Down Syndrome Critical Region (DSCR1) is a gene located on human chromosome 21 and has been implicated in such disease models as Alzheimer's and Down Syndrome. The protein encoded by DSCR1 (MCIP1) and its homologue in yeast were shown to bind and inhibit the protein phosphatase calcineurin. In addition, members of this protein family, termed calcipressins, were transcriptionally regulated by calcineurin, forming a conserved negative feedback inhibition loop. Recently, a study in which MCIP1 was overexpressed in cardiac hypertrophic hearts of mice showed specific inhibition of hypertrophic conditions, suggesting alternative treatment methods of cardiac hypertrophy using this endogenous inhibitor of calcineurin. In light of these observations, we sought to characterize
rcn-1, the DSCR1 homologue in C. elegans.
rcn-1 is expressed throughout embryonic stages to adulthood in hypodermal cells, nerve cords and various neurons throughout the body, vulva epithelial cells, marginal cells of the pharynx, and diagonal muscle, sensory rays, and spicules of the male tail. Observations of
rcn-1 expression by GFP and RT-PCR analysis in calcineurin mutant backgrounds suggest that
rcn-1 may be upregulated by calcineurin activity. RCN-1 specifically binds to calcineurin A from C. elegans lysate in a calcium-dependent manner, and potently inhibits bovine calcineurin phosphatase activity dose-dependently confirming its conserved role as a calcipressin. Calcineurin promoter-driven RCN-1 overexpression in wild-type animals results in calcineurin-deficient phenotypes such as small body size, cuticle defects, fertility defects, slow growth, and serotonin-resistant egg-laying defects. In addition, a consitutively active calcineurin A mutant,
cna-1(gf), was isolated by target-selected mutagenesis, and showed hyperactive serotonin-mediated egg laying. Calcineurin promoter-driven RCN-1 overexpression in
cna-1(gf) animals restored the abnormal egg-laying response to normal serotonin-mediated egg laying levels. These results confirm a potent and specific inhibition of calcineurin in vitro and in vivo.