NAD+ is a vital molecule in cellular redox reactions and acts as a cosubstrate for NAD+ consuming enzymes, which is critical to a variety of biological processes. Our studies have revealed a novel developmental role of NAD+ metabolism; compromised NAD+ biosynthesis affects muscle development and function in C. elegans. PNC-1 is a key enzyme in the NAD+ salvage pathway, acting as a nicotinamidase that catalyzes the deamination of nicotinamide (NAM) to nicotinic acid (NA), which is eventually processed to nicotinamide adenine dinucleotide (NAD+). We discovered that
pnc-1 mutants exhibit male mating defects. Male mating behavior is a coordinated multi-step process including finding a mate, locating the vulva, insertion of the copulatory spicules and ejaculation.
pnc-1 males are capable of locating the hermaphrodite vulva, but are severely defective in spicule insertion. A portion of mating defective
pnc-1 males also show crumpled spicules. The spicule morphology and insertion defects are likely due to compromised nicotinamidase activity of
pnc-1, as supplementation of
pnc-1 males with NA (product of nicotinamidase) during development can rescue both the spicule morphology and the spicule insertion defects, while supplementation of NAM (substrate of nicotinamidase) to wild-type males during development causes a mild mating defect. Since both spicule formation and insertion require proper function of the spicule muscles, these phenotypes suggest a role for
pnc-1 in muscle development and/or function. We have used pharyngeal pumping as an assay to study muscle function of
pnc-1 more generally. Our data show that
pnc-1 mutants have a lower pharyngeal pumping rate than N2. Additionally, Hart and Sinclair labs indicate that overexpression of
pnc-1 increases the pumping rate[1]. These results are consistent with our hypothesis that impaired NAD+ metabolism impacts muscle function. Reference [1] Personal communication with Anne C. Hart and David A. Sinclair labs, Harvard University.