Pathologic alpha-synuclein (alpha-syn) spreads from cell-to-cell, in part, through binding to the lymphocyte-activation gene 3 (Lag3). Here we report that amyloid beta precursor-like protein 1 (Aplp1) forms a complex with Lag3 that facilitates the binding, internalization, transmission, and toxicity of pathologic alpha-syn. Deletion of both Aplp1 and Lag3 eliminates the loss of dopaminergic neurons and the accompanying behavioral deficits induced by alpha-syn preformed fibrils (PFF). Anti-Lag3 prevents the internalization of alpha-syn PFF by disrupting the interaction of Aplp1 and Lag3, and blocks the neurodegeneration induced by alpha-syn PFF in vivo. The identification of Aplp1 and the interplay with Lag3 for alpha-syn PFF induced pathology advances our understanding of the molecular mechanism of cell-to-cell transmission of pathologic alpha-syn and provides additional targets for therapeutic strategies aimed at preventing neurodegeneration in Parkinson disease and related alpha-synucleinopathies.

In a search for novel genes on chromosome 18 (HC18), on which several regions have been linked to bipolar disorder, we applied exon trapping to HC18-specific cosmids. Among the 1138 exons trapped, 1052 of them have been mapped to HC18, and the remaining 86 have not been localized. No exons were localized to genomic regions other than HC18. BLAST database search revealed that 190 exons were identical to 98 Unigenes on HC18; 98 identical to additional 82 clusters of ESTs not present in the HC18 Unigene set; 39 homologous to genes from human and other species (eo10 À3 ); and the remaining 811 exons had no significant homology to transcripts in public databases. The mapped exons were compared to the 867 annotated genes on HC18 in the Celera databases; 216 exons were identical to 104 Celera 'genes' and the remaining 836 exons were not found in the Celera databases. On average, there were two exons for a matched transcript (known genes and ESTs). Therefore, the 850 novel exons may represent hundreds of novel genes on chromosome 18.