Protons Act as a Transmitter for Muscle Contraction in C. elegans

Beg A. A., Ernstrom G. G., Nix P., Davis M. W. and Jorgensen E. M.

 2008. Cell 132, 149-160

Speaker: Yute Chang (張有德)                    Time: 15:00-16:00; Feb 20, 2008

Commentator: Dr. Meng-Ru Shen (沈孟儒老師)     Place: Room 601

Abstract:

Caenorhabditis elegans is a model organism in genetic research. Its herma- phroditic life style and short life time facilitate the screening for genetic mutants¹. The defecation cycle of C. elegans is a rhythmic behavior and can be divided into three independent actions: posterior body contraction (pBoc), anterior body contraction (aBoc) and enteric muscle contraction (Emc) that excrete excrement. The calcium wave that initiates from intestine and proceeds posteriorly controls the dynamics of pBoc. However, neither of laser ablation and synaptic transmission mutants disrupts the pBoc. So it appears that the signaling control of pBoc depends on a non-neuronal pathway. After screening for mutants that defective in pBoc, two genes, pbo-4 and pbo-5, were identified in these mutants. pbo-4gene encodes a protein of 783 amino acids that shares 26% identity with Na⁺/H⁺ exchangers I (NHE1). A transgene with superecliptic pHluorin GFP (a pH- sensitive GFP that is quenched by acidic media) inserted into the N-terminal domain of PBO-4 was constructed and expressed in pbo-4 mutants. pHluorin::PBO-4 was expressed on the basolateral surface of intestine that juxtaposed to the posterior body muscle and rescued the defect in contraction. Moreover, the coelomic space acidified by the protons transported by PBO-4, and the acidification occurred immediately before the pBoc. Another gene, pbo-5, was expressed in the muscle of posterior body. Though PBO-5 protein contains necessary features of cys-loop ligand-gated ion channel subunit, none of known classical neurotransmitters activates PBO-5 injected eggs. Interestingly, protons alone activate PBO-5. Altogether, this article suggests a mechanism for the induction of pBoc: protons released by putative Na⁺/H⁺ exchanger PBO-4 act as transmitter to activate the PBO receptor that is composed of PBO-5 and is

essential for the pBoc.

Reference:

1. Jorgensen E. M. and Mango S. E. 2002. The Art and Design of Genetic Screens: Caenorhabditis elegans . Nat. Rev. Gen. 3. 356-369.