For degenerative disorders of the central nervous system, the major obstacle to therapeutic advancement has been the challenge of identifying the key molecular mechanisms underlying neuronal loss. We developed a combinatorial approach including translational profiling and brain regulatory network analysis to search for key determinants of neuronal survival or death. Following the generation of transgenic mice for cell type-specific profiling of midbrain dopaminergic neurons, we established and compared translatome libraries reflecting the molecular signature of these cells at baseline or under degenerative stress. Analysis of these libraries by interrogating a context-specific brain regulatory network led to the identification of a repertoire of intrinsic upstream regulators that drive the dopaminergic stress response. The altered activity of these regulators was not associated with changes in their expression levels. This strategy can be generalized for the elucidation of novel molecular determinants involved in the degeneration of other classes of neurons.

Highlights d Ribosomal profiling of AD vulnerable/resistant neurons in 5-, 12-, 24-month old mice d Using human neuron-type functional networks and GWASs to model vulnerability d Identification of axon plasticity genes linking Aß, aging, tau in vulnerable neurons d PTB, regulator of tau exon 10 splicing, might contribute to selective vulnerability

A major obstacle to treating Alzheimer's disease (AD) is our lack of understanding of the molecular mechanisms underlying selective neuronal vulnerability, which is a key characteristic of the disease. Here we present a framework to integrate highquality neuron-type specific molecular profiles across the lifetime of the healthy mouse, which we generated using bacTRAP, with postmortem human functional genomics and quantitative genetics data. We demonstrate human-mouse conservation of cellular taxonomy at the molecular level for AD vulnerable and resistant neurons, identify specific genes and pathways associated with AD pathology, and pinpoint a specific functional gene module underlying selective vulnerability, enriched in processes associated with axonal remodeling, and affected by both amyloid accumulation and aging. Overall, our study provides a molecular framework for understanding the complex interplay between Aβ, aging, and neurodegeneration within the most vulnerable neurons in AD.

Theiler's virus, a picornavirus, persists for life in the central nervous system of mouse and causes a demyelinating disease that is a model for multiple sclerosis. The virus infects neurons first but persists in white matter glial cells, mainly oligodendrocytes and macrophages. The mechanism, by which the virus traffics from neurons to glial cells, and the respective roles of oligodendrocytes and macrophages in persistence are poorly understood. We took advantage of our previous finding that the shiverer mouse, a mutant with a deletion in the myelin basic protein gene (Mbp), is resistant to persistent infection to examine the role of myelin in persistence. Using immune chimeras, we show that resistance is not mediated by immune responses or by an efficient recruitment of inflammatory cells into the central nervous system. With both in vivo and in vitro experiments, we show that the mutation does not impair the permissiveness of neurons, oligodendrocytes, and macrophages to the virus. We demonstrate that viral antigens are present in cytoplasmic channels of myelin during persistent infection of wild-type mice. Using the optic nerve as a model, we show that the virus traffics from the axons of retinal ganglion cells to the cytoplasmic channels of myelin, and that this traffic is impaired by the shiverer mutation. These results uncover an unsuspected axon to myelin traffic of Theiler's virus and the essential role played by the infection of myelin/oligodendrocyte in persistence.

Forebrain dopamine-sensitive (dopaminoceptive) neurons play a key role in movement, action selection, motivation, and working memory. Their activity is altered in Parkinson's disease, addiction, schizophrenia, and other conditions, and drugs that stimulate or antagonize dopamine receptors have major therapeutic applications. Yet, similarities and differences between the various neuronal populations sensitive to dopamine have not been systematically explored. To characterize them, we compared translating mRNAs in the dorsal striatum and nucleus accumbens neurons expressing D1 or D2 dopamine receptor and prefrontal cortex neurons expressing D1 receptor. We identified genome-wide cortico-striatal, striatal D1/D2 and dorso-ventral differences in the translating mRNA and isoform landscapes, which characterize dopaminoceptive neuronal populations. Expression patterns and network analyses identified novel transcription factors with presumptive roles in these differences. Prostaglandin E2 was a candidate upstream regulator in the dorsal striatum. We pharmacologically explored this hypothesis and showed that misoprostol, a prostaglandin E2 (PGE2) receptors agonist, decreased the excitability of D2 striatal projection neurons in slices and diminished their activity in vivo during novel environment exploration. We found that it also modulates mouse behavior including by facilitating reversal learning. Our study provides powerful resources for characterizing dopamine target neurons, new information about striatal gene expression patterns and regulation. It also reveals the unforeseen role of PGE2 in the striatum as a potential neuromodulator and an attractive therapeutic target.