to the toxicity of ammonia, an efficient ammonia detoxification or excretion system is crucial to maintain hemolymph ammonia levels within a tolerable range, and to insure normal cellular function. Rh proteins, candidate genes involved in ammonia excretion strategies (AES), are highly conserved through evolution, but their physiological significance and functional essentiality in metazoans is poorly understood. C. elegans was subjected to various environmental stresses to investigate whether and to what extent Rh proteins are involved in AES. Also, gene expression analysis revealed that both Rh proteins respond to HEA, suggesting that there are likely involved in ammonia regulation. Our results about C. elegans following exposure to various pH regimes suggest that ammonia excretion is sensitive to environmental pH, with enhanced excretion rates in low pH environments. This suggested that the ammonia excretion mechanism involves ammonia trapping with an apical pathway likely via Rh proteins. Also, our tissue localization studies revealed a strong presents of Rh-r2 in the hypodermis. We used SIET to re-evaluate whether the Rh-r2 protein is critical for H+ secretion and it was shown that H+flux rates across the hypodermis are hampered in ΔRhr-2 strain compared to wild type (N2) animals. Enhanced ammonia excretion rates in N2 animals exposed to a low pH environment completely vanished in ΔRh-r2, which indicates a role of Rh-r2 in AES. Our yeast complementation assay results strongly suggested that the Rh-r1 of C. elegans is indeed capable at mediating the transport of ammonia when expressed in yeast. Taken together, our data provide the first evidence that indicates the essentiality of the Rh proteins in ammonia homeostasis in a nematode.
