Nmf9 Encodes a Highly Conserved Protein Important to Neurological Function in Mice and Flies.

Many protein-coding genes identified by genome sequencing remain without functional annotation or biological context. Here we define a novel protein-coding gene, Nmf9, based on a forward genetic screen for neurological function. ENU-induced and genome-edited null mutations in mice produce deficits in vestibular function, fear learning and circadian behavior, which correlated with Nmf9 expression in inner ear, amygdala, and suprachiasmatic nuclei. Homologous genes from unicellular organisms and invertebrate animals predict interactions with small GTPases, but the corresponding domains are absent in mammalian Nmf9. Intriguingly, homozygotes for null mutations in the Drosophila homolog, CG45058, show profound locomotor defects and premature death, while heterozygotes show striking effects on sleep and activity phenotypes. These results link a novel gene orthology group to discrete neurological functions, and show conserved requirement across wide phylogenetic distance and domain level structural changes.

Modeling clinically heterogeneous presenilin mutations with transgenic Drosophila.

To assess the potential of Drosophila to analyze clinically graded aspects of human disease, we developed a transgenic fly model to characterize Presenilin (PS) gene mutations that cause early-onset familial Alzheimer's disease (FAD). FAD exhibits a wide range in severity defined by ages of onset from 24 to 65 years . PS FAD mutants have been analyzed in mammalian cell culture, but conflicting data emerged concerning correlations between age of onset and PS biochemical activity . Choosing from over 130 FAD mutations in Presenilin-1, we introduced 14 corresponding mutations at conserved residues in Drosophila Presenilin (Psn) and assessed their biological activity in transgenic flies by using genetic, molecular, and statistical methods. Psn FAD mutant activities were tightly linked to their age-of-onset values, providing evidence that disease severity in humans primarily reflects differences in PS mutant lesions rather than contributions from unlinked genetic or environmental modifiers. Our study establishes a precedent for using transgenic Drosophila to study clinical heterogeneity in human disease.