Altered Activity, Social Behavior, and Spatial Memory in Mice Lacking the NTAN1p Amidase and the Asparagine Branch of the N-End Rule Pathway

Abstract

The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. N-terminal asparagine and glutamine are tertiary destabilizing residues, in that they are enzymatically deamidated to yield secondary destabilizing residues aspartate and glutamate, which are conjugated to arginine, a primary destabilizing residue. N-terminal arginine of a substrate protein is bound by the Ubr1-encoded E3α, the E3 component of the ubiquitin-proteasome-dependent N-end rule pathway. We describe the construction and analysis of mouse strains lacking the asparagine-specific N-terminal amidase (Nt^N-amidase), encoded by the Ntan1 gene. In wild-type embryos,Ntan1 was strongly expressed in the branchial arches and in the tail and limb buds. The Ntan1^−/− mouse strains lacked the Nt^N-amidase activity but retained glutamine-specific Nt^Q-amidase, indicating that the two enzymes are encoded by different genes. Among the normally short-lived N-end rule substrates, only those bearing N-terminal asparagine became long-lived in Ntan1^−/− fibroblasts. TheNtan1^−/− mice were fertile and outwardly normal but differed from their congenic wild-type counterparts in spontaneous activity, spatial memory, and a socially conditioned exploratory phenotype that has not been previously described with other mouse strains.

ACKNOWLEDGMENTS

We are grateful to members of the Caltech Transgenic Facility, especially S. Pease, B. Kennedy, and A. Granados, for the care of mice and expert technical help. We thank S. Grigoryev for helpful discussions at the beginning of this study, N. Barteneva for assistance with some of the early experiments, S. Offermanns for advice and help with preparation of embryonic fibroblasts, and R. C. Mulligan and R. Jaenisch for gifts of plasmids.

This work was supported by grants GM31530 and DK39520 from the National Institutes of Health to A.V.