The Ku70-Ku80 (Ku) heterodimer binds rapidly and tightly to ends of DNA double-strand breaks and recruits several factors of the Non-Homologous End Joining (NHEJ) pathway through molecular mechanisms that remain unclear. Here, we describe the crystal structures of the Ku-binding motifs (KBM) of the NHEJ proteins APLF (A-KBM) and XLF (X-KBM) bound to a Ku-DNA complex. The two KBMs motifs bind on remote sites of Ku80 α/β domain. The X-KBM occupies an internal pocket formed after an unprecedented large outward rotation of the Ku80 α/β domain. We reveal independent recruitment at laser-irradiated sites of the APLF-interacting protein XRCC4 and of XLF through the respective binding of A- and X-KBMs to Ku80. Finally, we show that mutations on the X-KBM and A KBM binding sites in Ku80 compromises efficiency and accuracy of end-joining and cellular radiosensitivity. A- and X-KBMs may represent two initial anchorage points necessary to build the NHEJ intricate interactions network.

Brain lipid homeostasis is important for maintenance of brain cell function and synaptic communications, and is intimately linked to age-related cognitive decline. Because of the bloodbrain barrier's limiting nature, this tissue relies on a complex system for the synthesis and receptor-mediated uptake of lipids between the different networks of neurons and glial cells. Using immunofluorescence, we describe the region-specific expression of the lipolysis-stimulated lipoprotein receptor (LSR), in the mouse hippocampus, cerebellum Purkinje cells, the ependymal cell interface between brain parenchyma and cerebrospinal fluid, and the choroid plexus. Colocalization with cell-specific markers revealed that LSR was expressed in neurons, but not astrocytes. Age-related cognitive decline associated with higher risk of neurodegenerative disorders has become an important public concern as life expectancy increases in industrially developed countries. Although the molecular mechanisms underlying the decrease in memory and other brain-related functions with age are under active investigation, the processes Address correspondence and reprint requests to Frances T. Yen, Lipidomix, Université de Lorraine, ENSAIA, 2 avenue de la Forêt de Haye, 54501 Vandoeuvre-lès-Nancy, France. E-mail: frances.yen-potin@univ-lorraine.fr 1 CS and AP contributed equally to this work.Abbreviations used: BBB, blood-brain barrier; FFA, free fatty acid; GFAP, glial fibrillary acidic protein; LDL-R, low-density lipoprotein receptor; LpL, lipoprotein lipase; LRP1, low-density lipoprotein receptor-related protein 1; LSR, lipolysis-stimulated lipoprotein receptor; NeuN, neuronal nuclei; PBS, phosphate-buffered saline; PFA, paraformaldehyde. Journal of Neurochemistry

Skeletal dysplasias are a clinically and genetically heterogeneous group of bone and cartilage disorders. A total of 436 skeletal dysplasias are listed in the 2015 revised version of the nosology and classification of genetic skeletal disorders, of which nearly 20% are still genetically and molecularly uncharacterized. We report the clinical and molecular characterization of a lethal skeletal dysplasia of the short-rib group caused by mutation of the mouse Fop gene. Fop encodes a centrosomal and centriolar satellite (CS) protein. We show that Fop mutation perturbs ciliogenesis in vivo and that this leads to the alteration of the Hedgehog signaling pathway. Fop mutation reduces CSs movements and affects pericentriolar material composition, which probably participates to the ciliogenesis defect. This study highlights the role of a centrosome and CSs protein producing phenotypes in mice that recapitulate a short rib-polydactyly syndrome when mutated.