Imprinted Nesp55 Influences Behavioral Reactivity to Novel Environments

Abstract

Genomic imprinting results in parent-of-origin-dependent monoallelic expression of selected genes. Although their importance in development and physiology is recognized, few imprinted genes have been investigated for their effects on brain function. Gnas is a complex imprinted locus whose gene products are involved in early postnatal adaptations and neuroendocrine functions. Gnas encodes the stimulatory G-protein subunit Gsα and two other imprinted protein-coding transcripts. Of these, the Nesp transcript, expressed exclusively from the maternal allele, codes for neuroendocrine secretory protein 55 (Nesp55), a chromogranin-like polypeptide associated with the constitutive secretory pathway but with an unknown function. Nesp is expressed in restricted brain nuclei, suggesting an involvement in specific behaviors. We have generated a knockout of Nesp55 in mice. Nesp55-deficient mice develop normally, excluding a role of this protein in the severe postnatal effects associated with imprinting of the Gnas cluster. Behavioral analysis of adult Nesp55 mutants revealed, in three separate tasks, abnormal reactivity to novel environments independent of general locomotor activity and anxiety. This phenotype may be related to prominent Nesp55 expression in the noradrenergic locus coeruleus. These results indicate a role of maternally expressed Nesp55 in controlling exploratory behavior and are the first demonstration that imprinted genes affect such a fundamental behavior.

ACKNOWLEDGMENTS

G.K. and L.S.W. are supported by the Biotechnology and Biological Sciences Research Council and by a Synergy Initiative award from the Babraham Institute; G.K. is a Senior Fellow of the Medical Research Council. R.F.-C. was supported by grant P16389-B05 from the Austrian Science Foundation.

We thank Jo Peters for critical reading of the manuscript, Martin Evans for IMT-11 ES cells, and staff at the Babraham Institute animal facilities for dedicated husbandry.